Anti-reflective coating with IR protection and mirroring at higher angles of incidence

Abstract

Layer system (100; 110; 120; 130) comprising infrared mirror coating - a substrate base (11) comprising a substrate layer (a) with a substrate area (F) a ); and - a plurality of descending layer layers (2, 4, 6) and a plurality of descending layer layers (1, 3, 5, 7), wherein an descending and a descending layer layer alternately form on the substrate surface (F a ) are arranged such that the layer system (100; 110; 120; 130) at a detection angle of approximately 0° with at least one substrate normal (N1, N2, N3; N a , N b ) of the substrate area (F a ) • has a reflectivity for electromagnetic radiation of R ≥ 15% for at least one wavelength range between approximately 680 nm and approximately 1100 nm; and • has a reflectivity for electromagnetic radiation of R ≤ 5% for at least one wavelength range between approximately 400 nm and approximately 680 nm; wherein the reflectivity from a wavelength of approximately 630 nm for a viewing angle α of approximately 45° - is between about 10% and 20% higher than with a viewing angle α of about 30°; - is between approximately 20% and 30% higher than with a viewing angle α of approximately 15°; and - is between approximately 23% and 33% higher than with a viewing angle α of approximately 0°.

Description

[0001] The invention relates to a layer system and a method for producing a layer system, which is used, for example, in optical elements such as lenses, in particular for spectacle lenses.

[0002] Furthermore, the invention can also be used for glass panes, in particular for display glass to protect screens or displays in the mobile communications and computer sectors.

[0003] Furthermore, the invention can also be applied to glass panes, in particular to the coating of vehicle windows.

[0004] Transparent optical systems with UV mirroring are known. For example, UV absorbers are often integrated into known materials for spectacle lenses to protect the eye from harmful UV radiation. An alternative to this UV protection implemented in the material can be a coating on the spectacle lens that also achieves effective protection against UV radiation. For example, such a coating system is known from WO 2016 / 110339 A1. This system achieves high reflectivity values, particularly above 60%, primarily in the spectral UV wavelength range (UV range), while remaining relatively transparent to electromagnetic radiation and light in the visible and infrared ranges. Reflection in the UV range has the advantage, especially for spectacle lenses and / or vehicle windows, of protecting or shielding the user from harmful UV radiation.However, there is still a demand for improved systems to protect users from harmful electromagnetic radiation.

[0005] Document DE 10 2016 120 122 B3 discloses a spectacle lens with a lens substrate and a coating applied to the lens substrate. The coating has a first reflectivity of at least 20% for near-infrared light of a first wavelength striking the coating at an angle of incidence of 0°, and a second reflectivity for near-infrared light of the first wavelength striking the coating at an angle of incidence of 35°, which is reduced by at least 10% compared to the first reflectivity.

[0006] Document WO 2021 / 023774 A1 discloses a portable optical article comprising an optical substrate and an interference coating. The interference coating can be configured to selectively reflect light of at least one wavelength range in the near-infrared spectrum. A peak reflectance, measured perpendicular to the optical article, can be at least 70%. The interference coating has an average reflectance of less than 1.5% in the visible light range.

[0007] Document US 2015 / 0 293 284 A1 discloses a near-infrared blocking filter capable of suppressing the influence of light on a captured image when the angle of incidence of the light to the near-infrared blocking filter is large. The near-infrared blocking filter comprises a substrate to transmit at least light in the visible wavelength range. An infrared-reflecting layer is arranged on at least one side of the substrate, configured as a multilayer film with alternating layers of a high-refractive-index film (H) and a low-refractive-index film (L). Alternatively, it is configured as a multilayer film with alternating layers of a high-refractive-index film (H), a medium-refractive-index film (M), and a low-refractive-index film (L).The near-infrared blocking filter has such light transmission properties that the difference between a maximum value and a minimum value of the decrease rates of the mean transmission in region R, region G and region B is at most 0.05.

[0008] According to one aspect, the task is to provide a system and a method for manufacturing the system that enables improved protection of a user from certain electromagnetic radiation.

[0009] The problem is solved by the layer system and the method for producing the layer system according to the independent claims. Advantageous embodiments are the subject of the dependent claims.

[0010] Layer system with infrared mirroring, comprehensively designed according to one aspect a substrate base, for example a spectacle lens or a vehicle windshield or a window pane, in particular a building window pane, comprising a substrate layer with a substrate surface through which electromagnetic radiation can propagate or pass at least partially; and a plurality of low-refractive layer layers and a plurality of high-refractive layer layers, wherein a high-refractive layer layer or a layer layer with high-refractive properties and a low-refractive layer layer or a layer layer with low-refractive properties are arranged alternately on or at the substrate surface such that the layer system, at a detection angle of approximately 0°, is aligned with at least one substrate normal of the substrate surface. has a reflectivity for electromagnetic radiation or light of approximately R ≥ 15%, in particular of approximately R ≥ 25% and especially R ≥ 50% for at least one wavelength range between approximately 680 nm and approximately 1100 nm; and has a reflectivity for electromagnetic radiation or light of approximately R ≤ 5%, in particular of approximately R ≤ 2.5%, and particularly preferably of approximately R ≤ 0.5% for at least one wavelength range between approximately 400 nm and approximately 680 nm, where the reflectivity increases from a wavelength of approximately 630 nm for a viewing angle α of approximately 45° • is between about 10% and 20% higher than with a viewing angle α of about 30°; • is between approximately 20% and 30% higher than with a viewing angle α of approximately 15°; and • is between about 23% and 33% higher than at a viewing angle α of about 0°, so that the layer system is essentially transparent to electromagnetic radiation in at least one section of the visible range.

[0011] The term "approximately" in this and other specifications refers to a deviation of + / - 10%, preferably + / - 5%, particularly preferably + / - 3%, and especially + / - 1% of the respective specified value(s), in particular the target value and / or the limit value.

[0012] A detection angle of approximately 0° means measuring at an angle as close to 0° as possible, depending on the measuring apparatus. In other words, it is known to those skilled in the art that a measurement at a detection angle of 0° is not performed exactly at 0°, but will deviate from 0° due to the limitations of the measurement technique.

[0013] A layer system with infrared mirroring is particularly preferred. a substrate base, for example a spectacle lens or a vehicle windshield or a window pane, in particular a building window pane, comprising a substrate layer with a substrate surface through which electromagnetic radiation can propagate or pass at least partially; and a plurality of low-refractive layer layers and a plurality of high-refractive layer layers, wherein a high-refractive layer layer or a layer layer with high-refractive properties and a low-refractive layer layer or a layer layer with low-refractive properties are arranged alternately on or at the substrate surface such that the layer system, at a detection angle of approximately 0°, is within the limits of measurement accuracy with at least one substrate normal of the substrate surface has a reflectivity for electromagnetic radiation or light of R ≥ 15%, in particular R ≥ 25% and especially R ≥ 50% for at least one wavelength range between 680 nm and 1100 nm; and a reflectivity for electromagnetic radiation or light of R ≤ 5%, in particular of R ≤ 2.5%, and particularly preferably of R ≤ 0.5% for at least one wavelength range between 400 nm and 680 nm, such that the layer system is essentially transparent to electromagnetic radiation in at least one section of the visible range.

[0014] Unless otherwise stated, refractive index values ​​always refer to a reference wavelength of 550 nm.

[0015] The wavelength range between approximately 680 nm and approximately 1100 nm includes parts of the infrared range, in particular the near-infrared range, and parts of the visible range, in particular the spectral red tones of the visible range.

[0016] The wavelength range between approximately 300 nm and approximately 680 nm includes parts of the UV range, particularly the UV-A and UV-B ranges, and parts of the visible range, especially violet tones. It may also include blue tones of the visible range.

[0017] The coating system described above has the surprising effect of exhibiting high reflectivity for wavelengths from or greater than approximately 700 nm. In particular, it achieves high reflectivity for a wavelength range in the near-infrared region, especially in the IR-A range. Simultaneously, it achieves exceptionally low reflectivity, i.e., high anti-reflection properties, meaning excellent transmittance or transparency for electromagnetic radiation in the visible range. This coating system is therefore particularly advantageous for coating optical elements, such as lenses, including spectacle lenses, window lenses, and / or vehicle windshields, which must be transparent to light across a broad visible spectrum while also exhibiting high reflectivity for at least some of the longer wavelengths.

[0018] An optical element coated with a layer system according to the above aspect has the advantage of at least partially shielding a person, and in particular the eyes of a person using the optical element, from electromagnetic radiation in the IR-A range, while simultaneously improving the aesthetic appearance of the optical element in the visible range. The harmful effects of electromagnetic radiation, especially in the infrared spectral range, are described in detail in the guideline "Incoherent Visible and Infrared Radiation from Artificial Sources" (German Association for Radiation Protection, document no. FS-2018-176-AKNIR, May 28, 2018). Thus, users of such an optical element can be advantageously protected, to a substantial extent, from the effects of harmful electromagnetic radiation by means of the layer system applied to it according to the present aspect.Electromagnetic radiation in the IR-A range is particularly prevalent in road traffic. The increased use of night vision assistance systems in road traffic, for example, leads to increased exposure to electromagnetic radiation in the IR-A range, which – without appropriate filtering – reaches the human eye almost unimpeded.

[0019] Due to the high reflectivity of radiation in the IR-A range and the simultaneously high transmittance of the coating system for visible radiation, it is advantageous to apply the coating system, as described above, to vehicle windows, for example, car windshields and / or rear windows, and / or to spectacle lenses, so that the eyes of a user, such as a driver and / or a wearer of glasses, can be largely protected from harmful IR radiation. At the same time, particularly good visibility of visible electromagnetic radiation is ensured, so that the user's vision is essentially unaffected. The described coating is particularly suitable as a coating on the convex side, the front side, or the side facing the incident light in normal use, of a spectacle lens.

[0020] Furthermore, the layered system offers an aesthetic advantage, for example, in the case of spectacle lenses. In particular, a spectacle lens wearer can identify the protective effect of the lenses in the infrared range simply by looking at the outer surface of the lens at the appropriate angle, observing the red reflection, and thus potentially distinguish it from conventional spectacles.

[0021] Preferably, the majority of low-refractive index layers are a system of essentially homogeneous low-refractive index layers, and the majority of high-refractive index layers are a system of essentially homogeneous high-refractive index layers. In other words, a specific material or material mixture is preferably used for a system of homogeneous low-refractive index layers, and another specific material or material mixture is used for a system of homogeneous high-refractive index layers. In particular, SiO₂ is used as the material for the low-refractive index layers, and ZrO₂ is preferably used as the material for the high-refractive index layers. Thus, two specific materials are used for the system of homogeneous low-refractive index layers and the system of homogeneous high-refractive index layers, respectively, although this does not preclude the use of other materials in the layer system.

[0022] Preferably, one of the low-refractive-index layers comprises SiO2. The low-refractive-index layer can consist entirely of SiO2. In this case, this low-refractive-index layer, in combination with the other layers, is intended to provide an anti-reflective effect in the visible wavelength range. In other words, a low-refractive-index layer containing SiO2, integrated into the arrangement of alternating low-refractive-index and high-refractive-index layers, enables a special anti-reflective effect in the visible wavelength range. In particular, a low-refractive-index layer containing SiO2, deposited on a high-refractive-index layer, exhibits an anti-reflective effect.

[0023] In particular, the low-refractive index layer furthest from the substrate contains SiO2 to achieve the anti-reflective effect. The low-refractive index layer containing SiO2, located furthest from the substrate, has a particularly strong anti-reflective effect because it is applied to a high-refractive index layer.

[0024] Thus, the layer system comprises a low-refractive layer with a layer thickness of, in particular, approximately 70 nm to approximately 77 nm, wherein the low-refractive layer preferably comprises quartz, i.e., SiO2, and is suitable, in combination with the other layers, which are alternating low-refractive and high-refractive layers, for anti-reflective coating of the layer system in the visible wavelength range. As already mentioned, this low-refractive layer is the layer furthest from the substrate, or the uppermost low-refractive layer. The low-refractive layer furthest from the substrate is deposited on a high-refractive layer and, in particular, thereby has an anti-reflective effect.

[0025] Further functional layer layers can be arranged on the last or uppermost or outermost breaking layer, such as a maintenance layer, which can serve in particular to prevent the adhesion of contaminants.

[0026] Preferably, the last optically active layer is a refracting layer.

[0027] As explained above, optically active layers are those layers that significantly influence or determine the optical properties of the layer system or the optical element on which the layer system is arranged, in particular the transmission and / or reflection of the layer system or the optical element. Functional layers, which are preferably not optically active, differ from these because they do not significantly influence or determine the optical properties of the layer system or the optical element on which the layer system is arranged, in particular the transmission and / or reflection of the layer system or the optical element.

[0028] The layer system is equipped with a final, or uppermost, essentially optically active layer, wherein this layer is one of the low-refractive layers and preferably consists of SiO₂. This structure proves particularly advantageous in terms of its anti-reflective properties, at least partially in the visible wavelength range. Amorphous SiO₂, for example, has a refractive index n of approximately 1.46 (measured at a wavelength of approximately 550 nm, which corresponds to the center of the eye's sensitivity). Alternatively, low-refractive MgF₂ could also be used, which has a refractive index n of approximately 1.38; however, this material can only be deposited at high temperatures of approximately 300°C.

[0029] Preferably, the layer layers are arranged, applied, or deposited on the substrate surface such that the layer system, at a detection angle of approximately 0° with the substrate normal of the substrate surface, has a reflectivity for electromagnetic radiation of approximately R ≥ 10%, in particular approximately R ≥ 20%, and particularly preferably approximately R ≥ 60% for at least one wavelength range between approximately 280 nm and approximately 400 nm.

[0030] This layered system is particularly suitable for protection against potentially harmful electromagnetic radiation in the UV range, especially in the UV-A and UV-B spectrum. This UV protection is especially beneficial due to the carcinogenic effects of UV radiation on human tissue, thus protecting the user from such harmful exposure.

[0031] In addition to the aforementioned IR protection, the coating also offers high UV protection. An optical element and / or window glass coated with this system can therefore protect a user not only from harmful infrared radiation, but also from harmful UV radiation, while simultaneously maintaining high transmission properties in the visible wavelength range.

[0032] This UV protection also provides additional protection to the glass material, the applied coatings, as well as the dyes contained in the glass against the potentially harmful effects of UV radiation.

[0033] The layering system is therefore particularly suitable for sports, mountaineering and ski goggles, as the exposure to UV and IR radiation is particularly high under the influence of solar radiation, especially at high altitudes and in snow.

[0034] This layer system is also well-suited for coating display glass to protect displays from harmful electromagnetic radiation. In this case, the user is not positioned on the side of the layer system facing away from the incident light, but rather on the side facing the incident light. The display or screen, such as an LED screen, is typically located on the side facing away from the incident light.

[0035] Another area of ​​application is equipment in nautical science, for example navigation instruments on board a ship or boat and / or sail and / or hull elements of a boat, since the radiation on the water is particularly high due to the reflection of sunlight at the water's surface and the corresponding material is therefore subjected to considerable stress.

[0036] Optionally, the layered layers are arranged, applied, or deposited on the substrate surface in such a way that the layered system aligns with the substrate normal of the substrate surface at a detection angle of approximately 0°. for at least one wavelength range between about 480 nm and about 580 nm has a reflectivity maximum of electromagnetic radiation of about R ≤ 5%, in particular of about R ≤ 3% and especially preferably of about R ≤ 1%.

[0037] The reflectivity maximum between approximately 480 nm and 580 nm can be determined by comparing the absolute maximum value with local, surrounding, or neighboring reflectivity values, thus identifying the maximum. Alternatively, the difference in reflectivity between the local maximum and the local minima on both sides (i.e., at higher and lower wavelengths) can be determined. In this case, the local minima on both sides of the local maximum will be approximately the same, particularly at a reflectivity of approximately 0%. If this is not the case and the reflectivity increases with wavelength, the mean difference in reflectivity between the local maximum and the local minima on both sides can be used, or a baseline can be considered.

[0038] When applying an anti-reflective coating to a surface in the visible wavelength range, a comparatively low reflection maximum for green tones often occurs between approximately 480 nm and 580 nm. This maximum differs from neighboring reflection values ​​by at most 1%, resulting in a comparatively low reflection property in this region, particularly for green tones. Consequently, the transmission properties are exceptionally high across a broad wavelength range of visible light, and tones are reflected only to a very small extent at the layers of the coating system. In other words, the coating system does not significantly distort the perception of an observer on the side of the coated object facing away from the incident light in the visible range.

[0039] Preferably, the majority of high-refractive index layer layers comprise at least one of the following materials: Ta2O5, TiO2, Ti x O y, ZrO2, Al2O3, Nd2O5, Pr2O3, PrTiO3, La2O3, Nb2O5, Y2O3, HfO2, ITO (Indium Tin Oxide), ZnS, Si3N4, MgO, CeO2 and their modifications, especially their other oxidation states.

[0040] Particularly preferred high-refractive-index layers include ZrO2 and / or Ta2O5. In particular, a high-refractive-index layer may comprise a single one of the materials mentioned herein. Alternatively, a high-refractive-index layer may comprise several of the aforementioned materials, either as a mixture or as a combination of composite materials, each comprising at least one of the aforementioned materials. A layer system may comprise several high-refractive-index layers of the same material or, alternatively, at least two high-refractive-index layers of different materials.

[0041] The materials mentioned are particularly suitable because they can be deposited or applied to the substrate surface and / or to layered surfaces by means of physical vapor deposition and / or chemical vapor deposition and / or sputtering.

[0042] Sputtering particularly prefers the majority of breaking layer layers of at least one of the following materials: SiO, SiO2, silanes, siloxanes, a mixture comprising SiO2 and Al2O3, in particular a mixture with at least about 80 wt% SiO2, preferably a mixture with at least about 90 wt% SiO2.

[0043] Particularly preferred low-breaking layers consist of SiO2. In particular, a low-breaking layer can consist of a single one of the materials mentioned here. Alternatively, a low-breaking layer can comprise several of the above-mentioned materials, either as a mixture or as a combination of composite materials, each comprising at least one of the materials. A layer system can comprise several low-breaking layers of the same material or, alternatively, at least two low-breaking layers of different materials.

[0044] The materials mentioned are particularly suitable because they can be deposited or applied to the substrate surface and / or to layered surfaces by means of physical vapor deposition and / or chemical vapor deposition and / or sputtering.

[0045] Preferably, the layered layers, starting from the substrate base, comprise the following sequence: a first high-refracting layer; a first breaking layer; a second high-refracting layer; a second descending layer; a third high-refracting layer; a third descending layer; a fourth high-refracting layer; and a fourth refractive layer, in particular a SiO2- dh quartz layer, which is suitable for at least partially anti-reflective coating of the layer system in the visible range.

[0046] Preferably, the low-refractive layer layers homogeneously consist of a low-refractive material and / or the high-refractive layer layers homogeneously consist of a high-refractive material, and preferably the high-refractive material does not consist of or is not a very high-refractive or extremely high-refractive material.

[0047] Preferably, the layered layers, starting from the substrate base, comprise the following sequence: a first high-refractive-index layer with a layer thickness of at least approximately 118 nm; a first refraction layer with a layer thickness of at least approximately 135 nm; a second high-refractive-index layer with a layer thickness of at least approximately 70 nm; a second refractive layer with a layer thickness of at least approximately 80 nm; a third high-refractive-index layer with a layer thickness of at least approximately 5 nm; a third refractive layer with a layer thickness of at least approximately 35 nm; a fourth high-refractive-index layer with a layer thickness of at least approximately 55 nm; and a fourth refractive layer with a layer thickness of at least approximately 60 nm.

[0048] In other words, a preferred layer system, starting from the substrate base, comprises the following in the following order: a first layer comprising one of the high-refractive-index layers, namely the first high-refractive-index layer, and having a layer thickness of at least approximately 118 nm; a second layer comprising one of the descending layer layers, namely the first descending layer layer, and having a layer thickness of at least approximately 135 nm; a third layer comprising one of the high-refractive-index layers, namely the second high-refractive-index layer, and having a layer thickness of at least approximately 70 nm; a fourth layer comprising one of the refracting layers, namely the second refracting layer, and having a layer thickness of at least approximately 80 nm; a fifth layer comprising one of the high-refractive index layers, namely the third high-refractive index layer, and having a layer thickness of at least approximately 5 nm; a sixth layer comprising one of the descending layers, namely the third descending layer, and having a layer thickness of at least approximately 35 nm; a seventh layer comprising one of the high-refractive-index layers, namely the fourth high-refractive-index layer, and having a layer thickness of at least approximately 55 nm; and a final, essentially optically active layer comprising one of the refracting layers, namely the fourth refracting layer, and having a layer thickness of at least about 60 nm.

[0049] The layered layers, particularly preferably arranged from the substrate base, comprise the following sequence: a first high-refractive-index layer with a layer thickness of at most approximately 130 nm; a first refractory layer with a layer thickness of at most about 160 nm; a second high-refractive-index layer with a layer thickness of at most approximately 120 nm; a second descending layer with a layer thickness of at most approximately 105 nm; a third high-refractive-index layer with a layer thickness of at most approximately 15 nm; a third refractory layer with a layer thickness of at most approximately 45 nm; a fourth high-refractive-index layer with a layer thickness of at most approximately 80 nm; and a fourth refractive layer with a layer thickness of at most approximately 80 nm.

[0050] In other words, a preferred layer system has the layer layers arranged in the following order, starting from the substrate base: a layer comprising one of the high-refractive-index layers, namely the first high-refractive-index layer, and having a layer thickness of at most approximately 130 nm; a layer comprising one of the descending layer layers, namely the first descending layer layer, and having a layer thickness of at most approximately 160 nm; a layer comprising one of the high-refractive-index layers, namely the second high-refractive-index layer, and having a layer thickness of at most approximately 120 nm; a layer comprising one of the descending layer layers, namely the second descending layer layer, and having a layer thickness of at most approximately 105 nm; a layer comprising one of the high-refractive index layers, namely the third high-refractive index layer, and having a layer thickness of at most approximately 15 nm; a layer comprising one of the descending layer layers, namely the third descending layer layer, and having a layer thickness of at most approximately 45 nm; a layer comprising one of the high-refractive-index layers, namely the fourth high-refractive-index layer, and having a layer thickness of at most approximately 80 nm; and a final, essentially optically active layer, comprising one of the refracting layers, namely the fourth refracting layer, and having a layer thickness of at most about 80 nm.

[0051] The layered layers, particularly preferably arranged from the substrate base, comprise the following sequence: a high-refractive-index layer with a layer thickness of approximately 121.5 nm; a refractive layer with a layer thickness of approximately 151 nm; a high-refractive-index layer with a layer thickness of approximately 106.2 nm; a refractive layer with a layer thickness of approximately 95.2 nm; a high-refractive-index layer with a layer thickness of approximately 12.1 nm; a refractive layer with a layer thickness of approximately 42.0 nm; a high-refractive-index layer with a layer thickness of approximately 59.6 nm; and a fourth refractive layer with a layer thickness of approximately 74.9 nm.

[0052] In other words, a layer system preferably comprises the layer layers arranged in the following order, starting from the substrate base: a layer comprising one of the high-refractive-index layers, in particular ZrO2, and having a layer thickness of approximately 121.5 nm; a layer comprising one of the refractive layers, in particular SiO2, and having a layer thickness of approximately 151 nm; a layer comprising one of the high-refractive-index layers, in particular ZrO2, and having a layer thickness of approximately 106.2 nm; a layer comprising one of the refractive layers, in particular SiO2, and having a layer thickness of approximately 95.2 nm; a layer comprising one of the high-refractive-index layers, in particular ZrO2, and having a layer thickness of approximately 12.1 nm; a layer comprising one of the refractive layers, in particular SiO2, and having a layer thickness of approximately 42 nm; a layer comprising one of the high-refractive-index layers, in particular ZrO2, and having a layer thickness of approximately 59.6 nm; and a final, essentially optically active layer comprising one of the refractive layers and in particular having SiO2 and a layer thickness of about 75 nm, in particular about 74.9 nm.

[0053] Advantageously, for layer systems of the aforementioned embodiments, a maximum reflectivity for electromagnetic radiation is achieved between approximately 680 nm and approximately 1100 nm, the position, height, and width of which are particularly favorable for the reflection of IR-A radiation. Simultaneously, the transmission of visible light is also particularly favorable, allowing a high proportion of visible light to propagate through the layer system and, for example, in the case of spectacle lenses, thus appearing visible to the wearer and ensuring good vision. The maximum between approximately 680 nm and approximately 1100 nm is positioned such that, according to the weighting of the 2013 ICNIRP guidelines, as much of the potentially harmful IR-A radiation as possible is reflected, and its spectral half-width is particularly favorable, as a sufficiently broad spectral range of IR-A radiation can be reflected with sufficient intensity.Thus, this embodiment results in particularly favorable IR protection, i.e., particularly good shielding of electromagnetic radiation, especially in the IR-A range.

[0054] According to the present description, it has been found that the above advantageous effect occurs particularly when the layer system has the above-mentioned layer sequence with the above-mentioned layer thicknesses and / or materials. It may also be possible that the above advantageous effect occurs at least partially when two or three of the high-refractive-index layers and / or two or three low-refractive-index layers are formed, as described above.

[0055] In addition to the aforementioned IR protection, the coating also offers high UV protection. This UV protection also shields the user from potentially harmful electromagnetic radiation. Furthermore, the substrate, particularly glass, applied coatings, and / or dyes contained within the glass can be protected from UV radiation.

[0056] Preferably, the layer system further comprises a functional layer which may consist in particular of Al2O3; and / or preferably The shift system also includes a nursing shift.

[0057] The layer system is particularly favorably characterized by further advantages The system comprises a functional layer, which may consist in particular of Al₂O₃ and may have a layer thickness of at least approximately 8 nm and at most approximately 11 nm; and / or, particularly preferably, the layer system further comprises a maintenance layer with a layer thickness of at least approximately 1 nm and at most approximately 20 nm. The functional layer may additionally or alternatively also comprise or consist of ITO and / or another similar material.

[0058] In other words, according to one embodiment, the layer system further comprises the following optional layer layers. - a functional layer, in particular made of Al2O3, which preferably has a layer thickness of at least about 8 nm and at most about 11 nm; the fourth refractive layer, in particular made of SiO2 and with a preferred layer thickness of at least about 70 nm and at most about 77 nm, is attached to this functional layer made of Al2O3; and / or - a care layer, in particular with fluorine-containing molecules and preferably with a layer thickness of at least about 1 nm and at most about 20 nm.

[0059] In other words, according to a preferred embodiment, the layer system comprises ten layers, wherein the first seven layers are the alternating first to fourth high-refractive-index layers and the first to third low-refractive-index layers. The functional layer made of Al₂O₃ is arranged on the fourth high-refractive-index layer. The fourth low-refractive-index layer is arranged on the functional layer made of Al₂O₃. The maintenance layer is arranged on the fourth low-refractive-index layer. This layer system can, for example, be applied directly to a substrate in successive application steps. Alternatively, it is also possible for one or more layers, e.g., comprising an adhesion promoter, a hard coating, etc., to be arranged between the layer system and the substrate.

[0060] The protective layer can be applied to the last optically relevant layer of the coating system and may contain fluorine molecules. The function of this protective layer is typically to provide improved care properties, such as water and oil repellency, at a surface energy of typically less than 15 mN / m.

[0061] Preferably the substrate base also includes: a protective layer, which can also be referred to as a hard coat layer or scratch-resistant layer and in particular comprises a lacquer layer or an organic layer, with a layer thickness of at least approximately 500 nm and at most approximately 5 µm; and preferably an adhesion layer, which in particular comprises low-grade metal oxides, chromium, silanes and / or siloxanes, with a layer thickness of at least about 1 nm and at most about 20 nm.

[0062] Preferably, a further layer, which can be called a primer coat, is applied between the scratch-resistant coating and the substrate. This primer coat acts as an adhesion promoter and / or provides increased impact resistance.

[0063] In other words, the substrate base preferably also has the following layered layers: a layer comprising a protective layer or a hard coat layer and preferably having a layer thickness of at least about 500 nm and at most about 5 µm; and preferably a layer comprising an adhesion layer, in particular comprising low-fracturing metal oxides, chromium, silanes and / or siloxanes, and preferably having a layer thickness of at least about 1 nm and at most about 20 nm.

[0064] A protective coating layer has the advantage of protecting the substrate from external influences, thus making the entire system particularly resistant. This protective coating layer can, in particular, consist of urethane-based and / or acetate-based coatings as primers and / or buffer coatings (applied before the protective coating layer) to improve adhesion and increase impact resistance.

[0065] Preferably, a primer coat can be arranged between the substrate and the protective layer or scratch-resistant layer as an adhesion promoter and, in particular, to improve impact resistance.

[0066] An adhesion layer allows or facilitates the application of the subsequent layers of the coating system. For example, such an adhesion layer can contain an element, such as chromium, or adhesive molecules, such as silane compounds. The adhesion layer acts as a mediator, establishing a reliable chemical bond to the substrate surface and, in particular, chemically binding the material of the first layer.

[0067] Such layer systems can therefore include, in addition to the optically relevant layers, which essentially comprise the high- and low-refractive-index layers, further functional layers, maintenance layers, protective layers, and / or adhesion layers that are essentially not relevant to the optical properties. Alternatively, however, an optically relevant layer can also be functionalized, for example, by applying a mixture of materials.

[0068] Preferably, the substrate base comprises an optical element, in particular a lens and preferably a spectacle lens.

[0069] Due to its high reflectivity in the infrared range and the resulting high glare protection in the IR-A range, as well as its high light transmission in the visible wavelength range, this coating system is particularly suitable for use on eyeglasses worn by drivers. Thanks to its high IR-A protection, the coating is also especially suitable for optical components in vehicles, such as windshields.

[0070] Optionally, the substrate base comprises a disc, in particular a vehicle disc and preferably a windshield and / or a rear window and / or a mirror and / or a side window of a vehicle.

[0071] This preferred layer system exhibits high scotopic and mesopic visual properties over a wide angular range, or angle of incidence of the incident light, and can thus support a driver's night vision and / or twilight vision. Scotopic vision, also known as twilight vision or rod vision, refers to light perception in low light conditions, with the transitional range in twilight corresponding to the mesopic range or twilight vision.

[0072] Electromagnetic radiation in the IR-A range is particularly prevalent in road traffic. The increased use of night vision assistance systems in road traffic also leads to increased exposure to electromagnetic radiation in the IR-A range, which – without appropriate filtering – reaches the human eye almost unimpeded.

[0073] Due to its suitable transmission capacity for visible electromagnetic radiation combined with high reflection of electromagnetic radiation in the IR-A range, this preferred coating system is advantageous for application to vehicle windows, such as car windshields. This allows for the extensive protection of a user's eyes, for example, a driver's, from harmful IR radiation, while simultaneously providing favorable transmission properties in the visible range. In other words, a windshield coated in this way allows for high visibility in the visible spectral wavelength range while offering high protection against IR radiation and, preferably, UV radiation.

[0074] The coating system, based on one of the aforementioned embodiments, can be used not only for spectacle lenses and / or vehicle windshields, but can also be applied to many types of optical articles. For example, the coating could be used on a display glass as a screen protector. The display could be located in a vehicle. Alternatively or additionally, the display could be a screen from a conventional electronic device. The display beneath such a coated glass receives a high level of protection against IR-A radiation (heat protection), and the viewer's privacy is protected. Due to the reflective effect, observers from the side will see a red reflection at higher angles of incidence, while the viewer themselves can use the excellent anti-reflective coating to view the display with high transmission properties at the usual viewing angle (α≈0°).

[0075] Preferably, the reflectivity of electromagnetic radiation in a wavelength range between about 560 nm and about 1000 nm, more preferably between about 570 nm and about 920 nm and particularly preferably between about 580 nm and about 900 nm, exhibits a slope of reflectivity between about 20% per 100 nm and about 80% per 100 nm, more preferably between about 30% per 100 nm and about 60% per 100 nm and particularly preferably between about 35% per 100 nm and about 45% per 100 nm.

[0076] In other words, the reflectivity plot against wavelength shows a positive reflectivity change or slope near a maximum for viewing angles between approximately 0° and 60°, particularly for viewing angles between approximately 0° and 45°, and especially for a wavelength range between approximately 580 nm and 900 nm, where the comparatively high reflectivity slope occurs. In this range, the slope is approximately 40% per 100 nm. The wavelength range of this comparatively high slope can vary, for example, depending on the viewing angle.

[0077] A sub-section can, for example, correspond to a smaller wavelength range within the aforementioned wavelength ranges. For a reflectivity determined at a viewing angle of approximately 0°, a sub-section of the wavelength range between approximately 560 nm and approximately 1000 nm can, for instance, correspond to a smaller wavelength range between approximately 600 nm and approximately 870 nm. In this smaller wavelength range between approximately 600 nm and approximately 870 nm, the comparatively high reflectivity slope, for example, of approximately 40% per 100 nm, occurs essentially constantly. It is also possible that the wavelength range with the comparatively high reflectivity slope exhibits a saddle point and / or a slope, meaning that the reflectivity slope does not essentially remain constant at a fixed value.For example, all values ​​for the reflectivity slope in a wavelength range between about 600 nm and about 870 nm can be between about 25% per 100 nm and about 45% per 100 nm, so that a slight rise, a sharp rise and a flattened rise near the maximum of the said wavelength range can occur.

[0078] A high mirror effect is characterized in particular by a particularly steep increase in reflectivity within a wavelength range. This is due, on the one hand, to the high transparency in the visible wavelength range and, on the other hand, to the high reflectivity in the infrared wavelength range. Essentially, at the boundary between approximately 560 nm and 1000 nm, a particularly steep slope in reflectivity as a function of wavelength results in a particularly good ratio of transparency in the visible range to shielding by reflectivity in the infrared range. Ideally, the reflectivity is particularly low in the visible wavelength range. Preferably, the layer system is at least partially almost 100% transparent in the visible wavelength range and particularly opaque in the infrared range, at least for an angular range below which the surface is viewed.The slope of the reflectivity is at least for a sub-region at least about 30% per 100 nm, in particular at least about 40% per 100 nm and preferably at least about 50% per 100 nm.

[0079] Preferably, with respect to wavelength, the reflectivity profile, which is recorded at an angle α of 45°, exhibits a rise of one flank to high values ​​from about 580 nm onwards, and the rise or the reflectivity slope in the range between about 600 nm and about 680 nm has a value of about 15% to about 50% per 100 nm, in particular from about 20% per 100 nm to about 40% per 100 nm.

[0080] At a viewing angle α of approximately 45°, an observer can easily determine whether the coating system offers IR protection. For example, a spectacle wearer can easily check whether their chosen lenses provide IR protection before using them. In addition to this practical benefit, the aesthetic appearance of spectacles with such mirrored lenses is also advantageous.

[0081] A reflectivity starting at a wavelength of approximately 630 nm is preferred, particularly at approximately 680 nm for a viewing angle α of approximately 45°. • between about 10% and about 20% higher, in particular about 15% higher than with a viewing angle α of about 30°; • between approximately 20% and approximately 30% higher, in particular approximately 25% higher than at a viewing angle α of approximately 15°; and • between about 23% and about 33% higher, in particular about 27% higher than at a viewing angle α of about 0°.

[0082] Preferably, the reflectivity exhibits a viewing angle α of approximately 45° and a wavelength of • at approximately 630 nm a value between approximately 10% and approximately 20%, in particular between approximately 13% and approximately 17%; • at approximately 680 nm, a value between approximately 30% and approximately 40%, particularly between approximately 33% and approximately 39%; and • at approximately 730 nm, a value between approximately 43% and approximately 53%, particularly between approximately 45% and approximately 50%.

[0083] At a viewing angle α of approximately 45°, an observer can easily determine, according to the aforementioned preferred features, whether the coating system provides IR protection. In particular, a wearer of spectacle lenses can determine, before using a spectacle lens, especially by viewing it at approximately 45°, whether their chosen spectacles offer IR protection.

[0084] Method for producing a layer system with infrared mirroring according to one aspect comprehensive Providing a substrate base comprising a substrate layer with a substrate area; and Arranging a plurality of low-refractive layer layers and a plurality of high-refractive layer layers on the substrate surface, wherein a layer layer with high-refractive properties and a layer layer with low-refractive properties are arranged alternately, such that the layer system is aligned with a substrate normal of the substrate surface at a detection angle of approximately 0°. has a reflectivity for electromagnetic radiation of approximately R ≥ 15% for at least one wavelength range between approximately 680 nm and approximately 1100 nm; and has a reflectivity for electromagnetic radiation of approximately R ≤ 5% for at least one wavelength range between approximately 400 nm and approximately 680 nm; and The reflectivity from a wavelength of approximately 630 nm for a viewing angle α of approximately 45° • is between about 10% and 20% higher than with a viewing angle α of about 30°; • is between approximately 20% and 30% higher than with a viewing angle α of approximately 15°; and • is between approximately 23% and 33% higher than with a viewing angle α of approximately 0°.

[0085] The coating system exhibits a particularly high, or even optimized, antireflection in the visible spectrum. It can be applied to a substrate using standard coating equipment. The resulting antireflection across nearly the entire visible spectrum, as well as the reflective coating in the IR-A range and partially in the visible boundary, especially for red tones, is directly visible. This effect can be verified by observing a red-toned reflection when viewed directly from the surface of the coating system and / or at an angle from the side facing the incident light. However, reflections of the invisible spectral components in the IR-A and UV ranges are essentially not perceived. A suitable detector can detect such spectral components from one or more viewing angles.

[0086] Furthermore, the layered system does not necessarily require very high or even ultra-high refractive index (URI) materials. A refractive index of n less than approximately 1.55, for example, around 1.38, is considered low refractive index. A refractive index n between approximately 1.55 and approximately 1.8, particularly between approximately 1.55 and approximately 1.7, is considered medium refractive index. A refractive index n between approximately 1.8 and approximately 2.1 is considered high refractive index. A refractive index n greater than or equal to 2.4, particularly greater than or equal to 2.5, is considered very high or ultra-high refractive index. Very high refractive index materials often contain titanium.

[0087] The process for producing the layer system, i.e., coating the substrate base with the layer system, can be carried out using conventional coating processes, in particular physical vapor deposition (PVD) and / or chemical vapor deposition (CVD), and does not necessarily require plasma / ion coating. However, the plasma / ion coating process can also be used.

[0088] It is also possible to apply layers using alternative coating processes. Besides PVD and / or CVD, material layers can alternatively or additionally be deposited using sputtering, electroplating, spin coating, or chemical coatings based on Langmuir absorption. For example, a protective layer, such as a lacquer, can be deposited or applied to the coating system using spin coating.

[0089] Preferably, the method comprises arranging the majority of low-refractive index layers and the majority of high-refractive index layers according to the preferred sequence and preferred layer thicknesses mentioned above.

[0090] The advantageous properties of the layer system are achieved primarily through the layer arrangement, without the need for any process engineering measures. In particular, reflectivity is not a parameter or process parameter that requires monitoring, especially during the manufacturing of the layer system. In other words, the optical properties, especially the reflectivity of the layer system, can be considered an intrinsic or inherent material property of the layer system. Reflectivity is therefore not a requirement in the manufacturing process of the layer system, i.e., in the coating process. The coating is not carried out with the requirement of achieving the aforementioned reflectivities, but rather with the requirement of arranging the majority of low-refractive-index layer layers and the majority of high-refractive-index layer layers according to the preferred sequence and preferred layer thicknesses mentioned above.

[0091] The coating system is specifically an interferometric multilayer system in which the spectral reflectivity is precisely controlled between the visible and IR-A ranges. The coating system allows for high antireflection in the visible range while achieving high reflectivity, particularly in the IR-A range.

[0092] The visible range is described by the parameters Rv, Rv', L*, C*, h* and by RM_(380-780nm) in the visible range and RM_(780-1150nm) in the IR-A range, as well as by suitable calculation of the reflection values ​​in the IR-A range with the thermal weighting function described according to ICNIRP Guidelines 2013.

[0093] The parameters L*, C*, and h* refer specifically to luminance, saturation, and hue in the color wheel in polar coordinates (DIN 11664-1 / 2). Rv and Rv' refer specifically to the visual reflectance (DIN 13666), with Rv pertaining to daytime vision and Rv' to twilight vision. RM refers to the average reflectance. Specifically, RM_(380-780nm) refers to the reflectance in the visible range, specifically for the range between 380 nm and 780 nm, and RM_(780-1150nm) refers to the reflectance in the infrared range between 780 nm and 1150 nm. The reflectance is averaged by averaging all reflectance values ​​over all wavelengths within the corresponding wavelength range. The average reflection is calculated according to DIN EN ISO 13666:2019, whereby the integration limits are adjusted accordingly.

[0094] The coating system can exhibit characteristic features, particularly regarding the position, height, and width of the IR maximum. Specifically, the coating system allows for the reflection of the highest possible proportion of damaging IR-A radiation, as determined by weighting according to the 2013 ICNIRP guidelines, and its spectral half-width can be improved or even optimized. However, extending the IR maximum of the spectral reflectivity to wavelengths above 1200 nm is not of primary importance. In other words, the coating system's reflection behavior for wavelengths greater than 1200 nm is of lesser or no interest. In addition to the aforementioned IR protection, the coating preferably offers high UV protection. This UV protection can further protect the glass material, the applied coatings, and any dyes contained within the glass.

[0095] In other words, an advantageous effect lies in the combination of effective anti-reflection in the visible range with the described IR protection, since a user can perceive light across a broad visible spectral range while simultaneously being protected from harmful IR-A radiation and, preferably, also largely from harmful UV radiation. In other words, the coating system allows the transmission of a large portion of visible light, whereas a large portion of harmful invisible light—specifically, a high proportion of IR-A light and preferably also a high proportion of UV light—is reflected and not transmitted through the coating system.

[0096] The effect of the mirror coating in the IR range and the anti-reflective coating in the visible range becomes "visible" to an observer from the outside when viewed at a minimum angle, for example, when the glasses are in a position other than their usual wearing position: When viewed straight on, i.e., at a viewing angle α ≤ 30°, an observer from the outside or front perceives a high anti-reflective effect, specifically as a negligible residual reflection of a green tone, i.e., for wavelength ranges in which electromagnetic radiation appears green to an observer. When viewed at an angle α > 30°, an observer perceives the protective property against IR-A radiation, specifically through the partially visible mirror coating for red tones.

[0097] The high anti-reflective effect is maintained up to a certain viewing angle. Beyond this angle, the anti-reflective coating becomes a visible red mirrored effect, clearly indicating the IR protection to the observer. A viewing angle of approximately 30° essentially corresponds to the angle at which the reflective effect of the coating system becomes particularly noticeable. Beyond this angle, the coating system no longer allows an external observer to see behind it, as the mirrored effect or reflectivity reaches a high value in the visible spectrum. This angle can be moderately varied by changing the coating thicknesses, while maintaining the described properties.This allows the typical position of the lenses in the frame to be taken into account during the layer development process, in order to prevent disturbing glare effects for the wearer of the glasses due to the red mirror coating being applied too early.

[0098] Some exemplary embodiments are described in more detail below, although the invention is not limited to the described embodiments. Further advantages may be associated with specific features according to examples and / or embodiments. Individual features described in a particular embodiment can be combined as desired, in particular with detailed features of another embodiment, provided they are not mutually exclusive. Furthermore, various features provided together in the exemplary embodiments are not to be considered as limiting the invention. Brief description of the drawings: Fig. Figure 1 shows a schematic side view of a layer system according to one embodiment in simplified representation; Fig. 2 shows a schematic side view of a layer system according to one embodiment in simplified representation; Fig. Figure 3 shows a schematic side view of a layer system according to one embodiment in simplified representation; Fig. Figure 4 shows a tabular representation of a layer system according to one embodiment; Fig. Figure 5 shows a spectral plot of the reflectivity of a [material / structure] according to Fig. 4 specified layer systems at a viewing angle of approximately 0°; Fig. Figure 6 shows a detailed view of an area of ​​the spectral plot of reflectivity from Fig. 5; Fig. Figure 7 shows the spectral plot of the reflectivity of the in Fig. 4 layer systems shown for four different viewing angles; Fig. 8a) schematically shows an exemplary arrangement of the area to be examined with regard to the incident and reflected light; Fig. Figure 8b) schematically shows an exemplary measurement setup at an angle of incidence of approximately 45°; Fig. Figure 8c) schematically shows an exemplary measurement setup at an angle of incidence of approximately 80°; Fig. Figure 9 shows a tabular example representation of spectral parameters for four different viewing angles; Fig. Figure 10 a) shows an exemplary progression of the residual reflection color when varying the viewing angle α from about 0° to about 45°, where the color value is plotted in polar coordinates on the color circle; Fig. 10 b) shows an exemplary progression of the residual reflection color when varying the viewing angle α from about 0° to about 45°, where the color value is chosen as a colored application against the viewing angle α; Fig. Figure 10 c) shows an exemplary plot of luminosity L* against the viewing angle α; Fig. Figure 10 d) shows an exemplary plot of the visual light reflectance Rv' for twilight vision against the viewing angle α; and Fig. 10 e) shows an exemplary plot of the visual light reflectance Rv for day vision against the viewing angle α.

[0099] A detailed description of exemplary embodiments in conjunction with the drawings is given below: Fig. Figure 1 shows a schematic side view of a layer system 100 according to one embodiment in a highly simplified representation. The layer system 100 comprises a plurality of layer layers 1-7, 9 and a substrate base 11 with a substrate layer a. The substrate base 11 comprises in Fig. 1 merely a substrate layer a, on which high-refractive layer layers 1, 3, 5, 7 and low-refractive layer layers 2, 4, 6, 9 are arranged alternately in layers.

[0100] The first layer 1 starting from the substrate base 11 is a first high-refractive-index layer 1, which lies on the substrate surface F a the substrate layer a, and has a layer thickness d1. The layer thickness d1 preferably has a value between about 90 nm and about 150 nm, in particular between about 110 nm and about 130 nm, and preferably between about 115 nm and about 125 nm.

[0101] The second layer 2, starting from the substrate base 11, which is arranged on the first layer 1, is a first refractory layer 2, which has a layer thickness d2. The layer thickness d2 preferably has a value between about 120 nm and about 180 nm, in particular between about 140 nm and about 160 nm, and preferably between about 145 nm and about 155 nm.

[0102] The third layer 3, starting from the substrate base 11, which is arranged on the second layer 2, is a second high-refractive-index layer having a layer thickness d3. The layer thickness d3 preferably has a value between about 70 nm and about 130 nm, in particular between about 90 nm and about 115 nm, and preferably between about 100 nm and about 110 nm.

[0103] The fourth layer 4, starting from the substrate base 11, which is arranged on the third layer 3, is a second refractory layer having a layer thickness d4. The layer thickness d4 preferably has a value between about 65 nm and about 125 nm, in particular between about 80 nm and about 110 nm, and preferably between about 90 nm and about 100 nm.

[0104] The fifth layer 5, starting from the substrate base 11, which is arranged on the fourth layer 4, is a third high-refractive-index layer having a layer thickness d5. The layer thickness d5 preferably has a value between about 2 nm and about 20 nm, particularly between about 5 nm and about 15 nm, and preferably between about 11 nm and about 13 nm.

[0105] The sixth layer 6, starting from the substrate base 11, which is arranged on the fifth layer 5, is a third refractory layer having a layer thickness d6. The layer thickness d6 preferably has a value between about 20 nm and about 60 nm, in particular between about 35 nm and about 50 nm, and preferably between about 40 nm and about 44 nm.

[0106] The seventh layer 7, starting from the substrate base 11, which is arranged on the sixth layer 6, is a fourth high-refractive-index layer having a layer thickness d7. The layer thickness d7 preferably has a value between about 40 nm and about 80 nm, particularly between about 50 nm and about 70 nm, and preferably between about 55 nm and about 65 nm.

[0107] Other layers can also be arranged between the first layer 1 and the substrate layer a. For example, an adhesion layer can be arranged on the substrate layer a. A substantially precipitating layer can also be arranged between the substrate layer a and the first layer 1.

[0108] On the seventh layer 7, a further, fourth refracting layer 9, in particular a quartz layer, is arranged. Between the seventh layer 7 and the refracting layer 9, a functional layer with a specific function can be arranged (not shown here). The last refracting layer 9, in conjunction with the other layers, serves in particular to provide anti-reflection in the visible range.

[0109] In the present case, layer layers 1-7, 9, and the substrate layer a of the substrate base 11 are depicted as planar layers. Such an embodiment can be advantageous as a highly simplified representation for essentially non-planar substrates, such as the freeform surfaces of a spectacle lens. This embodiment can also apply to planar substrates, such as essentially flat planar window glass. Ideally, all layer layers 1-7, 9 are essentially homogeneous in their respective layer thicknesses across the entire surface. However, deviations can occur. In this case, the layer thickness can correspond to a layer thickness averaged over the surface, a maximum layer thickness, or a layer thickness at a specific section of the surface.

[0110] The final layer 9, as mentioned previously, is in particular a low-refractive-index layer, preferably a SiO2 layer, which is suitable for antireflection of the layer system, especially for visible electromagnetic radiation. Layer 9 is particularly preferred in layer systems due to its good antireflection properties.

[0111] In the general case, a user B1 is in a typical operating position on the side facing away from the incident light L0, i.e., behind layer system 100 or on the side facing away from layers 1-7, 9. In other words, the typical operating position is characterized by the fact that a user B1, or rather their eyes, are on the side of layer system 100 facing away from the incident electromagnetic radiation L0 and layers 1-7, 9. Thus, a user B1 can be protected from harmful electromagnetic radiation by the reflection of the radiation from layer system 100. However, this does not apply to a typical user of a display protected by the layer system, since a display user is usually positioned on the side facing the incident light.

[0112] At the same time, the layer system 100 allows at least a proportion, preferably a high spectral proportion, of visible light L. t to pass through or traverse the layer system 100 or to propagate through the layer system 100, so that the user B1 is allowed or guaranteed the best possible view through the layer system 100.

[0113] The reflectivity R essentially corresponds to the ratio between intensity I r the reflected electromagnetic radiation L r and intensity I0 of the incident electromagnetic radiation L0. The intensities I r and I0 can be detected depending on the wavelength, especially between about 200 nm and 1400 nm, at different angles or viewing angles using one or more light-sensitive detectors.

[0114] The term "incident light L0" refers to electromagnetic waves that strike the surface of the layer system at an angle α' of approximately -90° to approximately 90°, and especially at approximately 0°, with the normal or substrate normal. The incident light L0 thus essentially enters the uppermost layer of the layer system from the side facing the layer layers, for example, the ninth layer 9.

[0115] The term "reflected light L r “ denotes, with regard to spectrum and intensity, the proportion of the incident light L0 which is reflected at the layer layers, for example at the top layer and / or at one of the other layer layers below the top layer layer.

[0116] The term “transmitted light L t“L0” denotes, with regard to spectrum and intensity, the fraction of the incident light that passes through the layer system and the substrate layer. Therefore, the transmitted light L t the proportion of incident light L0 that can reach the back, i.e., the side of the layer system facing away from the layer system.

[0117] Reflectivity (R) is a measure of the reflectivity of a surface. It can also be referred to as reflectance, reflectance value, or reflectivity. This quantity essentially corresponds to the ratio between reflected intensity or power and incident intensity or power. Reflectivity can be expressed as follows: R=IrI0=PrP0 where I r the intensity of reflected light L rand I0 corresponds to the intensity of incident light L0 and where P r P0 corresponds to the power of reflected light and P0 to the power of incident light.

[0118] The spectral infrared (IR) range of light essentially corresponds to electromagnetic radiation in the wavelength range from approximately 780 nm to approximately 1 mm. In this document, the term "infrared range" refers specifically to the near-infrared (NIR) range between approximately 780 nm and approximately 3 µm, and more specifically to the IR-A range between approximately 780 nm and approximately 1.4 µm. Electromagnetic radiation in the IR range can also be understood as non-visible or invisible light.

[0119] The visible spectral range of light corresponds to electromagnetic radiation in the wavelength range from approximately 380 nm to approximately 780 nm, and in particular from approximately 400 nm to approximately 750 nm. In this text, the term "visible range" refers specifically to the portion of electromagnetic radiation that is generally and essentially perceptible to humans. Electromagnetic radiation in the visible range can also be understood as visible light.

[0120] The ultraviolet (UV) spectral range of light corresponds to electromagnetic radiation in the wavelength range of approximately 100 nm to approximately 380 nm. In this document, the term "UV range" refers specifically to the UV-A and UV-B ranges, with UV-A lying between approximately 315 nm and approximately 380 nm and UV-B between approximately 280 nm and approximately 315 nm. However, the UV-C range, which lies between approximately 100 nm and approximately 280 nm, may also be included. Electromagnetic radiation in the UV range can also be understood as non-visible or invisible light.

[0121] Generally, the term "range" refers in particular to the wavelength range of electromagnetic radiation.

[0122] Fig. Figure 2 is a schematic side view of a layer system 110 according to an embodiment comprising a substrate base 11 with a substrate layer a and additional layer layers b, c. Furthermore, the layer system 110 comprises a plurality of layer layers 1-10 arranged on the substrate layer. Essentially, the Fig. 2 layer system 110 shown the individual elements, in particular the layer layers 1-7, 9, which are in the layer system 100 of the Fig. 1 are shown as examples and schematically, as well as further layer layers b, c, 8 and 10. Also those in the Fig. The two layers shown, 1-10, b, c and the substrate layer a, are essentially formed as planar layers.

[0123] In the present case, the substrate base 11 comprises, in addition to the substrate layer a, essentially two further layer layers b, c with respective layer thicknesses d. b and d c, namely, for example, a hard coating that is preferably applied directly to the substrate surface F a The substrate layer a is applied and, for example, includes an adhesion layer, preferably applied directly to the hard coating. Layer b is, in particular, a protective layer, also known as a hard coating or hard coat layer, and may, for example, comprise a hard lacquer, which is particularly suitable for providing scratch resistance. Alternatively or additionally, the layer system may include a primer lacquer designed to ensure high impact resistance and thus high stability. This is particularly advantageous for spectacle lenses or windshields.

[0124] The first layer 1, which here also corresponds to the first high-refractive-index layer, is applied to the adhesion layer c. The adhesion layer c has the effect of establishing reliable adhesion between the hard coating or hard layer b and the first layer 1, so that the first layer 1, along with all the other layers 2-10, adheres permanently to the substrate base 11, or rather to the last layer c of the substrate base, namely the adhesion layer. The adhesion is based primarily on a chemical bond between the adhesion layer c and the first layer 1. If a material is applied to a substrate surface, especially a relatively smooth one, it can happen that the material does not adhere sufficiently to the substrate surface and detaches from it under minimal influence.For this reason, an adhesion layer c is advantageous or required to prevent layer layers 1-10 or parts of the layer system 110 from detaching from the substrate base 11.

[0125] In other words, the adhesion layer c can be applied directly to the substrate surface F for better adhesion. a or serve on the applied hard layer b. This adhesion layer c can, for example, comprise substoichiometric low-reducing metal oxides, chromium, silanes, as well as siloxanes.

[0126] The layer system 110 comprises the three uppermost layer layers 8-10, each with three layer thicknesses d8, d9 and d 10 .

[0127] The eighth layer 8, arranged on the seventh layer 7, is preferably a functional layer, i.e., a substantially optically inactive layer, for example comprising Al₂O₃. The ninth layer 9, arranged on the eighth layer 8, is a fourth refractive layer. The tenth layer 10, arranged on the ninth layer 9, may preferably be a clean-effect layer.

[0128] An observer B2 of the layer system 110, who views it from the side of the incident light L0, can, at certain angles α, essentially see reflections of the reflected light L rPerceived, provided they lie within the visible spectral range. Alternatively, the position of an observer B2 can also be occupied by a light-sensitive detector. The observer B2 or detector can assume different viewing angles α. The angle α is determined by the substrate normal N. a or N b with a propagation direction of the reflected light L r This includes the light that falls into the eye of observer B2 or onto a sensor field of the detector. At approximately 0°, observer B2 of layer system 110 is essentially looking directly from "above" parallel to the substrate normal N. a or N b on the layer system 110, i.e. in the plumb line, from the side of layer layers 1-10, i.e. from the side of the incident light L0 and the light source that generates it.

[0129] The substrate normals N a or N bThey are characterized by forming a right angle with the planar surface, or a substantially planar surface segment, or an approximately planar surface segment to all sides of the surface. In other words, the substrate normals N are a or N b each around a perpendicular of the respective surface sections. The substrate normals N a or N b are parallel to each other in the present case, since the substrate layer a is an essentially planar substrate surface F a exhibits and thus different surface sections each have surface normals that have essentially the same direction and are therefore essentially parallel to each other.

[0130] This is a highly simplified case that may apply, for example, to planar window glass and / or display glass used to protect displays, but not to typical optical lenses with non-planar surfaces. The viewing angle α is determined here by the substrate position a or the substrate area F. a defined, since the substrate layer a in reality represents a significantly thicker layer compared to the layer layers 1-10, b, c, and the individual layer layers 1-10, b, c are essentially located on the substrate surface F a They are arranged in such a way that they essentially replicate these, since they have essentially homogeneous layer thicknesses. Thus, a substrate normal N corresponds to a or N b the substrate area F a essentially the respective normals of the layer surfaces of layer layers 1-10, b, c. In this way, the substrate normal N a or N bFor the sake of simplicity, simply referred to as substrate area F a The viewing angle α, used to characterize reflectivity, lies particularly between approximately 0° and approximately 45°. Within this range, at least partial reflections of visible light L can also be observed. r to be considered or recorded.

[0131] In contrast to observer B2, who reflected proportions L r The user B1, perceiving the incident light L0, sees on the other side of the layer system 110 non-reflected, i.e., transmitted, components of the incident light L0, which represent at least a part of the transmitted component L t of the incident light L0.

[0132] In particular, the exemplary and simplified layer system 110 of the Fig. 2, which essentially has no uneven surfaces, can be used to quantify, test, or demonstrate the technical effect (as a proof of principle), since in this case the viewing angles α are relatively easy to determine. A prototype or sample can correspond to this embodiment.

[0133] Fig. Figure 3 is a schematic side view of a layer system 120 according to an embodiment with a substrate base 11 comprising a substrate layer a and with a plurality of layer layers 1-4. The substrate layer a of the layer system 120 in Fig. In contrast to the shift systems 100 and 110, 3 has Fig. 1 and Fig. 2 a convex-concave shape, where the substrate area F acorresponds to a convex surface. In this case, it could, for example, be an optical lens. The substrate layer a is, by way of example, coated with a plurality of layer layers 1-4 comprising four layer layers 1, 2, 3, 4. In particular, the layer arrangement of the Fig. 1 or the Fig. 2. Applicable. Although the layer system has a convex shape, the individual layer layers can have essentially a constant thickness or only a slight variation in thickness. This is especially true if the thickness is small compared to the radius of curvature.

[0134] The first layer 1 can preferably be a first high-refractive-index layer with a layer thickness of d1. The second layer 2 can preferably be a first low-refractive-index layer with a layer thickness of d2. The third layer 3 can preferably be a second high-refractive-index layer with a layer thickness of d3. The fourth layer 4 can preferably be a second low-refractive-index layer with a layer thickness of d4. As in Fig. As indicated in point 3, further layers can be arranged on the fourth layer, namely those that are already present in the Fig. 1 and Fig. 2 were described. In particular, the ones described in the Fig. 1 and Fig. 2 layer systems shown in the Fig. The shape shown in 3, for example, could be designed as a lens shape.

[0135] The layer thicknesses d1, d2, d3, d4 are not homogeneous over the substrate area F in this case.a As illustrated, in the exemplary case shown here, the layer thicknesses d1, d2, d3, d4 each have a substantially maximum layer thickness near the central axis, which decreases towards the edge of the substrate layer a. The central axis coincides with the substrate normal N1 at the center or on the middle of the substrate surface F. a essentially agree.

[0136] However, in many preferred cases the layer thicknesses d1, d2, d3, d4 can also be essentially homogeneous, at least for partial sections of the substrate area F. a be designed. In other words, the layer thicknesses can preferably be designed such that they are uniform across the entire substrate surface F. a each layer has the same thickness.

[0137] In the present case, the exemplary substrate normals N1, N2, N3 are perpendicular to the substrate surface F. aThe substrate normals N1, N2, and N3 are not parallel to each other. According to a particular embodiment of the invention, the substrate normals N1, N2, and N3 are not parallel to each other because, in preferred cases, the substrate layer a and the layer layers 1-4 deviate substantially from a planar surface, i.e., they exhibit a curvature. This is the case, for example, when the substrate layer a is an optical lens, particularly a spectacle lens. If the substrate layer a is a window glass, the substrate layer a and the layer layers can each have substantially planar surfaces. Alternatively, non-planar substrate layers a are also suitable for window glass, particularly for vehicle windshields, which often have curvatures.

[0138] An observer B2, who is located on the side of the incident light L0 or on the side of the majority of the layer layers 1-4, can, unlike with a planar surface, see reflected visible light L on a non-planar surface. r A photodetector can perceive electromagnetic radiation from different viewing angles α1 and α2 without changing its position. Similarly, a photodetector can detect electromagnetic radiation from different viewing angles α1 and α2 without having to shift and / or rotate it. As a result, different wavelengths arrive at the eye or the detector from different angles. In the Fig. 3. This is indicated by the rays L. 01 and L 02The diagram shows angles α1 and α2, respectively, enclosed by normals N1 and N2, which are not parallel to each other due to the curvature. Therefore, a planar substrate without curvature is generally more suitable for the isolated observation and investigation of the spectrally resolved reflectivity for different viewing angles α1 and α2.

[0139] Fig. Figure 4 is a tabular representation of a layer system 130 according to an embodiment comprising a plurality of layer layers 1-10 and a substrate base 11 with a substrate layer a and further layer layers b, c.

[0140] The first layer 1 starting from the substrate base 11 is a first high-refractive-index layer comprising ZrO2, which is arranged on the substrate base 11 and has a layer thickness d1 of about 121.5 nm.

[0141] The second layer 2 starting from the substrate base 11, which is arranged on the first layer 1, is a first refraction layer comprising SiO2, which has a layer thickness d2 of about 151.0 nm.

[0142] The third layer 3 starting from the substrate base 11, which is arranged on the second layer 2, is a second high-refractive-index layer comprising ZrO2, which has a layer thickness d3 of about 106.2 nm.

[0143] The fourth layer 4 starting from the substrate base 11, which is arranged on the third layer 3, is a second refractive layer comprising SiO2, which has a layer thickness d4 of about 95.2 nm.

[0144] The fifth layer 5 starting from the substrate base 11, which is arranged on the fourth layer 4, is a third high-refractive-index layer comprising ZrO2, which has a layer thickness d5 of about 12.1 nm.

[0145] The sixth layer 6 starting from the substrate base 11, which is arranged on the fifth layer 5, is a third refractory layer comprising SiO2, which has a layer thickness d6 of about 42.0 nm.

[0146] The seventh layer 7 starting from the substrate base 11, which is arranged on the sixth layer 6, is a fourth high-refractive-index layer comprising ZrO2, which has a layer thickness d7 of about 59.6 nm.

[0147] The eighth layer 8 starting from the substrate base 11, which is arranged on the seventh layer 7, is a functional layer comprising Al2O3, which has a layer thickness d8 of about 9.8 nm.

[0148] The ninth layer 9 starting from the substrate base 11, which is arranged on the eighth layer 8, is a fourth descending layer comprising SiO2, which has a layer thickness d9 of about 74.9 nm.

[0149] The tenth layer 10, starting from the substrate base 11, which is arranged on the ninth layer 9, is a maintenance layer, for example comprising fluorine-containing molecules, which has a layer thickness d 10 The tenth layer, 10, is the uppermost layer in the layer system 130, located furthest from the substrate base.

[0150] In the present layer system 130, the substrate base 11 comprises, in addition to the substrate layer a, an exemplary hard layer b with an exemplary layer thickness d. b of approximately 2700 nm and an exemplary adhesion layer c with an exemplary layer thickness dc of about 10 nm.

[0151] According to one or more embodiments, one or more layer thicknesses d can be determined. 1-10, b, c each deviate by approximately 10%, in particular by approximately 5%, from the value stated above, i.e., be up to 10% thicker or thinner, in particular up to 5% thicker or thinner.

[0152] A layer system according to one embodiment can also comprise only layer layers 1 to 7 and in particular the ninth layer 9, and for example do without the tenth layer 10.

[0153] The hard layer b can, for example, also have a significantly thinner or significantly thicker layer thickness d. b exhibit. Alternatively, the hard layer b can be completely omitted, particularly in the preferred case that the hard layer b does not contribute to the optical properties of the layer system 130.

[0154] The hard layer b can be formed as an organic lacquer layer or as an inorganic layer such as SiO2, possibly with additives. Before the layer system is applied, the substrate area F can be prepared. a They can be conditioned using plasma treatment. The plasma treatment can aim at activation or functionalization.

[0155] The shift system 110 of the Fig. 2 can, for example, specify the tabular representation of the layer system 130 from Fig. exhibit 4. Also the 120-layer system made of Fig. 3 can have these specifications.

[0156] Fig. Figure 5 is a spectral plot of a measured reflectivity of a system similar to that in Fig. 4 specified layer system at a viewing angle of approximately 0°, for example at 8°. In other words, the spectral plot of reflectivity R corresponds to the fraction of reflected light L. r in relation to the incident light L0 when viewed perpendicularly from the top or furthest surface of the layer layers, starting from the substrate base. The observer here can be, in particular, a photodetector that spectrally resolves intensities I r of the reflected light L r can detect, in particular between about 280 nm and about 1400 nm. In particular, the reflectivity for a certain angular range, in particular between about 0° and about 60°, preferably between about 8° and about 50°, is recorded by means of a Perkin Elmer apparatus for detecting directional transmission and reflection.

[0157] To determine the reflectivity R, the intensity I0 of the incident light L0 is also recorded with spectral resolution, so that a relationship between I r and I0 can be used to determine reflectivity. A photodetector (e.g., a goniophotometer) can, for example, be mounted on a goniometer arm and the arm can be moved or rotated around the viewing angle 0° with the perpendicular or the substrate normal in order to perform further such spectral measurements at other viewing angles α.

[0158] The spectral plot of reflectivity R essentially comprises three regions: U for parts of the UV range, in particular the UV-A and UV-B ranges, V for the visible range, and I for parts of the near-infrared range, in particular the IR-A range.

[0159] The spectral plot of reflectivity R shows essentially three distinct maxima M1, M2, M3 and a comparatively weak maximum M4. In particular, the plot shows a "window region" in which the reflectivity is particularly low and which essentially covers the majority of the visible range.

[0160] As can be seen from the maximum M1, the reflectivity R at approximately 300 nm is nearly 70%, and in particular about 65-68%. This results in a particularly high level of protection against UV-B radiation, since almost 70% of the incident light L0 is reflected by the layers, and the eyes or tissue of a user are largely shielded from this harmful radiation by the layer system.

[0161] A maximum M2 at approximately 380 nm reaches a reflectivity of about 20%, particularly about 16-18%. The maximum M2 encompasses parts of the spectral UV-A range and parts of the spectral visible range, essentially the violet and possibly blue tones of the visible range.

[0162] The maxima M1 and M2 result according to a particularly preferred embodiment of the invention, wherein in addition to IR-A protection, UV protection is also to be achieved for a user.

[0163] According to the invention, a particularly prominent and broad maximum M3 is observed between approximately 680 nm and approximately 1100 nm at a viewing angle of approximately 0°. In the exemplary spectral plot of the Fig. In section 5, this maximum M3 is located at approximately 900 nm and reaches nearly 60%. Specifically, the reflectivity R rises sharply at approximately 670 nm, reaches the maximum M3 at approximately 880–900 nm, and then decreases at higher wavelengths, reaching a minimum of approximately 0% at approximately 1280 nm. The wavelength range around the maximum M3, in which the reflectivity is above 5–10%, partially encompasses the visible range with red tones and a large portion of the IR-A range, particularly the range in which the radiation has been found to be harmful. The spectral width at half maximum (WHM) of the maximum M3 is approximately 400 nm in this case. The spectral WHM of the maximum M3 is generally approximately 200 nm to approximately 900 nm, preferably approximately 300 nm to approximately 500 nm, and most preferably approximately 350 nm to approximately 450 nm.

[0164] The maximum M3 exhibits a region of steep slope between approximately 680 nm and approximately 880 nm. The slope in this region is approximately 40% per 100 nm. The region of steep slope can vary, for example, depending on the viewing angle and may lie, in particular, between approximately 560 nm and approximately 1000 nm, preferably between approximately 570 nm and approximately 920 nm, and most preferably between approximately 580 nm and approximately 900 nm. The slope in this region is, in particular, between approximately 20% per 100 nm and approximately 80% per 100 nm, more preferably between approximately 30% per 100 nm and approximately 60% per 100 nm, and most preferably between approximately 35% per 100 nm and approximately 45% per 100 nm.

[0165] In other words, the high reflectivity around the maximum M3 over a wide range, especially encompassing the IR-A range, indicates a high reflectivity that ensures particularly good protection of a user against IR-A radiation.

[0166] Fig. Figure 6 is a detailed view of a region of the spectral plot of reflectivity R. Fig. 5. The spectral plot of reflectivity between 380 nm and 780 nm is shown, clearly highlighting the maximum M4 at approximately 510–530 nm. At wavelengths higher and lower than the maximum M4, the reflectivity R reaches approximately 0%. For example, near-complete transmission, i.e., a reflectivity of approximately 0%, is achieved at around 480 nm and between approximately 580 nm and 630 nm. The maximum reflectivity M4, which occurs at slightly shorter wavelengths than 530 nm, reaches an absolute reflectivity value of approximately 2 to 3%. Another, but significantly smaller, maximum reflectivity R exists between approximately 430 nm and 480 nm. This maximum will not be described in detail here.

[0167] The reflection behavior beyond 780 nm is particularly irrelevant in the present case.

[0168] Fig. Figure 7 is the spectral plot S1, S2, S3, S4 of a measured reflectivity R of a system similar to the one in Fig. The four layer systems shown represent four different viewing angles, specifically approximately 45°, 30°, 15°, and 0°. As can be seen in the plots, the profiles of the respective spectrally plotted reflectivity R are relatively similar for the different viewing angles, but the profiles are shifted relative to each other. The spectral plot S1 for the viewing angle of approximately 45° is shifted to lower wavelengths relative to the other plots. For example, the rise to the maximum M3 begins at approximately 580 nm, whereas S2, at a viewing angle of approximately 30°, begins to rise to the maximum M3 at approximately 630 nm, and S3, for a viewing angle of approximately 15° and for a viewing angle of approximately 0°, begins to rise to the maximum M3 at approximately 650 nm. Furthermore, the maxima M2 and M4 are also shifted to approximately the same extent for the different spectral plots S1, S2, S3, and S4.

[0169] This results in a clearly visible reflection in red tones at a viewing angle of approximately 45°. As the viewing angle decreases, the reflection becomes less and less visible because, as described above, the spectral distribution of reflectivity shifts at small viewing angles such that the maximum, or the rise to the maximum M3, lies at higher wavelengths, particularly in the IR-A range.

[0170] This is particularly evident from the fact that the reflectivity R increases from a wavelength of about 630 nm, especially at about 680 nm and at a viewing angle α of about 45°. • is between about 10% and 20%, in particular about 15% higher, than with a viewing angle α of about 30°; • is between approximately 20% and 30% higher, in particular approximately 25% higher, than with a viewing angle α of approximately 15°; and • is between approximately 23% and 33%, in particular approximately 27% higher, than with a viewing angle α of approximately 0°.

[0171] Furthermore, the reflectivity R at a viewing angle α of approximately 45° and a wavelength of • at approximately 630 nm a value between approximately 10% and approximately 20%, in particular between approximately 13% and approximately 17%; • at approximately 680 nm, a value between approximately 30% and approximately 40%, particularly between approximately 33% and approximately 39%; and • at approximately 730 nm, a value between approximately 43% and approximately 53%, particularly between approximately 45% and approximately 50%.

[0172] The remaining reflectivity in the optical range, particularly for green and red tones, becomes "visible" especially when viewed from a minimum angle: When viewed straight on, i.e., at a viewing angle of approximately α ≤ 30°, particularly at approximately 0°, an observer perceives a high anti-reflective effect, especially in the visible range, including the red wavelength range, and only a negligible residual reflection of a green tone, i.e., for wavelength ranges in which electromagnetic radiation appears green to an observer. When viewed from an angle of approximately α > 30°, an observer can infer the protective property against IR-A radiation from the reflection in the red wavelength range, since from this viewing angle onward, some of the still partially visible red tones are also reflected.

[0173] The high anti-reflective effect in the visible wavelength range is maintained up to a certain viewing angle. Beyond this angle, the anti-reflective coating becomes a visible red mirrored effect, clearly indicating the IR protection to the observer. A viewing angle of approximately 30° corresponds essentially to the angle at which the reflective effect of the coating system becomes particularly noticeable. From this angle onward, the coating system prevents an observer from the outside—that is, from the side of the incident light, for example, the side opposite the wearer of the glasses—from seeing behind it, as the mirrored effect or reflectivity in the visible range reaches a high value. This angle can be moderately varied by changing or varying the coating thicknesses, while maintaining the described properties.This allows the typical position of the lenses in the frame to be taken into account during the layer development process, in order to prevent disturbing glare effects for the wearer of the glasses due to the red mirror coating being applied too early.

[0174] The maximum M3 exhibits a region of high slope between approximately 580 nm and approximately 900 nm for all indicated viewing angles α. Within this region, the slope is approximately 40% per 100 nm for all plots shown. The region of high slope can vary, for example, depending on the viewing angle and may lie, in particular, between approximately 560 nm and approximately 1000 nm, preferably between approximately 570 nm and approximately 920 nm, and most preferably between approximately 580 nm and approximately 900 nm. Within this region, the slope is particularly between approximately 20% per 100 nm and approximately 80% per 100 nm, more preferably between approximately 30% per 100 nm and approximately 60% per 100 nm, and most preferably between approximately 35% per 100 nm and approximately 45% per 100 nm.

[0175] A layer system based on one of the aforementioned aspects and / or embodiments can be determined theoretically using a simulation by basing the calculation on the optical constants and layer thicknesses of a chosen material. Alternatively, an existing layer system can be examined for its reflective properties using suitable reflection measurements. Of particular interest is determining at which angle which spectral components of light are reflected or transmitted. In other words, a reflection measurement should reveal which colors are reflected by or transmitted through the layer system at which angles of incidence and viewing.

[0176] Reflectance measurements are preferably performed on a substantially planar layer system with negligible surface curvature, such as in Fig. 1 and Fig. 2 shown – this was done in particular to better control the relationship between the angles of incidence and observation. However, it is also conceivable that a curved surface of a layered system, for example a lens, especially a spectacle lens – as for example in Fig. Figure 3 illustrates how reflectivity can be investigated using a suitable reflection measurement. In practice, however, it is relatively difficult to strike the same point on a planar surface at different angles, especially at high angles, with the incident light beam. Therefore, it can be difficult to reliably characterize a curved surface with respect to its reflectivity. In general, it is comparatively difficult to obtain reliable data for high angles of incidence, particularly for angles between approximately 40° and 90°, with regard to polarization, beam profile, measurement spot size, and beam displacement by the back of the sample. For example, the reflectivity and transmission properties can vary considerably for different polarizations of the incident light, especially in the range between approximately 40° and 85° for the angle of incidence.Furthermore, the area that is irradiated can also vary at different, particularly shallow, angles of incidence.

[0177] Commercial spectrometers, such as those sold by manufacturers like PerkinElmer, are particularly suitable for investigating the reflection properties of a layer system. For example, the "PerkinElmer Lambda 750 UVNis / NIR" model, equipped with a suitable accessory (URA, Universal Reflectance Accessory), reliably enables essentially unpolarized reflection measurements at various angles. Such a setup was used for the reflection measurements presented in this paper.

[0178] Fig. Figure 8 a) schematically shows an exemplary arrangement of the surface F under investigation with respect to the incident light EL and the reflected light RL. A fictitious plane of incidence EE indicates the symmetries. The plane of incidence is essentially determined by the normal L of the surface under investigation at the point of incidence of the incident light EL and the wave vector or direction of propagation of the incident light EL.

[0179] Ideally, especially under laboratory conditions, the incident light should consist of essentially coherent and parallel radiation. At a minimum, when measured, the incident light exhibits a main direction of propagation and a high proportion of parallel beams, allowing the angle between the normal (L) and the incident light (EL) to be defined as precisely as possible. In practice, it goes without saying that everyday light sources generally do not consist of parallel beams and are therefore isotropic or scattering light sources.

[0180] The measuring setup generally does not permit reflection measurements at an angle of incidence α' and an observation angle α of exactly 0°. Typically, the actual smallest angle α' or α below which reflectivity can just be measured lies above 0° and below approximately 15°, specifically between approximately 3° and approximately 10°. This actual, measurable angle is device-specific and may therefore be, for example, approximately 3° or approximately 8°, depending on the device. The angles α' and α of approximately 0° given in this document thus actually include angles slightly above 0°. In particular, the smallest measurable angle α' or α is approximately 3°, so the sum of both angles α' and α, which corresponds to the opening angle enclosed by the incident light EL and the reflected light RL, is approximately 6°, i.e., twice 3°.The angle of incidence α' and the angle of observation α are the respective half-angles enclosed by the normal of the surface at the point of impact of the light and the incident light ray or the reflected light ray, respectively.

[0181] The Fig. 8 a) indicates that at least parts of the light EL incident on the surface F under investigation and the light RL reflected from the surface may exhibit a polarization, for example a polarization P parallel to the plane of incidence EE and / or a polarization S perpendicular to the plane of incidence EE.

[0182] The measurements shown in this document, in particular the reflectivity plots or reflection curves, as they are shown, for example, in Fig. 5, Fig. 6 and Fig. The measurements shown in Figure 7 were essentially performed with unpolarized incident light. In other words, at least the incident light does not exhibit any collective polarization, for example in the S or P direction.

[0183] Fig. Figure 8 b) schematically shows an exemplary measurement configuration at an angle of incidence α' of approximately 45°. Fig. Figure 8 c) schematically shows an exemplary measurement configuration at an angle of incidence α' of approximately 80°. The angle of incidence α' and the angle of reflection α, which corresponds to the viewing angle, are adjusted using rotatable mirrors so that the incident light EL is directed from below onto the surface under investigation by means of a first mirror, and the reflected light is reflected at an angle α by a surface that is at least partially reflective and exits the setup via the second mirror. The measurement configuration shown in Fig. Figure 8 c) indicates particularly large angles α' and α to the normal. Alternatively, instead of rotatable mirrors, the setup can also include optically reflective elements on at least one actuator and / or on a rotatable goniometer arm to cover different angular positions.

[0184] Fig. Figure 9 is the tabular representation of spectral parameters of the in Fig. Figure 5 shows the reflection curve of an exemplary layer system for four different viewing angles α, namely approximately 0°, 15°, 30°, and 45°. The trends for each of the quantities shown, depending on the respective viewing angle α, are explained in more detail below. A supplementary explanation is provided in connection with Fig. Given 10a-e.

[0185] The reflection properties are described by the parameters Rv, Rv', L*, C*, h* and by RM_(380-780nm) in the visible range and RM_(780-1150nm) in the IR-A range, as well as by suitable calculation of the reflection values ​​in the IR-A range with the thermal weighting function, which is described according to ICNIRP Guidelines 2013.

[0186] The parameters L*, C*, and h* refer specifically to luminance, saturation, and hue in the color wheel in polar coordinates (DIN 11664-1 / 2). Rv and Rv' refer specifically to the visual reflectance (DIN 13666), with Rv pertaining to daytime vision and Rv' to twilight vision. RM refers to the average reflectance. Specifically, RM_(380-780nm) refers to the reflectance in the visible range, specifically for the range between 380 nm and 780 nm, and RM_(780-1150nm) refers to the reflectance in the infrared range between 780 nm and 1150 nm. The reflectance is averaged by averaging all reflectance values ​​over all wavelengths within the corresponding wavelength range. The average reflection is calculated according to DIN EN ISO 13666:2019, whereby the integration limits are adjusted accordingly.

[0187] The luminosity L* increases gradually from low angles to approximately 45°. In other words, the luminosity at 45° is comparatively higher than at lower angles, at approximately 18.8, whereas the luminosity at approximately 0° is only about 4.7.

[0188] Just like luminance, saturation C* increases with increasing angle. For example, at approximately 45° the saturation has a value of about 41.2, whereas at approximately 0° it has a value of about 2.8.

[0189] The color value in the color wheel in polar coordinates h* is approximately 195.1 at about 0° and drops to about 10.7 at about 45°. This essentially corresponds to a color shift from predominantly green to red colors, which in Fig. 10 ae will be explained in more detail.

[0190] The light reflection values ​​Rv for day vision and Rv' for twilight vision increase from approximately 0.52% and approximately 0.77% respectively at approximately 0° to approximately 2.7% and approximately 1.4% respectively.

[0191] The reflectivity in the visible range RM_(380-780nm) increases from a value of approximately 8% at 0° to approximately 16.7% at approximately 45°. Conversely, the reflectivity in the IR range RM_(780-1150nm) decreases from a value of approximately 35.8% at approximately 0° to approximately 23.6% at approximately 45°.

[0192] In the Fig. 10 a) A C*h* plot for residual reflectance colors is shown as the viewing angle α is varied from approximately 0° to approximately 45°. In other words, the progression of the residual reflectance colors as the viewing angle α is varied from approximately 0° to approximately 45° is shown, with the color value plotted in polar coordinates on the color circle. The points on the color circle each correspond to a color and are colored accordingly in the plot between approximately 0° and approximately 45°. The trend of the residual reflectance color can be seen: at an angle α of approximately 0°, it appears green, at an angle α of approximately 23°, it exhibits green and red color components, and at an angle α of approximately 45°, it is essentially red.

[0193] Fig. Figure 10 b) shows the progression of the residual reflected color in a different representation, specifically when varying the viewing angle α from approximately 0° to approximately 45°, with the color value being plotted against the viewing angle α. Here, too, the trend is evident that the residual reflected color appears essentially green at an angle α of approximately 0°, exhibits green and red color components at an angle α of approximately 23°, and is essentially red at an angle α of approximately 45°.

[0194] Fig. Figure 10c) shows the plot of luminosity L* against the viewing angle α. Between approximately 0° and 25°, the luminosity exhibits essentially constant values ​​of about 4. From about 30° onwards, the luminosity L* increases steadily, and particularly between approximately 38° and 43°, it appears to increase constantly by about 10 units per 10°, reaching a value of approximately 15 L* at about 45°. Thus, the luminosity increases steadily with increasing viewing angle α.

[0195] The applications in Fig. 10 d) and Fig. 10 e) largely exhibit similar behavior to the application of the Fig. 10 c). Fig. Figure 10 d) shows the plot of the visual reflectance Rv' for twilight vision against the viewing angle α. Between approximately 0° and 25°, the visual reflectance Rv' shows essentially constant values ​​of about 0.6%. From about 35° onwards, the visual reflectance Rv' increases steadily, reaching a value of approximately 1.1% at about 45°. Thus, the visual reflectance Rv' for twilight vision increases steadily with increasing viewing angle α. Fig.Figure 10 e) shows the plot of the visual reflectance Rv for daytime vision against the viewing angle α. The visual reflectance Rv shows essentially constant values ​​of about 0.5% between approximately 0° and 25°. From about 35° onwards, the visual reflectance Rv increases steadily and reaches a value of Rv' of about 1.8% at about 45°. Thus, the visual reflectance Rv for daytime vision increases steadily with increasing viewing angle α.

[0196] The following section specifies and describes in more detail further features that are referenced in the description.

[0197] Vehicle windows include, in particular, windows such as windshields and / or rear windows for motor vehicles, passenger vehicles and trucks, and / or windows for trains, aircraft, motorcycles or other vehicles.

[0198] The high-refractive-index and low-refractive-index layers essentially correspond to optically active or optically relevant layers, which are primarily responsible for the reflectivity of the layer system. It cannot be ruled out that other functional layers may also be high- or low-refractive-index and thus contribute to optical activity; however, such layers preferably contribute little or nothing to the reflectivity of the layer system.

[0199] Suitable examples of coating materials with different refractive indices are silicon dioxide (SiO2) with a refractive index n of approximately 1.46, aluminum oxide (Al2O3) with a refractive index n of approximately 1.7, zirconium dioxide (ZrO2) with a refractive index n of approximately 2.05, praseodymium titanium oxide (PrTiO3) with a refractive index n of approximately 2.1, titanium oxide (TiO2), and zinc sulfide (ZnS), each with a refractive index n of approximately 2.3. The values ​​mentioned represent average values ​​measured at a wavelength of approximately 550 nm, and the values ​​can vary by up to 10% depending on the coating process and layer thickness. Typical optical glasses have refractive indices between approximately 1.5 and 2.0.Layer materials with refractive indices less than approximately 1.5, such as MgF₂, SiO₂, and Al₂O₃, are therefore referred to as low-refractive-index materials when combined with optical glasses. Layer materials with refractive indices greater than approximately 2.0, such as ZrO₂, PrTiO₃, TiO₂, and ZnS, are referred to as high-refractive-index materials when combined with optical glasses. The difference in refractive indices between high- and low-refractive-index materials is therefore at least 0.2 to at least 0.5, depending on the coating process and layer thickness.

[0200] High-refractive-index layers can, in particular, contain at least one of the following materials: Ta₂O₅, TiO₂, ZrO₂, Al₂O₃, Nd₂O₅, Pr₂O₃, PrTiO₅, La₂O₃, Nb₂O₅, Y₂O₃, HfO₂, ITO (indium tin oxide), Si₃N₄, MgO, CeO₂, and their modifications, especially their other oxidation states. These materials are known as materials with a high classical refractive index for use in optical elements, such as for coating spectacle lenses. However, the high-refractive-index layers can also contain SiO₂ or other low-refractive-index materials, as long as the refractive index of the entire sublayer is greater than 1.6.

[0201] The lower refractive index layers can, in particular, comprise at least one of the following materials: SiO₂, SiO₂, silanes, or siloxanes. However, the lower refractive index layers can also contain a mixture of SiO₂ and Al₂O₃. Preferably, the lower refractive index layers contain at least 80% by weight of SiO₂, and more preferably at least 90% by weight of SiO₂.

[0202] The materials used for these types of coatings are typical materials applied in optics using processes such as PVD (Physical Vapor Deposition) or CVD (Chemical Vapor Deposition). This means that SiO2 and mixtures containing SiO2 are preferred as low-refractive-index materials. All typical high-refractive-index oxide materials and their mixtures are suitable as high-refractive-index materials (e.g., Ta2O5, Ti). x O y, ZrO2, etc.). The choice of a specific material composition, as was sometimes necessary with previous coatings, is no longer required with the coating system according to the invention. Thus, all typical high-refractive-index metal oxides and their mixtures used in the optical industry (Ta2O5, Ti) can be used as high-refractive-index materials. x O y , ZrO2 and the like).

[0203] All typical low-refractive-index metal oxides and their mixtures used in the optical industry can be used as low-refractive-index materials (SiO, SiO2, SiO2 with additions Al, SiO as well as silanes and siloxanes in pure form or with their fluorinated derivatives and the like).

[0204] SiO2 typically has a refractive index of 1.46 to 1.62, depending on the packing density, while Al2O3 typically has a refractive index of 1.67. The difference in refractive indices between the higher and lower refractive sublayers is therefore between 0.2 and 0.5.

[0205] The surfaces of the layered components and / or the substrate surface can be activated and / or functionalized by means of plasma conditioning. For example, a plasma for this purpose can include Ar, O2, N2, or similar gases.

[0206] A reflectivity maximum can generally be determined by calculating the absolute value of the local maximum reflectivity. Alternatively, the difference in reflectivity between the local maximum and the local minima on either side can be determined. In particular, the local minima on both sides of the local maximum are approximately the same value, especially when the reflectivity is around 0%. If this is not the case, the mean difference in reflectivity between the local maximum and the local minima on both sides can be used, or a baseline can be considered.

[0207] All values ​​given are to be understood as approximate values ​​within the limits of measurement accuracy. Reference symbol list 1 First layer: First high-refracting layer 2 Second layer: First descending layer 3 Third layer: Second high-refracting layer 4 Fourth layer: Second descending layer 5 Fifth layer: Third high-breaking layer 6 Sixth layer: Third descending layer 7 Seventh layer: Fourth high-refracting layer 8 Eighth layer: functional layer 9 Ninth layer: Fourth descending layer 10 Tenth layer: Nursing shift layer 11 Substrate base 100 layer system according to one embodiment 110 Layer system according to one embodiment 120 layer system according to one embodiment 130 layer system according to one embodiment α, α1, α2 Viewing angle, reflection angle α' Angle of incidence a substrate position of the substrate base b Hard layer B1 users, for example, eyeglass wearers in the usual usage position on the side of the layer system facing away from the incident light B2 Viewer in top view from the side of the layer system facing the incident light c adhesion layer d1 Layer thickness of the first layer d2 Layer thickness of the second layer d3 Layer thickness of the third layer d4 Layer thickness of the fourth layer d5 Layer thickness of the fifth layer d6 Layer thickness of the sixth layer d7 Layer thickness of the seventh layer d8 Layer thickness of the eighth layer d9 Layer thickness of the ninth layer d 10 Layer thickness of the tenth layer d b Layer thickness of layer b of the substrate base d c Layer thickness of layer c of the substrate base EE level of incidence EL Light incident on a surface F At least partially reflective surface F a Substrate area I Spectral infrared range L perpendicular to the surface under investigation at the point of incidence of the incident light L0, L 01 , L 02 Incident light with intensity I0 L r , L r1 , L r2 Reflected light with intensity I r Lt Transmitted light with intensity I t M1 Reflectivity maximum M2 Reflectivity maximum M3 Reflectivity Maximum M4 Reflectivity Maximum N1 substrate normals N2 substrate normals N3 substrate normals N a Substrate normals N b Substrate normals P Parallel polarized light RL Light reflected from a surface S Vertically polarized light S1 reflectivity spectrum S2 reflectivity spectrum S3 reflectivity spectrum S4 reflectivity spectrum U Spectral ultraviolet range V Spectral visible range

Claims

[1] Layer system (100; 110; 120; 130) comprising infrared mirror coating - a substrate base (11) comprising a substrate layer (a) with a substrate area (F) a ); and - a plurality of descending layer layers (2, 4, 6) and a plurality of descending layer layers (1, 3, 5, 7), wherein an descending and a descending layer layer alternately form on the substrate surface (F a ) are arranged such that the layer system (100; 110; 120; 130) at a detection angle of approximately 0° with at least one substrate normal (N1, N2, N3; N a , N b ) of the substrate area (F a ) • has a reflectivity for electromagnetic radiation of R ≥ 15% for at least one wavelength range between approximately 680 nm and approximately 1100 nm; and • has a reflectivity for electromagnetic radiation of R ≤ 5% for at least one wavelength range between approximately 400 nm and approximately 680 nm; wherein the reflectivity from a wavelength of approximately 630 nm for a viewing angle α of approximately 45° - is between about 10% and 20% higher than with a viewing angle α of about 30°; - is between approximately 20% and 30% higher than with a viewing angle α of approximately 15°; and - is between approximately 23% and 33% higher than with a viewing angle α of approximately 0°. [2] Layer system (100; 110; 120; 130) according to claim 1, wherein the layer layers are attached to the substrate surface (F) a ) are arranged such that the layer system (100; 110; 120; 130) is aligned with the substrate normal (N1, N2, N3; N) at a detection angle of approximately 0° a , N b ) of the substrate area (F a ) has a reflectivity for electromagnetic radiation of R ≥ 10% for at least one wavelength range between approximately 280 nm and approximately 400 nm. [3] Layer system (100; 110; 120; 130) according to one of the preceding claims, wherein the layer layers are attached to the substrate surface (F) a ) are arranged such that the layer system is aligned with the substrate normal (N1, N2, N3; N) at a detection angle of approximately 0°. a , N b ) of the substrate area (F a ) has a reflectivity maximum of R ≤ 1% for at least one wavelength range between approximately 400 nm and approximately 680 nm. [4] Layer system (100; 110; 120; 130) according to one of the preceding claims, wherein the plurality of high-refractive-index layer layers (1, 3, 5, 7) comprise at least one of the materials: Ta2O5, TiO2, Ti x O y , ZrO2, Al2O3, Nd2O5, Pr2O3, PrTiO3, La2O3, Nb2O5, Y2O3, HfO2, ITO (indium tin oxide), ZnS, Si3N4, MgO, CeO2. [5] Layer system (100; 110; 120; 130) according to any of the preceding claims, wherein the plurality of breaking layer layers (2, 4, 6, 9) comprises at least one of the materials: MgF2, SiO, SiO2, silanes, siloxanes, a mixture comprising SiO2 and Al2O3. [6] Layer system (110; 120; 130) according to one of the preceding claims, wherein the layer layers, starting from the substrate base (11), comprise arranged in the following sequence: a first high-refracting layer(1); a first descending layer (2); a second high-refracting layer (3); a second descending layer (4); a third high-refracting layer (5); a third descending layer (6); a fourth high-refracting layer (7); and a fourth descending layer (9). [7] Layer system (110; 120; 130) according to claim 6, wherein the low-refractive layer layers homogeneously comprise a low-refractive material and / or the high-refractive layer layers homogeneously comprise a high-refractive material and wherein the high-refractive material does not comprise a high-refractive or very high-refractive material. [8] Layer system (110; 120; 130) according to one of the preceding claims, wherein the layer layers, starting from the substrate base (11), comprise arranged in the following sequence: a first high-refractive-index layer(1) with a layer thickness (d1) of at least approximately 118 nm; a first refraction layer (2) with a layer thickness (d2) of at least approximately 135 nm; a second high-refractive-index layer (3) with a layer thickness (d3) of at least approximately 70 nm; a second refractive layer (4) with a layer thickness (d4) of at least approximately 80 nm; a third high-refractive-index layer (5) with a layer thickness (d5) of at least approximately 5 nm; a third refractive layer (6) with a layer thickness (d6) of at least approximately 35 nm; a fourth high-refractive-index layer (7) with a layer thickness (d7) of at least approximately 55 nm; and a fourth refractive layer (9) with a layer thickness (d9) of at least about 60 nm. [9] Layer system (110; 120; 130) according to any of the preceding claims, wherein the layer layers, starting from the substrate base (11), comprise arranged in the following sequence: a first high-refractive-index layer(1) with a layer thickness (d1) of at most about 130 nm; a first refractory layer (2) with a layer thickness (d2) of at most about 160 nm; a second high-refractive-index layer (3) with a layer thickness (d3) of at most about 120 nm; a second refractory layer (4) with a layer thickness (d4) of at most about 105 nm; a third high-refractive-index layer (5) with a layer thickness (d5) of at most about 15 nm; a third refractory layer (6) with a layer thickness (d6) of at most about 45 nm; a fourth high-refractive-index layer (7) with a layer thickness (d7) of at most about 80 nm; and a fourth refractive layer (9) with a layer thickness (d9) of at most about 80 nm. [10] Layer system (110; 120; 130) according to one of the preceding claims, wherein the layer layers, starting from the substrate base (11), comprise arranged in the following sequence: a first high-refractive-index layer(1) with a layer thickness (d1) of about 121.5 nm; a first refraction layer (2) with a layer thickness (d2) of about 151 nm; a second high-refractive-index layer (3) with a layer thickness (d3) of approximately 106.2 nm; a second refraction layer (4) with a layer thickness (d4) of approximately 95.2 nm; a third high-refractive-index layer (5) with a layer thickness (d5) of about 12.1 nm; a third refractory layer (6) with a layer thickness (d6) of about 42 nm; a fourth high-refractive-index layer (7) with a layer thickness (d7) of approximately 59.6 nm; and a fourth refractory layer (9) with a layer thickness (d9) of approximately 74.9 nm. [11] Layer system (110; 130) according to one of the preceding claims, further comprising a functional layer (8), in particular comprising Al2O3, which has a layer thickness (d5) of at least about 8 nm and at most about 11 nm. [12] Layer system (110; 130) according to one of the preceding claims, wherein the substrate base further comprises: a protective layer (b), in particular a lacquer layer or an organic layer, with a layer thickness (db) of at least about 500 nm and at most about 5 µm; and preferably an adhesion layer (c), in particular comprising low-fracturing metal oxides, chromium, silanes and / or siloxanes, with a layer thickness (d c ) of at least approximately 1 nm and at most approximately 20 nm. [13] Layer system (100; 110; 120; 130) according to one of the preceding claims, wherein the substrate base (11) comprises an optical element. [14] Layer system (100; 110; 120; 130) according to one of the preceding claims, wherein the substrate base (11) comprises a disk, in particular a disk of a display. [15] Layer system (100; 110; 120; 130) according to one of the preceding claims, wherein the reflectivity (R) of electromagnetic radiation in a wavelength range between about 560 nm and about 1000 nm has a slope between about 20% per 100 nm and about 80% per 100 nm, at least for a sub-section of the wavelength range. [16] Layer system (100; 110; 120; 130) according to one of the preceding claims, wherein the reflectivity at about 680 nm for a viewing angle α of about 45° • is approximately 15% higher than with a viewing angle α of approximately 30°; • is approximately 25% higher than with a viewing angle α of approximately 15°; and • is approximately 27% higher than with a viewing angle α of approximately 0°. [17] Layer system (100; 110; 120; 130) according to one of the preceding claims, wherein the reflectivity at a viewing angle α of about 45° and a wavelength of • at approximately 630 nm, it exhibits a value between approximately 10% and approximately 20%; • at approximately 680 nm, it exhibits a value between approximately 30% and approximately 40%; and • at approximately 730 nm, it exhibits a value between approximately 43% and approximately 53%. [18] Method for producing a layer system (100; 110; 120; 130) comprising infrared mirroring Providing a substrate base (11) comprising a substrate layer (a) with a substrate area (F) a ); and Arrange on the substrate surface (F a ) a plurality of low-refractive layer layers (2, 4, 6, 9) and a plurality of high-refractive layer layers (1, 3, 5, 7), wherein a layer layer with high-refractive properties and a layer layer with low-refractive properties are arranged alternately, such that the layer system (100; 110; 120; 130) at a detection angle of approximately 0° with a substrate normal (N1, N2, N3; N a , N b ) of the substrate area (F a ) has a reflectivity of electromagnetic radiation of R ≥ 15 % for at least one wavelength range between about 680 nm and about 1100 nm; has an electromagnetic reflectivity of R ≤ 5% for at least one wavelength range between approximately 400 nm and approximately 680 nm; and The reflectivity from a wavelength of approximately 630 nm for a viewing angle α of approximately 45° - is between about 10% and 20% higher than with a viewing angle α of about 30°; - is between approximately 20% and 30% higher than with a viewing angle α of approximately 15°; and - is between approximately 23% and 33% higher than with a viewing angle α of approximately 0°.

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