Optical filter and artificial light illumination device that reproduce empty and sunlight using the same thing

Abstract

The present invention relates to an entrance surface (101) and an exit surface (102) that are substantially flat and parallel, and a plurality of locally planar and locally parallel to each other visible light absorption sectors (108) extending in a sector length (L) between the entrance surface (101) and the exit surface (102), a plurality of solid transparent sectors (103) made of at least one solid material transparent to visible light, each transparent sector (103) of the plurality of transparent sectors being arranged between two absorption sectors (108) and forming an alternating arrangement in which the transparent sectors (103) and the absorption sectors (108) are adjacent to and in contact with each other. Each visible light absorption sector (108) of the plurality of visible light absorption sectors (108) is in contact with at most two transparent sectors (103) of the plurality of transparent sectors, and / or the distance between adjacent absorption sectors (108) of the plurality of absorption sectors (108) is substantially constant. Each transparent sector (103) of the plurality of transparent sectors is provided with a first parallel light (201) that hits the entrance surface (101) along the incident direction (D) in a local region of the entrance surface (101), and the transparent sector (103) focuses the first parallel light (201) along a first focal line (203) orthogonal to the local incident surface (P), and / or a second parallel light (202) that hits the exit surface (102) along the incident direction (D) in a local region of the entrance surface (101) is provided, and the transparent sector (103) is locally arranged and configured to have a refractive power to focus the second parallel light (202) along a second focal line (204) orthogonal to the local incident surface (P). A plane orthogonal to the entrance surface (101) and including a normal (N) to the absorption sector (108) of the plurality of absorption sectors D in a local region of the entrance surface (101) defines the local incident surface (P), and the intersection between the local incident surface (P) and the surface of the absorption sector (108) defines an incident direction (D) that is substantially common to the entire entrance surface (101), referring to an optical filter (100).

Description

Technical Field

[0001] The present invention generally relates to a new optical filter, and is particularly suitable for obtaining a uniform and clear sky effect in an illumination device for artificial reproduction of sky and natural sunlight, removing the low-angle glare effect in a ceiling illumination device, or preventing side viewing (side view) of a display.

Background Art

[0002] The main feature of a device adapted to reproduce sky and natural sunlight is, in particular, the ability to generate an image of the sun perceived by an observer as being like an infinite distance and a clear sky image that is clearly contrasted with the sun. For this purpose, the applicant has shown in International Application No. WO2014 / 075721 one of the possible approaches of generating direct or collimated light that mimics the sun characterized by a spatially uniform angular luminance profile and direct light CCT (correlated color temperature), and a spatially uniform diffused light that mimics the light of the sky with a diffused light CCT significantly higher than the direct light CCT.

[0003] In order to obtain the effects necessary to reproduce natural light with a small, lightweight, and economical device that has not been industrially produced according to market standards to date, the applicant has proposed illuminating a nanostructured diffuser panel with a plurality of appropriately collimated LED light sources. In order to make the presence of a plurality of different light sources hardly perceptible and to obtain the uniformity of luminance necessary to infinitely generate the image of a single sun, the applicant proposed in WO2015 / 172794 the use of a homogenizing filter made of a set of lens arrays coupled to each other by a common focal length and spaced apart, also called a "tandem filter" or a "fly's eye condenser". However, this solution has the well-known problem of crosstalk between adjacent channels, where multiple ghost images of the sun are generated. For the miniaturization, weight reduction, and cost reduction of the device, the applicant has also proposed using a Fresnel optical system instead of a conventional optical system for the collimation of direct light. However, this solution has the limitation of generating significant stray light, i.e., unwanted light. The stray light propagates at an angle greater than the angle useful for reproducing the image of the sun, generating a background of direct light that reduces the contrast between the empty image and the image of the sun, and generating an image of the sun diffused in the dark sky or an image with unnatural light streaks in the sky. The solution proposed by the applicant to at least partially solve the above-mentioned problems is to adopt a two-dimensional multi-channel spatial filter with absorption channels, formed by a two-dimensional matrix of empty channels separated from each other by absorption walls, such as honeycomb filters, as a solution to remove both the ghost images generated by the tandem filter and the stray light generated by the Fresnel optical system.However, this solution presents a triple problem of (i) low transmission efficiency, i.e., having a 50% transmittance for incident light having a constant luminance profile with respect to directions within the angular acceptance cone of the filter, (ii) being costly due to complex manufacturing, as the required channel length / diameter ratio values for generating a realistic solar image are high, and (iii) generating a spatially modulated luminance pattern in sequence. The applicant has proposed the use of a low-angle diffusion filter (frost) to remove this. As shown by the applicant, such a low-angle diffuser has the further advantage of being able to convert a square solar image, such as the image obtained in an optical system that projects the image of an LED infinitely, or a hexagonal solar image, such as the image obtained using a hexagonal cell tandem filter, into the conventional round solar image within an optical system that reproduces a reliable image of the sun. However, such a low-angle diffuser necessarily degrades the contrast and creates a blurred image of the sun, such as occurs in nature due to the presence of fog or haze. SUMMARY OF THE INVENTION

[0004] The applicant has surprisingly noticed that spurious light, such as that generated by a Fresnel optical system, which is normally present in devices adapted to reproduce images of the sky and the sun, is not statistically uniform and / or isotropic. In contrast, spurious light typically appears from specific points of an optical system along specific known directions. Therefore, the applicant has realized that the removal of spurious light may require an optical filtering system that is much simpler and less expensive than previously thought and / or can provide a light transmittance clearly higher than 50% for incident light having a constant luminance profile with respect to directions within the angular acceptance cone of the filter.

[0005] Accordingly, an object of the present invention is to devise an optical filter that can overcome the drawbacks of the prior art.

[0006] Within the scope of this problem, an object of the present invention is to devise an optical filter that can realize an illumination device for reproducing natural light of the sky and the sun, which is inexpensive, compact, and has a clear contrast with an image of the sun perceived at an infinite distance from the sun.

[0007] Another object of the present invention is to effectively and efficiently remove the problem of "stray light" of a radial type Fresnel collimator, such as one used for collimating light generated by an LED light source, or a linear type Fresnel collimator, such as one used for deflecting the propagation direction of light in a transmission or reflection pattern to make the size of the device compact.

[0008] A further object of the present invention is to devise an optical filter that eliminates the need for the use of tandem filters and / or multi-channel spatial filters having absorption channels and / or filters, and low-angle diffusion filters when employed in an illumination device for reproducing natural light of the sky and the sun.

[0009] An object of the present invention is to devise an optical filter that, in combination with a Fresnel collimator illuminated at the focus by a source of square or rectangular or other shape, creates an infinite circular source and thus an image of a circular sun.

[0010] Finally, an object of the present invention is to realize an anti-glare filter commonly employed in the lighting sector to remove light radiated from a wide-angle illumination device with respect to the main emission direction.

[0011] An object of the present invention is to realize a privacy filter for a display having high efficiency and high angular selectivity.

[0012] A further object of the present invention is to develop an illumination device for reproducing natural light of the sky and the sun, which is inexpensive, compact, and can generate an image of the sun and a clear sky with a sharp contrast to the image of the sun perceived at an infinite distance from the sun.

[0013] These and other objects of the present invention are achieved by an optical filter for an illumination device for reproducing natural light of the sky and the sun, which incorporates the features of the appended claims that form an integral part of this specification.

[0014] Accordingly, in a first aspect of the present invention, there is provided a multilayer optical filter having an absorption sector, comprising: a substantially flat and parallel inlet surface and outlet surface; a plurality of visible light absorption sectors that are locally planar and locally parallel to each other and extend in a sector length between the inlet surface and the outlet surface; and a plurality of solid transparent sectors made of at least one solid material that is transparent to visible light, each transparent sector of the plurality of transparent sectors being sandwiched between two absorption sectors to create an alternating arrangement of transparent sectors and absorption sectors that are adjacent to and in contact with each other. In the multilayer optical filter, each transparent sector of the plurality of transparent sectors is locally arranged and configured to have the following refractive power. · When a first parallel light strikes the inlet surface along an incidence direction in a local region of the inlet surface of the optical filter, the transparent sector focuses the first parallel light along a first focal line orthogonal to the local incidence surface, and / or · When a second parallel light strikes the outlet surface along the incidence direction in a local region of the inlet surface of the optical filter, the transparent sector focuses the second parallel light along a second focal line orthogonal to the local incidence surface, and / or · In a local region of the inlet surface, an inlet direction configured on the incidence surface, with a non-zero incident angle δ , , , in , acc , at which, in any case, the acceptance angle θ of the filter measured with respect to the incident direction D accBy hitting the entrance surface along an entrance direction that is offset with respect to the incident direction and is smaller than, the light exits from the exit surface along the direction formed in the plane of incidence, and with respect to the incident direction, for example The deviation angle δ to which TIFF2025524506000002.tif11150 is applied out There is at least one third parallel light that generates at least one transmitted light component that is displaced. The visual transmittance with respect to the third parallel light is a value obtained by subtracting the loss due to reflection at the entrance surface and / or the exit surface, and is significantly higher than 50%, preferably higher than 60%, more preferably higher than 70%, and / or · In a local region of the exit surface, the entrance direction formed in the plane of incidence, with a non-zero angle of incidence δ in In any case, the acceptance angle θ of the filter measured with respect to the incident direction D acc By hitting the exit surface along an entrance direction that is offset with respect to the incident direction and is smaller than, the light exits from the entrance surface along the direction formed in the plane of incidence, and with respect to the incident direction, for example The deviation angle δ to which TIFF2025524506000003.tif11150 is applied out There is at least one fourth parallel light that generates at least one transmitted light component that is displaced. The visual transmittance with respect to the fourth parallel light is a value obtained by subtracting the loss due to reflection at the entrance surface and / or the exit surface, and is significantly higher than 50%, preferably higher than 60%, more preferably higher than 70%. A plane including the normal of one of the plurality of absorption sectors in a local region of the entrance surface of the optical filter and orthogonal to the entrance surface defines a local plane of incidence, and the intersection of the local plane of incidence and the surface of the absorption sector defines an incident direction that is substantially common to the entire optical filter.

[0015] In the context of this specification and the appended claims, the local region of the entrance surface means a region in which the normal to one of the plurality of absorption sectors has a substantially constant direction.

[0016] In the context of this specification and the appended claims, the condition of "concentrating collimated light along a focal line orthogonal to a local entrance surface" is that the illuminance profile is characterized by the contrast along a direction orthogonal to the focal line and / or by an illuminance peak value that is greater, respectively, than the contrast and / or the illuminance peak value obtained in another plane parallel to the entrance and / or exit surface behind or in front of the focal plane, when there is a focal plane parallel to the entrance and / or exit surface.

[0017] In the context of this specification and the appended claims, the "acceptance angle θ" acc " is intended to denote an angle such that light impinging on the entrance or exit surface along a direction configured in the entrance surface at an incident angle δ greater than the acceptance angle θ acc generates a luminous transmittance lower than 15%. In the context of this specification and the appended claims, the "acceptance cone" or "angular acceptance cone" is intended to denote a set of directions configured in the entrance surface forming an incident angle δ smaller than the acceptance angle θ in with the incident direction D. acc " and the incident angle δ in smaller than the acceptance angle θ

[0018] In the context of this specification and the appended claims, the "non-zero incident angle δ" in " is intended to denote an angle greater than 0.1θ acc , preferably greater than 0.2θ acc , more preferably greater than 0.4θ acc .

[0019] In the context of this specification and the appended claims, an angle correlated with the propagation direction of light means that it is measured in air.

[0020] Advantageously, the optical filter according to the invention has a locally one-dimensional structure. Therefore, it is not more expensive than a two-dimensional multi-channel spatial filter having absorption channels and can be easily manufactured. The applicant actually mentions that, unlike the case of a two-dimensional multi-channel spatial filter having absorption channels where the manufacturing process becomes particularly complicated as the channel length increases, the manufacturing process does not become particularly complicated as the sector length L increases.

[0021] Specifically, the applicant mentions that the optical filter according to the invention has, locally, for the light reaching the entrance face and / or the exit face, in particular for the entrance direction which is outside the acceptance angle of the filter measured with respect to the incident direction and which belongs to the local incident face, a maximum in the direction belonging to the local incident face and a minimum in the direction belonging to the plane orthogonal to the local filtering direction, the local filtering direction being defined as the normal to the absorption sector in the local region of the entrance face of the optical filter, and comprises absorption sectors configured and arranged so as to ensure an absorption effect.

[0022] Advantageously, therefore, the optical filter subject of the invention can efficiently remove the stray light generated by a Fresnel lens or a mirror or, generally, by a Fresnel optical system. A Fresnel optical system is generally characterized by a prism structure having edges locally oriented along a direction defining a local Fresnel incident face orthogonal thereto, such a prism being configured to collimate, deflect or otherwise change the direction of the light in the local Fresnel incident face. The optical filter according to the invention is configured such that at each point the local incident face of the filter coincides with the local incident face of the Fresnel optical system and can efficiently remove the "stray light" generated by the Fresnel optical system, in particular the "stray light" generated by the edges of the prism structure. This is because such "stray light" appears at each point only substantially along the direction belonging to the local Fresnel incident face of the filter from the Fresnel optical system.

[0023] The applicant recognizes that an optical filter configured such that the absorption sector selectively operates on a single surface where "stray light" exists has a loss level of the main light that is much lower than the loss level of a two-dimensional multi-channel spatial filter with absorption channels configured to remove "stray light" with equivalent selectivity, for example, at a local Fresnel incident surface. Furthermore, the refractive power of the transparent sector of the optical filter according to the present invention means that at least a part of the light that should be absorbed by the absorption sector is instead transmitted here, and the filter is brighter and more efficient than in the case of a conventional optical filter made of a transparent sector without refractive power.

[0024] The above problems and the object of the present invention are also achieved by an illumination device that reproduces the light of the sky and the sun according to claim 20 of the appended claims.

[0025] Further features of the preferred embodiments of the optical filter and illumination device according to the present invention are the subject of the dependent claims.

Brief Description of the Drawings

[0026] The accompanying drawings, which are incorporated herein and constitute a part of this description, illustrate exemplary embodiments of the present invention and, together with the description, are intended to explain the principles of the present invention. In the drawings,

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DETAILED DESCRIPTION OF THE INVENTION

[0027] The following is a detailed description of exemplary embodiments of the present invention. The exemplary embodiments described herein and illustrated in the drawings are intended to convey the principles of the present invention, and those skilled in the art can implement and use the present invention in a number of different situations and applications. Accordingly, the exemplary embodiments are not intended to limit, nor should they be construed as limiting, the scope of patent protection. Rather, the scope of patent protection is defined by the appended claims.

[0028] For the purpose of explaining the drawings, in the following description, the same numbers or symbols are used to indicate components having the same functions. Further, for the sake of clarity of illustration, some reference numerals may not be repeated in all the drawings.

[0029] The use of "for example", "etc.", "or" indicates non-limiting, non-exclusive alternatives unless otherwise indicated. The use of "comprises" and "includes" means "comprises, or includes", although not limited thereto unless otherwise indicated.

[0030] Furthermore, the use of terms such as "about", "substantially", "essentially" in connection with dimensions, values, shapes, and geometric references (such as perpendicular and parallel) is understood to mean "unless there is no measurement error" or "unless there is no inaccuracy due to manufacturing tolerances", and in any case, "unless there is a slight deviation with respect to the value, dimension, shape, or geometric reference to which the term relates".

[0031] Finally, terms such as "first", "second", "upper", "lower", "main", and "subordinate" are generally used to distinguish components belonging to the same type and do not necessarily imply an order or priority of relationship or position.

[0032] Referring to the accompanying drawings, some embodiments of the optical filter according to the present invention, generally indicated at 100, are schematically shown.

[0033] The optical filter 100 includes a substantially flat and parallel inlet surface 101 and an outlet surface 102. Between the inlet surface 101 and the outlet surface 102, a plurality of visible light absorption sectors 108 that are locally planar and locally parallel to each other, and a plurality of solid transparent sectors 103 made of at least one solid material that is transparent to visible light, extend over a sector length L. Each transparent sector 103 of the plurality of transparent sectors is interposed between two absorption sectors 108 and forms an alternating arrangement of adjacent and contacting transparent sectors 103 and absorption sectors 108. In particular, the absorption sectors 108 are arranged such that the distance between adjacent absorption sectors 108 of the plurality of absorption sectors 108 is substantially constant.

[0034] According to the present invention, each transparent sector 103 of the plurality of transparent sectors is locally arranged and, as schematically shown in FIGS. 1 and 1a, when a first parallel light 201 impinging on the inlet surface 101 along the incident direction D is provided in a local region of the inlet surface 101 of the optical filter 100, the transparent sector 103 focuses the first parallel light 201 along a first focal line 203 orthogonal to the local incident surface P, and / or when a second parallel light 202 impinging on the outlet surface 102 along the incident direction D is provided in a local region of the inlet surface 101 of the optical filter 100, the transparent sector 103 is configured to have a refractive power to focus the second parallel light 202 along a second focal line 204 orthogonal to the local incident surface P.

[0035] Specifically, the local incident surface is defined by a plane that is orthogonal to the entrance surface 101 and includes the normal N to one of the plurality of absorption sectors, i.e., the absorption sector 108, in the local region of the entrance surface 101 of the optical filter 100. Further, the intersection of the local incident surface P and the surface of the absorption sector 108 defines the incident direction D. The incident direction D may be parallel or inclined with respect to the normals to the entrance surface 101 and the exit surface 102.

[0036] In one embodiment of the present invention, when each transparent sector 103 of the plurality of transparent sectors is provided with the first parallel light 201 that hits the entrance surface 101 along the incident direction D in the local region of the entrance surface 101 of the optical filter 100, the transparent sector 103 is orthogonal to the local incident surface P and is along the first focal line 203 located at the first focal distance f1 from the entrance surface 101 measured along the incident direction D. The first focal distance f1 satisfies the following relationship: 0.5L < f1 < 2L, preferably 0.7L < f1 < 1.6L, more preferably 0.7L < f1 < 1.4L, still more preferably 0.9L < f1 < 1.2L. The transparent sector 103 is locally arranged and configured to have a refractive power that concentrates the first parallel light 201. In a further preferred embodiment, the first focal distance f1 is substantially equal to the sector length L.

[0037] Alternatively or additionally, when each transparent sector 103 of the plurality of transparent sectors is provided with the second parallel light 202 that hits the exit surface 102 along the incident direction D in the local region of the entrance surface 101 of the optical filter 100, the transparent sector 103 is orthogonal to the local incident surface P and is along the second focal line 204 located at the second focal distance f2 from the exit surface 102 measured along the incident direction D. The second focal distance f2 satisfies the following relationship: 0.5L < f2 < 2L, preferably 0.7L < f2 < 1.6L, more preferably 0.7L < f2 < 1.4L, still more preferably 0.9L < f2 < 1.2L. The transparent sector 103 is locally arranged and configured to have a refractive power that concentrates the second parallel light 202. In a further preferred embodiment, the second focal distance f2 is substantially equal to the sector length L.

[0038] In this specification and the appended claims, the first focal length f1 and the second focal length f2 mean the distances measured along the respective incident directions D of the first focal line 203 and the second focal line 204 from the respective entrance surface 101 or exit surface 102. The first focal line 203 and the second focal line 204 are included in respective planes parallel to the entrance surface 101 and the exit surface 102, and this distance is measured by illuminating each of the entrance surface 101 or the exit surface 102 with green light having a wavelength in the range of 532 nm.

[0039] The applicant has found that the following characteristics related to the refractive power of the transparent sector 103 of the optical filter according to the present invention (i) When the first parallel light 201 incident on the entrance surface 101 is given along the incident direction D, the transparent sector 103 concentrates the first parallel light 201 close to the exit surface 102. (ii) When the second parallel light 202 incident on the exit surface 102 is given along the incident direction D, the transparent sector 103 concentrates the second parallel light 202 close to the entrance surface 101. are the same as those guaranteed by conventional tandem filters. Different from conventional tandem filters, these filters guarantee this optical property for each incident surface, but are affected by the "crosstalk" problem. Otherwise, the optical filter 100 guarantees this property limited to the concentration of light on the local incident surface, but there is no crosstalk due to the effect of the presence of the absorption sector, which was lacking in conventional tandem filters. [[ID=...]]

[0040] [[ID=...]] Specifically, the applicant is aware. By strict analogy with the behavior of conventional tandem filters, the present invention refers to a substantially planar optical filter that is locally configured to convert into transmitted or filtered light 130 a third collimated ray 211 (inside or outside the acceptance cone of the filter) and / or a fourth collimated ray 212 (inside or outside the acceptance cone of the cone) that is incident on the entrance face 101 or exit face 102, respectively, along a direction that belongs to the local plane of incidence P, in which: (i) The acceptance angle θ of the filter, measured with respect to the incident direction D acc For an incident direction inside the cut angle θ (shown as 205 in FIG. 1 a), the transmitted light 130 is characterized by an angular intensity profile at the plane of incidence P of a substantially flat-top type, and the substantially flat-top profile is cut a profile characterized by high contrast for varying exit angles across a range of, or cut angle θ cut means a profile having values close to a maximum for smaller angles (shown as 207 in FIG. 1 a), the angles being measured with respect to the incident direction D, and values substantially close to zero elsewhere, the luminance profile further being substantially independent or only slightly dependent on the direction of the input collimated light 201, 202, 211, 212; (ii) Filter acceptance angle θ acc For incident directions outside of this, the transmitted light 130 is substantially zero.

[0041] In the context of this specification and the appended claims, "cut angle θ cut " is the transmitted light I(δ) obtained by illuminating an optical filter with diffuse light, i.e., light characterized by an angular profile of substantially constant luminous intensity. out ) angular profile of luminous intensity at the cut angle θ cut greater than the deviation angle δ out The angle is intended to indicate an angle at which the value is less than 15% of the peak value.

[0042] In a preferred embodiment, the luminous transmittance T(θ in ) of the optical filter 100 with respect to the third parallel light 211 and the fourth parallel light 212 that propagate along the direction of the incident surface P forming an angle θ such that the incident direction D and |θ in >|>Aθacc, illuminating the entrance surface 101 or the exit surface 102 respectively, satisfies T(θ in ) < BT0, where A = 1.3, preferably A = 1.2, more preferably A = 1.1, B = 0.20, preferably B = 0.15, more preferably B = 0.10, still more preferably B = 0.05, and T0 is the average value of the luminous transmittance at an incident angle smaller than the angle at which the luminous transmittance is equal to 50% of the peak value, that is, for |θ in |<θ in |<θ 1-HWHM >, T0 ≡ <T(θ in )>, where T(θ 1-HWHM ) = T(0) / 2 in this case.

[0043] In another preferred embodiment, when the optical filter 100 is illuminated with diffused input light, that is, illuminated with substantially constant luminous intensity in all directions, the luminous intensity I(θ out ) of the light 130 transmitted or filtered by the optical filter 100 and propagating at an angle θ cut >Cθ out > satisfies I(θ out ) < DI0, where C = 1.3, preferably C = 1.2, more preferably C = 1.1, D = 0.20, preferably D = 0.10, more preferably D = 0.05, and I0 is the average value of the luminous intensity at an incident angle smaller than the angle at which the luminous intensity is equal to 50% of the peak value, that is, for |θ in |<θ 2-HWHM >, I0 ≡ <I(θ in )>, where I(θ 2-HWHM ) = T(0) / 2 in this case.

[0044] In a further embodiment, when the optical filter is illuminated with diffused input light, i.e., when the luminous intensity is substantially constant in all directions, the light intensity propagating at an angle θ out <Eθ cut is given by I(θ out )>FI0, where E = 0.7, preferably E = 0.8, more preferably E = 0.9, F = 0.3, preferably F = 0.4, more preferably F = 0.6, still more preferably F = 0.8, and I0 is the average value of the luminous intensity values at incident angles smaller than a positive angle at which the luminous intensity is equal to 50% of the peak value, i.e., for |θ in |<θ 2-HWHM , I0≡<I(θ in ), where I(θ 2-HWHM ) = T(0) / 2.

[0045] The Applicant recognizes that the ability of the optical filter according to the invention to generate a luminance angle profile substantially independent of, or slightly dependent on, the direction of the input parallel lights 201, 202 is particularly advantageous, and in the presence of an illuminator comprising a plurality of spatially separated LED light sources from each other, for example a plurality of LED light sources spatially distributed on a line, which necessarily illuminate the filter with input parallel lights 201, 202 whose direction changes from one point of the filter to another, so as not to make the observer inadvertently aware of the presence of a plurality of different illuminators, as required to infinitely generate the image of a single sun, it has been found that a substantially spatially uniform direct light luminance angle profile is generated. In particular, the Applicant recognizes that in order to infinitely generate the image of a single sun, it is substantially sufficient to illuminate the filter with a spatially relatively uniform illuminance with respect to the light impinging thereon from a direction inside the angular acceptance cone of the filter, i.e., a direction forming an angle smaller than the acceptance angle of the filter with respect to the incident direction.

[0046] The Applicant has also identified that the ability of the optical filter according to the present invention to generate a substantially flat-top luminance angle profile, rather than a Gaussian type as generated by a standard illuminator, and at the same time lacking a background, despite the presence of input spurious light, is particularly advantageous for generating an image of the sun with a sharp contrast against the sky. This sky appears clear and cloud- or haze-free because there is no background of direct light CCT, and the contour of the sun's image appears sharp because the luminance value is high in the vicinity of the cut-off angle.

[0047] In the embodiment of FIG. 1, the absorption sector 108 and the transparent sector 103 are in the shape of a parallelepiped, and the absorption sector 108 has a thickness that is considerably smaller than the thickness d of the transparent sector, for example, three times smaller, preferably five times smaller, and more preferably ten times smaller than the thickness d of the transparent sector 103. In particular, the thickness d of the transparent sector 103 is configured to be between 10 μm and 300 μm, preferably between 10 μm and 200 μm, and more preferably between 10 μm and 150 μm.

[0048] In such an embodiment, the absorption sectors 108 intersect the entrance surface 101 and the exit surface 102 along substantially straight lines that are parallel to each other. In other words, the normal N to one of the plurality of absorption sectors 108 has substantially the same direction N with respect to the entire optical filter 100. In a preferred embodiment, the incident direction D is inclined with respect to the normals of the entrance surface 101 and the exit surface 102. For example, the incident direction D forms an angle configured to be between 2 degrees and 80 degrees, preferably between 5 degrees and 70 degrees, and more preferably between 10 degrees and 60 degrees with respect to the normals of the entrance surface 101 and the exit surface 102. In another embodiment, the incident direction D is perpendicular to the entrance surface 101 and the exit surface 102.

[0049] The optical filter 100 according to the present invention can be easily manufactured by using known techniques. As a non-limiting example, in the first embodiment, a plurality of the absorption sectors 108 among the plurality of absorption sectors 108 intersect the entrance surface 101 and the exit surface 102 along a substantially straight line. The optical filter according to the present invention can be manufactured by a two-step process comprising at least the following two steps, by methods known in the art. (i) A plurality of flat sheets or laminates each comprising at least one material transparent to visible light are alternately bonded to a plurality of sheets or laminates made of a visible light absorbing material, for example, a sheet made of silicone, PMMA, PVDF, a fluorinated polymer, polycarbonate, or other polymer resin, to form a multi-layer parallelepiped block in which a sheet or laminate having at least one transparent material and a sheet or laminate having an absorbing material alternate. (ii) The manufactured multi-layer block is cut according to parallel planes to obtain slices in which transparent sectors and absorption sectors that are delimited by an entrance surface and an exit surface and are adjacent to and in contact with each other alternate.

[0050] Advantageously, in combination with a lens, a mirror, or generally a linear type Fresnel optical system, i.e., characterized by a prism structure whose edges are oriented along a single direction defining a single plane of Fresnel incidence common to the entire Fresnel optical system. The optical filter according to the present invention makes it possible to effectively remove the "stray light" generated by the Fresnel optical system at the entrance surface without operating the filter on a plane parallel to the absorption sectors.

[0051] In the preferred embodiment shown as a non-limiting example in FIG. 2, each transparent sector 103 of the plurality of transparent sectors comprises a layer of inhomogeneous transparent material characterized by an inhomogeneous refractive index profile having a gradient substantially parallel to the local filtering direction N. In particular, the layer of inhomogeneous material has a minimum value n of the refractive index profile in the outer layer 103'd located close to the sector wall adjacent to each absorption sector 108 of the plurality of absorption sectors 108e has a maximum value n in the inner sector layer 103’a that is substantially equidistant from the central portion or the sector wall i has. n i is the value of the refractive index of the inner layer, and n e is the value of the refractive index of the outer layer.

[0052] In the context of this specification and the appended claims, "the refractive index of a material" is intended to indicate the real part of the refractive index. This definition applies to both transparent materials in the visible range and absorption materials in the visible range that have a substantially transparent surface layer with a thickness defined as the optical path length of light, for example, a thickness on the order of several wavelengths of visible light.

[0053] More specifically, a layer of inhomogeneous transparent material comprises a plurality of layers 103' with different refractive indices. Specifically, the refractive index values of each layer 103' of the plurality of layers vary in separate manners along the local filtering direction N depending on the distance from the central sector portion 103'a, being substantially approximated by a parabolic function and / or monotonically decreasing from the central sector portion 103'a towards the sector wall adjacent to each absorption sector 108. More specifically, the refractive index values of each layer 103' of the plurality of layers vary along the local filtering direction N depending on the distance from the central sector portion 103'a such that the refractive power of a converging lens having a focal length f where the relationship 0.5L < f < 2L, preferably 0.7L < f < 1.6L, more preferably 0.7L < f < 1.4L, and even more preferably 0.9L < f < 1.2L is applied, is imparted to the transparent sector 103. In a further preferred embodiment, the focal length f is substantially equal to the sector length L.

[0054] In a preferred configuration, the following relationship applies among the sector length L, the thickness d of the transparent sector 103, the inner refractive index n i and the outer refractive index n e . TIFF2025524506000004.tif15150Here, n i is the value of the refractive index of the inner layer 103’a, and n eis the refractive index value of the outer layer 103’d, d is the thickness of the transparent sector 103, G < 3, preferably G < 2, more preferably G < 1.5, and / or G > 0.3, preferably G > 0.5, more preferably G > 0.7 is applied, or a more preferred configuration TIFF2025524506000005.tif8150 is applied.

[0055] Advantageously, the optical filter 100 configured in this way subtracts the losses due to reflection at the entrance surface 101 and the exit surface 102 and the losses due to the presence of the absorption sector 108 occupying a part of the entrance surface 101 and the exit surface 102, and transmits substantially all or most of the light that satisfies the following requirements. - Belonging to the incident surface P and hitting the entrance surface 101 or the exit surface 102 along the direction forming the incident angle δ in in air with the incident direction D. - For the incident angle, the relationship δ in < θ TIR is applied, where θ TIR is the total reflection angle inside the boundary between the refractive index n i of the inner layer 103’a and the refractive index n e of the outer layer 103’d, and the relationship is defined by TIFF2025524506000006.tif6150. Therefore, essentially, this relationship is the total internal reflection angle θ TIR which is TIFF2025524506000007.tif6150 means that it substantially coincides with the acceptance angle θ acc of the filter.

[0056] In other words, in a preferred configuration, between the sector length L, the thickness d of the transparent sector 103, the acceptance angle θ acc and the internal refractive index n i the following relationship applies. TIFF2025524506000008.tif14150 Here, G < 3, preferably G < 2, more preferably G < 1.5, and / or G > 0.3, preferably G > 0.5, more preferably G > 0.7 is applied, or a more preferred configuration TIFF2025524506000009.tif8150 is applied.

[0057] In the preferred configuration of the embodiment of FIG. 2, each transparent sector 103 of the plurality of transparent sectors 103 has a sector length substantially equal to 1.34 mm ( TIFF2025524506000010.tif6150 mm) and a thickness approximately equal to 0.1 mm (d = 0.1 mm), and comprises a heterogeneous transparent material formed as follows. (i) A first layer 103’a (PMMA) located at the central portion of the sector having a thickness of 0.0384 mm and a refractive index equal to 1.4924. (ii) A pair of second layers 103’b aligned with the first layer, each having a thickness of 0.0016 mm and a refractive index equal to 1.4916. [[ID=,14]](iii) A pair of third layers 103’c aligned with the second layer, each having a thickness of 0.0103 mm and a refractive index equal to 1.4907. (iv) A pair of fourth layers 103’d aligned with the third layer, each having a thickness of 0.0045 mm and a refractive index equal to 1.4898. Advantageously, the optical filter thus configured generates a photometric angular profile characterized by a cut-off angle of approximately 5 degrees.

[0058] In a different preferred configuration of the embodiment of FIG. 2, each transparent sector 103 of the plurality of transparent sectors 103 has a sector length substantially equal to 1.27 mm ( TIFF2025524506000011.tif6150 mm) and a thickness approximately equal to 0.1 mm (d = 0.1 mm), and comprises a heterogeneous transparent material formed as follows. (i) A first layer 103’a (silicone) located at the central portion of the sector having a thickness of 0.0385 mm and a refractive index equal to 1.416. (ii) A pair of second layers 103'b aligned with a first layer each having a thickness of 0.0159 mm and a refractive index equal to 1.4151. (iii) A pair of third layers 103'c aligned with a second layer each having a thickness of 0.0104 mm and a refractive index equal to 1.4133. (iv) A pair of fourth layers 103'd aligned with a third layer each having a thickness of 0.0044 mm and a refractive index equal to 1.4133. Advantageously, even with the optical filter configured as such, it generates an angular profile of luminous intensity characterized by a cut-off angle of about 5 degrees.

[0059] In a preferred embodiment (not shown) according to the present invention, each transparent sector 103 of the plurality of transparent sectors comprises, in order, a first layer 103'a located at the central portion of the sector and having an internal refractive index n i and a pair of second layers 103'b each aligned with the first layer 103'a and having a minimum or external refractive index n e and comprises a layer of a heterogeneous transparent material. In a specific embodiment, the second layer 103'b aligned with the first layer 103'a and having a minimum refractive index n e is the surface layer of a pair of absorption sectors 108 through which light passes without substantial absorption. Each absorption sector 108 is in contact with one side of the first layer 103'a, and the pair of absorption sectors 108 is made of a material having a minimum refractive index n e In particular, the surface layer of the absorption sector 108 through which light passes without substantial absorption is a layer having a thickness of 0.5 to 250 μm, preferably 0.5 to 100 μm, more preferably 0.5 to 50 μm.

[0060] Advantageously, on the entrance surface 101, when a third parallel light 211' inside the acceptance cone hits (shown as 205 in Fig. 1a), or, for the sake of brevity, the third internal parallel light 211', that is, the incident direction D' configured on the incident surface P and deviated by an incident angle δ in from the incident direction D eWhen the third parallel light 211’ hits along, as described above, the plurality of transparent sectors 103 made of a heterogeneous material having the first central layer 103’a and a pair of second layers 103’b arranged side by side with the first layer 103’a are formed at the incident surface P and are at an angle δ such as the TIFF2025524506000012.tif11150 with respect to the incident direction D OUT generate at least one component of the transmitted light that exits from the exit surface 102 along a deflected direction, and the apparent transmittance of the third internal parallel light 211’ is equal to about 60% after subtracting the losses due to reflection at the entrance surface 101 and the exit surface 102. Advantageously, in such an embodiment, for the fourth parallel light 212’ inside the acceptance cone 205 that hits the exit surface 102 and exits from the entrance surface 101 with an apparent transmittance equal to about 60% after subtracting the losses due to reflection at the entrance surface 101 and the exit surface 102, a similar behavior is observed.

[0061] In a preferred configuration, the following relationship applies among the sector length L, the thickness d of the transparent sector 103, the internal refractive index n i and the external refractive index n e of. TIFF2025524506000013.tif15150 Here, n i is the value of the refractive index of the internal layer, n e is the value of the refractive index of the external layer, d is the thickness of the transparent sector 103, G < 3, preferably G < 2, more preferably G < 1.5, and / or G > 0.3, preferably G > 0.5, more preferably G > 0.7 is applied, or a more preferred configuration TIFF2025524506000014.tif6150 is applied.

[0062] Advantageously, the optical filter 100 configured in this way subtracts the losses due to reflection at the entrance surface 101 and the exit surface 102 and the losses due to the presence of the absorption sector 108 occupying a part of the entrance surface 101 and the exit surface 102, and transmits substantially all or most of the light that satisfies the following requirements. - Belonging to the incident surface P and having an incident angle δ in the incident direction D and in the air inhits the inlet surface 101 or the outlet surface 102 along the direction of formation. - a relationship δ with respect to the angle of incidence in <θ TIR is applied, where θ TIR is the critical angle of total internal reflection inside the boundary between the refractive index n i of the inner layer 103’a and the refractive index n e of the outer layer 103’d, and the relationship is defined by TIFF2025524506000015.tif6150.

[0063] Condition TIFF2025524506000016.tif6150, that is, when G is substantially equal to 1, the sector length L is such that the geometric cut angle θ geo = θ TIR is created, and the geometric cut angle θ geo is equal to the maximum angle at which the light beam can pass through the transparent sector 103 without interacting with the adjacent absorption sector 108 when there is no refractive power in the channel. Therefore, the condition TIFF2025524506000017.tif6150 corresponds to the case where, when δ in <θ TIR if the incident light is reflected at the boundary between the layers and not absorbed, it guarantees the maximum transmission efficiency with the minimum sector length and thus the minimum cost of the device.

[0064] Figures 3 and 8 show two different embodiments different from the embodiment of FIG. 1 due to the fact that the absorption sectors 108 and the transparent sectors 103 are formed in a spiral shape, defining a plurality of spiral absorption sectors 108 and a plurality of spiral transparent sectors 103, respectively. In these embodiments, the set of spiral absorption sectors 108 intersects the inlet surface 101 and the outlet surface 102 along a spiral line. Preferably, the surface of at least one subset of the spiral absorption sectors 108 has a radius of curvature that is at least 5 times, preferably at least 10 times, more preferably at least 30 times greater than the distance between a pair of adjacent absorption sectors 108.

[0065] As a non-limiting example, an optical filter according to an embodiment in which the absorption sector 108 intersects the entrance surface 101 and the exit surface 102 along a spiral line can be manufactured in a three-step process comprising at least the following three steps. (i) A plurality of flat sheets or laminates comprising at least one material transparent to visible light are adhered to a plurality of sheets or laminates made of a visible light absorbing material, for example, a sheet made of silicone, PMMA, PVDF, a fluorinated polymer, polycarbonate, or other polymer resin, to obtain a laminate sheet comprising a bilayer of at least one transparent material and an absorbing material. (ii) The laminate sheet is wound around itself or a cylindrical support to form a multi-layer cylindrical block, for example, a multi-layer cylindrical block having a spiral structure. (iii) The manufactured multi-layer cylindrical block is cut according to a plane parallel and orthogonal to the axis of the cylinder to obtain slices in which transparent sectors and absorption sectors defined by the entrance surface and the exit surface alternate and are adjacent to and in contact with each other.

[0066] Advantageously, the optical filter according to the invention, in which the composite absorption sector 108 intersects the inlet face 101 and the outlet face 102 along concentric circles or along a spiral line, can efficiently remove spurious light generated by a conventional radial Fresnel lens, i.e., a lens having a rotationally invariant structure with respect to the optical axis. For this purpose, it is sufficient to have an optical axis parallel to the direction of incidence of the optical filter and to arrange the Fresnel lens so as to pass through the center of the concentric circles or the spiral line. In this way, the local filtering direction is the ray emerging from the optical axis of the Fresnel lens and lies in the plane of the inlet or outlet face of the filter. Except for the region of the filter close to the center of the spiral, the absorption sector substantially conforms to the outer surface of a concentric cylinder centered on the optical axis, and the local incident surface of the filter, i.e., the surface including the direction in which the filter performs the absorption action, is, at each point, the surface including the point in question and the optical axis of the lens, i.e., the surface including the direction in which the "stray light" takes its maximum value. For this reason, the optical filter 100 can effectively remove the "stray light" of the radial Fresnel lens without the need to use a two-dimensional multi-channel spatial filter having absorption channels.

[0067] Advantageously, the optical filter according to the invention, in which the absorption sector 108 intersects the inlet face 101 and the outlet face 102 along concentric circles or along a spiral line, in combination with a lens, or generally a radial-type Fresnel optical system or collimator, enables, starting from a square LED, a rectangular LED or other forms of light source, to generate an image in the circular solar eye as shown in FIGS. 5a and 5b, in a logarithmic scale and in any unit.

[0068] There is a square LED light source placed at the focus of a radial Fresnel lens, and when there is no optical filter according to the present invention, the Fresnel lens generates an angular luminance profile projected into the far field at each point. At the focus of the eye lens, as shown in logarithmic scale and in arbitrary units in FIGS. 4a and 4b, a square LED image is added to the image generated by "stray light". By combining such a Fresnel lens with the optical filter according to the present invention, since the refractive action of the filter operates only within the local incident plane at each point, an angular luminance profile locally generated at each point by the filter can be obtained to be rectangular. However, the applicant has surprisingly noticed that the overall angular luminance profile generated by the optical filter 100 according to the present invention, that is, the profile given to the sum of all contributions of the light emerging from the filter 100, is a perfect circle. This is due to the rotational invariant symmetry with respect to the introduced optical axis of the filter 100. Therefore, as usually occurs with small collimators coupled to individual LEDs, the observer perceives the image of the light source perceived by the observer as being arranged such that it is defined by the entire aperture of the filter 100 or a plurality of filter apertures 100, perceives the light source as a perfect circle, and perceives that there is no "stray light". Therefore, the optical filter 100 according to the present invention can obtain a perfect circular image of the sun simply by adding contributions at different angles according to the correct symmetry without using a circular mask that cuts or subtracts light in the object or any image plane.

[0069] Advantageously, the described solution can indeed generate a circular image, but it eliminates the need for a low-angle white light diffuser, or a "frost" diffuser, which significantly blurs the image of the sun and generates an image such as that perceived in nature with clouds or haze.

[0070] In the embodiments of FIGS. 3 and 3a, each transparent sector 103 of the plurality of transparent sectors comprises at least one solid transparent material having a first refractive index n and an interface surface 107c extending between two absorption sectors 108 in proximity to the inlet surface 101 and the outlet surface 102. As shown in detail in FIG. 4a, the interface surface 107c is rounded and delimited by the refractive element 107. In particular, the interface surface 107c locally conforms to the outer surface of a cylinder having the axis of the cylinder perpendicular to the local incident surface P, with the convex part facing inwards and characterized by a radius of curvature (ROC).

[0071] FIGS. 6 and 7 show two cross-sections at the local incident surface P of the optical filter 100 according to the present invention. FIGS. 6 and 7 refer to further embodiments where the transparent sector 103 may be parallelepiped-shaped or have another three-dimensional shape according to the present invention. In the embodiments of FIGS. 6 and 7, each transparent sector 103 of the plurality of transparent sectors is coupled to at least one external refractive element 107b via the interface surface 107c. The external refractive element 107b has an external surface that is substantially flat and parallel to the inlet surface 101 or the respective outlet surface 102, on the side opposite to the interface surface 107c. The external refractive element 107b is made of a transparent material having a second refractive index n2. This second refractive index n2 is smaller than the first refractive index n (n2 < n) when the interface surface 107c has a convex part facing the outside of the transparent sector, as shown in FIG. 6, and larger than the first refractive index n (n2 > n) when the interface surface 107c has a convex part facing the inside of the transparent sector, as shown in FIG. 7.

[0072] In the configuration shown in FIGS. 6 and 7, each transparent sector 103 of the plurality of transparent sectors includes an internal refractive element 107a defined by a boundary surface 107c made of a transparent material having a third refractive index n3 (n3≠n or n3=n) that is different from or equal to the first refractive index n. In particular, the external refractive element 107b forms a doublet 107 having the refractive power of the internal refractive element 107a defined by the boundary surface 107c and the refractive power of the converging cylindrical lens. In a preferred configuration, the values of the first refractive index n, the second refractive index n2, and the third refractive index n3, and the value of the radius of curvature ROC of the boundary surface 107c are such that in a medium having the first refractive index n, they locally provide the refractive power of a converging cylindrical lens having the axis and focal length f of a cylinder orthogonal to the local incident surface P to the boundary surface 107c. The relationship of 0.5L<f<2L is applicable, preferably 0.7L<f<1.6L, more preferably 0.7L<f<1.4L, still more preferably 0.9L<f<1.2L, and still more preferably, the focal length f is substantially equal to the sector length L.

[0073] Advantageously, the solutions shown in FIGS. 3, 3a, 6, and 7 are such that each transparent sector 103 includes at least a pair of curved boundary surfaces 107c in contact with air or the external refractive element 107b, and within the acceptance angle, the value of the transmission coefficient of the incident luminous flow coupled to the plurality of transparent sectors is significantly greater than 50%, for example greater than 60%, preferably greater than 70%, still more preferably greater than 80%, or even greater than 90%. The said value increases as the focal length f approaches the sector length L, and the theoretical limit is equal to 100% when f = L.

[0074] Furthermore advantageously, the use of the external refractive element 107b allows selection from a variety of values for the radius of curvature ROC of the boundary surface 107c at the same focal length f, and depending on the material, dimensions, and shape selected for the filter, enables selection of the most suitable surface manufacturing method from different methods such as inkjet printing, and / or chemical etching, and / or mechanical etching, and / or etching by plasma treatment.

[0075] In a preferred configuration of the optical filter according to FIG. 7, each of the plurality of transparent sectors has a sector length L = 0.8 mm, a thickness d = 0.1 mm measured along a direction perpendicular to the absorption sector, and is made of a homogeneous transparent material (silicone) with a refractive index n = 1.414. The boundary surface 107c has a convex portion facing the inside of the transparent sector 103 and is characterized by a value of the radius of curvature ROC being substantially equal to 0.068 mm. The external refractive element 107b is made of a transparent material having a second refractive index n2 = 1.429 (PMMA). In this way, the doublet 107 generates a focal point f of a desired value substantially equal to the sector length L = 0.8 mm in a medium with a refractive index n, TIFF2025524506000018.tif The acceptance angle θ defined at 6150 degrees acc and the cut angle θ cut are guaranteed. The plurality of external refractive elements 107b form a rigid monoblock having a flat outer surface and incorporate a plurality of boundary surfaces 107c.

[0076] Although different from the embodiments of FIGS. 3, 3a, 6, and 7, and similar to the embodiments of FIGS. 2 and 2a, in the embodiment of FIG. 8, each transparent sector 103 of the plurality of transparent sectors comprises a layer of inhomogeneous transparent material characterized by a non-uniform refractive index profile having a gradient substantially parallel to the local filtering direction N. The layer of inhomogeneous material has a minimum value of the refractive index profile close to the wall of the transparent sector 103 adjacent to each absorption sector 108 and a maximum value at the central portion of the transparent sector 103. In particular, the layer of inhomogeneous transparent material comprises a plurality of layers with different refractive indices. Specifically, the values of the refractive indices of the plurality of layers vary separately along the local filtering direction N in a dependence relationship that substantially approximates a parabolic function and / or a dependence relationship that monotonically decreases from the central portion of the transparent sector 103 towards the sector wall adjacent to each absorption sector 108. Also, the values of the refractive indices of the plurality of layers vary separately along the local filtering direction N in a dependence relationship that gives the refractive power of a lens having a focal length f in the transparent sector 103, and the relationship of 0.5L < f < 2L, preferably the relationship of 0.7L < f < 1.6L, more preferably the relationship of 0.7L < f < 1.4L, and even more preferably the relationship of 0.9L < f < 1.2L is applied. Even more preferably, the focal length f is substantially equal to the sector length L.

[0077] FIG. 9 shows a further embodiment that is different from the embodiment of FIG. 1 in that the absorption sectors 108 and the transparent sectors 103 are formed as concentric circles. In this embodiment, the absorption sectors 108 intersect the inlet surface 101 and the outlet surface 102 along the concentric circles. Also in this case, as in the spiral embodiment, each absorption sector 108 of the plurality of absorption sectors 108 has a radius of curvature that is at least 5 times, preferably at least 10 times, more preferably at least 30 times the distance between pairs of adjacent absorption sectors 108.

[0078] Similar to the embodiments of FIGS. 2 and 2a, in the embodiment of FIG. 9, each transparent sector 103 of the plurality of transparent sectors comprises a layer of inhomogeneous transparent material characterized by a non-uniform refractive index profile having a gradient substantially parallel to the local filtering direction N. The layer of inhomogeneous material has a minimum value n of the refractive index profile close to the wall of the transparent sector 103 adjacent to each absorption sector 108 e and a maximum value n at the central portion of the transparent sector 103 i Here, n1 is the value of the refractive index of the innermost or central portion of the transparent sector 103, and n e is the value of the refractive index of the outermost portion of the transparent sector 103.

[0079] In this case, the refractive index profile of each transparent sector 103 varies continuously from the central portion of the transparent sector 103 to the sector wall adjacent to each absorption sector 108, substantially following a parabolic and / or monotonically decreasing trend. Also, the refractive index profile of each transparent sector 103 varies continuously according to a tendency to locally impart the refractive power of a GRIN cylindrical lens having a focal length f to the transparent sector 103, and the relationship 0.5L < f < 2L, preferably 0.7L < f < 1.6L, more preferably 0.7L < f < 1.4L, and even more preferably 0.9L < f < 1.2L is applied. Even more preferably, the focal length f is substantially equal to the sector length L.

[0080] Even in this case, in a preferred configuration, the following relationship applies among the sector length L, the thickness d of the transparent sector 103, the internal refractive index n i and the external refractive index n e . TIFF2025524506000019.tif15150 Here, n i is the value of the refractive index at the innermost portion of the layer, and n eis the refractive index value at the outermost part of the layer, d is the thickness of the transparent sector 103, and G < 3, preferably G < 2, more preferably G < 1.5, and / or G > 0.3, preferably G > 0.5, more preferably G > 0.7 is applied, or a more preferable configuration TIFF2025524506000020.tif8150 is applied.

[0081] Advantageously, even in this case, the optical filter 100 configured in this way subtracts the losses due to reflection at the entrance surface 101 and the exit surface 102 and the losses due to the presence of the absorption sector 108 occupying a part of the entrance surface 101 and the exit surface 102, and transmits substantially all or most of the light that satisfies the following requirements. - Belongs to the incident surface P and hits the entrance surface 101 or the exit surface 102 along the direction forming the incident angle δ in in air with the incident direction D. - For the incident angle, the relationship δ in < θ TIR is applied, where θ TIR is the total internal reflection angle inside the boundary between the refractive index n i of the internal layer 103’a and the refractive index n e of the external layer 103’d, and the relationship TIFF2025524506000021.tif6150 is defined. Essentially, also in this case, this relationship is such that the total internal reflection angle θ TIR is TIFF2025524506000022.tif6150 that substantially coincides with the acceptance angle θ acc of the filter.

[0082] In other words, in a preferred configuration, between the sector length L, the thickness d of the transparent sector 103, the acceptance angle θ acc and the internal refractive index n i the following relationship applies. TIFF2025524506000023.tif14150 Here, G < 3, preferably G < 2, more preferably G < 1.5, and / or G > 0.3, preferably G > 0.5, more preferably G > 0.7 is applied, or a more preferred configuration TIFF2025524506000024.tif8150 is applied.

[0083] In a preferred embodiment, for example, referring to the cases of FIGS. 8 and 9, each transparent sector of the plurality of transparent sectors has a sector length L = 1.1 mm and a thickness d = 0.1 mm measured along the local filtering direction N, and is made of a material having a non-uniform refractive index that varies continuously along the local filtering direction N, or a plurality of layers of different materials having different refractive indices. Here, the refractive index of the layer at the center of the transparent sector is n0 = 1.412 (silicone), and the refractive index at a general position at a distance r from the center is n = n0 - Ar 2 is approximately described by the law of, where A = 1.471 mm -2 and r is expressed in mm. The distance from the center of the transparent sector is measured along the local filtering direction N, and the value of the refractive index with respect to the surface of the transparent sector 103 in contact with the absorption sector 108 is equal to n = 1.408. The applicant has noticed that in such an optical filter, each transparent sector functions like a GRIN lens having a continuous or discrete index profile, and the focal length in a medium having a refractive index equal to n = n0 having a value substantially equal to the length of the sector ( TIFF2025524506000025.tif6150), and the acceptance angle θ TIFF2025524506000026.tif6150 defined in degrees and the cut angle θ acc and the values in air cut are characterized by.

[0084] Advantageously, the refractive power of the transparent sectors does not result from the presence of a curved interface, and the solution that results from the use of a heterogeneous material or from the use of multiple layers of different materials leads to a significant simplification of the manufacturing process. In fact, it does not require the manufacture of a curved interface, but is limited to the cutting of a parallelepiped or cylindrical block made of a sheet or laminate into slices that successively exhibit a continuously variable or discrete refractive index along a direction perpendicular to the extension plane of the slice, according to the state of the art. This makes it possible to easily obtain a filter by slicing the block according to the cutting plane and the desired thickness, and to incorporate the slices thus obtained between two layers of transparent material having flat and parallel surfaces, obtaining the best mechanical support from the filter.

[0085] Obviously, each transparent sector 103 of the plurality of transparent sectors can comprise at least one layer of a heterogeneous transparent material characterized by a non-uniform refractive index profile that varies discretely or continuously, or by a substantially homogeneous material having a first constant refractive index n and adapted to impart the refractive power of a converging cylindrical lens to the interface 107c of the transparent sector, regardless of whether its structure is parallelepiped, concentric or helical.

[0086] Referring to FIG. 10, an example of an artificial light illumination device 1000 for reproducing sunlight by employing an optical filter 100 according to the present invention is shown. The artificial light illumination device 1000 comprises a direct light source 200 configured to emit visible light having a first color correlation temperature or CCT, in a non-isotropical manner, preferably along a direction in a range transverse to the main direction 206. In some embodiments according to the present invention, the direct light source 200 is configured to emit visible light having a fixed CCT greater than, for example, 5000 Kelvin. In other embodiments according to the present invention, the direct light source 200 is configured to emit visible light having a variable CCT in the range of, for example, 1700 to 8000 Kelvin.

[0087] Downstream of the direct light source 200 with respect to the main direction 206, an optical filter 100 according to the present invention is arranged.

[0088] The artificial light illumination device 1000 further comprises a diffusing light source 300 arranged downstream of the optical filter 100 with respect to the main direction 206. The diffusing light source 300 is configured to at least partially transmit the filtered light output from the filter 100. Specifically, the diffusing light source is configured to generate a diffused light component and a transmitted light component having an angular luminance profile similar to the angular luminance profile of the light filtered by the optical filter 100, that is, characterized by a similar value for the cut-off angle θ cut characterized by a similar value for the cut-off angle θ.

[0089] In some embodiments of the present invention, the diffusing light source 300 is configured to generate light having a direct component having a color correlated temperature or CCT of less than at least 20% of the color correlated temperature or CCT of the light generated by the direct light source 200. For example, the diffusing light source 300 is a Rayleigh diffuser.

[0090] In other embodiments of the present invention, the diffusing light source 300 is configured to generate light having a direct component having a CCT substantially the same as the CCT of the light generated by the direct light source 200. For example, the diffusing light source 300 is a "side-lit" diffuser panel, that is, laterally illuminated by a light source other than the direct light source.

[0091] In some embodiments of the present invention, the diffusing light source 300 is characterized by a divergence at least 2 times, preferably 3 times, more preferably 4 times greater than the divergence of the direct component, and / or a correlated color temperature or CCT at least 1.2 times, preferably 1.3 times, more preferably 1.5 times, even more preferably 1.8 times greater than the first CCT, and / or a CCT equal to 5600 Kelvin, and is further configured to generate a diffused light component characterized by an angular luminance profile.

[0092] In the first preferred embodiment, the direct light source 200 includes at least one LED light source collimated by a radial type collimator having a structure invariant by rotation with respect to its optical axis, such as a radial Fresnel collimator. Preferably, the optical filter 100 is oriented with respect to the direct light source 200 such that the entrance surface 101 is substantially orthogonal to the main direction 206. Preferably, the optical filter 100 has absorption sectors 108 intersecting the entrance surface 101 and the exit surface 102 along concentric circles or along spiral lines.

[0093] In the second preferred embodiment, the direct light source 200 includes at least a plurality of LED light sources arranged along a line of sources arranged to form, for example, a linear type illuminator. Preferably, the optical filter 100 is oriented with respect to the direct light source 200 such that the entrance surface 101 is substantially orthogonal to the main direction 206. Also, the optical filter 100 is oriented with respect to the direct light source 200 such that it has an entrance surface 101 that is angularly tilted, for example, between 0 degrees and 80 degrees, preferably between 10 degrees and 70 degrees, more preferably between 20 degrees and 60 degrees, with respect to the main direction 206. Preferably, the optical filter 100 is configured to have absorption sectors 108 intersecting the entrance surface 101 and the exit surface 102 arranged along a straight line parallel to each other and orthogonal to the source line.

[0094] In a third preferred embodiment, the lighting device 1000 includes a plurality of LED light sources disposed substantially in a source plane, and a refractive device or a liner type Fresnel reflector configured to deflect the direction of light incident thereon along a direction configured in a Fresnel incident plane orthogonal to the source plane. Preferably, the lighting device 1000 is configured to generate a direct light component propagating along a direction substantially different from the normal to the source plane downstream of the diffused light source 300. Preferably, the optical filter 100 is configured to have absorption sectors 108 intersecting the entrance surface 101 and the exit surface 102 along a straight line parallel to the Fresnel incident plane and a straight line orthogonal to the Fresnel incident plane. Preferably, the optical filter 100 is arranged to have an entrance surface 101 and an exit surface 102 substantially parallel to the source plane.

Claims

1. Substantially flat and parallel inlet surface (101) and outlet surface (102), and A plurality of locally planar and locally parallel to each other visible light absorption sectors (108) extending in a sector length (L) between the inlet surface (101) and the outlet surface (102), and A plurality of solid transparent sectors (103) made of at least one solid material transparent to visible light, each transparent sector (103) of the plurality of transparent sectors being disposed between two absorption sectors (108) and forming an alternating arrangement of adjacent and contacting transparent sectors (103) and absorption sectors (108), a plurality of solid transparent sectors (103) Comprising Each visible light absorption sector (108) of the plurality of visible light absorption sectors (108) is in contact with at most two transparent sectors (103) among the plurality of transparent sectors, and / or the distance between adjacent absorption sectors (108) of the plurality of absorption sectors (108) is substantially constant, Each transparent sector (103) of the plurality of transparent sectors In a local region of the entrance surface (101), an entrance direction (D) that is formed on the incident surface (P) and is offset by a non-zero angle of incidence (δ ｉｎ ) with respect to the incident direction (D), a third parallel light (211') that hits the entrance surface (101) is provided along the entrance direction (D ｅ ). When it is smaller than the acceptance angle (θ ａｃｃ ) of the filter measured with respect to the incident direction (D), in the output from the exit surface (102), it is formed on the incident surface (P) and with respect to the incident direction (D such that the declination angle (δ ｏｕｔ ) along the deflected direction, at least one component of the transmitted light exiting from the exit surface (102) is generated, and the luminous transmittance of the third parallel light (211') is a value obtained by subtracting the loss due to reflection at the entrance surface (101) and the exit surface (102), significantly higher than 50%, preferably higher than 60%, more preferably higher than 70%, and / or In a local region of the exit surface (102), an incident surface (P) is configured, and an incident angle (δ ｉｎ ), which is non-zero with respect to the incident direction (D), is offset. Along an entrance direction (D ｅ ), a fourth parallel light (212') that hits the exit surface (102) is provided. When it is smaller than the acceptance angle (θ ａｃｃ ) of the filter measured with respect to the incident direction (D), in the output from the entrance surface (101), an incident surface (P) is configured, and with respect to the incident direction (D) The declination angle (δ ｏｕｔ ) Along the deflected direction to which it is applied, at least one component of the transmitted light emerging from the entrance surface (101) is generated, and the apparent transmittance of the fourth parallel light (212') is a value obtained by subtracting the loss due to reflection at the entrance surface and the exit surface, significantly higher than 50%, preferably higher than 60%, more preferably higher than 70%. Is locally arranged and configured to have a refractive power, A plane perpendicular to the inlet surface (101) and including a normal (N) to one absorption sector (108) of the plurality of absorption sectors in a local region of the inlet surface (101) defines the local incident plane (P), and the intersection of the local incident plane (P) and the surface of the absorption sector (108) defines the incident direction (D) substantially common to the entire inlet surface (101), Each of the plurality of transparent sectors (103) includes a layer of inhomogeneous transparent material characterized by a non-uniform refractive index profile having a gradient substantially parallel to the normal (N) to the absorption sector (108), with a minimum refractive index (n ｅ ) adjacent to the wall of the transparent sector (103) adjacent to each absorption sector (108), and a maximum refractive index (n ｉ ) in the central portion of the transparent sector (103). Optical filter (100).

2. The thickness (d) of each transparent sector (103) of the plurality of transparent sectors (103) is configured to be between 10 μm and 300 μm, preferably between 10 μm and 200 μm, more preferably between 10 μm and 150 μm, The optical filter (100) according to claim 1.

3. The surface of each absorption sector (108) of the plurality of absorption sectors (108) has a radius of curvature of at least 5 times, preferably at least 10 times, more preferably at least 30 times the distance between adjacent absorption sectors (108), and / or A plurality of the plurality of absorption sectors (108) of the plurality of absorption sectors (108) intersect the inlet surface (101) and the outlet surface (102) along concentric circles, or along a spiral line, or along substantially straight lines parallel to each other, The optical filter (100) according to claim 1 or 2.

4. configured to convert the third parallel light (211) and the fourth parallel light (212) that respectively illuminate the entrance surface (101) and the exit surface (102) along the direction of the incident surface (P) into transmitted or filtered light, (i) The transmitted light (130) is measured with respect to the incident direction of the third and fourth parallel lights (211, 212) input inside the acceptance angle (205, θ ａｃｃ ) of the filter measured with respect to the incident direction (D), and is characterized by an angular luminance profile on the incident surface (P) having a value close to the maximum value for an angle smaller than the cut-off angle (207, θ ｃｕｔ ) measured with respect to the incident direction (D) and being zero elsewhere, and the luminance profile is substantially independent of, or slightly dependent on, the direction of the input parallel lights (201, 202). (ii) with respect to the incident directions of the input third and fourth parallel lights (201, 202) outside the acceptance angle of the filter (205), the transmitted light (130) is substantially zero, The optical filter (100) according to any one of claims 1 to 3.

5. the incident direction (D) and θ ｉｎ < Aθ ａｃｃ such as the input angle (θ ｉｎ ), for the third parallel light (211) and the fourth parallel light (212) that illuminate the entrance surface (101) and the exit surface (102) respectively along the direction of the incident surface (P) forming the input angle, the visual transmittance T(θ ｉｎ ) of the optical filter (100) satisfies T(θ ｉｎ ) < BT ０ is applied, where A = 1.3, preferably A = 1.2, more preferably A = 1.1, B = 0.20, preferably B = 0.15, more preferably B = 0.10, and even more preferably B = 0.05, and for |θ ｉｎ | < θ １－ＨＷＨＭ , T ０ ≡ < T(θ ｉｎ ), where T(θ １－ＨＷＨＭ ) = T(0) / 2, and / or θ ｏｕｔ > Cθ ｃｕｔ such as the output angle (θ ｏｕｔ ), the light intensity I(θ ｏｕｔ ) of the light (130) transmitted by the optical filter (100) propagating through the incident surface (P) is such that for diffusely incident light characterized by a substantially constant light intensity in all directions, I(θ ｏｕｔ ) < DI ０ is applied, where C = 1.3, preferably C = 1.2, more preferably C = 1.1, D = 0.20, preferably D = 0.10, more preferably D = 0.05, and |θ ｉｎ | < θ ２－ＨＷＨＭ for which I ０ ≡ < I(θ ｉｎ ), where I(θ 2－ＨＷＨＭ ) = T(0) / 2, and / or θ ｏｕｔ <Eθ ｃｕｔ such as the output angle (θ ｏｕｔ ), the light intensity I(θ ｏｕｔ ) of the light (130) transmitted by the optical filter (100) propagating through the incident surface (P) is characterized by a substantially constant light intensity in all directions. For the diffused input light, I(θ ｏｕｔ ) > FI ０ is applied, where E = 0.7, preferably E = 0.8, more preferably E = 0.9, F = 0.3, preferably F = 0.4, more preferably F = 0.6, still more preferably F = 0.8, and |θ ｉｎ | < θ ２－ＨＷＨＭ , I ０ ≡ < I(θ ｉｎ ), where I(θ 2－ＨＷＨＭ ) = T(0) / 2 The optical filter (100) according to any one of claims 1 to 4.

6. The layer of the inhomogeneous transparent material of the transparent sector (103) comprises a plurality of layers (103') with different refractive indices, The optical filter (100) according to any one of claims 1 to 5.

7. the value of the refractive index of each layer (103') of the plurality of layers (103') changes with a dependence that substantially approximates a parabolic function along the normal (N) to the absorption sector (108), and / or, from the central portion of the transparent sector (103) towards each sector wall adjacent to the absorption sector (108), it monotonically decreases, and / or, the value of the refractive index of each layer (103') of the plurality of layers (103') changes with a dependence that imparts a refractive power of a lens having a focal length (f) to the transparent sector (103) along the normal (N) to the absorption sector (108), and the relationship 0.5L < f < 2L, preferably the relationship 0.7L < f < 1.6L, more preferably the relationship 0.7L < f < 1.4L, even more preferably the relationship 0.9L < f < 1.2L is applied, or, even more preferably, the focal length (f) is substantially equal to the sector length (L), The optical filter (100) according to claim 6.

8. The first layer (103'a) located in the central part is made of a transparent material having a refractive index of the internal layer corresponding to the maximum value of the refractive index (n ｉ ), and a pair of layers (103'd) located in each adjacent absorption sector (108) is made of a transparent material having a refractive index of the external layer corresponding to the minimum value of the refractive index (n ｅ ). The sector length (L), the thickness (d) of the transparent sector (103), the acceptance angle (θ ａｃｃ ), and the maximum value of the refractive index (n ｉ ) satisfy the following relationship: where G < 3, preferably G < 2, more preferably G < 1.5, and / or, G > 0.3, preferably, G > 0.5, more preferably G > 0.7 is applied, or even more preferably, is applied, The optical filter (100) according to claim 6 or 7.

9. The plurality of layers (103') with different refractive indices are composed of a first layer (103'a) located in the central portion of each transparent sector (103) and a pair of second layers (103'b), and each second layer (103'b) of the pair of second layers is arranged side by side with the first layer (103'a), The optical filter (100) according to claim 6.

10. The first layer (103'a) located in the central part is made of a transparent material having a refractive index of the internal layer corresponding to the maximum value of the refractive index (n ｉ ), and the pair of layers (103'b) is made of a transparent material having a refractive index of the external layer corresponding to the minimum value of the refractive index (n ｅ ). Said sector length (L), thickness (d) of said transparent sector (103), total internal reflection angle (θ ＴＩＲ ), and maximum value of refractive index (n ｉ ), the following relationship is applicable: Here, the internal reflection angle (θ ＴＩＲ ) is the total internal reflection angle at the interface between the inner layer (103'a) and the outer layer (103'b), and G < 3, preferably G < 2, more preferably G < 1.5, and / or G > 0.3, preferably G > 0.5, more preferably G > 0.7 is applied, or even more preferably, to which The optical filter (100) according to claim 9 is applied.

11. The refractive index profile of each transparent sector (103) continuously changes substantially parabolically and / or monotonically decreasing from the central portion of the transparent sector (103) to the sector wall adjacent to each absorption sector (108), and / or The refractive index profile of each transparent sector (103) continuously changes according to a tendency to locally impart the refractive power of a GRIN cylindrical lens having a focal length (f) to the transparent sector (103), and a relationship of 0.5L < f < 2L, preferably a relationship of 0.7L < f < 1.6L, more preferably a relationship of 0.7L < f < 1.4L, and even more preferably a relationship of 0.9L < f < 1.2L is applied, or, even more preferably, the focal length (f) is substantially equal to the sector length (L), The optical filter (100) according to any one of claims 1 to 5.

12. The sector length (L), the thickness (d) of the transparent sector (103), the acceptance angle (θ ａｃｃ ), and the maximum value of the refractive index (n ｉ ), the following relationship applies, where G < 3, preferably G < 2, more preferably G < 1.5, and / or G > 0.3, preferably G > 0.5, more preferably G > 0.7 is applied, or even more preferably, to which The optical filter (100) according to claim 11 is applied.

13. Substantially flat and parallel entrance surface (101) and exit surface (102), A plurality of locally planar and locally parallel to each other visible light absorption sectors (108) extending a sector length (L) between the entrance surface (101) and the exit surface (102), A plurality of solid transparent sectors (103) made of at least one solid material transparent to visible light, each transparent sector (103) of the plurality of transparent sectors being disposed between two absorption sectors (108) and forming an alternating arrangement of adjacent transparent sectors (103) and absorption sectors (108), a plurality of solid transparent sectors (103) comprising Each visible light absorption sector (108) of the plurality of visible light absorption sectors (108) is in contact with at most two transparent sectors (103) among the plurality of transparent sectors (103), and / or the distance between adjacent absorption sectors (108) of the plurality of absorption sectors (108) is substantially constant, Each transparent sector (103) of the plurality of transparent sectors is A first parallel light beam (201) is provided that strikes the entrance surface (101) along the incident direction (D) in a local region of the entrance surface (101), and the transparent sector (103) focuses the first parallel light beam (201) along a first focal line (203) orthogonal to the local incident surface (P), and / or, A second parallel light beam (202) is provided that strikes the exit surface (102) along the incident direction (D) in a local region of the exit surface (102), and the transparent sector (103) focuses the second parallel light beam (202) along a second focal line (204) orthogonal to the local incident surface (P), is locally arranged and configured to have a refractive power, A plane that is orthogonal to the entrance surface (101) and includes a normal (N) to one of the plurality of absorption sectors in a local region of the entrance surface (101) defines the local incident surface (P), and an intersection of the local incident surface (P) and the surface of the absorption sector (108) defines the incident direction (D) that is substantially common to the entire entrance surface (101), Each transparent sector (103) of the plurality of transparent sectors comprises a layer of inhomogeneous transparent material characterized by a non-uniform refractive index profile having a gradient substantially parallel to the normal (N) to the absorption sector (108), having a minimum value close to the wall of the transparent sector (103) adjacent to each absorption sector (108) and a maximum value in the central portion of the transparent sector (103), Optical filter (100).

14. Each transparent sector (103) of the plurality of transparent sectors, A first parallel light beam (201) is provided that strikes the entrance surface (101) along the incident direction (D) in a local region of the entrance surface (101), and the transparent sector (103) focuses the first parallel light beam (201) along the first focal line (203) located at a first distance (f1) from the entrance surface (101) measured along the incident direction (D) and orthogonal to the local incident surface (P), and a relationship of 0.5L < f1 < 2L, preferably a relationship of 0.7L < f1 < 1.6L, more preferably a relationship of 0.7L < f1 < 1.4L, still more preferably a relationship of 0.9L < f1 < 1.2L is applicable, or still more preferably, the first focal distance (f1) is substantially equal to the sector length (L), and / or, In a local region of the exit surface (102), the second parallel light (202) hitting the exit surface (102) along the incident direction (D) is provided, and the transparent sector (103) is orthogonal to the local incident surface (P) and converges the second parallel light (202) along a second focal line (204) located at a second distance (f2) from the exit surface (102) measured along the incident direction (D), and a relationship of 0.5L < f2 < 2L, preferably a relationship of 0.7L < f2 < 1.6L, more preferably a relationship of 0.7L < f2 < 1.4L, and even more preferably a relationship of 0.9L < f2 < 1.2L is applied, or, even more preferably, the second focal length (f2) is substantially equal to the sector length (L). Locally arranged and configured to have refractive power. The optical filter (100) according to claim 13.

15. The thickness (d) of the transparent sector (103) of the plurality of transparent sectors (103) is configured to be between 10 μm and 300 μm, preferably between 10 μm and 200 μm, more preferably between 10 μm and 150 μm. The optical filter according to claim 13 or 14.

16. The surface of each absorption sector (108) of the plurality of absorption sectors (108) has a radius of curvature that is at least 5 times, preferably at least 10 times, more preferably at least 30 times the distance between adjacent absorption sectors (108), and / or A plurality of the absorption sectors (108) among the plurality of absorption sectors (108) intersect the entrance surface (101) and the exit surface (102) along concentric circles, or along a spiral line, or along substantially straight lines parallel to each other. The optical filter (100) according to any one of claims 13 to 15.

17. A substantially flat and parallel entrance surface (101) and exit surface (102), and A plurality of locally planar and locally parallel to each other visible light absorption sectors (108) extending a sector length (L) between the entrance surface (101) and the exit surface (102). A plurality of solid transparent sectors (103) made of at least one solid material transparent to visible light, each transparent sector (103) of the plurality of transparent sectors being disposed between two absorption sectors (108) and forming an alternating arrangement of adjacent and contacting transparent sectors (103) and absorption sectors (108). Comprising Each visible light absorption sector (108) of the plurality of visible light absorption sectors (108) is in contact with at most two transparent sectors (103) among the plurality of transparent sectors (103), and / or the distance between adjacent absorption sectors (108) of the plurality of absorption sectors (108) is substantially constant. Each transparent sector (103) of the plurality of transparent sectors In a local region of the entrance surface (101), a first parallel light (201) impinging on the entrance surface (101) along the incident direction (D) is provided, and the transparent sector (103) focuses the first parallel light (201) along a first focal line (203) orthogonal to the local incident surface (P), and / or In a local region of the exit surface (102), a second parallel light (202) impinging on the exit surface (102) along the incident direction (D) is provided, and the transparent sector (103) focuses the second parallel light (202) along a second focal line (204) orthogonal to the local incident surface (P). Locally arranged and configured to have a refractive power A plane orthogonal to the entrance surface (101) and including a normal (N) to one of the plurality of absorption sectors in a local region of the entrance surface (101) defines the local incident surface (P), and the intersection of the local incident surface (P) and the surface of the absorption sector (108) defines the incident direction (D) that is substantially common to the entire entrance surface (101). Of the plurality of transparent sectors, the at least one solid transparent material from which a plurality of transparent sectors (103) are made comprises at least one substantially homogeneous material having a first refractive index (n), and an interface surface (107c) that extends between two absorption sectors (108) adjacent to the inlet surface (101) and / or the outlet surface (102). The interface surface locally conforms to the outer surface of a cylinder having an axis of the cylinder perpendicular to the local incidence plane (P) and a convex portion facing the outside or inside of the transparent sector (103), and is characterized by a radius of curvature (ROC). Preferably, each transparent sector (103) of the plurality of transparent sectors is coupled to at least one external refractive element (107b) via the interface surface (107c). The external refractive element (107b) has an external surface facing the interface surface (107c). The external surface is substantially flat and parallel to the inlet surface (101) and / or the outlet surface (102), and is made of a transparent material having a second refractive index (n ２ ). When the interface surface (107c) has a convex portion facing the outside of the transparent sector, the second refractive index (n ２ ) is smaller than the first refractive index (n) (n ２ < n). When the interface surface (107c) has a convex portion facing the outside of the transparent sector, the second refractive index (n ２ ) is larger than the first refractive index (n) (n ２ > n). It comprises an internal refractive element (107a) bounded by an interface surface (107c) made of a transparent material having a third refractive index (n ３ ) different from or equal to the first refractive index (n). The first refractive index (n) of the interface surface (107c), the second refractive index (n ２ ), the third refractive index (n ３ )(and the value of the radius of curvature (ROC) is such that it locally imparts the refractive power of a converging cylindrical lens having the axis of a cylinder orthogonal to the local incident surface (P) and the focal length (f) in a medium of refractive index (n) to the boundary surface (107c), and the relationship 0.5L < f < 2L is applicable, preferably the relationship 0.7L < f < 1.6L, more preferably the relationship 0.7L < f < 1.4L, still more preferably the relationship 0.9L < f < 1.2L, and still more preferably, the focal length (f) is substantially equal to the sector length (L), An optical filter (100).

18. The thickness (d) of the transparent sector (103) of the plurality of transparent sectors (103) is configured to be between 10 μm and 300 μm, preferably between 10 μm and 200 μm, and more preferably between 10 μm and 150 μm. The optical filter according to claim 17.

19. The surface of each absorption sector (108) of the plurality of absorption sectors (108) has a radius of curvature that is at least 5 times, preferably at least 10 times, more preferably at least 30 times the distance between adjacent absorption sectors (108), and / or A plurality of the absorption sectors (108) among the plurality of absorption sectors (108) intersect the inlet surface (101) and the outlet surface (102) along concentric circles, or along a spiral line, or along substantially straight lines parallel to each other. The optical filter (100) according to claim 17 or 18.

20. A direct light source (200) configured to emit visible light along a direction in a range transverse to the main direction (206), wherein the light emitted by the direct light source (200) has a first CCT, the direct light source (200); The optical filter (100) according to any one of claims 1 to 19, disposed downstream of the direct light source (200) with respect to the main direction (206); A diffused light source (300) located downstream of the optical filter (100) with respect to the main direction (206), the diffused light source (300) being configured to at least partially transmit the filtered light (130) in the output from the filter (100), configured to generate a diffused light component, at least 2 times, preferably 3 times, more preferably 4 times greater than the divergence of the filtered light (130), and / or at least 1.2 times, preferably 1.3 times, more preferably 1.5 times, even more preferably 1.8 times greater than the first CCT, and / or characterized by an angular luminance profile characterized by a CCT equal to 5600 Kelvin, the diffused light source (300); Comprising An artificial light illumination device (1000) that reproduces the light of the sky and the sun.

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