Lighting device and optical element for a lighting device

Abstract

Lighting equipment (1) comprising: a light source (10) for emitting light, in particular a light-emitting diode, and an optical element (100) for reducing the divergence and changing the direction of the light emitted by the light source, wherein the optical element (100) has a light entry surface (110) for coupling in the light emitted by the light source and a light exit surface (120) for coupling out the coupled-in light, wherein the light emitted by the light source has a primary emission characteristic and the light coupled out of the optical element has a secondary emission characteristic, and wherein the secondary emission characteristic has a emission angle (β) which is smaller than the emission angle (α) of the primary emission characteristic in order to reduce the divergence of the light emitted by the light source, and wherein the optical axis of the light-exit surface (120) is inclined to the optical axis of the light-intake surface (110) in order to change the direction of the light emitted by the light source, and wherein the optical element comprises a plurality of light-guiding elements (200) which each form a part of the light-entry surface (110) and a part of the light-emission surface (120) of the optical element (100) and each comprise an interface (210) extending between the light-entry surface and the light-emission surface for reflection, in particular total internal reflection at this interface (210), of the coupled-in light, wherein the plurality of light-guiding elements (200) are designed as interconnected, in particular fused, individual fibers in a common drawing process, and wherein the light guiding elements each have a cross-section at the light exit surface (120) which is larger than the cross-section at the light entry surface (110), in particular such that the light exit surface (120) of the optical element is larger than the light entry surface (110) of the optical element, and wherein the optical element comprises a widening section (130) within which the cross-section of the light-guiding elements and / or the cross-section of the optical element increases and wherein the optical element has a curvature section (140) within which the optical axis of the optical element is curved, wherein the widening section (130) and the curvature section (140) are arranged apart from each other along the optical axis, such that the widening section (130) is located closer to the light entry surface and the curvature section (140) is located closer to the light exit surface.

Description

[0001] The invention relates to a lighting device with a light source and an optical element which reduces the divergence of the light and preferably changes the direction of the light, as well as a corresponding optical element and the use of the optical element or the lighting device, for example in a cabin lining of an aircraft cabin, in or on an aircraft seat, etc.

[0002] When using LEDs as light sources, the emission of light is generally directional, i.e., within a limited solid angle range. However, the divergence of the light is typically relatively high, meaning the angle within which most of the light is emitted is relatively large, for example, 120 degrees (±60 degrees). For a number of lighting solutions, however, narrower distributions are desired, for example, ≤ 60 degrees (≤ ±30 degrees).

[0003] Document US 5,371,826 A relates to a fiber optic light guide for generating concentrated, high-intensity light, comprising a plurality of bundled fiber optic strands, each strand being uniformly tapered to form an elongated tapered section and a curved section extending distally thereto. The light is coupled in at the wider end and coupled out at the narrower end to achieve light concentration for dental applications.

[0004] Document DE 32 16 439 A1 relates to an arrangement for illuminating observation planes in optical devices, in which a light guide rod is arranged at the light exit end of a fiber optic light guide in such a way that its emitting surface is imaged in the observation plane by means of optical lenses in order to avoid inhomogeneities caused by the fiber structure.

[0005] Document US 2003 / 0021124A1 relates to a handpiece 1 for irradiating a skin surface during a medical or cosmetic treatment, wherein an optical coupling element 6 consists of a bundle of light guides which are so close together laterally, at least in their end sections, that there are no optically ineffective gaps.

[0006] Document DE 10 2011 088 702 A1 relates to a fiber optic structure for a motor vehicle lighting device with multiple coupling branches, characterized by a transition section in which adjacent coupling branches curve and merge into one another, forming a common volume, in order to focus light from multiple LEDs with minimal loss. However, a continuous multitude of fiber optic elements in the sense of a fiber bundle from the coupling point to the coupling point is not shown.

[0007] Document DE 10 2012 112 125 A1 relates to a lighting device for vehicles with an elongated, curved light guide, the radius of curvature being greater than twice the transverse extent of the light guide in order to minimize light loss due to total internal reflection during deflection. No plurality of light guide elements in the sense of a bundle with a common entry and exit surface is shown.

[0008] Document DE 10 2012 215 124 A1 relates to a lighting device in which a light-emitting diode 20 emits light onto a reflector 28 via a rigid light guide 30, wherein the light-emitting surface 34 of the light guide is arranged at the focal point F of the reflector, as can be used in automotive headlights. A light guide consisting of a plurality of light guide elements in the sense of a fiber bundle is not shown.

[0009] Document US 2015 / 0043241A1 relates to a high transmittance (>90%), high refractive index (>1.4) and low turbidity (<10%) optical fiber comprising an organosiloxane block copolymer with specific molar proportions of disiloxy and trisiloxy units as well as silanol groups.

[0010] Solutions exist in which the light is collimated using a spherical or aspherical lens, a TIR optic, a mirror, or a combination of these elements, or the light cone is simply cut off by an aperture. Due to physical limitations, the light cone widens again after passing through the optical element, depending on its degree of collimation. The combination of LED PCB, optic, and mounting cannot be arbitrarily miniaturized. Typically, the optic has a diameter of at least 5 mm, usually 10 mm. Standard TIR optics have a diameter of over 10 mm and a height of over 8 mm. In applications with limited installation space at the light exit point, for example, behind the cabin lining of an aircraft cabin, it is often impractical to integrate such components or combinations thereof. An additional disadvantage is the reduced heat dissipation from the LED.Firstly, the limited installation space makes efficient heat transfer impossible. Secondly, the heat is transferred directly to the housing surface, generating undesirably high temperatures there. These disadvantages are exacerbated, particularly when the light emission is not perpendicular to the housing surface, as the required installation space often increases due to the tilting of the components and / or an additional light path is introduced, further widening the divergent light cone before it exits the light source.

[0011] The invention is therefore based on the objective of providing a lighting device which, in limited installation space at the light output, emits light, for example from a light-emitting diode, with a narrow beam angle, and optimally coordinates the properties of the light distribution, e.g. for cabin lights in aircraft.

[0012] To solve this problem, the invention discloses a lighting device with a light source for emitting, preferably directed, preferably divergent, light, which is in particular designed as a semiconductor-based light source, for example as a light-emitting diode, as well as an optical element for reducing the divergence and preferably for changing the direction of the light emitted by the light source.

[0013] The optical element has a light-intake surface (proximal) for coupling in the light emitted by the light source and a light-exit surface (distal) for coupling out the coupled-in light. The light-intake surface thus receives the light emitted by the light source and, in particular, forms a proximal end of the optical element, which faces the light source. The light-exit surface, which, in particular, forms a distal end of the optical element, re-emits the coupled-in light with a modified beam characteristic.

[0014] The light emitted by the light source therefore has a primary emission characteristic, and the light coupled out of the optical element has a secondary emission characteristic. The optical element is specifically designed to convert the primary emission characteristic into the secondary emission characteristic. In particular, the secondary emission characteristic has a beam angle that is smaller than the beam angle of the primary emission characteristic in order to reduce the divergence of the light emitted by the light source.

[0015] Preferably, the optical axis of the light-emitting surface is inclined relative to the optical axis of the light-intake surface in order to change the direction of the light emitted by the light source. This allows, for example, an inclined light emission without requiring the light source to be mounted at the desired angle at the emission point. While an inclined orientation of the optical axes of the light emission surface relative to the optical axis of the light-intake surface is preferred, it is not strictly necessary. It is also possible for the optical axes to be parallel or coincident, meaning that no change in the optical axis occurs.

[0016] Particularly preferably, the optical element comprises a plurality of light-guiding elements which each form a part of the light-entry surface and a part of the light-emission surface of the optical element and each comprise an interface between the light-entry surface and the light-emission surface for reflection, in particular for total internal reflection at this interface, of the coupled-in light, wherein the light-guiding elements each have a cross-section at the light-emission surface which is larger than the cross-section at the light-entry surface, such that the light-emission surface of the optical element is larger than the light-entry surface of the optical element.

[0017] Due to the at least partial enlargement or widening of the cross-section along the direction of light propagation and the reflection of the light at the interface, a light beam experiences an angle reduction relative to the central axis with each reflection at the interface. The larger cross-section of the light-guiding element at the light-exit surface compared to the cross-section at the light-inlet surface thus results in the secondary emission characteristic having a beam angle that is smaller than the beam angle of the primary emission characteristic, thereby reducing the divergence of the light emitted by the light source.

[0018] Although a plurality of light-guiding elements is particularly preferred, it should not be excluded that in a specific embodiment the optical element may comprise only one light-guiding element, with the light-intake and light-outtake surfaces being formed by the cross-section of the individual light-guiding element. However, the particularly preferred embodiment with a plurality of light-guiding elements will be the focus in the following.

[0019] If the optical element comprises not just a single light-guiding element, but a multitude of light-guiding elements, e.g., a multitude of individual fibers, each of which forms a nearly closed optical system with a core and a cladding, the divergence of the light at the distal end, i.e., the exit side of the optical element, is advantageously reduced over shorter lengths of the optical element for the same increase in cross-sectional area along the direction of light propagation. This is illustrated further below in the figure description. An optical element with a multitude of light-guiding elements is therefore particularly advantageous for illumination in confined spaces.

[0020] Preferably, the optical element comprises a widening section within which the cross-section of the light-guiding elements and / or the cross-section of the optical element increases, particularly conically. (Conical here does not refer to a truncated cone, i.e., a constant opening angle, but more generally to a body formed by rotating a curve around an axis. This means that while the widening section may contain a portion with a constant opening angle, a gradual increase or decrease in the opening angle occurs at both ends, particularly in the transition to the cylindrical region, due to the manufacturing process. In the limiting case of a short widening section, no region with a constant opening angle exists.)) Furthermore, the optical element preferably comprises a curvature section within which the optical axis of the optical element is curved, in particular along a circular arc.

[0021] The widening section and the curvature section are preferably spaced apart from each other along the optical axis, particularly preferably such that the widening section is arranged closer to the light entry surface and the curvature section closer to the light exit surface.

[0022] The optical element can also have one or more linear sections within which the cross-section remains constant and the optical axis runs in a straight line, wherein the linear section(s) are preferably arranged in front of and / or behind the widening section and / or the curvature section, and particularly preferably between the widening section and the curvature section.

[0023] Preferably, the widening section, the curvature section and / or the linear section(s) along the optical axis are monolithically formed together.

[0024] The secondary emission characteristic can have an emission angle (β) which is less than 60 degrees (i.e. ±30 degrees around the optical axis), preferably less than 50 degrees, and particularly preferably less than 40 degrees.

[0025] The optical element can define a ratio between the beam angle (β) of the secondary beam characteristic and the beam angle (a) of the primary beam characteristic, which is less than 0.7, preferably less than 0.6, and particularly preferably less than 0.5.

[0026] Furthermore, the optical element can be a ratio (sin α / sin β) 2for the radiation angle (α) of the primary radiation characteristic and the radiation angle (β) of the secondary radiation characteristic, which lies between 2 and 100, preferably between 3 and 50, particularly preferably between 4 and 25, and even more preferably between 5 and 15.

[0027] The secondary radiation characteristic can be characterized in particular by a triple of values ​​comprising roundness, inhomogeneity and the scattered light component.

[0028] For example, the secondary emission characteristic can have a roundness greater than 0.4, an inhomogeneity less than 0.35, and a scattered light component less than 0.2.

[0029] Preferably, the secondary emission characteristic can have a roundness greater than 0.65, an inhomogeneity less than 0.25, and a scattered light component less than 0.15.

[0030] Particularly preferably, the secondary emission characteristic can have a roundness greater than 0.85, an inhomogeneity less than 0.2, and a scattered light component less than 0.05.

[0031] The roundness can preferably be determined as follows: - Subdivision of the angular space into 8 rotation angle segments (φ1, φ2, φ3, φ4, φ5, φ6, φ7, φ8) - Calculation of the ratio of minimum intensity in a rotation angle segment to maximum intensity in a rotation angle segment, where this ratio is ideally 1 and in the worst case 0.

[0032] The proportion of scattered light can preferably be determined as follows: - For each light beam emitted outside the target angle range (beam angle β): - Calculation of the squared deviation of the beam angle from the maximum target angle. - Weighting of the squared deviation with the intensity of the light beam. - Summing of all light rays. - Normalization to the square of the maximum target angle.

[0033] The inhomogeneity can preferably be determined as follows: - Standard deviation of segment brightnesses (θ1, θ2, θ3, θ4) / Mean of segment brightnesses (θ1, θ2, θ3, θ4) - Evaluation via the target area of ​​the light distribution (beam angle β)

[0034] Example: An optical fiber with an area ratio of 1:9 results in a target area of ​​+ / - 14°. This translates to solid angles (sphere surface): tilt angle = 0 to 14°, rotation angle (azimuth) = 0 to 360°. The tilt angles are divided into 12 segments with equal solid angle proportions. In the case of a light source that is equally bright in all directions (constant luminous intensity across the target area), the same luminous flux falls into each segment. In real-world applications, a flat surface is typically illuminated, which may also be tilted at a specific angle to the optical axis of the light cone. To abstract from these various individual cases, the application-independent consideration of constant luminous intensity was chosen. The standard deviation was selected as the measure of the deviation between the different segments, as it takes all segments into account.An alternative would be a minimum-to-maximum analysis, but this can be heavily influenced by individual segments and therefore doesn't accurately reflect the overall impression. The standard deviation is divided by the mean brightness value, since relative brightness variations, not absolute ones, are crucial for homogeneity.

[0035] In the aforementioned definitions for determining roundness, scattered light component and inhomogeneity, a beam angle (β) can preferably be selected such that the above-mentioned triples are fulfilled, e.g. a beam angle designed as a conical solid angle can be selected within which 90 percent of the light intensity of the light falls.

[0036] The lighting device is preferably characterized by the fact that the ratio of the areas of the light emission surface and the light entry surface and / or the cross-sections of the light guiding elements at the light emission surface and the light entry surface is between 2 and 100, preferably between 3 and 50, particularly preferably between 4 and 25, and even more preferably between 5 and 15.

[0037] Furthermore, the optical element can have a cross-section formed perpendicular to the optical axis, which can be round, in particular circular, angular, in particular polygonal or square and / or wherein the shape of the cross-section remains congruent along the entire length of the optical axis.

[0038] It may be provided that the angle between the optical axis of the light exit surface and the optical axis of the light entry surface and / or the angle caused by the curvature section is greater than 10 degrees, preferably greater than 20 degrees, particularly preferably greater than 30 degrees, or greater than 40 degrees, or greater than 80 degrees.

[0039] The curved section or area may deviate from an ideal circular arc; that is, local radii of curvature may occur within the curved section that are partly larger and / or partly smaller than the radius of the ideal circular arc. Smaller local radii of curvature in one part of the curved section of the optical fiber can cause a disturbance in the light transmission, which may be barely or not at all compensated for by the smaller disturbance in the other part with the larger radius. Therefore, optically, light transmission along an ideal circular arc in the curved section represents the ideal case and is to be strived for.

[0040] Deviations from the ideal circular arc with larger or smaller local radii of curvature can still be advantageous, for example, because the deviating shape is easier to manufacture (especially if there is an inlet and outlet area with a larger local radius of curvature) or the installation space is occupied along the ideal circular arc, so that the curved section can be advantageously adapted to this, possibly with a smaller local radius of curvature. As a special case, the curved area can also contain one or more straight sections. In this way, a curvature with a large equivalent radius of curvature can be produced, with the forming process only taking place in certain areas. These curved sections deviating from the ideal circular arc can be described using an equivalent radius of curvature.The equivalent radius of curvature corresponds to the radius of curvature of the circular arc which is congruent with the optical axis of the optical element at least at the beginning and end of the curvature section.

[0041] Thus, the curvature section within which the optical axis of the optical element is curved, in particular along a circular arc, can also have or be described by an equivalent radius of curvature which is greater than 2 millimeters, preferably greater than 4 millimeters, particularly preferably greater than 8 millimeters, or greater than 16 millimeters or greater than 32 millimeters, and preferably less than 40 millimeters.

[0042] As already described, a plurality of light guide elements is preferably included. The plurality of light guide elements comprises, in particular, at least 10, preferably at least 100, more preferably at least 1000, and even more preferably at least 10000 light guide elements, which are in particular designed as individual, interconnected, and especially fused, optical fibers.

[0043] Preferably, the light-guiding elements each comprise a core and a cladding, wherein the core has a refractive index that is higher than the refractive index of the cladding, e.g., the refractive index of the core is greater than 1.55 and the refractive index of the cladding is less than 1.55.

[0044] The light-guiding elements can each comprise a core having a diameter of less than 1000 micrometers, preferably less than 200 micrometers, particularly preferably less than 100 micrometers, less than 50 micrometers, less than 16 micrometers, less than 8 micrometers, or less than 4 micrometers, wherein the diameter is particularly at the light-entry surface.

[0045] Furthermore, the light guiding elements can each comprise a sheath, wherein the ratio of the sheath thickness to the core radius is less than 0.5, preferably less than 0.1, particularly preferably less than 0.01, and / or wherein the sheath thickness is preferably at least 300 nanometers.

[0046] In a preferred embodiment, the ratio of the length of the widening section to the diameter of the core of the light guiding elements, particularly at the light entry surface, is at least 10, preferably at least 25, and most preferably at least 50.

[0047] Furthermore, it is preferably provided that the ratio of the radius of curvature of the curvature section, in particular the equivalent radius of curvature, and the diameter of the core of the light guiding elements, in particular in the curvature section, is at least 10, preferably at least 40, and particularly preferably at least 75.

[0048] Regarding the materials, the optical element, in particular the core of the light-guiding elements, can comprise or consist of a glass, especially a multi-component silicate glass. Furthermore, the light-guiding elements can comprise a core and a cladding, wherein the core and / or cladding glass of the light-guiding elements is free of lead and / or antimony and / or arsenic and / or other heavy metals, except for unavoidable traces. In addition, the light-guiding elements can have a numerical aperture to air of greater than 0.80, preferably greater than 0.85, and / or comprise or consist of a glass system which has an acceptance angle 2α of greater than 80°, particularly preferably greater than 100°, for the light to be guided.

[0049] Preferred core glasses comprise the following components in the following composition ranges in weight percent: component from until B2O3 0 24 SiO2 23 62,1 Al2O3 0 10 Li2O 0 10 Na2O 0 18,5 K2O 0 25,7 BaO 0 57,8 ZnO 0 40 La2O3 0 25 ZrO2 0 10 HfO2 0 14,2 SnO2 >0 2 MgO 0 8 component from until CaO 0 8 SrO 0 24,4 Ta2O5 0 22 Y2O3 0 11,9 Rb2O 0 15 Cs2O 0 21 GeO2 0 7,5 F 0 2 Σ R2O 5 20 Σ MgO, CaO, SrO, ZnO 20 42

[0050] R2O is the sum of the concentrations of all alkali metal oxides.

[0051] One or more of the following components may be included in the core glass: Cs2O, Rb2O, MgO, CaO, SrO, Gd2O3, Lu2O3, Sc2O3, Y2O3, In2O3, Ga2O3 and WO3.

[0052] The following components should preferably not be present in the core glass, or only in concentrations of no more than 500 ppm each, resulting from unavoidable impurities in the raw materials: TiO2, CeO2, Nb2O5, MoO3, Bi2O3, PbO, CdO, Tl2O, As2O3, Sb2O3, SO3, SeO2, TeO2, BeO, radioactive elements, and coloring components, unless otherwise described in the text. TiO2, in particular, should be omitted because this component can cause pronounced absorption in the UV range. In preferred embodiments, the component WO3 is also omitted.

[0053] The components TiO2, CeO2, Nb2O5 and / or Bi2O3 can be present in the core glass up to a maximum of 0.5 wt.%, preferably up to 0.3 wt.% and particularly preferably up to 0.2 wt.%. In a preferred embodiment, the core glass is free of these components.

[0054] Preferably, the core glass is free of optically active components, in particular Sm2O3, Nd2O3, Dy2O3, Pr2O3, Eu2O3, Yb2O3, Tb2O3, Er2O3, Tm2O3 and / or Ho2O3. CeO2 absorbs in the UV range, so preferred core glasses do not contain CeO2.

[0055] The total content of the components alkaline earth metal oxides, La₂O₃, Ta₂O₅, ZrO₂, and HfO₂ is preferably, and especially for core glasses with refractive indices greater than 1.65, at least 40 wt.%, more preferably at least 42 wt.%, more preferably at least 50 wt.%, and particularly preferably at least 55 wt.%. If the content of these components is too low, the preferred refractive index cannot normally be achieved. Due to formulation constraints, this total should not exceed 72 wt.%.

[0056] In a particular embodiment, the cladding glass has the following features: Preferably, the cladding glass has a SiO2 content of >60 wt.%, more preferably >65 wt.%, and particularly preferably at least 69 wt.%. The SiO2 content is preferably at most 75 wt.% and particularly preferably up to 73 wt.%. The cladding glass is generally exposed to stronger environmental influences than the core glass. A high SiO2 content provides better chemical resistance. Consequently, the content of this component in the cladding glass is preferably higher than in the core glass.

[0057] Preferably, the composition of the cladding glass is selected or adapted to that of the core glass such that the linear coefficient of thermal expansion of the cladding glass and that of the core glass differ as little as possible. In general, the coefficient of thermal expansion (CTE) can be the same or different for the fiber core and cladding within a temperature range of 20 to 300°C. In particular, the CTE is different. Preferably, the CTE of the cladding is smaller than the CTE of the fiber core; typically, it is at least 1.0 × 10⁻⁶. -6 / K smaller, but can also be, depending on the glass, typically at least 2.5*10 -6 / K. smaller. The fiber core typically has a CTE of 6.5*10 -6 up to 10*10 -6 on, the mantle has a CTE of 4.5*10 -6 up to 6*10 -6This ensures that the core of the fiber shrinks more than the fiber sheath when cooling, thereby creating a compressive stress in the fiber sheath that protects the fiber, which is beneficial for the mechanical strength of the fiber, especially its flexural strength.

[0058] The following table shows some preferred compositions of cladding glasses that can be used together with the core glasses. The cladding glasses comprise (in wt.% oxide-based): Oxide Group 1 Group 2 Group 3 Group 4 SiO2 70 - 78 63 - 75 75 - 85 62 - 70 Al2O3 5-10 1 - 7 1 - 5 1 - 10 B2O3 5 - 14 0-3 10-14 > 15 Li2O free 0-1 0-3 < 0,1 Na2O 0-10 8-20 2-8 0-10 K2O 0-10 0-6 0-1 0-10 MgO 0-1 0-5 free 0-5 CaO 0-2 1-9 free 0-5 SrO 0-1 free free 0-5 BaO 0-1 0-5 free 0-5 halogen free free free free

[0059] It is particularly advantageous if the optical element comprises or consists of a lead-free and heavy metal-free core and cladding glass. Such glass systems offer especially high transmission in the visible spectral range and, due to their comparatively high transmission in the blue spectral range, exhibit high color fidelity. This allows for the provision of lighting devices that, as a complete system consisting of light source and light guide (optical element), enable illumination, particularly with white light, e.g., using a white LED as the light source, with virtually no change in the CRI (Color Rendering Index) of the light source. Such glass systems are marketed by the applicant under the name SCHOTT PURAVIS. ® These fiber systems are known and their compositions are described in DE 102012100233 B4 and DE 102013208838 B4. Similar fiber systems, which are also lead-free, are also described in EP 2072477 B1.

[0060] It can be advantageous if the optical element consists of a glass system that has an acceptance angle 2α of greater than 80°, particularly preferably greater than 100°, for the light to be guided, which corresponds to a numerical aperture (NA) of greater than 0.64, particularly preferably greater than 0.77. This makes it possible, in particular, to couple light from LEDs, which typically have a very wide beam angle, into the optical element without complex optics at the proximal end and without incurring increased coupling losses.

[0061] The invention further relates to an optical element for reducing divergence and preferably for changing the direction of light, particularly for a lighting device as described above. The optical element according to the invention may, in particular, have one or more of the features disclosed for the optical element in the context of the lighting device described above.

[0062] Accordingly, the optical element comprises a light entry surface for coupling in light with a primary emission characteristic and a light exit surface for coupling out the coupled light with a secondary emission characteristic, wherein the secondary emission characteristic has a emission angle (β) which is smaller than the emission angle of the primary emission characteristic in order to reduce the divergence of the light.

[0063] Preferably, the optical axis of the light-emitting surface runs at an angle to the optical axis of the light-entry surface in order to change the direction of the light.

[0064] The optical element further comprises a plurality of light-guiding elements, each forming part of the light-entry surface and part of the light-emission surface, and each comprising an interface between the light-entry surface and the light-emission surface for reflection, in particular total internal reflection, of the coupled light.

[0065] The light guiding elements each have a cross-section at the light-emitting surface which is larger than the cross-section at the light-entry surface, in particular such that the light-emitting surface is larger than the light-entry surface.

[0066] The optical element, with a primary emission characteristic that essentially follows a Lambertian characteristic typically found in LEDs, can exhibit the following triplet values ​​for the roundness, inhomogeneity, and scattered light component of the secondary emission characteristic: - The secondary radiation pattern exhibits a roundness greater than 0.4, an inhomogeneity less than 0.35, and a scattered light component less than 0.2. - preferably a roundness greater than 0.65, an inhomogeneity less than 0.25, and a scattering component less than 0.15, - especially preferred is a roundness greater than 0.85, an inhomogeneity less than 0.2, and a scattered light component less than 0.05.

[0067] The invention further relates to a lighting device or an optical element according to the preceding description, wherein the dimension of the optical element perpendicular to the optical axis, in particular perpendicular to the optical axis of the light-entry surface, is less than 10 millimeters, preferably less than 7 millimeters, and particularly preferably less than 6 millimeters, in order to enable installation behind a panel, e.g. the interior panel, in particular the cabin panel of the aircraft, in or on a seat, e.g. an aircraft seat, preferably such that the optical axis of the light-entry surface runs parallel to the interior panel and / or the optical axis of the light-emission surface runs obliquely to the interior panel.

[0068] The invention further relates to the use of a lighting device or an optical element as described above for installation behind a panel, e.g. an interior panel with a light emission opening, e.g. in a cabin panel of an aircraft cabin, in or on a seat, e.g. an aircraft seat.

[0069] Finally, the invention relates to a diagnostic, surgical and / or therapeutic device comprising a lighting device or an optical element as described above, wherein preferably the optical element comprises or consists of a lead- or heavy metal-free core glass and / or cladding glass and / or wherein preferably the optical element comprises or consists of a glass system which has an acceptance angle 2α of greater than 80°, particularly preferably greater than 100°, for the light to be guided.

[0070] The invention is explained in more detail below with the help of some figures. These show: Fig. 1 Schematic of a lighting device which is arranged behind a wall with a light emission opening, wherein the lighting device comprises a lens, Fig. 2. Schematic of a lighting device arranged behind a wall with a light emission opening, wherein the lighting device comprises an optical element with a plurality of light guiding elements. Fig. 3. Schematic of a further lighting device which is arranged behind a wall with a light emission opening, wherein the lighting device comprises a lens, Fig. 4. Schematic of a further lighting device which is arranged behind a wall with a light emission opening, wherein the lighting device comprises an optical element with a plurality of light guiding elements, Fig. 5 an optical element consisting of a single light guiding element, Fig. 6 an optical element with a multitude of light guiding elements, Fig. 7 a curved optical element consisting of a single light-guiding element, Fig. 8 a curved light guide element of an optical element with a plurality of light guide elements, Fig. 9 an optical element with a widening section and a curvature section, Fig. 10 an optical element with a widening section, a curvature section and several linear sections, Fig. 11 a schematic distribution of light intensity in a plane perpendicular to the secondary optical axis, Fig. 12 a schematic distribution of light intensity in a plane perpendicular to Fig. 11, Fig.13-25 exemplary schematic distributions according to the representations in Fig. 11 and Fig. 12, which were generated by computer experiment, Fig. 26 exemplary values ​​of inhomogeneity plotted against the quotient of radius of curvature and core radius, Fig. 27 exemplary values ​​of roundness plotted against the quotient of radius of curvature and core radius, Fig. 28 exemplary values ​​of the scattered light component plotted against the quotient of radius of curvature and fiber core radius, Fig. 29-30 exemplary values ​​of optical efficiency plotted against cladding thickness, Fig. 31 Schematic of a curvature section within which the optical axis is curved and the corresponding equivalent radius of curvature.

[0071] Fig.Figure 1 shows a lighting device 1 which is arranged behind a wall 50 with a light emission aperture 60, for example, an interior paneling of an aircraft. The lighting device 1 comprises a light source 10 and a lens 90 to reduce the divergence of the light emitted by the light source 10 and to enable a narrower beam angle β. Since an oblique light emission is desired in this example, the lighting device 1 is installed obliquely behind the wall 50. This is because, in a design with lenses, the beam direction is typically predetermined, and thus the geometry of the lighting device is not very flexible unless further elements, such as mirrors, are provided. However, these increase the complexity and, at least in the case of plane mirrors, hardly change the emission characteristics.A disadvantage of the solution with an inclined design is that the installation space for the lighting device 1, in particular the height H, is relatively large. Another disadvantage is that the dimension 61 of the light exit aperture 60 is relatively large for the beam angle β, because the lens 90 has a relatively large distance to the aperture 60 due to the inclined position.

[0072] Fig. Figure 2, in contrast, shows a lighting device 1 according to the invention, comprising a light source 10 and an optical element 100. The light source can, for example, comprise one or more LEDs or, more generally, semiconductor-based light sources. The optical element 100 is designed as a light guide such that the light coupled in by the light source 10 is reflected at interfaces running between the light entry surface 110 and the light exit surface 120 of individual light guide elements (see Figure 2). Fig.10) is guided along the optical axis of the optical element 100. This allows the light source 10 to be positioned at a proximal end of the optical element 100 that is almost arbitrarily far from the light exit aperture 60, which also has the advantage that heat dissipation does not occur directly behind the wall 50 at the aperture 60. In addition to guiding the light, the optical element 100 also serves to modify the radiation pattern of the light source 10, so that, for example, the beam angle of the light source can be reduced to obtain a narrow beam angle β. For this purpose, the lighting device 1 has a widening section 130 in which the cross-section of the optical element 100 increases. In the example shown, the lighting device 1 also has a curved section 140 to enable the desired oblique light exit.With the lighting device 1 according to the invention, a low overall height H is therefore possible. Since the light emission surface 120 can be directly adjacent to the opening 60, a small dimension 61 for the light emission opening 60 is also possible.

[0073] Fig. Figure 3 shows another lighting device 1 with a lens 90, which enables perpendicular light emission from an opening in a cover 50. A disadvantage of this solution is that a relatively large installation space with respect to width B is required behind the cover 50. Furthermore, a relatively large opening is also necessary in this case due to the distance between the lens 90 and the light emission opening.

[0074] Fig. Figure 4, in contrast, shows a lighting device 1 according to the invention with a straight optical element 100. This makes it possible to reduce the required installation space in the width B as well as the size of the light emission aperture.

[0075] Fig. Figure 5 shows an optical element 100, which comprises only a single optical fiber. In this case, the optical element is designed as a monolithic, conical optical fiber. Due to the widening of the cross-section, a light beam is reduced towards the central axis with each reflection at the outer surface. In the depicted cone with outer surfaces inclined at 10°, the angle is reduced by 20° with each reflection. However, the number of reflections in this example is only 0 to 2.

[0076] Since the light beam is deflected towards the optical axis when it enters the optically denser medium (glass or plastic of the light guide, which typically has a refractive index between 1.4 and 2.0), the maximum angle occurring in the light guide is between 30° and 50°. A typical LED with Lambertian emission emits 75% of its radiant power within an angular range of 0° to ± 60°. After entering the optical medium, the majority of the angles therefore lie between 0° and ± 25° (refractive index 2.0) and ± 38° (refractive index 1.4).

[0077] If, for example, the light from an LED is to be collimated so strongly that the original emission angle is reduced from ±60° to ±20° or ±15°, a cone with a ratio of 1:2.5 or 1:3.4 (diameter of the inlet surface 110 mm to diameter of the outlet surface 120 mm) would be required. If the cone has an inlet diameter of 1 mm, this results in an outlet diameter of 2.5 mm or 3.4 mm, respectively.

[0078] If, for example, an outer surface with a 1° inclination is chosen, this results in a calculated cone height of over 40 mm (2.5 mm output side) or almost 70 mm (3.4 mm output side). Even at such lengths, a large portion of the rays are reflected only 5 times or less. This leads to angular discretization and thus to the formation of bright and dark rings in the far field. On the other hand, a space of 40 mm or 70 mm is simply not available for optical elements in many luminaires.

[0079] Fig. Figure 6 shows an optical element 100 with a plurality of light guiding elements 200, each of which has an interface 210 for the reflection of light.

[0080] If the optical element is not monolithic but composed of individual fibers 200, each of which forms a nearly closed optical system with its core and cladding, the diameter of each individual fiber cone 200 is reduced by a factor of 1 / squared root (number of fibers). For an example fiber count of 1000, this means a reduction in diameter by a factor of over 30.

[0081] If the outer surface of each individual fiber 200 had an inclination angle of 1° as in the above example of the monolithic cones, the optical element could be reduced from 40 mm or 70 mm to 1.3 mm to just over 2 mm.

[0082] For manufacturability of the cones, however, an inclination of the cone surface of 10° to 30° can be advantageous. The length of the cone then ranges from 1.3 mm (1:2.5 with a 30° inclination) to just under 7 mm (1:3.4 with a 10° inclination). It is thus significantly shorter than for monolithic cones. If the cone is chosen with a length of 10 mm, a considerably larger aspect ratio (length of the cone : diameter of the optical element at the entrance side) is also obtained, since with a monolithic cone the entire diameter (in this example 1 mm) must be considered, whereas with a fiber element only the diameter of the individual fiber (in this example approximately 0.03 mm) needs to be taken into account. The aspect ratio for the 10 mm long fiber cone is 300:1, compared to 40:1 or 70:1 for a monolithic cone. This increases the number of internal reflections and thus also minimizes ring formation.The result is a significantly smaller optical element 100, which is therefore compatible with the installation space and has a significantly improved optical function.

[0083] Fig. Figure 7 shows an optical element 100, which is designed as a monolithic optical fiber with a bend. The bending radius is on the order of the optical fiber diameter. The condition of total internal reflection is not met in every case. The deflection occurs via a few reflections. This leads to a widening of the angles.

[0084] Fig. Figure 8, in contrast, shows an exemplary light guide element 200 of an optical element, which comprises a multitude of light guide elements 200, i.e., is constructed as a light guide from individual fibers. In the individual fiber 200, the light is guided by many individual reflections at the same radius of curvature while maintaining the angle to the optical axis of the fiber.

[0085] In contrast to a monolithic optical fiber, light in a fiber optic optical fiber can therefore be guided more efficiently, with lower losses and without widening the beam cone around tight bending radii. A fiber optic optical fiber with a diameter of 3 mm can be bent with a bending radius of 3 mm on the inner side. This allows beam deflection to be achieved in limited installation space.

[0086] While a monolithic optical element 100 is therefore also suitable in principle for special embodiments, it is particularly advantageous in the case of curvature if the optical element 100 comprises a plurality of individual light guiding elements 200.

[0087] Fig.Figure 9 shows an optical element 100 according to the invention comprising a widening section 130 within which the cross-section d of the light-guiding elements and the cross-section of the optical element increase, in this example each increasing conically, and comprising a curvature section 140 within which the optical axis of the optical element 100 is curved, in this example following a circular arc with radius R. The optical element 100 has a plurality of light-guiding elements 200, one of which is highlighted by way of example in the figure. The light-guiding elements each have a core and a cladding with different refractive indices.

[0088] The optical fiber comprises a multitude, e.g., 100 to 10,000 or 500 to 5,000 optical fiber elements 200, which can, for example, be designed as individual fibers fused together in a common drawing process. In the conical expansion section 130, the diameter of the overall optical fiber changes, and proportionally, so does the diameter of the individual fibers. The change in diameter can be, for example, between 1:1.5 and 1:10 or between 1:2 and 1:5.

[0089] The light-entry area 110 (circle or incircle) can be at least as large as the entire light-entry area is covered by the luminous surface of a light source, e.g., an LED chip (maximum brightness per unit area, light losses in the corners of the LED chip). Furthermore, the light-entry area 110 can preferably be at most as large as the entire surface of the luminous LED chip is covered by the light guide (maximum efficiency, dark areas in the light guide).

[0090] The optical element 100 is preferably installed in a non-transparent housing that has an optical aperture only on its light-emitting end face (light exit surface 120), through which light can exit. The housing may partially comprise a transparent material (glass or plastic) and be made opaque in the non-light-emitting area by a surface treatment (printing, painting, etching, sandblasting, coating, vapor deposition, etc.). The transition may be gradual.

[0091] As also in Fig. As shown in Figure 9, the optical element 100 can be bent, preferably in the area of ​​the larger diameter, but also possibly in the area of ​​the smaller diameter or in the area of ​​the widening, in order to direct the light in a direction that does not correspond to the original emission direction of the light source.

[0092] The optical element 100 can be rectangular on the side facing the light source 10 in order to achieve both maximum efficiency and a minimal number of dark areas. This can be achieved, for example, by hot forming (pressing) the light guide.

[0093] The optical element 100 can be optically connected to the LED chip using a transparent material, e.g., silicone, to minimize reflection losses. This connection can also be implemented as an adhesive bond with a mechanical function.

[0094] Optical element 100 can be followed by a diffusing element or another optical element, such as a fixed or variable aperture, to vary the width of the light cone when a light guide is present. The diffusing element can also serve to soften the edge of the illuminated spot or to mask unwanted color aberrations.

[0095] The light guides assigned to different LEDs can differ in their aspects if the LEDs are assigned different functions. The light guide can be pressed. The light exit point can be shaped. The light guide can be shaped as desired along its path to transport the light through a confined space.

[0096] Fig. Figure 10 shows another optical element 100 according to the invention which in many aspects resembles the optical element 100 made of Fig.9 is similar. It also includes linear sections 150, each of which has a straight optical axis. The linear sections 150 at the proximal and distal ends can be very short; this may be due to manufacturing constraints and, in this case, preferably has no significant optical effect. The central linear section 150 geometrically bridges the distance between the light source and the light outlet in the luminaire assembly. This straight section can affect the angular distribution due to absorption in the housing. However, since the angles are already significantly reduced in the optically upstream cone, or very high angles are absorbed in the housing, this section preferably also has no significant influence on the light distribution.

[0097] Fig.Figure 11 shows a schematic distribution of light intensity in a plane perpendicular to the optical axis. To calculate inhomogeneity of the secondary emission characteristic, the azimuthal solid angle segments θ1, θ2, θ3, θ4 shown are used in particular. To calculate roundness, the polar solid angle segments φ1, φ2, φ3, φ4, φ5, φ6, φ7, φ8 shown are used in particular.

[0098] Fig. Figure 12 shows a schematic distribution of light intensity in a plane perpendicular to the plane in Fig. The distribution shown in Figure 11. The beam angle is denoted by β and can be defined, for example, such that 90% of the light is found within the beam angle. The light outside this angle is then referred to as scattered light S.

[0099] The Fig. Figures 13 to 25 show exemplary schematic distributions according to the levels in Fig. 11 and Fig. 12, which are based on an optical system according to Fig. Figure 9 was generated by computer simulation, where the core radius at the light-entry surface and the core radius at the light-emission surface were varied. The parameters underlying the figures are listed below, with reference to the Fig. 9 and Fig. 10 the expansion length corresponds to the length of the expansion section (L), the bending radius corresponds to the (equivalent) radius of curvature of the curvature section (R), the bending angle corresponds to the angle between the optical axis of the light entry surface and the optical axis of the light exit surface (χ), and the core radius corresponds to the radius of a core of a light guide element in the optical element: Fig. 13 cone bend Expansion length 5.00E-03 m Core radius light entry 1.500E-05 m 4.500E-05 m Core radius light exit 4.500E-05 m bending radius 4.500E-03 m bending angle 40.00° Fig. 14 cone bend Expansion length 5.00E-03 m Core radius light entry 3.000E-05 m 9.000E-05 m Core radius light exit 9.000E-05 m bending radius 4.500E-03 m bending angle 40.00° Fig. 15 cone bend Expansion length 5.00E-03 m Core radius light entry 6.000E-05 m 1.800E-04 m Core radius light exit 1.800E-04 m bending radius 4.500E-03 m bending angle 40.00° Fig. 16 cone bend Expansion length 5.00E-03 m Core radius light entry 1.200E-04 m 3.600E-04 m Core radius light exit 3.600E-04 m bending radius 4.500E-03 m bending angle 40.00° Fig. 17 cone bend Expansion length 5.00E-03 m Core radius light entry 1.500E-05 m 3.000E-05 m Core radius light exit 3.000E-05 m bending radius 4.500E-03 m bending angle 40.00° Fig. 18 cone bend Expansion length 5.00E-03 m Core radius light entry 3.000E-05 m 6.000E-05 m Core radius light exit 6.000E-05 m bending radius 4.500E-03 m bending angle 40.00° Fig. 19 cone bend Expansion length 5.00E-03 m Core radius light entry 6.000E-05 m 1.200E-04 m Core radius light exit 1.200E-04 m bending radius 4.500E-03 m bending angle 40.00° Fig. 20 cone bend Expansion length 5.00E-03 m Core radius light entry 1.200E-04 m 2.400E-04 m Core radius light exit 2.400E-04 m bending radius 4.500E-03 m bending angle 40.00° Fig. 21 cone bend Expansion length 5.00E-03 m Core radius light entry 2.500E-04 m 5.000E-04 m Core radius light exit 5.000E-04 m bending radius 4.500E-03 m bending angle 40.00° Fig. 22 cone bend Expansion length 5.00E-03 m Core radius light entry 4.000E-06 m 1600E-05 m Core radius light exit 1600E-05 m bending radius 4.500E-03 m bending angle 40.00° Fig. 23 cone bend Expansion length 5.00E-03 m Core radius light entry 7.500E-06 m 3.000E-05 m Core radius light exit 3.000E-05 m bending radius 4.500E-03 m bending angle 40.00° Fig. 24 cone bend Expansion length 5.00E-03 m Core radius light entry 1.500E-05 m 6.000E-05 m Core radius light exit 6.000E-05 m bending radius 4.500E-03 m bending angle 40.00° Fig. 25 cone bend Expansion length 5.00E-03 m Core radius light entry 3.000E-05 m 1.200E-04 m Core radius light exit 1.200E-04 m bending radius 4.500E-03 m bending angle 40.00°

[0100] From the simulations, and especially with the definitions described above, the following values ​​or triplets for inhomogeneity, roundness, and scattered light fraction can be determined, and / or a beam angle can be defined to arrive at these values ​​or triplets: Fig. 13: Inhomogeneity Roundness Scattered light effect 0.199 0.878 0.028 Fig. 14: Inhomogeneity Roundness Scattered light effect 0.143 0.822 0.128 Fig. 15 Inhomogeneity Roundness Scattered light effect 0.206 0.595 0.100 Fig. 16 Inhomogeneity Roundness Scattered light effect 0.345 0.154 0.922 Fig. 17 Inhomogeneity Roundness Scattered light effect 0.146 0.891 0.014 Fig. 18 Inhomogeneity Roundness Scattered light effect 0.172 0.906 0.020 Fig. 19 Inhomogeneity Roundness Scattered light effect 0.187 0.742 0.066 Fig. 20 Inhomogeneity Roundness Scattered light effect 0.248 0.426 0.068 Fig. 21 Inhomogeneity Roundness Scattered light effect 0.304 0.230 0.765 Fig. 22 Inhomogeneity Roundness Scattered light effect 0.162 0.945 0.001 Fig. 23 Inhomogeneity Roundness Scattered light effect 0.125 0.948 0.049 Fig. 24 Inhomogeneity Roundness Scattered light effect 0.186 0.575 0.167 Fig. 25 Inhomogeneity Roundness Scattered light effect 0.355 0.334 0.442

[0101] The Fig. 26, Fig. 27 and Fig.Figure 28 provides an overview of the inhomogeneity, roundness, and scattering effect. The values ​​are plotted against the ratio of the radius of curvature in the curvature section 140 (see Figure 28). Fig. 9, Fig. 10) and the radius of the fiber core. In the figures, R denotes the ratio of the light-exiting area to the light-intake area.

[0102] The Fig.Figure 29 shows the optical efficiency of an exemplary optical element plotted against the cladding thickness in µm, where the refractive index of the core is 1.624 and of the cladding 1.492. The influence of the cladding thickness can be described as follows: Along arrow 300, an additional cladding thickness improves the light transmission only marginally. Along arrow 301, the overall efficiency decreases because a proportionally larger amount of light is coupled into the cladding. Along arrow 302, the efficiency decreases because light is no longer completely transmitted through the thin cladding. This results in an optimal region, which is marked by a dashed box 303.

[0103] The Fig.Figure 30 shows the optical efficiency of an example optical element plotted against the cladding thickness in µm for various core radii. This reveals that the smaller the core radius, the lower the maximum achievable overall efficiency. This effect is particularly pronounced below 4 µm, as the core diameter and optimal cladding thickness are on the order of the wavelength of visible light. The need for tight light guidance limits the upper limit of the core radius. Conversely, the achievable efficiency limits the lower limit of the core radius.

[0104] The Fig.Figure 31 shows a portion of an optical element 100, namely its curvature section 140, within which the optical axis is curved. In this example, the optical axis of the optical element does not follow a perfect circular arc. The curvature section 140 begins at point P1 and ends at point P2. The two points are a distance s from each other. The direction of the optical axis changes by an angle α (the optical axis OA1 at point P1 and the optical axis OA2 at point P2 have an angle α between them). From the distance s and the angle α, the radius R of a circular arc that also connects points P1 and P2 can be calculated: R = s / (2*sin(α / 2)). A circular arc with this radius therefore results in the same change in the angle of the optical axis between the two points. R is called the equivalent radius of curvature.

Images