Lighting device

Abstract

A lighting device (1) comprising a light generating element (2; 3), and a micro-lens (4) comprising a focal plane (F.sub.p), wherein the light generating element (2; 3) comprises a first light generating component (2) and a second light generating component (3), wherein the first light generating component (2) comprises a light emitting surface (28) adapted for providing a diffuse light output component, wherein the second light generating component (3) comprises at least one array of light sources (3) adapted for providing a directional light output component, wherein the light generating element (2; 3) is arranged to emit a light output towards the micro-lens array (4), the light output being formed by a superposition of the diffuse light output component and the directional light N output component, and wherein the array of the light sources (3) is located in the focal plane (F.sub.p) of the micro-lens array (4).

Claims

1. A lighting device comprising: a light generating element, and a micro-lens array comprising a focal plane (Fp), wherein the light generating element comprises a first light generating component and a second light generating component, wherein the first light generating component comprises a light emitting surface adapted for providing a diffuse light output component, wherein the second light generating component comprises at least one array of light sources adapted for providing a directional light output component, wherein the light generating element is arranged to emit a light output towards the micro-lens array, the light output being formed by a superposition of the diffuse light output component and the directional light output component, and wherein the array of the light sources is located in the focal plane (F.sub.p) of the micro-lens array.

2. A lighting device according to claim 1, and further comprising at least one light source adapted for, in operation, emitting light in a direction of propagation, wherein the first light generating component comprises a light mixing element in which the at least one light source is arranged, wherein the light emitting surface is a cover layer forming part of the light mixing element, the cover layer being arranged downstream of the at least one light source in the direction of propagation, wherein a micro-lens array is arranged downstream of the cover layer in the direction of propagation, wherein the array of light sources is at least one array of light extraction elements, and wherein the cover layer of the light mixing element is a diffusely transparent layer with the at least one array of light extraction elements arranged therein.

3. A lighting device according to claim 2, wherein the light extraction elements are apertures, and wherein the cover layer comprises at least two arrays of apertures with different aperture pitches, p.sub.Ai, where i denotes the number of the array of apertures and i is an integer being 1 or more.

4. A lighting device according to claim 2, wherein the light extraction elements are apertures, and wherein the micro-lens array comprises a micro-lens pitch, p.sub.L, wherein the array, or each array, of apertures comprises an aperture pitch p.sub.Ai, and wherein the aperture pitch, or each of the aperture pitches, and the micro-lens pitch are chosen such as to fulfill the relation p.sub.Ai≤p.sub.L, where i denotes the number of the array of apertures and i is an integer being 1 or more.

5. A lighting device according to claim 2, wherein the light extraction elements are apertures, and wherein the micro-lens array comprises a micro-lens pitch, p.sub.L, wherein the array, or each array, of apertures comprises an aperture pitch p.sub.Ai, and wherein the aperture pitch, or each of the aperture pitches, and the micro-lens pitch are chosen such as to fulfill the relation (p.sub.L−p.sub.Ai)≤r.sub.i, where r is the radius of the apertures and i denotes the number of the array of apertures and i is an integer being 1 or more.

6. A lighting device (1) according to claim 2, wherein the at least one light source is arranged at a position in the light mixing element opposite to the cover layer, and wherein the at least one light source is covered with a diffusive layer.

7. A lighting device according to claim 2, wherein the light extraction elements comprise: at least two mutually different shapes, and/or at least two mutually different sizes, and/or wherein the light extraction elements are circular.

8. A lighting device according to claim 2, wherein the cover layer comprising an array of light extraction elements is a semi-transparent collimating element comprising a collimating glass element.

9. A lighting device according to claim 1, wherein the light generating element comprises: a light guide having a front surface facing towards the micro-lens array, a back surface facing away from the micro-lens array, and an edge surface separating the front surface from the back surface, and a first plurality of LEDs for emitting light into the light guide via the edge surface, wherein the light guide has a first set of light outcoupling structures representing the first light generating component for providing the diffuse light output component, and wherein the light guide has a second set of light outcoupling structures representing the second light generating component for providing the directional light output component.

10. A lighting device according to claim 9, wherein the first set of light outcoupling structures is formed by light scattering particles embedded in the light guide, and wherein the second set of light outcoupling structures is formed by an array of specular light extraction elements provided on at least one of the front surface and the back surface of the light guide.

11. A lighting device according to claim 1, wherein the light generating element comprises: a light guide having a front surface facing towards the micro-lens array, a back surface facing away from the micro-lens array, and an edge surface separating the front surface from the back surface, and a first plurality of LEDs for emitting light into the light guide via the edge surface, wherein the light guide has a first set of light outcoupling structures representing the first light generating component for providing the diffuse light output component, and wherein the light generating element further comprises a second plurality of LEDs provided on at least one of the front surface and the back surface of the light guide, each of the second plurality of LEDs being a micro- or mini-LED, the second plurality of LEDs representing the second light generating component for providing the directional light output component.

12. A lighting device according to claim 1, wherein the micro-lens array is covered by a cover layer having opaque regions defining an image on a transparent background.

13. A lighting device according to claim 2, wherein the lighting device further comprises a spacer glass element arranged between the light emitting surface comprising the array of light extraction elements and the micro-lens array.

14. A lighting device according to claim 1, and comprising at least two light sources, the at least two light sources being LEDs with different correlated color temperatures (CCTs) positioned differently on a substrate.

15. A lighting device according to claim 1, wherein the lighting device is any one of a luminaire, an office ceiling lighting device, a wall lighting device, a hospitality lighting device, a retail lighting device, and a lighting device configured for confined spaces outside view.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention.

(2) FIG. 1 shows a cross-sectional view of a first embodiment of a lighting device according to the invention.

(3) FIG. 2 shows a cross-sectional view of a second embodiment of a lighting device according to the invention.

(4) FIG. 3 shows a cross-sectional view of a third embodiment of a lighting device according to the invention.

(5) FIG. 4 shows a cross-sectional view of a fourth embodiment of a lighting device according to the invention.

(6) FIG. 5 shows a cross-sectional view of a fifth embodiment of a lighting device according to the invention.

(7) FIG. 6 shows a cross-sectional view of a sixth embodiment of a lighting device according to the invention.

(8) FIG. 7 schematically illustrates moving parallax optics and a possible application of a lighting device according to the invention as well as a light emitting device according to the invention and further comprising a cover.

(9) FIG. 8 schematically shows a lighting device according to the invention and configured to provide a virtual image or focus at infinity.

(10) FIG. 9 schematically shows a lighting device according to the invention and configured to provide a virtual image or focus at a distance Z being different from infinity.

(11) FIG. 10 schematically shows a lighting device according to the invention and configured to provide virtual images at various multiple depths.

(12) As illustrated in the figures, the sizes of layers and regions are exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of embodiments of the present invention. Like reference numerals refer to like elements throughout.

DETAILED DESCRIPTION

(13) The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

(14) FIG. 1 shows a lighting device 1 according to a first embodiment of the invention. Generally, and irrespective of the embodiment, the light emitting device comprises a light generating element comprising a first light generating component 2, the first light generating element comprising a surface 28 providing a diffuse light output component, and a second light generating component 3, the second light generating component comprising an array of light sources 31-33 generating a directional light output component, and a micro-lens array 4. The light generating element of the lighting device 1 is thus generally and irrespective of the embodiment arranged to emit a light output being formed as a superposition of the diffuse and directional light output components. Also, and still generally and irrespective of the embodiment, the second light generating component 3 is arranged in the focal plane F.sub.P of the micro-lens array 4, for instance such that the plane of the second light generating component 3 coincide with the focal plane F.sub.P of the micro-lens array 4.

(15) In the particular embodiment shown in FIG. 1, the light emitting device further comprises at least one light source 21-26. Typically, the one or more light sources 21-26 are LEDs. More particularly, in the specific example of FIG. 1, six light sources 21-26 are provided for. The light sources 21-26 are adapted for, in operation, emitting light in a direction of emission. The direction of emission or the direction of propagation of the light emitted by the at least one light source 21-26, is generally towards the array of light extraction elements 3 and the micro-lens array 4. The light sources 21-26 may be covered partially or fully with a diffusive layer or coating. A light guide with light sources at its edges and light extraction elements at its surface may also serve as a mixing element.

(16) Generally, and irrespective of the embodiment, the light sources may be LEDs, such as LEDs of the same color or of one or more different colors, or LEDs the same color temperature or with different correlated color temperatures.

(17) The first light generating component 2 is a light mixing element 2, which is typically provided as a chamber in the form of a box comprising a bottom surface or wall 27 and a cover layer 28. The wall 27 and the cover layer 28 are mutually opposite parts of the light mixing element 2. The light sources 21-26 are arranged in the light mixing element 2 at the wall 27 opposite to the cover layer 28. The cover layer 28 is arranged, when seen in the direction of propagation of the light emitted by the at least one light source 21-26, in front of, or downstream of, the at least one light source 21-26. The bottom surface or wall 27 may be reflective or provided with a reflective coating or film or surface layer. Alternatively, the first light generating component 2 may be a light guide.

(18) The cover layer 28 is a diffusely transparent layer. The cover layer 28 comprises a thickness t. The cover layer 28 comprises at least one array 3 of apertures 31-33 therein forming the light extraction elements 3. The light extraction elements 3 may also be other suitable light extraction features than apertures. Especially, when the first light generating component 2 is a light guide, the second light generating component, or the light extraction elements, can be specular light extraction elements or features.

(19) The diffusely transparent part of the cover layer 28 is thus adapted for providing a diffuse light output component and the at least one array 3 of apertures 31-33 is adapted for providing a directional light output component. The at least one array 3 of apertures comprises an aperture pitch, p.sub.A. The cover layer 28 may additionally or alternatively be a reflective layer. Such a reflective layer may be provided to enhance the efficiency of the light generation.

(20) The array 3 of apertures may have the same shape, such a circular, oval or rectangular or any other shape. Alternatively, the array 3 of apertures may comprise apertures with different shapes, such a circular, oval or rectangular or any other shape or combination thereof. Alternatively, or additionally, the array of apertures 3 may comprise apertures with different sizes.

(21) The micro-lens array 4 comprises a plurality of micro-lenses 41-43. The micro-lens array 4 is arranged, when seen in a direction of propagation of the light emitted by the at least one light source 21-26, in front of the cover layer 28 or downstream of the cover layer 28. The micro-lens array 4 comprises a micro-lens pitch, p.sub.L. Each micro-lens 41-43 comprises a radius of curvature R. The micro-lens array 4 may be made of a suitable glass material 44 (FIGS. 1 and 3) or polymer material 45 (FIG. 2). The micro-lens array 4 further comprises a focal distance f, a focal point F and a focal plane F.sub.P, in which the focal point F is situated. The light extraction elements 31-33 may be arranged in the focal plane F.sub.P of the micro-lens array 4, i.e. such that the plane of the light extraction elements 31-33 coincide with the focal plane F.sub.P of the micro-lens array 4.

(22) The light mixing element 2 is in other words covered by a diffusely transparent sheet 28 with an array of tiny light extraction elements 31-33 in the form of apertures. The light extraction elements 31-33 may be arranged in the focal plane F.sub.P of the micro-lens array 4. Each pair of aperture 31-33 and lens 41-43 creates a narrow directional light beam with an angular spread a determined by the radius r.sub.i of the aperture 31-33 and the focal distance f.sub.i of the micro-lens 41-43 as described by:

(23) $\alpha ={\sin }^{-1}\left(\frac{n_2}{n_1}\sin \left({\tan }^{-1}\frac{r_i}{f_i}\right)\right).$

(24) This equation expresses the beam half-angle α as a function of refractive indices n.sub.1 (air) and n.sub.2 (lens array), aperture radius r.sub.i and lens focal distance f.sub.i. It should be noted that this equation presupposes a situation where the micro-lenses are thick micro-lenses. Embodiments with thin micro-lenses with air spacer or thin micro-lenses with additional glass or light guide spacer (optionally with a different refractive index) are not described with this equation.

(25) Thus, and generally for all embodiments of the invention, in operation light emitted by the light sources 21-26 are mixed in the light mixing element 2 and optionally collimated such as to obtain a beam spread of β/2 at the array 3 of light extraction elements. This beam spread can be achieved, for instance, by the use of an array of vertical lamellae limiting the beam spread, or by using as a mixing element a light guide with specular light extraction features, or by other means know to a person skilled in the art. In an embodiment, β/2 equals 13 degrees or less. At the cover layer 28 with the array 3 of light extraction elements the light propagating through the diffusely transparent part of the cover layer 28 forms a diffuse output lighting component and light propagating through the light extraction elements 31-33 of the at least one array 3 of light extraction elements forms a directional output lighting component with a beam half-angle α. In an embodiment, the beam half-angle α equals 2 degrees or less. The lens array 4 then forms the two output lighting components into an image that is experienced by the viewer. As used herein, a denotes the beam angle of the light that emerges from the device, while R denotes the beam angle in which the light is focused by the micro-lens (numerical aperture).

(26) FIG. 2 shows a lighting device 10 according to a second embodiment of the invention. The lighting device 10 of FIG. 2 differs from that of FIG. 1 only in the construction of the cover layer 28 and array of light extraction elements 3. In this case the lighting device 10 comprises a collimating glass element 36 provided with a layer or coating 28 and 36 on each of two opposing surfaces facing towards the light sources 21-26 and the micro-lens array 4, respectively. The collimating glass element 36 may for instance be a glass plate/spacer which in combination with coating patterns applied on its planes provide the light collimation functionality.

(27) The coating 28 facing towards the light sources 21-26 forms the cover layer 28, and the coating 36 facing the micro-lens array 4 is a collimator coating. Both coatings 28 and 36 are provided with an array of light extraction elements 31-33. The array of light extraction elements 31-33 of the cover layer 28 and of the collimator coating 36, respectively, may be identical in position and/or shape and/or size or they may be different in position and/or shape and/or size.

(28) FIG. 3 shows a lighting device 100 according to a third embodiment of the invention. The lighting device 100 of FIG. 3 differs from that of FIG. 1 only in virtue of the following features.

(29) The lighting device 100 comprises a light mixing element 2 in the form of a glass material 29 with a coating or layer 28 in which the array of light extraction elements 3 is formed. Furthermore, a spacer glass material 5 is arranged between the array of light extraction elements 3 and the micro-lens array 4. The spacer glass material 5 ensures that the aperture 31 and the focal plane of the micro-lens 41 coincide. I spacer glass material 5 may be used as a light guide to distribute and extract light from a second light source.

(30) FIG. 4 shows a lighting device 100′ according to a fourth embodiment of the invention. The lighting device 100′ of FIG. 4 differs from that of FIG. 1 in that the first light generating component 2 is a light guide and that the second light generating component 3 is an array of specular light extraction elements. The lighting device 100′ of FIG. 4 further differs from that of FIG. 1 in that a coating which reflects yellow light (arrow 52) and transmits blue light (arrow 51) is provided. This mimics a diffuse blue sky while increasing the efficiency of the directional beam. To this end the lighting device 100′ comprises a layer 37 which is transparent for blue light and which reflects yellow light, and which comprises light extraction elements 31, 32, 33. The layer 37 may furthermore provide the transmitted blue light with a diffuse effect. For example, a layer 37 of one or more simple dichroic coatings could transmit blue light and reflect yellow light. The light transmitted through the light extraction elements 31, 32, 33 is emitted as directional white light (arrow 50).

(31) FIG. 5 shows a lighting device 102 according to a fifth embodiment of the invention. The lighting device 102 of FIG. 5 differs from that of FIG. 1 in that the first light generating component is a transparent light guide 2 and that the second light generating component 3 is an array of light out-coupling structures 310, 320, 330 arranged on the transparent light guide 2. Furthermore, the light guide 2 comprises a wall 280 made of a scattering material. In other words, a part of the light guide 2 is in this embodiment made of a scattering material 280. Also, the light guide 2 is side lit, which in practice is obtained by arranging a plurality of light sources 21, 22, typically LEDs, at a side wall 271 or 272 of the light guide 2. As shown in FIG. 5 the light sources 21, 22 are arranged at the lower side wall 271 of the light source 2.

(32) FIG. 6 shows a lighting device 103 according to a sixth embodiment of the invention. The lighting device 103 of FIG. 6 differs from that of FIG. 5 mainly in that the second light generating component 3 here is provided as an array of micro-LEDs or mini-LEDs 311-331. The array of micro-LEDs or mini-LEDs 311-331 are arranged on a wall 273 of the light guide 2 facing towards the array of micro-lenses 4. Furthermore, as shown in FIG. 6 the light sources 21, 22 are arranged at the upper side wall 272 of the light source 2.

(33) FIG. 7 shows a lighting device 101 according to a seventh embodiment of the invention. The lighting device 101 of FIG. 7 may be a lighting device according to any one of the above or below described embodiments. The lighting device 101 is furthermore provided with a cover 7 which is provided with transparent regions 71 and opaque regions 72. The cover 7 is arranged on the micro-lens array 4. The cover 7 may be a plate, a layer or a coating. Alternatively, the cover 7 may be replaced with a light guide. Such a light guide may be a transparent light guide. Additionally, the transparent light guide may be made of a scattering material. Also, the light guide may be side illuminated by means of LEDs emitting light, such as, but not limited to, blue light.

(34) FIG. 7 furthermore illustrates the eye 64-67 of a viewer observing a lighting device 101 according to the invention from four different positions. The viewer will see only one (or a few) aperture(s); the light from all other light extraction elements does not reach the eye. When moving the view point, e.g. from that of eye 64 to that of eye 66, a different aperture becomes visible, and the initial aperture becomes invisible. This creates the illusion of a moving light source as illustrated at 94, for instance a moving sun/moon/star effect, as well as an enhanced 3D effect as illustrated at 93. When the lighting device is covered by a colored transparency as illustrated at 94, e.g. as in a poster box, the illusion of moving parallax can be enhanced. For instance, in the example of the image 94 of the tree, the leaves and branches will dynamically block the light as the observer walks by.

(35) At 91 a further application is illustrated. When the viewer (eyes 61-63) observes the color transparency 91, which is a transmissive display illuminated from the back by a strongly collimated light source obtained by means of a light emitting device according to the invention, a resulting image will display a moving sun illusion, appearing and disappearing depending on the position and movement of the observer.

(36) FIG. 8 schematically shows a lighting device according to the invention comprising an array of light extraction elements 3 and a micro-lens array 4 and configured to provide a virtual image 98, 99 or focus at infinity. FIG. 9 schematically shows a lighting device according to the invention comprising an array of light extraction elements 3 and a micro-lens array 4 and configured to provide a virtual image 98 or focus at a distance Z being different from infinity. The lighting devices of FIGS. 6 and 7, respectively, may be a lighting device according to any one of the above or below described embodiments.

(37) The initially described problem as experienced by some viewers (eyes 68, 69) is illustrated in FIG. 8. When the pitch, p.sub.A, of the array of light extraction elements 3 is chosen equal to the pitch, p.sub.L, of the micro-lens array, virtual images are created at infinity. The two eyes 68 and 69 of the observer receive two images and fuse these into one only if the eyes converge at infinity, i.e. if they are parallel. But there is a natural tendency to focus the eyes at closer distance, i.e. where the eyes converge at a distance less than infinity. Thus, the observer may experience difficulties with fusing the two images into one. The design choice to create a virtual image at infinity also implies that the light beams as drawn in FIG. 1 can only be seen when standing right in front of the device, and not when looking at it under some angle.

(38) In contrast, and as shown in FIG. 9, if the pitch, p.sub.A, of the array 3 of apertures forming the light extraction elements is chosen to be smaller than the pitch, p.sub.L, of the micro-lens array 4 the following applies. From equal angles the following relation holds true:
(m*p.sub.A)/(Z−f.sub.a)=(m*p.sub.L)/Z,

(39) where m is any integer number, p.sub.A is the pitch of the aperture array, p.sub.L is the pitch of the micro-lens array, f.sub.a is focal length of the micro-lens array in air and Z is the distance from the micro-lens array to the virtual image. From the above equation it follows that the virtual image will appear at a distance
Z=f.sub.a*1/(1−(p.sub.A/p.sub.L))

(40) This is illustrated in FIG. 9. Also, when the observer stands a bit to the right or left of the light emitting device, an image can still be seen. This is in contrast to some prior art solutions, where all light beams emerge perpendicular to the device and when observed from an angle no light reaches the eyes.

(41) By way of examples: If p.sub.A=p.sub.L, then Z becomes infinity. If p.sub.Ai=0.99*p.sub.L, then Z is 100 times the focal length f Finally, if p.sub.Ai=0.98*p.sub.L, then Z is 50 times the focal length f.sub.a.

(42) In order to have a smooth viewing experience of smooth moving of the image across the lighting device, the angular spread a of the directional light beams need to be equal to or larger than the angular distance in between the individual light beams propagating after each of the micro-lenses of the micro-lens array. For that the following relation need to be fulfilled.
(p.sub.L−p.sub.A)≤r.sub.i.

(43) Therefore, the aperture pitch and the micro-lens pitch are in some embodiments chosen such as to fulfill the relation p.sub.Ai≤p.sub.L.

(44) FIG. 10 schematically shows a lighting device according to the invention comprising two arrays of apertures forming the light extraction elements, namely a first array of apertures 3 and a second array of apertures 3′, and a micro-lens array 4. The lighting device of FIG. 10 may be a lighting device according to any one of the above described embodiments. The first array of apertures 3 has a pitch equal to the pitch of the micro-lens array 4, and consequently the resulting image appears at infinity. The second array of apertures 3′ has a smaller pitch than that of the micro-lens array 4, and the resulting image appears closer. The lighting device of FIG. 10 is thus configured to provide by means of the first array of apertures 3 a virtual image 98, 99 or focus at a distance Z being equal to infinity, and to provide by means of the second array of apertures 3′ a virtual image 97 or focus at a distance Z being different from infinity. Hence, FIG. 10 illustrates how various images 97, 98, 99 can be created at different depths.

(45) Thus, in the embodiment shown in FIG. 10, the cover layer of the light emitting device comprises at least two arrays of apertures with different aperture pitches, p.sub.Ai, where i denotes the number of the array of apertures Ind i is an integer being 1 or more. The micro-lens array comprises a micro-lens pitch, p.sub.L. Each of the aperture pitches and the micro-lens pitch are chosen such as to fulfill the relation p.sub.Ai≤p.sub.L.

(46) Furthermore, each of the aperture pitches and the micro-lens pitch may be chosen such as to fulfill the relation (p.sub.L−p.sub.Ai)≤r.sub.i, where r is the radius of the apertures and i denotes the number of the array of apertures and i is an integer being 1 or more.

(47) To create an effect of moving sun with changing color temperature (e.g. lower correlated color temperature (CCT) when viewed from the large angles and higher CCT viewing from right in front of the lighting device) the light mixing element 2 may in an embodiment be provided with a non-uniform but smooth spatial color or CCT distribution. This can be realized e.g. by employing LEDs with different CCTs positioned differently on a substrate, such as a PCB, and covered with a diffuser plate.

(48) Also, a 3D effect may be generated. When using simple round apertures, all of the same shape, such a 3D effect is not exploited. But with an array of shapes, like printed 3D-views of a 3D object, each eye will see a different 3D-view, and a 3D image results.

(49) The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

(50) Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

LIST OF VARIABLE SIZES

(51) α Beam half angle (angular spread) of a light beam having propagated through a pair of aperture and lens β Acceptance angle of the micro-lenses of the micro-lens array f.sub.a Focal distance of the micro-lens array in air f.sub.i Focal distance of the micro-lens array F Focal point of the micro-lens array F.sub.P Focal plane of the micro-lens array i Integer number, i≥1 m Any integer number n.sub.1 Refractive index of air n.sub.2 Refractive index of micro-lens array p.sub.Ai Pitch of i.sup.th aperture p.sub.L Pitch of micro-lens array r.sub.i Radius of the aperture t Thickness of array of light extraction elements/collimator R Radius of curvature of lens of micro-lens array Z Distance to virtual image

LIST OF REFERENCE NUMERALS

(52) 1, 10, 100, 100′,101 Lighting device 2 Light mixing element 21-26 Light Sources 27 Bottom of light mixing element 271-273 Sides of light guide 28 Diffusive layer with light extraction elements 280 Scattering material 29 Aperture glass 3, 3′ Array of light extraction elements 31-33 Light extraction elements 310-330 Light out-coupling structures 311-331 Array of micro-LEDs 34 Collimator 35 Collimator glass 36 Collimator coating 37 Layer 4 Micro-lens array 41-43 Micro-lenses 44 Micro-lens glass 45 Micro-lens polymer 5 Spacer glass 50-52 Arrows 61-67 Eye(s) of the viewer 68 Left eye of the viewer 69 Right eye of the viewer 7 Cover layer 8 Light guide 91 Display 92 Display as seen by the viewer 93 Virtual 3D image as created by lighting device 94 Image of tree 97-99 Virtual images