TECHNICAL FIELD

The present disclosure relates to an illumination device, method and system and particularly, but not exclusively, to a lighting apparatus for use in a vehicle light. Aspects of the invention relate to an illumination system, an illumination device for use as a vehicle light, a method for providing illumination or illuminating light for use as a vehicle light, and to a vehicle.

BACKGROUND

Illumination devices for use in vehicle lights (e.g. headlights, taillights) may include a light source provided in combination with a lighting body to be illuminated with the light source. Some illumination devices make use of a hologram encoded or recorded in a holographic medium, so that illumination of the holographic medium causes an illuminated hologram to be visible. Holograms may be illuminated by a light source set at a significant distance back from a back face of the lighting body so that light from the light source passes through the lighting body, causing the hologram to be visible at the opposite face of the lighting body to the illuminated face, through transmission holography.

However, due to the separation distance required between the light source and lighting body for such transmission holography, use of such holographic lighting in a vehicle may be problematic because a large space is required to house the lighting body, light source, and space between in a lighting unit. Accommodating a large lighting unit may be difficult in a vehicle while achieving a desired look, shape and size of the rest of the vehicle, and challenging in positioning other elements in the vehicle around the space required by the lighting unit. Further, it may be difficult to achieve sufficient brightness of the hologram, due to the large distance between the lighting body and light source, since hologram brightness reduces as the distance between the lighting body and light source increases.

Holographic lighting may provide advantages in allowing improved flexibility of design of lighting units in vehicles, for example by allowing for different colour lights to be displayed, and for light to be displayed in particular shapes, according to how the hologram/s is/are recorded in the lighting body.

Therefore, examples disclosed herein aim to allow for holographic lighting to be used in a vehicle (e.g. as a taillight) while mitigating one or more of the problems mentioned above.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide an illumination device for use as a vehicle light, an illumination system optionally comprising aforesaid illumination device, a method of providing illumination or illuminating light for use as a vehicle light, and to a vehicle as claimed in the appended claims. According to an aspect of the invention, there is provided an illumination device for use as a vehicle light, comprising a lighting panel comprising a viewing face, a rear face opposite the viewing face, and an edge face located between the viewing face and the rear face, the lighting panel comprising a hologram recorded in at least a portion of the lighting panel; and a light source configured to, in use, output light to be incident on one or more of the edge face and the viewing face of the lighting panel to produce a holographic image visible on the viewing face.

Optionally, the lighting panel may comprise a plurality of coplanar layers, and wherein the plurality of coplanar layers comprise: a holographic layer containing the recorded hologram; and a display layer configured to display the holographic image when the light source is in use.

The light source may be configured to, in use, output light to be incident on the viewing face of the lighting panel to produce a reflection holographic image visible on the viewing face, and wherein: the viewing face is a first face of the display layer, and the holographic layer is adjacent to a second face opposite the first face of the display layer.

The lighting panel may comprise a light transmissive layer comprising a light transmission edge face at the edge face of the lighting panel, the light transmissive layer located coplanar with the holographic layer and the display layer and configured to: receive the light output by the light source in use, and channel the received light through the light transmissive layer by internal reflection to illuminate the holographic layer through internal reflection losses from the received channelled light.

The light transmissive layer may be located between the holographic layer and the display layer.

The light transmissive layer may be located adjacent to the holographic layer. The holographic layer may be located between the display layer and the light transmissive layer.

The light transmissive layer may comprise polycarbonate.

The hologram may be configured to, when illuminated by light of a first wavelength by the light source, produce a first hologram and, when illuminated by light of a second wavelength by the light source, produce a second hologram.

The hologram may be recorded to produce the first hologram at a first portion of the viewing face when illuminated by the first wavelength of light; and to produce the second hologram at a second portion of the viewing face when illuminated by the second wavelength of light, wherein the first portion of the viewing face is a different portion to the second portion of the viewing face.

The light source may be positioned at an acute angle to a normal of the edge face. When the light source is configured to, in use, output light to be incident on the edge face, the acute angle to the normal of the edge face may be in the range 24° to 33°. When the light source is configured to, in use, output light to be incident on the viewing face of the lighting panel, the acute angle to the normal of the edge face may be in the range 0. to 15°.

The edge face of the lighting panel may be a first edge face and the lighting panel may comprise a second edge face opposite the first edge face. The light source may be configured to, in use, output light to be incident on the first edge face and on the second edge face.

The light source may comprise a plurality of light sources. The plurality of light sources may each be arranged to direct light to a respective edge face of the lighting panel. For example, a first light source may direct light to the first edge face of the lighting panel, and a second light source may direct light to the second, different, edge face of the lighting panel.

The light source may be configured to, in use: output light of a first wavelength to be incident on the first edge face to produce a first hologram; and, output light of a second wavelength to be incident on the second edge face to produce a second hologram; wherein the first and second light wavelengths are different.

The light source may be configured to, in use: output light of a first wavelength to be incident on the first edge face and the second edge face to produce a first hologram; and output light of a second wavelength to be incident on the first edge face and the second edge face to produce a second hologram; wherein the first and second light wavelengths are different.

The lighting panel may further comprise a third edge face and a fourth edge face opposite the third edge face. The light source may comprise a first plurality of light sources which are configured to, in use, output light of a first wavelength to be incident on the first edge face and on the second edge face. The light source may further comprise a second plurality of light sources which are configured to, in use, output light of a second wavelength to be incident on the third edge face and on the fourth edge face. Each of the first, second, third and fourth edge faces may be different, and the first and second light wavelengths may be different.

Illumination devices disclosed herein may further comprise a mask coplanar with the viewing face and configured to be optically opaque to a wavelength of light emitted by the light source in use. The display layer of an illumination device as disclosed herein may comprise Polymethylmethacrylate, PMMA. Illumination devices disclosed herein may comprise an optically transparent substrate layer coplanar with and adjacent to the holographic layer. The optically transparent substrate layer of illumination devices disclosed herein may comprise cellulose triacetate, TAC.

Illumination devices disclosed herein may further comprise a focussing element located between the light source and the lighting panel, the focussing element configured to focus light emitted by the light source at the lighting panel. For example, the focussing element may comprise a Fresnel lens.

Illumination devices disclosed herein may further comprise a housing within which the lighting panel and the light source are located.

According to a further aspect of the invention, there is provided a method of providing illuminating light for use in a vehicle light, comprising illuminating a lighting panel using a light source, the lighting panel comprising a viewing face, a rear face opposite the viewing face, and an edge face located between the viewing face and the rear face, the lighting panel comprising a hologram recorded in at least a portion of the lighting panel, at the edge face or the viewing face of the lighting panel, and producing a holographic image visible on the viewing face.

According to a further aspect of the invention, there is provided a method of manufacturing an illumination device for use in a vehicle light, comprising providing a lighting panel comprising a viewing face, a rear face opposite the viewing face, and an edge face located between the viewing face and the rear face, recording a hologram in at least a portion of the lighting panel; and providing a light source positioned to, in use, output light to be incident on one or more of the edge face and the viewing face of the lighting panel to produce a holographic image visible on the viewing face.

According to another aspect of the invention, there is provided a vehicle comprising an illumination device as described herein.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of example only, with reference to the accompanying figures, in which:

Figures 1a and 1b illustrate example illumination devices according to examples disclosed herein;

Figure 2 illustrates an example reflection illumination devices according to examples disclosed herein;

Figures 3a and 3b illustrate example internal reflection illumination devices according to examples disclosed herein;

Figures 4a and 4b illustrate example internal reflection illumination devices according to examples disclosed herein;

Figure 5 shows an example illumination device illuminated at more than one edge according to examples disclosed herein;

Figures 6a and 6b illustrate example illumination devices illuminated at more than one edge according to examples disclosed herein;

Figure 7 shows an example illumination device located in a housing according to examples disclosed herein; Figure 8 shows an example illumination device comprising a light source itself comprising optic fibres and plural light outputs according to examples disclosed herein.

Figure 9 shows an example illumination device comprising a mask according to examples disclosed herein; Figure 10 shows a vehicle comprising an illumination device according to examples disclosed herein;

Figure 11 illustrates an example method of providing illuminating light for use in a vehicle light according to examples disclosed herein; and

Figure 12 illustrates an example method of manufacturing an illumination device for use in a vehicle light, according to examples disclosed herein.

DETAILED DESCRIPTION

Figures 1a and 1b schematically show cross sections of example illumination devices 100 for use in a vehicle light. Each illumination device 100 comprises a lighting panel 101 comprising a viewing face 102, a rear face 104 opposite the viewing face 102, and an edge face 106 located between the viewing face 102 and the rear face 104. The lighting panel 101 comprises a hologram recorded or encoded in at least a portion of the lighting panel. The lighting panel 101 may in some examples comprise a hologram recorded over the whole of the lighting panel. The illumination device 100 also comprises a light source 108 which is configured to, in use, output light to be incident on one or more of the edge face 106 and the viewing face 102 of the lighting panel 101 to produce a holographic image visible on the viewing face 102. The light source 108 may illuminate the whole, or a portion, of the lighting panel 101 according to different implementations as discussed below.

Figure 1a shows light from the light source 108 incident on the edge face 106 to produce a so-called "edge-lit” hologram. Further examples of edge lit holograms are discussed in relation to Figures 3a-3b and 4a-4b. Figure 1b shows light from the light source 108 incident on the viewing face 102 to produce a so-called "reflection” hologram. A further example of a reflection hologram is discussed in relation to Figure 2.

In both Figures 1a and 1b, the light source 108 is positioned at an acute angle to a normal 122 of the edge face (the normal 122 is illustrated with a dotted line). For illumination devices 100 configured to produce an edge lit hologram, the acute angle to the normal 122 of the edge face 106 may be in the range 24° to 33°. In this range, the light incident on the edge face 106 may enter the lighting panel 101 and undergo internal reflection (i.e. imperfect/”lossy” total internal reflection) in at least a portion of the lighting panel (in some examples, internal reflection occurs through substantially all the lighting panel). This is discussed in more detail in relation to Figures 3a-3b and 4a-4b. For illumination devices 100 configured to produce a reflection hologram, the acute angle to the normal 122 of the edge face 106 may be in the range 0.1° to 15°. In this range, the light incident on the viewing face 102 may undergo reflectance in the lighting panel 101 and emission from the viewing face 102. This is discussed in more detail in relation to Figure 2.

By positioning the light source 108 at an acute angle such that emitted light is directed to the edge face 106 or viewing face 108, the space requirements for the illumination device 100 are greatly reduced compared with an illumination device with a light source positioned behind the lighting panel 101 (such that emitted light is incident at the rear face 104 for transmission holography). The light source(s) used in examples disclosed herein are preferably placed as close as possible to the light transmission layer to improve capturing as much output light as possible before the light reaches the light transmission layer 116 at the chosen angle. In some examples, a separation distance (e.g. of around 10mm) between the lighting panel 101 and the light source 108 may be used, to allow for sufficient/enough illumination of the lighting panel 101 for the hologram to be visible. Lower separation distances than a threshold separation distance may not allow for enough of the lighting panel 101 to be illuminated for the hologram to be visible.

Such positioning for transmission holography requires a separation distance between the lighting panel 101 and the light source to be large enough that the cone of light emitted by the light source is large enough, upon light reaching the rear face 104, to illuminate substantially all the rear face 104 for transmission through the lighting panel 101 to the viewing face 102 to illuminate the recorded hologram in the lighting panel. By using a light source 108 -lighting panel 101 arrangement/geometry as shown in Figures 1 a-1 b, a more compact illumination device may be achieved since the light source 108 may be positioned very close to the lighting panel 101 and does not require the spacing between light source 108 and lighting panel 101 used in transmission holography.

Figure 2 illustrates an example reflection illumination device 100 comprising a plurality of coplanar layers 112, 114, 116. In this example, the plurality of coplanar layers comprises a holographic layer 114 containing the recorded hologram, a display layer 112, and an optically transparent substrate layer 116. The optically transparent substrate layer 116 provides a supporting layer for the holographic layer 114. The viewing face 102 is a first face of the display layer 112, and the holographic layer 114 is adjacent to a second face 113 opposite the first face 102 of the display layer 112.

The display layer 112 is configured to display the holographic image when the light sources 108a, 108b are in use. The light sources 108a, 108b are configured to, in use, output light to be incident on the viewing face 102 of the lighting panel 101 to produce a reflection holographic image visible on the viewing face 102. In this example, a plurality of light sources 108a, 108b are illustrated illuminating the viewing face 102 from different directions. While two light sources 108a, 108b are shown illuminating the viewing face 102 from the top and bottom of the lighting panel 101, in other examples there may be a plurality of light sources 108 illuminating the lighting panel 101 from one or more directions, or there may be a single light source 108 illuminating the lighting panel 101 at the viewing face 102.

The acute angle to the normal 122 of the edge face 106 formed between the viewing face 102 and the direction of light from each of the light sources 108a, 108b is shown for clarity as 15°, but in other examples may be any acute angle in an angular range allowing for reflection of the incident light from the lighting panel 101 to illuminate the recorded hologram to be visible on the viewing face 102 (e.g. in the range 0. to 15°).

Figures 3a and 3b illustrate example internal reflection illumination devices according to examples disclosed herein. Figures 3a and 3b both show an illumination device 100 comprising a lighting panel 101, the lighting panel 101 itself comprising a plurality of coplanar layers 112, 118, 114, 116. The plurality of coplanar layers comprise a display layer 112; a light transmissive layer 118; a holographic layer 114 and a substrate layer 116. The holographic layer 114 contains the recorded hologram. The light transmissive layer 118 in these examples is located between, and is located coplanar with, the display layer 112 and the holographic layer 114. The display layer 112 is configured to display the holographic image when the light source 108 is in use illuminating the lighting panel 101.

The light transmissive layer 118 comprises a light transmission edge face 106x at the edge face 106 of the lighting panel 101. The light transmissive layer 118 is configured to receive the light output by the light source 108 when in use, and channel the received light 110 through the light transmissive layer 118 by internal reflection to illuminate the holographic layer 114 through internal reflection losses from the received channelled light.

The light from the light source 108 passes through the light transmissive layer 118 in a "total internal reflection” manner, in which the light 110, upon reaching an interface (i.e. the boundary between the display layer 112 and the light transmissive layer 118, or the boundary between the light transmissive layer 118 and the holographic layer 114), reflects from the boundary back into the light transmissive layer 118. Reflection of this type occurs when the refractive index of the light transmissive layer 118 is greater than the refractive index beyond either face of the light transmissive layer 118; i.e. in the holographic layer 114 and the display layer 112. However, in real physical systems, the reflection of light 110 at the boundary is not 100% efficient and some light escapes from the boundary without internal reflection. This "lost” light illuminates the holographic layer 114 to produce the hologram visible at the viewing surface 102 of the display layer 112.

Further, for internal reflection to occur, the angle of incidence of the incoming light from the light source 108 (i.e. the angle between the incoming light and the normal to the edge face 106) must be less than the critical angle O _c (the critical angle is the angle between the incoming light and the normal to the edge face 106 at which the angle of refraction is 90° and the refracted ray travels along the boundary (i.e. along the edge face 106) between the air and the lighting panel 101).

The examples of Figures 3a and 3b show the light source(s) positioned to direct light incident on the edge face 106 towards the back of the lighting panel 101 (i.e. towards the back face opposite the viewing face of the display layer 112). Edge lit holograms illuminated in this way may be considered to be reflection-type edge lit holograms, as the incident light internally reflects with light losses illuminating the holographic layer 114, such that the light from the hologram is reflected back towards the viewing face 102 of the display layer 112 for viewing.

Figure 3a shows a single light source 108. Figure 3b shows two light sources 108a, 108b, each positioned at opposite edge faces of the lighting panel. In some examples, plural light sources 108a, 108b may be used to illuminate the holographic layer 114 from different sides/edges of the lighting panel 101 with the same wavelength of light (i.e. the same frequency of light since wavelength and frequency are related by the relationship "speed of light (constant) = wavelength x frequency”). As light travels 110 by internal reflection through the light transmissive layer 118, the intensity of the light may decrease as the light travels further into the light transmissive layer material due to losses in the material, and the portion of the holographic layer 114 illuminated by light from further in the light transmissive layer material (i.e. further from the edge face 106) may be illuminated less than the portion of the holographic layer 114 illuminated by light from closer to the edge face at which the light entered the light transmissive layer. By illuminating the light transmissive layer 114 from opposite edges, the holographic layer may be illuminated sufficiently well despite light losses from light traveling through the light transmissive layer 114, by supplementing the (weakest) light reaching a far edge of the light transmissive layer 114 from a first light source 108a at a first edge of the light transmissive layer, with light from a second light source 108b entering the light transmissive layer 114 at the far edge.

In the example of Figure 3b, the two light sources 108a, 108b each positioned at opposite edge faces of the lighting panel 101 provide light 110a, 110b of different respective wavelengths. For example, the first light source 108a may provide red light 110a (with a wavelength of around 680 nm), whereas the second light source 108b may provide amber light 110b (with a wavelength of around 590 nm). That is, the illumination device 100 (specifically in this example, the holographic layer 114) comprises a hologram configured to, when illuminated by light of a first wavelength by the light source 108a, produce a first hologram and, when illuminated by light of a second wavelength by the light source 108b, produce a second hologram.

Plural holographs may be recorded in the holographic layer 114 using different light wavelengths, and selectively illuminated by light sources of corresponding light wavelengths. In some examples, plural holograms may be recorded substantially across the whole area of the holographic layer 114 of different wavelengths. In some examples, a first portion of the area of the holographic layer 114 may contain a hologram recorded at a first wavelength and a second different portion of the area of the holographic layer 114 may contain a second hologram recorded at a second wavelength.

Figure 3b also illustrates an example illumination device 100 which comprises a focussing element 120a, 120b located between the light source 108a, 108b and the lighting panel 101. The focussing element 120a, 120b is configured to focus light emitted by the light sources 108a, 108b at the lighting panel 101. For example, a lens (e.g. Fresnel lens) or collimator may be used to focus/direct light onto the edge face 106 of the lighting panel 101. A Fresnel lens may provide a compact type of focussing lens which may be beneficial in solving the problem of reducing the overall size of the illumination device 100 for use in a vehicle. Other focussing elements which may be used in examples disclosed herein include sphero-cylindrical lenses, positive meniscus lenses, negative meniscus lenses, and sphero-aspherical lenses. The focussing element 120a, 120b in some examples may be a converging sphero- elliptical lens. It is preferable to obtain parallel straight light rays after the light interacts with the focussing element for channelling the light into the light transmission layer 118. Such focussing elements 120a, 120b may be present in any other examples disclosed herein.

Figures 4a and 4b illustrate example internal reflection illumination devices according to examples disclosed herein. Whereas the examples in Figures 3a-3b are configured to provide reflection-type edge lit holograms, the illumination devices in Figures 4a-4b are configured to provide transmission-type edge lit holograms.

Figures 4a and 4b both show an illumination device 100 comprising a lighting panel 101, the lighting panel 101 itself comprising a plurality of coplanar layers 112, 114, 116, 118. The plurality of coplanar layers comprise a display layer 112; a holographic layer 114; a substrate layer 116 and a light transmissive layer 118. The holographic layer 114 contains the recorded hologram. The light transmissive layer 118 in these examples is located on the opposite face of the lighting panel 101 to the display layer 112, coplanar with and adjacent to substrate layer 116 supporting the holographic layer 114. In examples in which no substrate layer 116 is used, the light transmissive layer 118 may be said to be located adjacent to the holographic layer 114, wherein the holographic layer 114 is located between the display layer 112 and the light transmissive layer 118. The light transmissive layer 118 material has a higher refractive index than the substrate layer 116 adjacent to the transmission face of the light transmissive layer 118 and higher than the air (refractive index = 1) at the back face of the light transmissive layer 118 and of the lighting panel 101 overall to allow internal reflection to takes place. The display layer 112 is configured to display the holographic image when the light source 108 is in use illuminating the lighting panel 101.

In some examples the substrate layer 116 may be absent such that the light transmissive layer 118 is coplanar with and adjacent to the holographic layer 114. In such examples the light transmissive layer 118 material in which internal reflection takes place has a higher refractive index than the adjacent holographic layer 114.

The light transmissive layer 118 operates as described in relation to Figure 4a and 4b by channelling received light to illuminate the holographic layer 114 through internal reflection losses from the received channelled light as described above. However, in this transmission-type mode it is light losses escaping from the face of the light transmissive layer 118 which is adjacent to the holographic layer 114 (in this example, through the intervening optically transparent substrate layer 116) which illuminate the holographic layer 114 so the hologram is visible at the viewing face 102 of the display layer 112. Since the holographic layer 114 is sandwiched between the display layer 112 and the light transmissive layer 118, light (lost from internal reflection) travels from the light transmissive layer 118 through the holographic layer 114 to the display layer in a transmissive way.

The examples of Figures 4a and 4b show the light source(s) positioned to direct light incident on the edge face 106 towards the viewing face of the lighting panel 101 (i.e. towards the front face opposite the back face of the lighting panel 101). Edge lit holograms illuminated in this way may be considered to be transmission-type edge lit holograms, as the incident light internally reflects with light losses illuminating the holographic layer 114, such that the light from the hologram is transmitted through the lighting panel 101 towards the viewing face 102 of the display layer 112 for viewing.

Similarly to Figures 3a and 3b, Figure 4a shows a single light source 108, and Figure 4b shows two light sources 108a, 108b, each positioned at opposite edge faces of the lighting panel. The two light sources 108a, 108b each positioned at opposite edge faces of the lighting panel 101 in Figure 4b may provide light of different respective wavelengths to illuminate different recorded holograms in the holographic layer 114. The two light sources 108a, 108b each positioned at opposite edge faces of the lighting panel 101 in Figure 4b may provide light of the same wavelength to illuminate the same hologram in the holographic layer 114 and compensate for light intensity loss due to travelling through the light transmissive layer 118 as described above.

In the examples of Figures 3a and 3b and Figures 4a and 4b, the display layer 112 may comprise PMMA with a refractive index of 1.48, the light transmissive layer 118 may comprise polycarbonate (PC) with a refractive index of 1.50 - 1.60 (higher than that of the display layer) and the holographic layer 114 may comprise photopolymer with a refractive index of 1.505, for example (again, higher than that of the display layer). In examples where an optically transparent substrate layer 116 is present, such a layer may comprise TAC and may have a refractive index of 1 .485, for example. The index of refraction of Polycarbonate (PC) is dependant of the wavelength of the light shone onto the material, which may be in the range of 500 nm to 700 nm.

Figure 5 shows an example illumination device illuminated at more than one edge according to examples disclosed herein. This example shows a view of the lighting panel 101 facing the viewing face 102. The light source in this example includes a first light source 108a, 108b configured to, in use, output light of a first wavelength (e.g. red light) to be incident on the first edge face 106a and the second edge face 106b to produce a first hologram; and a second light source 108c, 108d configured to, in use, output light of a second wavelength (e.g. amber light) to be incident on the first edge face 106a and the second edge face 106b to produce a second hologram. The first and second light wavelengths are different. The light source 108a-108d may comprise an array of LEDs in some examples. In such examples, plural holograms of different light colours/wavelengths may be produced while compensating for loss of light intensity as it travels through the light transmissive layer 118 by having first and second light sources opposite each other directed to the first and opposite second edges of the lighting panel 101 as described above in relation to a single wavelength.

Figures 6a and 6b shows an example illumination device illuminated at more than one edge according to examples disclosed herein. This example shows a view of the lighting panel 101 facing the viewing face 102. The lighting panel 101 comprise a first edge face 106a, a second edge face 106b opposite the first edge face 106a, a third edge face 106c and a fourth edge face 106d opposite the third edge face 106c. The light source in this example comprises a first plurality of light sources 108a, 108b which are configured to, in use, output light of a first wavelength to be incident on the first edge face 106a and on the second edge face 106b; and a second plurality of light sources 108c, 108d which are configured to, in use, output light of a second wavelength to be incident on the third edge face 106c and on the fourth edge face 106d. Each of the first, second, third and fourth edge faces 106a-d are different, and the first and second light wavelengths are different. The light source 108a-108d may comprise an array of LEDs in some examples. In such examples, plural holograms of different light colours/wavelengths may be produced while compensating for loss of light intensity as it travels through the light transmissive layer 118 by having a first light source 108a, 108b directed to first and opposite second edges 106a, 106b of the lighting panel 101, and having a further light source 108c, 108d directed to third and opposite fourth edges 106c, 106d of the lighting panel 101 as described above in relation to a single wavelength.

The example arrangements in Figures 5 and 6a-6b may be used with a viewing panel 101 comprising a hologram (e.g. recorded in a holographic layer) recorded to produce the first hologram at a first portion (e.g. region 500 of the viewing face in Figure 5; region 600 of the viewing face in Figures 6a-6b) when illuminated by the first wavelength of light; and to produce the second hologram at a second portion (e.g. region 502 of the viewing face in Figure 5; region 602 of the viewing face in Figures 6a-6b) of the viewing face when illuminated by the second wavelength of light, wherein the first portion of the viewing face is a different portion to the second portion of the viewing face.

Figure 7 shows an example illumination device 100 comprising a light source 108a itself comprising optic fibres and plural light outputs 108b according to examples disclosed herein. Thus the light source 108 may be a single light source which provides plural light output along one or more edges of the lighting panel 101, for example by directing light along plural optic fibres.

Throughout this disclosure, the term "light source” may be understood to be a light source providing a single point of illumination (e.g. a light emitting diode, LED), or providing a plurality of points of illumination (for example, if a core light source provides light which is channelled along a plurality of different paths, e.g. along optic fibres, to provide a plurality of points of illumination as shown in Figure 7).

The light source(s) 108 may, in some examples, be selectively operated under the control of a control means, for example in the form of a control unit, e.g. an Electronic Control Unit ("ECU”). That is, one or more light sources may be switched on and off according to a predetermined pattern (i.e. to illuminate and de-illuminate one or more predetermined regions of the lighting panel 101). For example, if a vehicle operator wishes to indicate the vehicle is about to turn right and operates a user control to show a right turning light, a signal may be transmitted from the user control to the control unit to cause illumination of one or more light sources 108 of a right tail light illumination device 100 in a predetermined arrangement to cause display of a right turn amber indication light. Other predetermined distributions may, for example, correspond to a stop light, a hazard warning light, a reversing indicator light, a text-based illuminated message, or other light signal.

Figure 8 shows an example illumination device 100 comprising a mask 800 according to examples disclosed herein. The mask 800 may comprise a film arranged to cover one or more pixels (i.e. some portion) of the viewing face. The mask 800 is arranged coplanar with the viewing face 102. The mask 800 in some examples may be configured to be optically opaque to a wavelength of light emitted by the light source 108 in use. The mask 800 in some examples may be configured to be non-homogeneously optically opaque to a wavelength of light emitted by the light source 108 in use, to cause a variation in the masking strength/optical opacity of the mask over the area of the mask, such that some portions of the mask prevent the passage therethrough of light to a greater or lesser extent than other portions of the mask. A mask may be used, for example, to allow light visible at the viewing face to have an intensity (that is, having an intensity profile varying with position at the viewing face 102) of a particular required profile; that is, the intensity of light visible at the viewing face is controlled by the mask 800. For example, to meet lighting regulations, the intensity of light produced at the viewing face 102 may be required to be within a particular intensity range and/or spatial intensity variation. As discussed above, edge-lit holograms may be brighter at the edge adjacent to the illuminating light source 108, with intensity decreasing with distance away from the light source 108 as the light passes via internal reflection through the lighting panel. Having light sources 108 at opposite edges as shown may result in the brightest light at the top and bottom edges of the viewing face 102. By using the mask 800, the brightest illuminated regions may be masked (obscured from view) and the central portion of the viewing face 102 may provide light of an acceptable intensity profile acceptable.

In illumination devices disclosed herein, the light transmissive layer may comprise polycarbonate. In illumination devices disclose herein, the display layer may comprise Polymethylmethacrylate, PMMA. Illumination devices disclosed herein may comprise an optically transparent substrate layer coplanar with and adjacent to the holographic layer. Such an optically transparent substrate layer may comprise cellulose triacetate, TAC.

Figure 9 shows an example illumination device, comprising the lighting panel 101 and light source 108, which is located in a housing 900. Elements 902 and 908 are not part of the illumination device and housing but are illustrated for dimension comparison. The housing 900 may be formed by casting, by machining or in any other convenient manner. The housing may be a one-piece cast housing or may be fabricated from multiple discrete components which are assembled in a suitable manner. The housing 900 has a depth dimension 910, allowing for positioning of the light source 108 for reflection or for internal reflection holography as discussed above. The depth dimension 910 of housing 900 is much smaller than the depth dimension 912 of a housing 902 which would be required to house an illumination device which requires a light source 908 to be positioned, perpendicular to a back face of the lighting panel 101, for transmission holography.

Figure 10 shows a vehicle 1000 comprising an illumination device 100 according to examples disclosed herein, for example as a taillight.

Figure 11 illustrates an example method 1100 of providing illuminating light for use in a vehicle light. The method comprises: illuminating a lighting panel using a light source 1102, the lighting panel comprising a viewing face, a rear face opposite the viewing face, and an edge face located between the viewing face and the rear face, the lighting panel comprising a hologram recorded in at least a portion of the lighting panel, at the edge face or the viewing face of the lighting panel, and producing a holographic image visible on the viewing face 1104.

Figure 12 illustrates an example method 1200 of manufacturing an illumination device for use in a vehicle light, comprising: providing a lighting panel 1202 comprising a viewing face, a rear face opposite the viewing face, and an edge face located between the viewing face and the rear face, recording a hologram in at least a portion of the lighting panel 1204; and providing a light source positioned to, in use, output light to be incident on one or more of the edge face and the viewing face of the lighting panel to produce a holographic image visible on the viewing face 1206. Although examples are illustrated in relation to lighting for a vehicle, it will be understood that examples disclosed herein may be used in general lighting applications, such as domestic lights. Further, examples are not limited to use within specific types of vehicle and may be used, for example, in automobiles, cycles, motorcycles, marine craft and aircraft.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. The claims should not be construed to cover merely the foregoing embodiments, but also any embodiments which fall within the scope of the claims.