TECHNICAL FIELD The present disclosure relates to a lighting device for a vehicle cabin and particularly, but not exclusively, to a device for providing ambient light to the upper cabin environment. Aspects of the invention relate to a device, to a vehicle interior trim component and to a vehicle. BACKGROUND

A vehicle, such as a car, includes a structural frame generally comprising a body, a roof and a number of pillars extending between the body and the roof which frame the windows of the vehicle. Along each side of the vehicle, moving from the front of the vehicle to the rear, the pillars are respectively designated in alphabetical order, starting from the A-pillars which are located between the windshield and the front doors of the vehicle.

The internal surfaces of the structural frame of the vehicle are covered by interior trim components. For example, pillar trim components are attached to the pillars to define portions of the walls of a cabin and a headliner trim component is attached to the roof of the vehicle to define the ceiling of the cabin. The vehicle additionally includes a number of other trim components, for example door and boot trim components. It is known for the trim components to be manufactured by a moulding process, in which case they are typically known as 'trim mouldings'.

For the comfort of the users of the vehicle and ambience of the vehicle interior, it is desirable for the cabin to be suitably illuminated. Therefore, modern vehicle interiors often include lighting devices that provide ambient light throughout the vehicle cabin. In particular, it is known to illuminate the upper cabin environment using uplighters mounted on the pillar trim mouldings. However, such devices are unsightly, especially when not illuminated, and may cast shadows in the vehicle cabin. Accordingly, there is a need for improved lighting devices for illuminating the upper cabin environment of vehicles. It is an aim of the present invention to provide an improved lighting device for a vehicle cabin in consideration of these issues. SUMMARY OF THE INVENTION

According to an aspect of the present invention there is provided a lighting device for a vehicle cabin. The device comprises: at least one light source; a blending lens; and a diffusing lens. The at least one light source is configured to transmit light to the blending lens; the blending lens is configured to receive light from the at least one light source and transmit blended light to the diffusing lens; and the diffusing lens is configured to receive blended light from the blending lens and transmit diffused light into the vehicle cabin. It should be noted at this stage that references to a 'vehicle cabin' are intended to include any enclosed space within the interior of the vehicle, not just the occupant capsule of the vehicle. For example, the lighting device is suitable for a cargo holding area of a vehicle such as a boot or trunk. This aspect of the invention provides a lighting device that processes light emitted by the light sources and ultimately transmits it from a light output surface of the diffusing lens in such a way that the lighting device is capable of illuminating the upper environment of a vehicle cabin whilst overcoming some of the disadvantages associated with the prior art. The lighting effect provided is aesthetically pleasing.

The lighting device may comprise two light sources located at opposite ends of the blending lens.

The light source(s) may include at least one light emitting diode (LED).

A power system connector may be installed to provide electrical power to the light source(s) from a vehicle electrical power source. A control unit may be provided to control the light source(s). For example, the control unit may allow a vehicle user to selectively turn the light source(s) on or off. In other embodiments, the control unit may be connected to other vehicle systems in order to control the lighting source(s). For example, the control unit may be configured to turn the light source(s) on when a door of the vehicle is opened. The blending lens may change the direction of the light emitted by the light source(s), away from the optical axes defined by the light source(s) in order to direct light towards the diffusing lens. In some embodiments of the lighting device, an optical axis from the blending lens to the diffusing lens is substantially perpendicular to an optical axis from a light source to the blending lens.

The blending lens may be configured to homogenise the light emitted by the light source(s) and transmit a uniform light beam to the diffusing lens. In some embodiments of the lighting device, light is emitted from the blending lens substantially uniformly across a light output surface of the blending lens. The light received by the diffusing lens is therefore uniform.

Light may be emitted from the diffusing lens substantially uniformly along the length of a light output surface of the diffusing lens. Therefore, the light transmitted by the diffusing lens is advantageously uniform along the length of the lighting device.

Across the width of the light output surface of the diffusing lens, light may be emitted across a range of angles. This allows the lighting device to transmit light across a relatively large spatial region. The lighting device may comprise a cover element for preventing stray light from being emitted from the lighting device. 'Stray light' includes light from the light source(s) that is not launched into the blending lens and also light that is transmitted by the blending lens that is not received by the diffusing lens, in particular light that is transmitted by the blending lens from faces other than the light output face. The cover element prevents stray light from escaping the lighting device and being emitted from the lighting device in erratic and unwanted directions.

In such embodiments, the cover element may have an internal reflective surface for reflecting stray light in order to maximise a proportion of light transmitted to the diffusing lens. The reflective surface directs stray light back towards the blending lens in order to maximise the proportion of light emitted by the light source(s) that is collected by the blending lens and transmitted to the diffusing lens. Ultimately, this maximises the light that is transmitted by the diffusing lens.

The surface of the blending lens opposing a light output surface of the blending lens may include optical features configured to optimise the direction of the light travelling through the lens. The optical features may direct light towards the output face of the blending lens such that light passes through the diffusing lens as a uniform beam.

Lighting devices according to this aspect of the invention can be appropriately configured to conform to strict geometric requirements that may be necessitated by the configuration of the vehicle cabin. For example, the lighting device may be configured for installation at the interface between two vehicle interior trim components.

According to another aspect of the invention, there is provided an interior trim component for a vehicle incorporating the lighting device of the previous aspect.

The lighting device is optionally mounted on the rear face of the trim component, with the trim component defining an aperture through which light is transmitted. As will be explained in more detail, the lighting device is therefore embedded within the trim component; that is to say, the lighting device is integrated into the design of the vehicle interior and is hidden when not illuminated. Thus, lighting devices in accordance with these embodiments of the invention do not impair the appearance of the vehicle cabin interior. The lighting device may be sub-assembled to the trim component during manufacture of the vehicle. If the trim component is a trim moulding, the cover element of the lighting device may be moulded as part of the trim moulding manufacturing process. The diffusing lens may be received by the aperture and in such cases the light output surface of the diffusing lens may be flush with the interior surface of the trim component. Therefore the trim component does not cause the lighting device to cast shadows within the vehicle cabin. According to a further aspect of the invention, there is provided a vehicle comprising at least one lighting device or trim component according to a previously-described aspect of the invention. The lighting device is optionally provided at the interface between two interior trim components. For example, the lighting device may be provided at the interface between a pillar trim moulding and the headliner trim component. In other embodiments, the lighting device may be provided at any appropriate interface between trim components.

One of the two trim components may protrude into the vehicle cabin in order to accommodate the lighting device. For example, a pillar trim moulding may protrude into the vehicle cabin in order to accommodate the lighting device. The vehicle may comprise a plurality of lighting devices according to the first aspect in order to appropriately illuminate the upper cabin environment. For example, corresponding pillars on the left- and right-hand side of the vehicle may each include a lighting device. In some embodiments, each side of the vehicle may comprise four pillars; however, the skilled person will be aware of other vehicle structural frame configurations, having more or fewer pillars as appropriate, to which embodiments of the invention are equally applicable. 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

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a perspective view of a portion of a vehicle cabin interior which includes a plurality of lighting devices according to an embodiment of the invention;

Figure 2 shows a cross-sectional view of one of the lighting devices in situ; and

Figure 3 shows a perpendicular cross-section of the lighting device of Figure 2 in isolation

DETAILED DESCRIPTION

Referring initially to Figure 1 , a portion of the interior of the cabin 10 of a vehicle 12 is shown. The B-pillars 14 of the vehicle 12 are shown, one on each side of the cabin 10, situated just forward of the rear seat 16. The C-pillars 18 are located rearward of the rear seat 16, one on each side of the cabin 10. The A-pillars are not visible in Figure 1 . In order to provide ambient light to the upper cabin environment, the B-pillars 14 and C-pillars 18 are each provided with a lighting device in accordance with an embodiment of the invention.

As described previously by way of background, the interior of the vehicle cabin 10 is provided with a number of trim components that are mounted to the interior surface of the structural frame of the vehicle 12. Each lighting device is installed at the interface between a respective pillar trim moulding 20 and the headliner trim component 22 and directs light upwards onto the headliner trim component 22, thereby illuminating the upper cabin environment.

Having described the general position of the lighting devices within the vehicle cabin 10, the configuration of the lighting devices will now be described in more detail with reference to Figure 2 which shows a cross-sectional view of the region generally indicated by the dashed circle 24 in Figure 1 . In particular, Figure 2 shows the interface between the B-pillar trim moulding 20 and the headliner trim component 22 on the right-side (as shown in Figure 1 ) of the vehicle 12, including a lighting device 26. In the following description, reference is made to one of the lighting devices; it should, however, be appreciated that the description equally applies mutatis mutandis to the other lighting devices.

In Figure 2, components of the lighting device 26, specifically a blending lens 28, a diffusing lens 30 and a cover element 32, can be seen in cross-section recessed within a wall of the vehicle cabin 10.

It should be noted at this stage that the accompanying figures are schematic representations to illustrate features of the invention and are not intended to be realistic representations or reflect the scale or relative proportions of the various components. The skilled person will appreciate that the representations have been simplified for the purposes of clarity and to avoid unnecessary detail obscuring the principle form of the invention. In practice, of course, the vehicle 12 would include many more components and since these additional conventional components would be present in a practical implementation of embodiments of the invention, their presence is implied.

The skilled person will be aware of the typical construction of trim components as shown in Figure 2. Generally, the trim components 20, 22 comprise a unitary structure having a front face 20a, 22a and a rear face 20b, 22b. The front face 20a, 22a forms the visible surface of the trim component 20, 22, i.e. on the vehicle cabin side and a decorative covering is typically applied to this face. On the opposite side of the trim component 20, 22, the rear face 20b, 22b faces the structural frame 34 of the vehicle 12.

The upper portion of the B-pillar trim moulding 20 is shown in Figure 2. As can be seen, the front face 20a of the pillar trim moulding 20 presents a convex profile to the vehicle cabin 10 in cross-section. Specifically, the profile of the pillar trim moulding 20 is such that the cross-section of the upper portion of the pillar trim moulding 20 comprises a generally vertical wall region 36 and a perpendicular sill region 38, connected via a curved section 40, substantially forming an inverted L-shape, The cross-section of the headliner trim component 22 includes a flat alignment region 42 which abuts the sill region 38 of the pillar trim moulding 20 and a ceiling region 44 which presents a concave profile to the vehicle cabin 10. The ceiling region 44 and alignment region 42 are connected by a curved section 46.

The pillar trim moulding 20 is offset relative to the headliner trim component 22 such that the pillar trim moulding 20 protrudes further into the vehicle cabin 10 than the headliner trim component 22. Thus, a portion of the front face 20a of the sill region 38 of the pillar trim moulding 20 is exposed.

The exposed portion of the sill region 38 includes an aperture 48 that accommodates the diffusing lens 30 of the lighting device 26. The light output surface 30b of the diffusing lens 30 is level (or flush) with the front face 20a of the sill region 38 of the pillar trim moulding 20.

The blending lens 28 is located below the diffusing lens 30, behind the rear face 20b of the pillar trim moulding 20. The light sources, not shown in Figure 2, are located at either end of the blending lens 28.

The lenses 26, 28 and light sources are partially surrounded by a cover element 32 which is generally L-shaped in cross section, comprising two perpendicular straight sections. Each perpendicular straight section of the cover element terminates in a flange portion 52 that abuts the rear face 20b of the pillar trim moulding 20. Thus, an enclosed region 54 is defined between the interior surface 32a of the cover element 32 and the rear face 20b of the pillar trim moulding 20. The arrangement of the cover element 32 prevents stray light from escaping the lighting device 26.

The interior surface 32a of the cover element 32 is reflective. In some embodiments, the cover element 32 may have a reflective coating on its interior surface 32a. In other embodiments, the cover element 32 may be moulded out of a material that has an inherent high level of reflectivity. Therefore, not only does the cover element 32 prevent stray light from escaping the lighting device 26 but also reflects stray light towards the blending lens 28 in order to maximise the light from the light sources that is collected by the blending lens 28 and received by the diffusing lens 30. Ultimately, this serves to maximise the light transmitted by the diffusing lens 30 into the vehicle cabin 10. The configuration of the lighting device 26 will now be described in more detail with reference to Figure 3, which shows a cross-section of the lighting device 26 in isolation. Figure 3 shows a cross-section taken along the length of the device 26, perpendicular to the cross-section of Figure 2. Accordingly, in Figure 3 the width of the device 26 is into and out of the plane of the page.

As shown in Figure 3, the lighting device 26 comprises two light sources 56. In other embodiments, the lighting device 26 may comprise any number of light sources as appropriate, for example depending on the length of the lighting device. In this example, the light sources 56 each include an LED array 58. The individual LEDs within the LED arrays 58 may be any appropriate colour depending on the visual effect desired. For example, the LED arrays 58 may comprise blue LEDs. Alternatively, the arrays 58 may comprise a number of different coloured LEDs, allowing the device 26 to be configured to transmit light of a specific desired light colour. In some embodiments, the different coloured LEDs may be separately and selectively controlled such that the lighting device 26 may be configured to transmit different coloured light in dependence on one or more vehicle parameters. For example, the colour of the transmitted light may be different when the vehicle engine is switched on compared to when it is switched off. Alternatively or additionally, the lighting device 26 may be configured such that a user of the vehicle 10 can select a desired colour of the transmitted light.

Generally, light is launched from each of the LED arrays 58 into a respective end of the blending lens 28. Light enters the ends of the blending lens 28 via the light incident surfaces 28a of the blending lens 28. The airgaps between the light sources 56 and the associated light incident surfaces 28a of the blending lens 28 should be as small as possible to maximise the proportion of the light emitted by the LED arrays 58 that is collected by the blending lens 28. In this example, the airgaps are approximately 5mm. In other embodiments, there may be no gap between the light sources 56 and the light incident surfaces 28a of the blending lens 28. The blending lens 28 has several functions. It collects light from the LED arrays 58, changes the direction of the light emitted by the LED arrays 58 such that light is emitted from a light output surface 28b perpendicular to the light incident surfaces 28a and homogenises the light emitted by the LED arrays 58 such that it is emitted substantially uniformly from across the light output surface 28b of the blending lens 28.

Light from the LED arrays 58 enters the blending lens 28 via the light incident surfaces 28a at opposite ends of the blending lens 28. This light is internally reflected within the lens 28. The bottom surface of the blending lens 28, opposing the light output surface 28b, comprises a number of optical features in the form of small protrusions (one of which is labelled in Figure 3 with reference numeral 60). The optical features re-direct the light within the blending lens 28 such that light exits the blending lens 28 normal to the light output surface 28b. As an alternative to the small protrusions, other optical features may also be used, including angled surfaces or prisms. Materials such as clear polymer resins filled with glass micro beads may also be used to re-direct the light within the lens 28.

The diffusing lens 30 receives blended light from the blending lens 28 via a light incident surface 30a. The airgap between the blending lens 28 and the diffusing lens 30 should also be as small as possible in order to maximise the proportion of light transmitted by the blending lens 28 that is received by the diffusing lens 30.

The light incident surface 30a has a surface texture applied to it that means that light exiting the diffusing lens 30 via the light output surface 30b is diffused into the vehicle cabin 12. For example, the surface texture Tenibac 'BK-171 1 ' could be applied to the light incident surface 30a of the diffusing lens 30.

As best illustrated in Figure 2, the light incident surface 30a of the diffusing lens 30 is inclined relative to the light output surface 30b. The angular relationship between the light incident surface 30a and the light output surface 30b of the diffusing lens 30 at least partly defines the angular deflection of the light emitted from the diffusing lens 30 compared to the light received by the diffusing lens 30. The angular relationship may be selected to direct light from the light output surface 30b of the diffusing lens in order to illuminate the desired region of the vehicle cabin 10. The skilled person will appreciate that the exact configuration of the diffusing lens 30, and in particular the light incident and output surfaces 30a, 30b of the lens 30, may depend on the specific application of the lighting device 26 and may for example include non-parallel flat surfaces (as illustrated) and/or one or more contoured surfaces (not illustrated) to concentrate and diffuse the light in a particular direction.

In this example, both lenses 28, 30 are made from Poly(methyl methacrylate) (PMMA) with a refractive index of approximately 1 .49 and luminous transmittance of approximately 0.92. In other embodiments, the lenses may be made from any suitable material and the skilled person will appreciate that the exact configuration of the lenses 28, 30, including any surface texture applied to the light incident surface 30a of the diffusing lens 30, will depend on the material of which they are made. In Figure 3, light is shown emitted normally and uniformly from the light output surface 30b of the diffusing lens 30. However, in reality, light is emitted across a range of angles across the width of the light output surface 30b of the diffusing lens 30. Accordingly, a region of the headliner trim component 22 is illuminated by the lighting device 26.

Many modifications may be made to the above examples without departing from the scope of the present invention as defined in the accompanying claims.