Field of invention

The present invention relates to lighting units comprising optics, in particular lighting units for use in automotive signal lamps.

Background

It is often desirable to provide a lighting system that provide a uniform illumination of a certain object. For example in automotive lighting units, such as tail lights, indicator lights and brake lights, it is often desirably to provide an object that appears homogeneously illuminated to a person viewing the lighting unit. When attempting to provide such a result, it is known to illuminate the surface of a diffuser. Consequently an illumination source may be configured to produce fully collimated light.

In optical systems where the light source dimension is greater than about 10% of the focal length of the system, it is not possible to fully collimate the light output by the system, rather the emitted light has an angular divergence determined by the properties of the system. This is the case for the LEDs that are particularly useful in automotive applications. In order to shape the light produced by the system, the light output by the LEDs (and other light sources) must be modified. To do this, it is known to provide a collimating optic that alters the angular intensity distribution of the LED (or other light source) such as circularly symmetrical Fresnel lenses, total internal reflection (TIR) collimators, compound parabolic concentrator (CPC) lenses/reflectors, parabolic reflectors and aspheric lenses.

Such collimating optics are highly sensitive to dimensional tolerances and light source position. In addition, automotive lighting units have inherent dimensional package requirements placing further constraints on the dimensions of the optics used. As a result, the manufacture of lighting units incorporating collimators, in particular for the automotive industry requires costly precision tooling in order to ensure the position and the dimensions of the collimator is within the prescribed tolerances. Alternatively, in order to achieve a more homogenous-looking illuminated object, it is known to provide a greater density of light sources, for example LEDs in the lighting unit. However it can be costly to provide greater numbers of light sources. An object of the present invention is to mitigate at least some of the issues above.

Summary of invention

In order to address at least some of the issues above there is provided a lighting unit and method for manufacturing a lighting unit as defined in the appended independent claims. The dependent claims define preferred features of the invention.

In the preferred embodiment there is provided lighting unit comprising: a plurality of light sources; a diffuser having an inner surface facing the plurality of light sources; and one or more optics, wherein: the one or more optics are positioned relative to the plurality of light sources such that light emitted by each of the plurality of light sources passes through at least one of the one or more optics, thereby providing a modified light output. Each of the one or more optics preferably has a substantially elliptical cross section in a plane extending through at least one of the light sources and the diffuser. Other shapes of lenses could be used, however they are less optimal than those with substantially elliptical cross sections. The position of each of the one or more optics relative to the plurality of light sources and the diffuser is such that the modified light output illuminates (preferably substantially all of) the inner surface of the diffuser.

Preferably there is also provided a method for manufacturing a lighting unit comprising: providing one or more light sources; providing a diffuser having an inner surface facing the plurality of light sources; providing one or more optics each of which having a substantially elliptical cross section in a plane extending though at least one of the light sources and the diffuser, the cross section having a radius; positioning the one or more optics in a first location such that light emitted by each of the plurality of light sources passes through at least one of the one or more optics, thereby providing an modified light output; wherein the first location is chosen based on the radius and a position and shape of the diffuser such that the modified light output illuminates substantially all of the inner surface of the diffuser. Advantageously, optics of such a shape modify the light output by light sources to achieve an angular intensity distribution suitable for illuminating the diffuser such that resulting diffused light appears homogeneous across the diffuser. Moreover such optics provide benefits in terms of being simple to manufacture (and don't need the high precision tooling used in the prior art), they are less sensitive to positioning within the lighting unit (meaning that lighting units can be manufactured to less stringent tolerances), and requires the use of fewer light source components to achieve the desired effect. Thus the present invention provides for easier and cheaper manufacture of lighting units providing a homogenous diffused output. The lighting unit of the present invention may be used as an automotive lighting unit, such as an automotive signal lamp.

Brief description of the drawings

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

Figure 1 shows a schematic of a portion of a cross section of a lighting unit according to the present invention.

Figure 2A shows a schematic top view of a lighting unit in accordance with a first exemplary embodiment of the invention.

Figure 2B shows a schematic front view of the lighting unit 200 of figure 2A.

Figure 3A shows a schematic top view of a lighting unit in accordance with a second exemplary embodiment of the invention.

Figure 3B shows a schematic front view of the lighting unit 300 of figure 3 A.

Figure 4A shows a schematic top view of a lighting unit in accordance with a third exemplary embodiment of the invention.

Figure 4B shows a schematic front view of the lighting unit 400 of figure 4A. Figure 5 shows a flow chart of a method of manufacture in accordance with the present invention.

Detailed description

In the following description and drawings like numerals refers to like elements.

Figure 1 shows a schematic of a portion of the cross section of a lighting unit 100 for an automotive signal lamp. The lighting units illustrated in the figures have a plurality of light sources 102, the light sources 102 preferably being LEDs. The cross section shown in figure 1 runs through one of the plurality of light sources 102. We describe a particular lighting unit below with reference to figure 1. The lighting unit 100 also includes a diffuser 104, the diffuser being configured to diffuse light incident upon it. The diffuser has an inner surface 103 facing the plurality of light sources, and an outer surface 105 facing away from the plurality of light sources. Preferably the diffuser is Evonik Plexiglas® 8N df23, alternatively the diffuser can be one of any proprietary light diffusing injection moulding compound such as Sabic Lexan™LUX2114G, or any available light diffusion film such as Covestro Makrolon® DX/ Lumen XT or Luminit Light Shaping Diffuser films. Optionally one or both of the inner and outer surfaces 103 105 of the diffuser 104 are textured to assist in diffusing the light incident on the diffuser 104 (for example by incorporating multiple facets or other features onto the surface in question, the facets or other features being disposed at different angles and orientations relative to the surface in question in order to scatter light).

The lighting unit 100 also includes at least one optic 106, the optic 106 being substantially transparent to at least some of the wavelengths of light emitted from the light source 102, and having a higher refractive index than the medium surrounding the optic 106. The optic 106 has a substantially elliptical cross section 108 in a plane 109 that extends through the light source 102 (in particular through a light emitting part of the light source 102) and the diffuser 104. As shown in figure 1, the pane 109 is the same as the plane of the cross section of the lighting unit 100 (i.e. the plane 109 is the same as the plane of the page). The elliptical cross section 108 causes the focussing of light from the light source 1 14 in the plane 109 as described below, such that light can travel in the plane 109 from the light source 102 to the diffuser 104 via the optic 106. Cross section 108 is substantially circular as shown in figure 1, however the elliptical cross section need not be circular. The substantially elliptical cross section 108 is defined by at least one radius 1 10.

The optic 106 is positioned such that it has a certain distance 1 12 from the light sources 102. Whilst the distance 112 as shown in figure 1 is defined between a focus of the elliptical cross section (in this case the centre of the circular cross section) and the rear of the light source 102, the person skilled in the art will recognise the distance 112 can also be defined with respect to any particular point on the optic 106 (for example a surface) and any particular point on the light source 102 (for example the front surface).

The light 1 14 emitted by the light source 102 passes through the optic 106, resulting in a modified light output 1 16, the modified light output 116 having a different angular intensity distribution to the light 114 emitted by the light source 102. Preferably the modified light 1 16 is at least partially collimated as compared to the light 1 14 emitted by the light source 102. In particular, the modified light output 116 is either convergent, divergent or collimated in the plane 109 of the cross section 108. The optic 106 directs the modified light 116 onto the diffuser 104, the distance between the optic 106 and the diffuser 104 and the angular spread of the modified light output 116 determining the width 118 of the area of the diffuser 104 illuminated by the modified light output 116. The degree to which the modified light output 116 is collimated/convergent/divergent is determined by the radius 110 and the distance 112 - advantageously by choosing different radii 110 and/or distances 112, the angular spread of the modified light output 116 can be tuned to be appropriate for the particular lighting unit 100 in which the optic 106 is employed. In particular, by selecting an appropriate radius 1 10 and distance 112, the width 1 18 of the area of the diffuser 104 illuminated by the modified light output 116 can be tuned - for example the width 1 18 of a beam of modified light 1 16 can be matched to the width of the diffuser 104 at that point of illumination, thereby ensuring full and even illumination of the inner surface 103 of the diffuser 104. Similarly the beam width 1 18 can be tuned as described above to account for the diffuser 104 not being parallel to the plane of the light sources and/or optics 106. By illuminating the inner surface 103 of the diffuser 104 fully and preferably evenly, the diffused light leaving the diffuser 104 from the outer surface 105 has a substantially isotropic intensity distribution - in other words the outer surface 105 appears homogenous.

For example, in an automotive signal lamp utilising LEDs each having an active area of around 4mm ² , a radius 110 of between 3.75mm and 4.25mm with a distance 1 12 of between 6.5mm and 7.5mm has been found to provide a beam width of around 12mm.

The optic 106 is preferably made from optical grade Acrylic (PMMA) such as Evonik Plexiglas® 8N. Alternatively, the optic 106 may be made from any material having a suitable refractive index, such as optical grade Polycarbonate (PC) such as Covestro Makrolon® LED2045/ LED2245/ AL2447 or Sabic Lexan™ LS I/ LS2 or any other injection moulding or rapid prototyping material suitable for transparent optical components.

Advantageously, the optic 106 is easy and cheap to manufacture, as it does not require the precision tooling that is needed to create, for example, complex Fresnel refraction surfaces on traditional collimating optics. Furthermore, the optic 106 is not as sensitive to precise positioning as traditional collimating optics for automotive signal lamps - thus the tolerances for locating the optic 106 during manufacture of the lighting unit 100 are less strict than for traditional optics, meaning that the cost of manufacture of the lighting unit itself is further reduced. In particular having an elliptical cross section enables enhanced stability as compared to traditional lenses, in that the present system is less sensitive to the exact position of the source relative to the surface of the optic.

In addition, the elliptical cross section 108 ensures that the focal length of the optic 106 is short. For example an optic 106 made from PMMA having a radius of 4mm has a focal length in the plane of the cross section 108 of around 2mm. This allows the optic 106 to be placed close to the light source 102 whilst providing a suitable beam width 1 18. This reduces the amount of space occupied by the optic 106 in the lighting unit 100 as compared to prior art optics. We note that the term "elliptical" as used above is used in a generic sense that includes "circular" - indeed in many circumstances circular cross sections are particularly beneficial. Consequently the present invention allows for the productions of smaller, more effective, and cheaper lighting units incorporating optics for use in automotive signal lamps.

The optic 106 may take the form of substantially any shape having a substantially elliptical cross section in the planes 109. In a preferred embodiment, the optic 106 is elongate such that it has a length that is longer in one dimension than its width across the elliptical cross section 108. Examples of such a shape include a straight cylinder, a curved cylinder, and a cylinder having both curved and straight portions along its length. Such cylinders have elliptical cross sections 108. Optionally the cylinders have circular cross sections 108. Optionally the radius 110 of the cross section 108 is constant along the length of the cylinder. Alternatively the radius 110 changes along the length of the cylinder, such that the cross section 108 is not constant along the length of the cylinder - for example the elliptical cross section may be of a first size and circular at a first position on the cylinder, but a different size and non-circular at a different position on the cylinder. Optionally the ends of the cylinder are connected, so provide a continuous loop shape (for example a torus). Alternatively the ends of the cylinder are defined by straight edges, or by curved edges (such as a hemisphere).

Advantageously, such an elongate shape allows light from a plurality light sources 102 to be modified using a single optic 106. Moreover, the extended optic can be made into any number of complex shapes and can thus be made to match the shape of the diffuser 104, thereby tailoring the modified light output 1 16 to the shape of the diffuser 104, and thus improving the coverage and uniformity of the light 1 16 illuminating the diffuser. In further embodiments, the lighting unit may include more than one optic, for example two or more extended optics having different shapes, but having some or all of the characteristic of the lighting unit 100.

Exemplary optics are shown in figures 2A to 4B.

In a first example a lighting unit 200 has an optic 206 having an extended shape, such as a torus (a special case of a curved cylinder) as shown in figures 2A and 2B. Figure 2A shows a schematic top view of the lighting unit 200, which comprises a plurality of light sources 102 and an annular diffuser 204, with the torus-shaped optic 206 disposed in between. Figure 2B shows a schematic front view of the lighting unit 200 (i.e. the view facing the annular diffuser 204), with the locations of the light sources 102 and the torus-shaped optic 206 relative to diffuser 204 indicated by dashed lines. A partial cross section through the lighting unit 200 at any point including a light source 102, the optic 206 and the diffuser 204 would correspond to the cross section portion shown in figure 1. In this example, the diffuser 204 preferably has an annular shape centred about an axis corresponding to a central axis of the torus-shaped optic 206. The lighting unit 200 functions in the same manner as lighting unit 100 described above in relation to figure 1. In this example, the light 114 from all the light sources 102 is modified using the single optic 206 so as to project a ring of illumination onto annular diffuser 204, the ring of illumination preferably corresponding to the dimensions of the annular diffuser 204. Accordingly, when illuminated, the annular diffuser 204 diffuses light and provides a substantially homogenous output across its surface.

Figure 3A shows a schematic top down view of a second example in which a light source 300 includes a plurality of substantially spherical optics 306, each optic 306 corresponding to a particular light source 102. Figure 3B shows a schematic front view of the lighting unit 300 (i.e. the view facing the diffuser 304), with the locations of the light sources 102 and the optics 306 relative to diffuser 304 indicated by dashed lines. A partial cross section through the lighting unit 300 at any point including a light source 102, an optic 306 and the diffuser 304 would correspond to the partial cross section shown in figure 1. The optics 306 are positioned between the light sources 102 and the diffuser 304. The pattern of light sources 102 and corresponding optics 306 can be made to match the shape of the diffuser 304 so as to provide substantially full illumination coverage of the diffuser 304. In the example of figures 3A and 3B, the diffuser 304 is "L" shaped, and accordingly the light sources 102 and corresponding optics 306 are arranged in a corresponding "L" shape. The optics 306 may each be of different radius and/or distance from the corresponding light source 102 so as to produce beams of modified light 116 to best match the shape of the diffuser 304 (so as to match the width of the projected beam 1 18 to the corresponding width of the diffuser).

Figure 4A shows a schematic top down view of a second example in which a light source 400 includes a plurality of substantially spherical optics 406, each optic 406 corresponding to a particular light source 102. Figure 4B shows a schematic front view of the lighting unit 400 (i.e. the view facing the diffuser 404), with the locations of the light sources 102 and the optics 406 relative to diffuser 404 indicated by dashed lines. A partial cross section through the lighting unit 400 at any point including a light source 102, an optic 406 and the diffuser 404 would correspond to the partial cross section shown in figure 1. The optics 406 are positioned between the light sources 102 and the diffuser 404. The pattern of light sources 102 and corresponding optics 406 can be made to match the shape of the diffuser 404 so as to provide substantially full illumination coverage of the diffuser 404. In the example of figures 4A and 4B, the diffuser 404 is "L" shaped, and accordingly the light sources 102 and corresponding optics 406 are arranged in a corresponding "L" shape. The optics 406 may each be of different radius and/or distance from the corresponding light source 102 so as to produce beams of modified light 116 to best match the shape of the diffuser 404 (so as to match the width of the projected beam 118 to the corresponding width of the diffuser). Furthermore, the optics 406 may have different orientations to produce beams of modified light 1 16 to best match the shape of the diffuser 404.

A method of manufacture 500 is illustrated in figure 5.

In step S502 a plurality of light sources are provided, such as light sources 102 described above. Preferably these are LEDs as noted above.

In step S504 a diffuser is provided, such as diffuser 104 as described above. The diffuser may define any shape.

In step S506 one or more optics such as optics 106 are provided, the optics having an elliptical cross section defined by at least one radius as described above in relation to figures 1 to 4B. Preferably, the number and shape(s) of the one or more optics are chosen to match the shape of the diffuser as described above. The optics are configured to modify the light emitted by the light sources to create a modified output light beam as discussed above.

In step S508, the one or more optics are positioned based on the desired width of the output beam of light. The desired width is determined by the shape of the diffuser to be illuminated. The position of the one or more optics is based on the radius of the optics. Alternatively, the radius of optics can be chosen based on a required position of the optics due to other constraints. Thus the resulting modified light output illuminates substantially all of the inner surface of the diffuser. It should be noted that whilst steps S502 to S508 are shown in sequence in figure 5, the sequence is not essential to all implementations. In particular the provision of the light sources, the diffuser and the one or more optics can alternatively occur in any chronological order.

The above embodiments are provided as examples only and are not intended to limit the scope of the invention. The scope of the invention is defined by the following claims.