GB2297149A

GB2297149A - Lighting apparatus

Info

Publication number: GB2297149A
Application number: GB9600882A
Authority: GB
Inventors: Barry Thomas Wright
Original assignee: Dorman Traffic Products Ltd
Current assignee: Dorman Traffic Products Ltd
Priority date: 1995-01-20
Filing date: 1996-01-17
Publication date: 1996-07-24
Also published as: GB9600882D0; GB9501137D0

Abstract

A lighting apparatus that produces a single unified beam comprises multiple light sources 2, e.g. light emitting diodes, and a generally convex composite lens 20 comprising an array of lens elements 4, each with a focal point 10. Each lens element 4 has a plurality of stepped concentric rings provided on the inside surface thereof and an array of a plurality of generally convex rectangular facets 8 formed on the outside surface thereof. Each of the lens elements 4 has associated with it a single LED 2 at its respective focal point 10. The lighting apparatus is suitable for use as warning lamps, especially for vehicles.

Description

LIGHTTN APPARATUS This invention relates to lighting apparatus, especially, though not exclusively, warning lamps such as for vehicles or for other hazard, warning or indicating purposes.

Various types of lighting apparatus comprising a single light source and a lens constructed and arranged to form a beam therefrom are known and are used in a great variety of lighting applications. Common examples include head- and tail-lights of vehicles of most kinds and stationary hazard or warning lamps such as those used on roads and motorways.

In certain applications, however, devices comprising a single light source suffer from the drawback of providing insufficient light intensity to meet necessary criteria such as minimum lamp brightness or visibility, as may be required by law. This problem is more significant in the context of solid state light sources (e.g. LED's), as opposed to conventional filament bulbs which can typically be made with much greater power ratings.

Thus, in cases where limited and/or insufficient light source intensities are experienced, it can be desirable to employ a plurality of such light sources, with a lens arranged to act upon the light emitted by the multiple light sources collectively so as to generate a unified beam having an intensity correspondingly higher than that obtainable from a similar device including just a single light source.

Although lighting devices comprising a plurality of light sources and a single lens, as described above, can provide the desired increased light beam intensity, they unfortunately exhibit an associated problem which is the generation of secondary maxima. That is to say, because physically not all of the multiple light sources can be at the focal point of the lens and thus at least one or some of them will inevitably not be at the focal point, the collected images from the plurality of light sources do not coincide and the resulting interference causes the overall light beam image produced by the apparatus to comprise alternating regions of comparatively high and low light intensity.This phenomenon is undesirable in many warning or hazard lighting applications, because the resulting variation in light intensity across the field of the beam can result in confusion as to the operating condition of the device or at the very least renders the device incapable of fully and assuredly fulfilling its warning or indicating function to an observer, wherever positioned within the field of the beam.

US-A-4654629 discloses a marker light which is intended for use as a warning light for trains. Although more than one lens is provided, a plurality of light emitting diodes are associated with each lens, and the LED's lie at different distances from the focal point of the respective lens with which they are associated. Thus, the problem of secondary maxima occurs with the marker light disclosed in this reference.

It is an object of the present invention therefore to provide lighting apparatus which generates a beam of enhanced light intensity but without or substantially without the problem of secondary maxima.

Accordingly, the invention provides a lighting apparatus comprising a plurality of light sources, and an array of lens elements, each lens element being associated with and arranged to act upon light emitted by a respective one of the light sources at or adjacent its focal point, wherein the lens elements are constructed and arranged such that the light emitted therefrom combines to form a single unified beam.

In accordance with the invention, each of the lens elements of the array creates its own independent image from the respective light source behind it. By virtue of the array arrangement of the lens elements and by appropriate selection of the shape and dimensions of each lens element, the resultant array of discrete images from the plurality of light sources merge into one another (or overlap, preferably overlap to as great a degree as possible), thereby creating a "smeared over" effect, the result of which being that any sharp transitions in light intensity across the field of the resulting beam are minimised or preferably eliminated altogether.

In a particularly preferred lighting apparatus according to the invention, all of the discrete images produced by the lens elements of the array are substantially the same size and shape as one another and substantially coincide with one another, thereby building up a resultant total image generally the same size and shape as each discrete image, and having a total image intensity that is approximately the sum of the intensities of the individual discrete images making up the total beam.

Therefore, according to the invention it is possible to provide a composite lighting unit whose discrete elements (each one comprising a light source with a corresponding lens element) combine to generate a single unified beam having desired total breadth and height of field and light intensity profile according to the demands of any particular given practical application, wherein the beam does not exhibit any significant sharp changes (if any at all) in intensity across the major proportion of its field.

In a further aspect, the invention provides a composite lens comprising an array of individual lens elements, for use in the lighting apparatus defined above.

In practical embodiments of the lighting apparatus of the invention the plurality of light sources may each be of any desired type, e.g. filament bulbs (such as tungsten filament bulbs) or solid state devices such as light emitting diodes (LED's), or any other type of light source suitable for a particular given application. Though not limited to this, the invention is especially applicable to solid state light-emitting devices, for the reasons discussed above.

Preferably each light source is located in the focal plane of its associated lens element and most preferably at (or closely adjacent) the focal point thereof. Particularly preferred embodiments of the apparatus of the invention include only a single light source behind each lens element.

However, less preferred embodiments may comprise more than one light source behind each lens element, for example to achieve a desired total light intensity required for a practical application in question and depending upon the power of each light source available for use. In embodiments of the invention comprising multiple light sources associated with each lens element, typically two or three or perhaps four or possibly even more light sources are associated with each lens element and the light sources are preferably located in the focal plane of the lens element and equispaced around the circumference of a circle centred at the focal point. In practice, the multiple light sources would be positioned as close together and as close to the focal point as possible.

In practical embodiments of the invention the basic type of lens element used may take any form that provides the desired configuration of light output for the application for which the lighting apparatus is intended.

By way of example, light directing and/or focusing elements such as Fresnel rings and/or prismatics (both of which are well known devices in the optics art, so will not be described further here) may be incorporated into the lens element, and are preferably formed on the inner surface thereof (which is that surface facing the respective light source(s)). Typically, the or each lens element will be constructed and arranged to generate a generally parallel beam. Alternatively, one or more, or respective reflectors, e.g. parabolic reflectors, may be mounted behind the light source(s) to direct the light in the desired manner, or any other suitable light directing and/or focusing means, examples of which are well known in the optics art, or any suitable combination of such means, may be used.

The shape, dimensions and spacial disposition of the lens elements of the array may be selected to provide an appropriately shaped and directed resultant beam of light as required of the application for which the lighting apparatus is to be used.

In particularly preferred embodiments of the apparatus of the invention, a surface of each lens element, which is that surface other than the one upon which are formed the light directing and/or focusing elements (i.e. in preferred embodiments the outer surface of each lens element), has formed thereon an array of facets, each facet having a convex spherical surface, the radius of curvature of each facet being smaller than the radius of curvature of the said surface of the respective lens element.

In such embodiments, each of the curved facets on each lens element acts in its own right as what may be termed a "sub-lens element", which creates its own independent image from the light source(s) behind it. By virtue of the array arrangement of the facets over the surface (preferably substantially the whole surface) of each lens element, and preferably also by virtue of appropriate selection of the radius and centre of curvature of each of the facets, these independent images combine with one another in the same manner as do the discrete images provided by the lens elements of the array (as described above), to form a single unified beam.

The shape and dimensions of each of the facets may be designed, preferably in combination with any light directing and/or focusing means used, to shape and direct their respective images as required for the practical application for which the lighting apparatus is intended to be used.

The appropriate shape and dimensions of each facet may be determined using standard lens calculations as will be apparent and well known to persons skilled in the art. Such standard calculations can be found for example in the "IES Lighting Handbook 1984" published by the Illuminating Engineering Society of North America.

The lens elements of the apparatus of the invention may be made of any suitable material, preferably a transparent or translucent plastics material e.g. polycarbonate.

Conveniently, each lens element, with its array of facets (if used) and light directing and/or focusing elements such as Fresnel rings and/or prismatics (if that type of lens element is used) formed on opposite surfaces thereof, may be formed as a one piece moulding. In preferred embodiments of the apparatus, the lens elements are all of the same material and are formed in combination together as a unitary multi-component lens.

In a presently particularly preferred embodiment, the lens elements correspond in their basic form and configuration to the lens of a known traffic hazard warning lamp, e.g. that sold by ourselves under the trade mark DORMAN TrafiLITE.

In a further presently particularly preferred embodiment, the plurality of light sources are provided with control means, which can switch all of the light sources on and off together, resulting in a flashing beam of light, if the switching procedure is carried out repeatedly. Such control means are preferably provided by electronic circuitry and are well known in the art. They are employed, for instance in a known traffic hazard warning light, e.g.

that sold by ourselves under the trade mark DORMAN TrafiLITE.

A preferred embodiment of the lighting apparatus of the invention will now be described in detail, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a top plan view of a preferred composite lens for use in the preferred lighting apparatus according to the invention; Figure 2 is a cross-sectional view along line Il-I I of the lens of Figure 1, additionally showing the location of a single light source associated with each lens element; Figure 3 is a bottom plan view of the lens of Figure 1; and Figure 4 is a schematic representation of the way in which a fragment of the lens of Figure 1 acts on light emitted by its associated light source.

Referring to Figures 1 to 3, a lighting apparatus according to the invention comprises multiple light sources 2, for instance light emitting diodes (e.g. H2000 L.E.D.'s, ex. Stanley), and a generally convex composite lens 20 comprising an array of lens elements 4. Each lens element 4 has a plurality of stepped concentric rings 6 (although these are not all shown in Figure 3, for clarity) provided on the inside (lower) surface thereof and an array of a plurality of generally convex rectangular facets 8 formed on the outside (upper) surface thereof. Each of the lens elements 4 has associated with it a single LED 2 at the focal point 10 of the lens element as shown in Figure 2.

Those of the stepped concentric rings 6 which are located relatively near the outer edge of each lens element 4 are shaped to act as "Fresnel" rings and the remaining stepped concentric rings, i.e. those located relatively near the centre of each lens element 4, are shaped to act as "prismatic" rings. The diameter at which the action of the stepped concentric rings 6 changes from Fresnel to prismatic may be selected in accordance with the desired or required light directing characteristics and with respect to other physical parameters of the lighting apparatus, as will be appreciated by persons skilled in the art.

The rectangular facets 8 are arranged on each lens element 4 in a symmetrical array which substantially covers the outer surface of the respective lens element 4. Each facet 8 is formed as a spherical surface, its radius of curvature being smaller than the general radius of curvature of the lens element 4 itself.

The actual radius and centre of curvature of each facet 8 are selected such that the size, shape and relative location of each of the array of discrete images produced by the respective facets of each of the lens elements 4 overlap (or preferably substantially coincide with) one another and generate a "smearing over" effect across the field of the beam generated by the composite lens 20. In this embodiment with rectangular facets 8, a similar rectangular shaped beam is created.

Figure 4 shows schematically the manner in which a single facet 8', in combination with a section of a single stepped concentric ring 6' (in this example a prismatic ring) directs light from an associated light source 2'. The prismatic ring 6' is shaped to internally reflect light from the light source 2' and to direct it towards the surface of the facet 8' as parallel rays, which are then further directed and shaped by refraction at the surface of the facet 8'. By appropriate selection of the shape and dimensions of the prismatic ring 6' and the facet 8' the projected image may be shaped and directed as required.

Standard lens calculations which may for example by found in the "IES Lighting Handbook 1984" published by the Illuminating Engineering Society of North America, may be used to determine these shapes and dimensions.

The Fresnel rings (i.e. those stepped concentric rings 6 located relatively near the outer edge of each lens element 4) direct light in combination with the facets 8 in a similar way to that described above in relation to the prismatic rings, with the exception that the Fresnel rings are shaped to refract light from their associated light source as opposed to reflecting it.

Suitable values therefore of the curvature parameters of the lens facets 8, the lens elements 4 and the composite lens 20 itself may be selected according to the skilled person's skill, understanding and wishes. By way of example, however, each lens element 4 may in principle have the same form as a known multi-facetted lens, either on its present scale or in a scaled down size, namely the lens already known in the context of a traffic hazard warning lamp sold by ourselves under the trade mark DORMAN TrafiLITE.

The composite lens 20, with its lens elements 4 including stepped concentric rings 6 (i.e. Fresnel rings and prismatic rings) and convex facets 8, is formed as a unitary injection moulding from a transparent or translucent plastics material, e.g. polycarbonate, which may be coloured (e.g. red, amber or green), as is already known in the art of hazard warning lamps.

The LED's 2 of the unit are located at the focal point of their associated respective lens elements 4. The LED's 2 are maintained in this spacial relationship by any suitable mounting means, for instance, by virtue of being mounted directly on a circuit board (not shown) fitted behind the composite lens 20 and on which all the other electrical or electronic circuitry of the device may be mounted. The whole unit is in practice contained within a housing (also not shown) which may also contain a power source, if required, as is commonly the case in the art, and so will not be described in further detail here.

In order to achieve greater total light intensities, more than one LED may be used with each lens element. In such a case, each LED cluster is preferably arranged symmetrically surrounding the focal point of the respective lens element, the LED's of each cluster being as close together as possible.

When the LED's are switched on (by any suitable means, possibilities for which are well known in the art), each of the individual lens elements 4 act upon the light emitted by its associated LED 2, each of the facets 8 creating its own discrete image. The array of like images from each respective array of facets overlap, and preferably substantially coincide, and merge into one another and thereby combine to generate a unified beam of light (in this illustrated embodiment, a rectangular beam) having an intensity profile with no significant sharp changes across the major proportion of its width and height, by virtue of the shape, dimensions and spatial disposition of the lens elements 4 and the facets 8 formed thereon.In this regard, the arrangement of the lens elements 4 is preferably symmetrical and in this illustrated exemplary embodiment takes the form of a star-like array, with a plurality of elements (e.g. six) equiangularly surrounding a central single lens element. Any suitable arrangement may be employed however, provided of course that the array of lens elements combine in the required manner to generate a single unified light beam having the characteristic intensity profile with no sharp changes across the major proportion of its width and height.

It is to be understood that the present invention has been described above by way of example only with reference to a specific exemplary preferred embodiment. Many variations and modifications from that which has been specifically described and illustrated are possible within the scope of the invention, as will be readily apparent to persons skilled in the art.

Claims

1. Lighting apparatus comprising a plurality of light sources, and an array of lens elements, each lens element being associated with and arranged to act upon light emitted by a respective one of the light sources at or adjacent its focal point, wherein the lens elements are constructed and arranged such that the light emitted therefrom combines to form a single unified beam.

2. Lighting apparatus according to Claim 1, in which each of the lens elements creates its own independent image from the respective light source, wherein said images are substantially the same size and shape as another and substantially coincide with one another.

3. Lighting apparatus according to Claim 1 or Claim 2, in which the light sources are solid state lighting devices.

4. Lighting apparatus according to any one of the preceding claims, in which there is a single light source associated with each lens element.

5. Lighting apparatus according to any one of claims 1 to 3, in which there is a pluraltiy of light sources associated with each lens element.

6. Lighting apparatus according to Claim 5, in which the multiple light source associated with each lens element are located in the focal plane of the lens element and equispaced around the circumference of a circle centred at the focal point.

7. Lighting apparatus according to any one of the preceding claims, in which light directing elements are incorporated in each lens element.

8. Lighting apparatus according to any one of the preceding claims, in which light focusing elements are incorporated in each lens element.

9. Lighting apparatus according to Claim 7 or Claim 8, in which the light focusing and/or light directing element are formed on the surface of each lens element closest to the light sources.

10. Lighting apparatus according to any one of the preceding claims, in which an array of facets is formed on the surface of each lens element which is furthest from the light sources, wherein each facet has a convex spherical surface, the radius of curvature of each facet being smaller than the radius of curvature of the said surface of the respective lens element.

11. Lighting apparatus according to any one of the preceding claims, in which the lens elements are all of the same material and are formed in combination together as a unitary multi-component lens.

12. Lighting apparatus according to any one of the preceding claims, further including electronic control means for causing flashing of the light sources.

13. Lighting apparatus essentially as described herein with reference to the accompanying drawings.

14. A composite lens including an array of individual lens elements suitable for use in lighting apparatus according to any one of the preceding claims.