GB2191572A

GB2191572A - Light source comprising an annular lens

Info

Publication number: GB2191572A
Application number: GB08613187A
Authority: GB
Inventors: Peter Roger Pearce-Harvey
Original assignee: PEARCE HARVEY PETER ROGER
Current assignee: PEARCE HARVEY PETER ROGER
Priority date: 1986-05-30
Filing date: 1986-05-30
Publication date: 1987-12-16
Anticipated expiration: 2006-05-30
Also published as: GB8613187D0; GB2191572B

Abstract

A light source assembly comprises a source of light 10, which is surrounded by an annular lens 16, preferably of aspherical cross-section and having an internal cylindrical surface, the axis of the annular lens being substantially at the location of the source. The lens produces a radial disc of light extending outwardly therefrom and this is preferably reflected or refracted to form a beam having its axis parallel to the axis of the lens. <IMAGE>

Description

SPECIFICATION Light source The present invention relates to a light source.

It is a requirement of almost all light projection systems to attempt to collect as much light as possible from the source. The source radiates its light throughout a 360 arc. One of the traditional ways of producing a very intense light is to use, as the source of light, an arc which may be a conventional carbon arc or a xenon arc or like. There are a numberof deductions from the full 360 arcthat result from the physical shape ofthe source, its envelope, the power connection terminals and the filamentorthe electrodes.

The usual practice is to generate a beam of light and to collectthe lightfrom the source with an optical system and to collect the light output and focus itto a point determined by the requirements of the particular piece of equipment. These optical systems include mirrored reflectors, aspherical lenses, and combinations ofthese.

Many known systems are, however, inherently inefficient in collecting the amount of light emanating from the source of light itself and some only manage no more than about 25% of this light.

Since the light source itself is an inherently rather inefficient system, the amount of light energy which is made availableforfinal use is only a very small fraction ofthe amount of electricai energywhich has been put into the system.

It is now proposed, according to the present invention, to provide a light source assembly comprising a source of light, an annular lens surrounding said source and having its axis substantially at the location of said source,said annular lens being effective to produce a radial disc of light extending outwardly therefrom.

It is possible, with such an arrangement, to collect a much greater proportion ofthe light emanating from the source itself and by designing the diameter ofthe annular lens relative to the outside diameter of the source, as much as 50% or more ofthe light leaving the source can be incident on the inner surface ofthe lens and can beusedtoformthedisc.

While the inner surface can have a number of different shapes, it is preferably a cylindrical inner surface. The outer surface can, for example, be aspherical so as to produce a radial disco light having substantially parallel, radial, planarsides.

If special effects are desired, however, the outer surface ofthe annular lens could be provided with a plurality of facets, at least one of which could be coloured.

In a preferred construction according to the present invention, means are provided, surrounding said annular lens, to reflect or refract the disc of light to form a beam having its axis extending in a direction generally parallel to the axis ofthe beam, advantageously, so as to form a substantially parallel sided beam or beam convergent to a point along the axis of the beam.

These means could comprise a mirrororlens having a conical reflective, or internally reflective surface, the cone angle of the surface being 45".

Alternatively, these means could comprise a light source to claim 7 wherein said means comprise a mirror having a parabolic or elliptical reflective or internal reflective surface. The point of focus 'P' above may be changed by moving the parabolic reflector along the axis ofthe light source. In most instances, it would be preferable to provide a focusing lens upon which this beam oflightis incident.

With such a system it is possible to utilize a much larger proportion ofthe light emanating from the source itself and to make the whole construction very much smallerforthesamefinal output. Because itisverymuch smaller,itcan be madevery significantly less expensive, use far less energy and be far less wasteful since it will produce much less unwanted heat energy.

It is a function of light sources of the carbon arcor xenon type that the light intensity of the source output cannot be substantially varied by means of reducing the electrical power. A mechanical apparatus in the form of a variable shutter and/or iris is commonly used. However, according to a further feature ofthis invention that the dimming can be achieved by means of a tube of material, such as a coloured translucent material or a screen, is axially movable within said annular lens closely adjacent to the radially inner surface thereof.

In orderthatthe invention may more readily be understood, the following description is given, merely by way of example, reference being made to the accompanying drawing, in which the sole Figure is a schematic cross-section through one embodiment of light source assembled according to the present invention.

The light source assembly shown in the Figure includes a conventional carbon arc or xenon source oflight 10 having an arc produced atthe point 12.

The axis ofthe light source 10is shown at 14.

Coaxially mounted around the light source 10 is an annularaspherical lens 16 having a cylindrical inner surface 18 and an aspherical outer surface 20.

Positioned again coaxiallywith the light source, and surrounding the annular lens 16 is a conical mirror 22 having a conical reflective surface 24 subtending a cone angle of 45", i.e. an apex angle of 90".

Positioned to the right, in the drawing, of the light source is a focusing lens 26.

The light source is shown as emanating, from its centre 12, rays 28 of which about 50% are incident on the innercylindrical surface 18 ofthe annular lens 16.

The design of the lens is such as to produce a radially outwardly extending disc28 of light having parallel, planar side surfaces 30 and 32. This disc is incident on the reflective surface 24 which reflects the disc to form a beam 34 which is parallel sided and coaxial with the axis 14 of the system. This parallel sided beam 34 is incident upon the focusing lens 26 which can be used to focus the beam as desired.

It will be appreciated that such a structure utilizes a very much larger proportion ofthe light emanating from the source 10 and reduces very significantlythe field scatter, thereby producing a far more efficient system than has been conventional.

While the inner surface ofthe lens 18 has been shown as cylindrical, it is contemplated that it could be otherthan cylindrical and indeed could be polygonal. Similarly, the outer surface could be provided with a plurality of facets; at least some of which could becoloured,forexample,soasto produce interesting light effects in the beam 34to be focused by the lens 26. Again, instead of having a reflective mirror 22, total internal reflection could be achieved using a lens system surrounding the annular lens 16.

The intensity of light can be varied by moving a cylindrical dimmingtube40axiallywithinthe annular lens 16 with its outer surface closely adjacent the inner cylindrical surface 18 ofthe lens.

This dimming tube may be of coloured, e.g. grey, translucent material or may include a light intensity reducing screen.

Claims

1. A light source assembly comprising a source oflight, an annular lens surrounding said source and having its axis substantially at the location of said source, said annular lens being effective to produce a radial disc of light extending outwardly therefrom.

2. A light source according to claim 1, wherein said annular lens has a substantially cylindrical inner surface.

3. Alightsourceaccordingtoclaim 1 or2, wherein said lens is of aspherical cross-section, to produce a radial disc of light having substantially parallel, radial, planarsides.

4. Alensaccordingto claim 1 or2,whereinthe outer surface of said annular lens is provided with a plurality offacets.

5. A light source according to claim 4,wherein at least one of said facets is coloured.

6. A light source according to any preceding claim, wherein means are provided, surrounding said annular lens, to reflect or refract the disco light to form a beam having its axis directed generally parallel to the axis of the beam.

7. A light source according to claim 6,wherein said means are designed to form a substantially parallel sided beam.

8. Alightsource according to claim 7,wherein said means comprise a mirror or lens having a conical reflective, or internal reflective, surface, the cone angle of said surface being 45 .

9. A light source according to claim 7,wherein said means comprise a mirrorhaving a parabolicor elliptical reflective or internal reflective surface.

10. A light source according to claim 6,7 or 8 and including a focusing lens upon which said beam of light is incident.

11. A light source according to any preceding claim, wherein a tube of material, such as a coloured translucent material or a screen, is axially movable within said annular lens closely adjacent to the radially inner surface thereof.

12. A light source substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.