GB2240167A - A light source assembly - Google Patents

Abstract

A light source assembly in which a source of light is surrounded by an annular lens, 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.

Description

T,TC,HT 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 3600 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 number of deductions from the full 3600 arc that result from the physical shape of the source, its envelope, the power connection terminals and the filament or the electrodes.

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

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 available for final use is only a very small fraction of the amount of electrical energy which has been put into the system.

An improvement is proposed in GB-A-2191572 which provides a light source assembly comprising a source of light, an annular lens surrounding the source and having its axis substantially at the location of the source, the 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 of the light emanating from the source itself and, by designing the diameter of the annular lens appropriate to the outside diameter of the source, as much as 50 h or more of the light leaving the source can beincident on the inner surface of the lens and can be used to form the disc. However, this leads to a rather bulky and unnecessarily expensive device.

It is now proposed according to the present invention to provide a light source assembly comprising a source of light, an 1annular 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; and an annular mirror adapted to reflect part of the light emitted directly from said light source to pass through said annular lens. Preferably, the mirror is concave and one of said lens or said mirror is positioned in front of the other in the assembly.

Advantageously, said lens and said mirror touch one another, the point at which they touch being at the same longitudinal position in said assembly as the centre of said light source. 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 disc of light having substantially parallel, radial, planar sides.

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

Preferably, means are provided, surrounding said annular lens, to reflect or refract the disc of light to form a beam having its axis directed generally parallel to the axis of the beam.

These means could comprise a mirror or lens having a conical reflective, or internally reflective surface, the cone angle of the surface being 450 Alternatively, these means could comprise a mirror with a parabolic or elliptical reflective or internal reflective surface having a predetermined point of focus. The point of focus of the light reflected off of the surface may be changed by moving the parabolic reflector along the axis of the light source.

In most instances, it would be preferable to provide a focusing lens upon which this beam of light is incident.

With such a system it is possible to utilize a much larger proportion of the light emanating from the source itself and to make the whole construction very much smaller for the same final output. Because it is very much smaller, it can be made significantly less expensive, use less energy and be less wasteful since it will produce less unwanted heat energy.

It is a function of light sources of the carbon arc or 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 of this invention the dimming can be achieved by means of a tube of material, such as a coloured translucent material or a screen, which is axially movable within said annular lens closely adjacent to the radially inner surface thereof. Alternatively, dimming can be achieved by moving the light source relative to the annular lens and mirror assembly. This will result in misalignment of the light source and hence in the less emanated light passing through the annular lens.

In order that the invention may more readily be understood, the following description is given, merely by way of example, with reference to the accompanying drawings; in which: Figure 1 is a schematic cross-section through one embodiment of light source assembly according to the present invention; Figure 2 is a schematic cross-section of another embodiment of light source.

The light source assembly shown in the Figure, includes a conventional carbon arc or xenon source of light 10 having an arc produced at the point 12. The axis of the light source 10 is shown at 14.

Coaxially mounted around the light source 10 is an annular aspherical lens 16ihaving a cylindrical inner surface 18 and an aspherical outer surface 20. The front surface 19 of the lens 16 is shown ending at the mid-point of the light source 12. An annular mirror 25 is provided in front of the mid-point 12. The positions of the lens 16 and mirror 25 may be reversed relative to one another producing the same effect described below.

Various constructions of the annular mirror 25 are possible, such as the construction shown in Figure 2 where the annular mirror 25 is shown flush with outer surface 20 of the annular lens 16. Alternatively, the mirror 25 could be part of an assembly supporting the light source 10.

It is most preferable to have that portion of the light, which in the assembly shown in Figures 1 and 2 is within the sector defined by the ray 28 and an the edge 19 of the lens 16, reflected back so that it passes through the lens 16. Thus, the annular mirror could be a construction supporting the or part of the front half of the round portion of the light source 10 or any annular mirror within that sector. Alternatively, a half of the light source 10 could be provided with a reflective coating. Preferably, as shown, an annular mirror 25 is attached to the lens 16.

Positioned again coaxially with 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 450, i.e. an apex angle of 900.

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

The light source is shown as emanating, from its centre 12, rays of which about 50% are incident on the inner cylindrical surface 18 of the annular lens 16 and mirror 25.

Light directed in front of the point 12 and within the area covered by the mirror 25 is reflected back through the light source 10 towards the annular lens 16. The annular lens 16 and mirror 25 preferably cover such an area so as to catch all the light emanating forwardly of the assembly which would otherwise not be received by the focusing lens 26.

The design of the lens is such as to produce a radially outwardly extending disc 29 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 of the light emanating from the source 10 and reduces very significantly the field scatter, thereby producing a far more efficient system than has been conventional. The mirror 25 concentrates the emanated light by reflecting part of it back through the annular lens 16 in such a manner that the reflective surface 24 can be much smaller than prior art surfaces (eg in the type disclosed in GB-A-2191572).

While the inner surface of the lens 18 has been shown as cylindrical, it is contemplated that it could be other than cylindrical and indeed could be polygonal.

Similarly, the outer surface could be provided with a plurality of facets, at least some of which could be coloured, for example, so as to produce interesting light effects in the beam 34 to 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 dimming tube 40 axially within the annular lens 16 with its outer surface closely adjacent the inner cylindrical surface 18 of the lens. This dimming tube may be of coloured, e.g. grey, translucent material or may include a light intensity reducing screen.

The light passing through the lens 26 will include;a component from the annular beam 34, which will be focused at a predetermined point beyond the lens 26 and determined by the focal length of the lens. A second component will originate directly from the light source 10 and will form a cone of light beyond the lens 26, the taper of the cone being dependent on the spacing between the light source 10 and the lens 26 and also on the focal length of the lens 26.

By the addition of means to move the assembly, formed of the light source 10, and annular lens 16 and the annular mirror 25, relative to the reflective surface 22, the taper of the light cone from the light source 10 can be altered.

This will affect the amount and spread of "background" light produced and thus the intensity of light at the point of focus of the light component from the annular beam 34.

Claims (16)

1. 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; and an annular mirror adapted to reflect part of the light emitted directly from said light source to pass through said annular lens.

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

3. A light source according to claim 1 or 2, wherein said lens is quadrant-shaped in cross-section to produce a radial disc of light having substantially parallel, radial, planar sides.

4. A lens according to claim 1 or 2, wherein the outer surface of said annular lens is provided with a plurality of facets.

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 said mirror is concave and one of said lens or said mirror is positioned in front of the others in the assembly.

7. A light source according to any preceding claim, wherein said lens and said mirror touch one another, the point at which they touch normally being at the same longitudinal position in said assembly as the centre of said light source.

8. A light source according to any preceding claim, including drive means to move said light source axially of said annular lens and annular mirror.

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

10. A light source according to claim 9, wherein said means are designed to form a substantially parallel sided beam.

11. A light source according to claim 9 or 10, wherein said means comprise a mirror or lens having a conical reflective, or internal reflective, surface, the cone angle of said surface being 450.

12. A light source according to claim 9, wherein said means comprise a mirror having a parabolic or elliptical reflective or internal reflective surface.

13. A light source according to any one of claims 9 to 12, including altering means to move said light source, annular lens and annular mirror axially of said means.

14. A light source according to any preceding claim, including a focusing lens upon which said beam of light is incident.

15. 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.

16. A light source substantially as hereinbefore described with reference to and as illustrated in Figure or in Figure 2 of the accompanying drawings.