EP1300712A2

EP1300712A2 - Optical systems including reflectors

Info

Publication number: EP1300712A2
Application number: EP02256927A
Authority: EP
Inventors: George Heftman
Original assignee: Nicotech Ltd
Current assignee: Nicotech Ltd
Priority date: 2001-10-05
Filing date: 2002-10-07
Publication date: 2003-04-09
Also published as: GB0223133D0; GB2381065A; GB2381065B; EP1300712A3; GB0123979D0

Abstract

An optical system includes conical reflectors (32) axially aligned back to back with a xenon tube (35) located in the throat (36) formed by their truncated apices, for emitting light in two opposite directions. Each reflector (32) is enclosed by a transparent cover (33) that includes a central lens (37) for evening out axial light-distribution. Alternatively, a xenon tube (15) may be located between the apices of two mutually-inverted conical reflectors (16,17) at right angles to their common axis (18) for emitting light from their external reflective surfaces throughout 360 degrees. As further alternatives, a single conical or pyramidal reflector (3,10) may be used with a LED (1) as light source, and the systems may be used for reception of light.

Description

This invention relates to optical systems including reflectors.
It is an object of the present invention to provide an improved form of optical system including a reflector
According to the present invention there is provided an optical system including a reflector, wherein the reflector has a conical or pyramidal light-reflecting surface, and a light-emitter or -receptor is located in the region of the apex of reflector for, respectively, emitting light onto, or receiving light from, said surface.
The reflector may have an internal reflective surface and the light-emitter or -receptor may then be located within the reflector. In this case, the system may include two axially-aligned conical reflectors that have internal reflective surfaces and truncated apices, the reflectors being retained with their truncated apices forming a common throat, and the light-emitter or -receptor being located within the throat for, respectively, emitting light into, or receiving light from, the reflective surfaces of both reflectors.
As an alternative, the reflector may be of conical form having an external reflective surface, and the light-emitter or -receptor in this case may be located in the region of the apex externally of the reflector. Two axially-aligned conical reflectors having external reflective surfaces may be provided, and in these circumstances they may be retained axially aligned and mutually inverted with the light-emitter or -receptor located between their apices for, respectively, emitting light onto, or receiving light from, both reflectors.
Optical systems in accordance with the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Figures 1 and 2 are representative end- and sectional side-elevations respectively, of a first optical system according to the invention;
Figures 3 and 4 are representative end- and sectional side-elevations respectively, illustrative of a second optical system according to the invention;
Figures 5 and 6 are, respectively, a side-elevation and a plan of a third optical system according to the invention, the plan of Figure 6 showing the system with the upper of its two reflectors removed;
Figure 7 is illustrative of a fourth form of optical system according to the invention; and
Figures 8 and 9 are respectively, a sectional side-elevation and an end-elevation of an implementation of the fourth form of optical system according to the invention.
Referring to Figures 1 and 2, a light source, which in this case is in the form of a light-emitting diode (LED) 1, is located on the axis 2 of a reflector 3. The reflector 3 has the form of a right circular cone that is truncated at its apex to give the reflector 3 a small throat 4 that accommodates the LED 1. The inner surface 5 of the reflector 3 is reflective, and light-rays emitted by the LED 1, such as those identified individually as d to h in Figure 2, exit the reflector 3 either directly without reflection as in the case of rays e and h, or after one reflection as in the case of the ray d, or after more than one reflection as in the case of light-rays f and g.
The light emitted from within the reflector 3 is largely contained within its solid apex-angle A, with the extreme angle of exit illustrated by the ray h deviating from this by an angle X. The deviation angle X is dependent on the axial length of the conical reflector 3 and arises from light, as in the case of the ray h, that originates from an outer edge of the LED 1 and just glances the rim 6 of the reflector 3. All the light emitted by the LED 1 is accordingly contained within the solid angle (A + 2X), and is thus well-defined by the geometry of the reflector-cone and the position of the light source within it.
The larger the reflector-cone, the nearer the angle of light emitted from it approaches the apex-angle A of the cone. Choice of the angle A, the axial length of the cone and the location of the light source within it, determines the solid angle of the resultant emission from the system.
The relationship between the horizontal and vertical angles of emitted light may be varied by change of geometry of the cone. This is illustrated in Figures 3 and 4 where a reflector 10 in the form of a 'rectangular cone' or pyramid is used, having horizontal and vertical dimensions H and V respectively. The horizontal and vertical emission angles can be changed simply by changing the values of H and V.
Figures 5 and 6 illustrate an optical system which emits light over 360 degrees, in this case in azimuth, from an elongate light source 15 (for example a xenon tube). The source 15 is located between the apices of two externally-reflective and mutually-inverted conical reflectors 16 and 17. More particularly, the source 15 extends horizontally at right angles to the vertical, common axis 18 of the axially- aligned reflectors 16 and 17, with its centre on the axis 18. Where the reflectors 16 and 17 have the same apex angle A as one another, all light-rays emitted by the system are largely contained within the angle B which equals (A - 180) degrees.
Rays that run along a line joining the edge of the source 15 to the rim of either reflector 16 and 17, for example the ray j to the rim of the cone 17, will deviate outside the angle B by an angle Y. The maximum angle of vertical emission is accordingly (B + 2Y) throughout the 360 degrees in azimuth.
Figure 7 illustrates an optical system which emits light in two, opposite directions. In the regard, two internally- reflective reflectors 20 and 21 of conical form with truncated apices are joined together back to back to form a common throat 22 that accommodates symmetrically a light source 23 having a largely-omnidirectional output. Light is emitted in opposite directions from the two reflectors 20 and 21, the polar diagram applicable for each direction being dictated by the geometry of the respective reflector 20 and 21. Accordingly, the same or different distributions of light can be achieved for the two directions according to whether the cone geometries are the same or different.
An implementation of an optical system using the principle of Figure 7, that provides the same distribution of emitted light in both directions, will now be described with reference to Figures 8 and 9.
Referring to Figures 8 and 9, two identical lamp units 30 and 31, each including a frusto-conical reflector 32 within a transparent, polycarbonate cover or cup 33, are mounted together back to back. The inner surface 34 of each reflector 32 is chromium plated, and a tubular light source 35 (for example a xenon tube) is mounted axially and symmetrically within the common, truncated-apex throat 36 of the two reflectors 32.
A small lens 37 is incorporated centrally of each cup 33 so as to be located on the axis of the respective reflector 32. This compensates for the lack of light emission axially from the tubular source 35 by redistributing some of the light emitted from within reflector 32 so to even it out and avoid a central dark region.
The implementation of optical system described with reference to Figures 8 and 9, may be used with advantage for warning and signal lighting in road and rail applications.
It will be appreciated that the polar-diagram advantages of the use of a conical or pyramidal reflector for emission of light as described above, are correspondingly realisable in relation to reception of light. In the latter case, the light-receptor merely replaces the light-emitter.

Claims

An optical system including a reflector, wherein the reflector has a conical or pyramidal light-reflecting surface, and a light-emitter or -receptor is located in the region of the apex of reflector for, respectively, emitting light onto, or receiving light from, said surface.
An optical system according to Claim 1 wherein the reflector has an internal reflective surface and the light-emitter or -receptor is located within the reflector.
An optical system according to Claim 2 including two axially-aligned conical reflectors that have internal reflective surfaces and truncated apices, wherein the reflectors are retained with their truncated apices forming a common throat, and wherein the light-emitter or -receptor is located within the throat for, respectively, emitting light into, or receiving light from, the reflective surfaces of both reflectors.
An optical system according to Claim 3 wherein the apex angles of the two reflectors are the same as one another.
An optical system according to Claim 3 or Claim 4 for emitting light, wherein an elongate light-emitter is located within the throat to extend axially of the reflectors.
An optical system according to Claim 5 wherein a lens for evening out distribution of light is provided on the axis of each reflector.
An optical system according to Claim 1 wherein the reflector is of conical form having an external reflective surface, and the light-emitter or -receptor is located in the region of the apex externally of the reflector.
An optical system according to Claim 7 including two axially-aligned conical reflectors having external reflective surfaces, wherein the reflectors are retained axially aligned and mutually inverted with the light-emitter or -receptor located between their apices for, respectively, emitting light onto, or receiving light from, both reflectors.
An optical system according to Claim 8 wherein the apex angles of the two reflectors are the same as one another.
An optical system according to Claim 8 or Claim 9 for emitting light, wherein an elongate light-emitter is located between the apices to extend at right angles to the axis of each reflector.
An optical system according to any one of Claims 5, 6 and 10 wherein the light-emitter is a xenon tube.