AN ILLUMINATOR

Abstract: An illuminator is formed as a light pipe (12) having a substantially planar front surface (14) and a faceted back surface (16) comprising a series of angled facets (18) arranged to reflect light towards and through the planar front surface (14), and a light input port (20, 22; 40) through which light is fed into the light pipe (12). The light pipe (12) is looped to define an endless light path and the walls (24, 26) of the looped light path are arranged such that light entering the light pipe (12) travels about the loop such that the loop is illuminated throughout the front surface (14).

Description: AN ILLUMINATOR Field of Invention The invention relates to an illuminator and is of particular advantage for use in illuminating dials and knobs. Background of the invention Faceted light pipes are well known for the illumination and back lighting of liquid crystal displays where a planar surface is back lit by a tapered light pipe having a planar front surface and a faceted back surface. Light is fed into the light pipe and the light travels along the light pipe until it hits a facet whereupon it is reflected towards and through the front surface. The light pipe includes a series of angled facets along its length thus illuminating the whole surface overlying the light pipe. Summary of the invention According to the invention there is provided an illuminator formed as a light pipe having a substantially planar front surface and a faceted back surface comprising a series of angled facets arranged to reflect light towards and through the planar front surface, and a light input port through which light is fed into the light pipe, characterised in that the light pipe is looped to define an endless light path and the walls of the looped light path are arranged such that light entering the light pipe travels about the loop such that the loop is illuminated throughout the front surface. Thus the loop may surround an object which needs to be illuminated rather than having to illuminate a whole surface part of which may lie behind a solid object through which light may not pass. Once light has entered the tapered light pipe, it travels about the light path by total internal reflection so that the energy required to light such a loop is kept low. In order for there to be minimal light losses, the loop is preferably annular or partially annular so that it may be us.ed to illuminate round objects such as dials, knobs etc. This is particularly useful for lighting dials and knobs on an instrument panel of for example a motor vehicle. In the preferred embodiment of the invention, the light pipe is tapered, the rear surface being stepped at each reflective facet such that the distance between the front and rear surfaces of the light pipe decreases with increasing distance from the light input port. Preferably, the illuminator includes two light input ports arranged on diametrically opposite regions of the looped light pipe in order to achieve more even illumination. The light pipe is typically of a clear acrylic or polycarbonate material. Preferably, the light source comprises light emitting diodes. Though it is not essential for the rays entering through the light input ports to be collimated, there may be cases, for example when the light path is long or and the loop diameter is large, when collimated light will help to ensure that the entire loop is illuminated. It is preferred that the light pipe should taper along its length. When two light input ports are provided, the light pipe may taper from a maximum cross-section at one light input port to a minimum at the next light input port. Preferably each light input port comprises a first convex lens arranged such that its principal focus lies substantially at the light source such that rays of light from the light source after passing through the lens are substantially parallel to the principal axis of the first lens, and an auxiliary light collecting device, extending from the periphery of the first .lens, and comprising a plurality of secondary convex lenses, the principal focus of each secondary lens substantially coinciding with the light source and the principal axis of each secondary lens lying at an angle to the principal axis of the first lens, each secondary lens producing collimated light at an angle to the principal axis of the first lens, and for each secondary lens, a reflective surface arranged such that collimated light having passed through the secondary lens is reflected to a direction substantially parallel to the principal axis of the first lens. Typically the depth of the light path is between 1cm and 5cm, and the diameter of the curved loop is up to 20cm. Brief description of the drawings The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view from behind of a light pipe illuminator of the invention; Figure 2 is a section through part of Figure 1; and Figure 3 is a section similar to that of Figure 2 showing an alternative embodiment of the invention. Description of the Preferred Embodiment In Figures 1 and 2, a light pipe illuminator 10 comprises a looped light pipe 12 made up of two tapering sections which together defiled an endless light path. The looped light pipe 12 has a substantially planar front surface 14 and a faceted rear surface 16 comprising a series of angled facets 18 arranged about - A - the loop to reflect light towards and through the planar front surface 14. Each section of the light pipe 12 has a respective light input port 20, 22 through which light is fed from a respective LED 28, 30 into the light pipe 12 substantially along the light path. The side walls 24 and 26 of the light pipe are arranged such that light entering the light pipe 3 undergoes total internal reflection and therefore continues to travel about the loop until reflected by one of the facets 18 to exit through the front face 14, as illustrated in Figure 2. The illustrated illuminator has two light input ports in order to improve the evenness of the illumination. Using a single light input port, the light intensity tends to reduce noticeably with the angular distance from the light input port, whereas two light input ports provide uniform halo lighting. Of course, one can use more that two light input ports but that merely adds unnecessarily to the cost and complexity. The light pipe is preferably made of moulded polycarbonate and includes mounting brackets 32, 34 for the mounting the illuminator 1 about the item to be illuminated. As the light path is part annular, it may be placed over and around a dial or it may be used to illuminate round knobs upon a car radio. In operation, light from the LED's 28, 30 is fed into the light pipe 12 through the two diametrically opposed light input ports 20, 22 and then passes along the light path by total internal reflection until some of the rays impinge upon the facets 18 and are reflected towards and through planar front surface 14 to illuminate the annulus . The light pipe 12 tapers because the facets 18 are arranged in steps which decrease the depth of the light pipe 3 in a direction away from the light input ports 20 and 22. In a practical embodiment in which the illuminator has a diameter of 14.8 cm, the depth of the light pipe 12 may decrease typically from 4 cm to 1.8 cm along half the light path in an anti-clockwise direction, as viewed in Figure 1. In the case of the embodiment of Figures 1 and 2, the light from the LED's 28 and 30 enters the light pipe 12 through a planar surface and is not collimated. As a result, as represented by the light ray designated 36 in Figure 2, light can undergo total internal reflection from the front and rear faces 14 and 16 of the light pipe before impinging on one of the reflecting facets 18. The light input port of the alternative embodiment of the invention shown in Figure 3 differs from the planar light input ports 20 and 22 previously described in two respects. First, the light entering the light pipe is collimated. Second, the light enters the light pipe at right angles to the light path rather than directly along it. This allows the LEDS to be directly mounted on a circuit board to which the illuminator is attached by means of the mounting brackets 32 and 34. In Figure 3, the light input port generally designated 40 has a reflective surface 42 arranged at an angle to the light path defined by the light pipe 12. The surface 42 is arranged to turn the light from a collimator section, generally designated 44, through a right angle, to avoid the need for supporting the LED 56 in the same plane as the light pipe 12. The collimator 44 could be formed as a single lens or as a Fresnel lens but the one illustrated has three lens elements 46, 48 and 50. The light collimated by the lens element 48 passes directly towards the reflective surface 42, while the light collimated by the lens elements 46 and 50 is first reflected by a respective reflective facet 52, 54 before being reflected by the surface 42 into the light pipe.

Claims: CLAIMS 1. An illuminator formed as a light pipe (12) having a substantially planar front surface (14) and a faceted back surface (16) comprising a series of angled facets (18) arranged to reflect light towards and through the planar front surface (14), and a light input port (20, 22; 40) through which light is fed into the light pipe (12), characterised in that the light pipe (12) is looped to define an endless light path and the walls (24, 26) of the looped light path are arranged such that light entering the light pipe (12) travels about the loop such that the loop is illuminated throughout the front surface (14). 2. An illuminator as claimed in claim 1, wherein the light pipe is tapered, the rear surface (16) being stepped at each reflective facet (18) such that the distance between the front (14) and rear (16) surfaces of the light pipe decreases with increasing distance from the light input port (20, 22). 3. An illuminator as claimed in claim 1 or 2, in which the light path is substantially annular. 4. An illuminator as claimed in claim 1, 2 or 3, including two diametrically opposed light input ports (20, 22) . 5. An illuminator as claimed in any one of the preceding claims, in which the light pipe is of clear acrylic or polycarbonate material . 6. An illuminator as claimed in any one of the preceding claims, in which the light source comprises at least one light emitting diode (28, 30; 56). 7. An illuminator as claimed in any preceding claim, in which each light input port (40) includes means for collimating the light entering the light pipe (12) . 8. An illuminator as claimed in any preceding claim, wherein each input port includes a reflective surface (42) for enabling a light source (56) supplying light to the light input port (40) to be mounted in a plane different from that of the light pipe (12) .

Inventors: BIJLHOT JOEP, LEPLEY GEOFFREY PETER, BIJLHOT, JOEP, LEPLEY, GEOFFREY, PETER
Applicants: BIJLHOT JOEP, FORD GLOBAL TECH INC, LEPLEY GEOFFREY PETER, BIJLHOT, JOEP, FORD GLOBAL TECHNOLOGIES, INC., LEPLEY, GEOFFREY, PETER
Application year: 1998
Main classification: F21V8
IPC codes: E05B1, F21V8, F21Y101, G02B6