GB2154741A - Illumination device - Google Patents

Abstract

An instrument illumination device includes a wedge plate (5) for directing light (7) onto an instrument display (not shown) and arranged to be illuminated through a bevelled edge (8) from lamps (2) through a filter (6). The illumination plate may be arranged for use in conjunction with night goggles having a restricted range of light wavelengths over which they are operable, and then the filter may be arranged to pass light outside that restricted range of wavelengths. <IMAGE>

Description

SPECIFICATION Illumination device This invention relates to an illumination device, for example, for illuminating the dial of an instrument in a vehicle and one object is to provide means for illuminating a cockpit instrument so that the normal function of night vision goggles to monitor the "outside world" is unrestricted and so that the instrument may be easily observed.

It is often necessary to wear night vision goggles if the driver of a vehicle is to be able to see his surroundings through a windscreen or the equivalent, and that can cause difficulty if he also wants to look at the vehicle's instruments without taking off the goggles.

One type of goggles allows the driver to view the instrument directly through a gap between the goggles eyepiece and the driver's face while another, less common type, is bifocal and allows both the outside world and the instrument panel to be focused through the goggles by the driver. The invention is particularly concerned with the first-mentioned type, and with such goggles it is necessary to provide means for illuminating such objects as an internal vehicle instrument without render ing the goggles useless for external viewing.

According to the present invention, an instrument illumination device includes a wedge plate and means for illuminating its interior through a light filter, the plate having one face through which light from the interior can illuminate an instrument, and a second face through which (and the one face) the illumi nated instrument can be viewed.

The device may include a housing for the wedge plate, and one or more lamps constituting the illuminating means can be mounted in the housing, and arranged to project light substantially only into the wedge plate through its wide edge.

Then the light filter can be positioned so that only light which has passed the filter can enter the wedge plate for illuminating the instrument and for subsequent viewing of the instrument.

Night vision goggles tend to have a restricted range of light wavelengths over which they are operable, and if they receive light inside that range, "overloading" will occur in the goggles so that they cannot be readily used for viewing the dark surroundings of the vehicle.

If the filter is chosen to have a pass band outside the range of wavelengths to which the goggles are operable, then the light from the instrument will only be in that wavelength range so that the goggles will tend not to be overloaded and will be immediately useful when the user turns away from reading an instrument through the wedge plate to view ing the outside directly through the goggles.

Light entering the wedge plate through its edge passes throughout the plate to and fro by total internal reflection and light which strikes the inner face of the wedge plate at an angle of incidence below a critical angle leaves the plate for illuminating the instrument while other light eventually leaves the wedge plate through the edge.

The wedge plate may have a bevelled edge at the wider end where the light enters.

It will be appreciated that the illumination device may be an integral assembly for fitting over an existing instrument or may be built integrally with the instrument.

It may be necessary to have a fibre optics face plate or the equivalent for collecting spurious light from the housing and front face or edges of the wedge plate.

A light reflector may be included adjacent the edge of the wedge opposite the light source for reflecting spurious light to the instrument.

The invention may be carried into practice in various ways, and one embodiment will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is an elevation of an instrument illumination plate in accordance with the invention, Figure 2 is a section on the line X-X in Fig.

1 to an increased scale; Figure 3 is a section of the line Y-Y in Fig.

1; Figure 4 is a detail of Fig. 3 to an increased scale; and Figure 5 is a rear view corresponding to Fig. 1 of a modified plate with a lamp and filter block and cutouts for instrument control knobs removed or clarity.

The figures show a lighting plate which is for illuminating the face of an instrument at night, and the plate may be supplied separately and fitted over an existing instrument or may be built into the instrument during manufacture to form its front face.

It is necessary to have an illumination system which enables the instrument face to be viewed through the plate by an observer wearing night vision goggles by direct view through the goggles, without interfering with the operation of the goggles.

The plate is built up from an external opaque mounting ring 1 having a central circular opening for a wedge glass 5 seated in a rebate in the edge of the ring 1.

The wedge plate is illuminated at its thicker edge by means of a pair of sets of tungsten filament lamps 2 giving white light through a filter 6 which may be an absorption filter such as Schott BG7 or a VG14 filter, or an interference type filter. The filter passes from the white light substantially only light outside the sensitivity frequency range of the night goggles. The sensitive range is about 400-900 nanometers wavelength for S20 Litton XT0123 goggles and is about 600-900 nanometers from Anvis-Gen 3 goggles, and clearly the particular filter used will be chosen in accordance with the particular goggles used, the spectral characteristics of the filter used to limit the sensitivity of the goggles, the particular characteristics of the lamps 2, and possibly the nature of the reflecting front face of the instrument with which the panel is to be used.By filtering out light inside the sensitivity range of the night goggles "overload" of the goggles can be avoided so that the goggles will still respond to external ambient light when they are not directly towards the instrument.

Light from the wedge glass 5 is directed generally in the direction of the arrow 7 towards the face of the instrument, and from there it is reflected back through the wedge glass for direct viewing by the viewer wearing the night goggles.

The shape of the wedge in the view shown in Fig. 1, will of course be tailored to the particular instrument with which it is to be used, and the top face is at an angle between 2 and 44 to the bottom face which is parallel to the face of the instrument. The thick edge of the wedge is somewhat bevelled as shown in Fig. 2 at 8, and is a ground surface to spread the illumination through the wedge. All parts of the edge other than the bevelled part 8 are painted white. Although a wedge "glass" is referred to, the wedge could be of a clear plastics material. In either case, the front and rear faces will be coated with an anti-reflection coating to prevent glare occurring by reflection of light from external sources.

Light is totally internally reflected from the bottom and top faces of the wedge glass, but eventually escapes either generally in the direction of the instrument as shown by arrow 7, or through the edge of the wedge glass.

In general light is transmitted through the bottom face when it strikes that face at an angle of incidence less than 41.8e.

The wedge glass 5 is seated between inner and outer rings 3 and 4 in the rebate in the mounting ring 1, and they define a bezel for the wedge glass. Internal surfaces are blackened matt black as shown at 9 in Fig. 4, except adjacent the bevelled edge 8 of the wedge. That part is whitened to reflect stray light into the bezel. The rings are sealed in position by a cement as indicated at 10. The bezel overlaps-the edge of the wedge enough to mask the bright line created at the edge of the wedge from the observer's view, as shown at 3 in Fig. 5.

The lamps 2 are mounted each in its own fitting 11 in a hole in the mounting ring 1, and covered by a cap 1 2. Electrical connections to a power supply indicated generally in Fig. 1 are connected to the terminals of each lamp, one, 14, on the fitting 11, and the other, 15, in the cap 1 2. Power is fed to the bezel through the connector 1 8 in Fig. 5.

It is important that the plate does not produce any spurious light externally which has not been reflected from the face of the instrument, because such spurious light may be reflected off other surfaces and upset the operation of the goggles or may be a source of radiation which can be picked up externally.

The arrangement of the lamps in the plate and the blackening of all internal surfaces other than the entry to the wedge glass tend to reduce the possibility of such spurious light appearing. Further, a slanted louvered filter can be placed over the front face of the wedge to absorb stray light that might otherwise be emitted from the front of the wedge.

A fibre optics face plate may be used instead of the louvered filter for the same purpose.

The brightness of the lower part of the instrument can be further increased by incorporating a reflector into the bezel as shown at 19 in Fig. 5 and 22 in Fig. 1. This is particularly useful for instruments with spherical displays such as an altitude and direction indicator.

It is to be noted that the filter 6 is between each lamp and the wedge glass 5 so that it is only light at wavelengths outside the range of the goggles that enters the wedge glass, or indeed can escape from the fittings 11 and caps 12.

If part of the instrument requires more illumination, when for instance the instrument display surface is spherical and as a result the lower part is not adequately illuminated, then spurious light can be reflected back into the display by placing a suitable reflector adjacent to the edge of the wedge and opposite the light sources. Such an optional reflector can, as shown at 21 in Fig. 4, be strip white vinyl tape instead of the matt black 9 around the part of the curved inner surface of the ring 3 opposite the lamps 2 and filters 6. That can be associated with a baffle plate 22, indicated in part in Figs. 1 and 4, and painted matt black on its outer surface, and matt white on the inner face.

Subsequently the illumination on any predetermined part of the display can be increased.

Claims (10)

1. An instrument illumination device including a wedge plate and means for illuminating its interior through a light filter, the plate having one face through which light from the interior can illuminate an instrument, and a second face through which (and the one face) the illuminated instrument can be viewed.

2. A device as claimed in Claim 1 including a housing for the wedge plate and one or more lamps constituting the illuminating means and mounted in the housing and arranged to project light substantially only into the wedge plate through its wide edge.

3. A device as claimed in Claim 2 in which the light filter is positioned so that only light which has passed the filter can enter the wedge plate for illuminating the instrument.

4. A device as claimed in any of the preceding claims in which the wedge plate has a bevelled edge at the wider end where the light enters.

5. A device as claimed in any of the preceding claims including means for collecting spurious light from the housing and front face or edges of the wedge plate.

6. A device as claimed in any of the preceding claims including a light reflector included adjacent the edge of the wedge plate opposite the light source for reflecting spurious light to the instrument.

7. An instrument illumination device constructed and arranged substantially as herein specifically described with reference to the accompanying drawings.

8. An instrument illumination device as claimed in any of the preceding claims and forming an integral part of the face of an instrument.

9. An instrument illumination device as claimed in any of claims 1 to 8 adapted to be fitted over the face of an instrument.

10. An instrument illumination device as claimed in any of the preceding claims in combination with night goggles having a restricted range of light wavelengths over which they are operable, and in which the filter is arranged to pass light outside that restricted range.