GB2136186A

GB2136186A - Illumination equipment for a transmissively-operable passive display

Info

Publication number: GB2136186A
Application number: GB08401724A
Authority: GB
Inventors: Dr Rolf A Cremers; Manfred Barth
Original assignee: Borg Instruments AG
Current assignee: Borg Instruments AG
Priority date: 1983-01-22
Filing date: 1984-01-23
Publication date: 1984-09-12
Also published as: GB8401724D0; DE3302156A1; DE3302156C2; IT8419210A0; IT8420564V0; FR2539900A3; FR2539900B3; IT8420563V0; IT1173061B; GB2136186B

Abstract

Illumination equipment (3), more particularly for a colour liquid crystal display for the instrument-panel of motor vehicles, enables a transition between different light colours according to the ambient light conditions. A housing (1) is sub-divided by a colour-filter partition (17) and includes a display (3) that is to be transirradiated. The surfaces of the housing walls (11), situated about the display aperture (2), and partitions (17) are aselectively diffusely-reflecting in design, for example by the application of a white coating. The opposite surface of the transparent partition (17) bears a coloured coating (18), possibly with regional grading of its light transmittancy. The light penetrating through the partition (17) is coloured as a result of the coating and mixes with the light, generated directly behind the display aperture (2), into an extremely uniform, diffuse background illumination, the colour mixture or colour intensity and brightness of which is adjustable by the control of the light sources (5, 6) which may be switched on alternatively or simultaneously. A plurality of housings 1 and/or plurality of partitions 17 may be provided when different colours are to be selected e.g. by the display control circuitry and specific regions of the display are to be selectively irradiated by reason of different information content. <IMAGE>

Description

SPECIFICATION Illumination equipment for a transmissivelyoperable passive display This invention relates to illumination equipment for a transmissively-operable passive display, more particularly but not exclusively a colourrepresenting liquid crystal display.

Illumination equipment of this kind is shown in German Offenlegungsschrift No. 21 60611.

Individual light sources are arranged laterally beyond or behind the display between light shades in such a way that a lateral light incidence falls from behind the display.

However, a low illumination efficiency tends to result and also relatively large dimensions are required for the wall of the light-source housing on which the display is arranged.

For a change of illuminating colour, individual light sources of different light colouration are provided and these can be operated alternately or in overlapping manner. However, from the positioning of these differently-coloured light sources there results a shift of the brightness distribution over the display on transition from one illumination colour to the other; this can be a considerable hindrance to a simple visual and easy comprehension of the precise display content when viewing in unfavourable ambient light conditions.

Uniformity of brightness distribution and transition possibilities between differentlycoloured presentations of the background illumination achieved with known illumination equipment tends not to satisfy increased demands, such as encountered more particularly in the case of vehicle dash-board instrumentation, where extremely fluctuating ambient light conditions can occur.

An object of the present invention is to provide illumination equipment, for a transmissivelyoperable passive display, of a relatively simple construction which may yield a very homogeneous background illumination over all of the required display surface whilst maintaining the possibility of a colour change of this homogeneous background illumination.

According to the present invention there is provided illumination equipment for a transmissively operable passive display, for example a liquid crystal display, comprising at least two light sources for coloured background illumination of the display from behind the display for coloured information representation, said at least two light sources being arranged in a housing behind an aperture provided for the reception of a display and being adjacent to reflecting parts of the housing, and the reflecting housing parts being inner walls of the housing which reflect light in a colour-neutral diffuse manner, at least one of said at least two light sources being separated or partitioned off relative to at least the other of said at least two light sources and from said aperture by a light-filter partition which, on its surface towards the display aperture is designed so as to be colour-neutral diffusely-reflecting and is equipped on its opposite surface with a coloured coating or covering.

Further according to the present invention there is provided apparatus or device for illuminating a display, for example a liquid crystal display, comprising a housing having an aperture through which, in use, illuminating light is capable of being passed onto the display from at least two light sources, said at least two light sources in use being separated off from one another in the housing by a light-filter partition of the apparatus or device, said partition being in between said aperture and a compartment in the housing which in use receives one of said at least two light sources, the walls of the housing being light reflective, and the arrangement being such that, in a selected manner in use, light rays can travel from the light source in said compartment through the partition which imparts a colour to said light rays which are then transmitted through said aperture onto the display to illuminate the display in a particular colour mode in unfavourable ambient light conditions and/or light rays can travel from the other of said at least two light sources through said aperture without travelling through said partition.

In the present invention, use is made of the fact that an illumination, particularly uniform in area, of a transflector (light-filter partition) may result when the light source is arranged behind the transflector in a housing with diffusely-reflecting walls, Depending upon which side of the transflector partition (colour-coated on one side) that the light source is now switched on, a background illumination of the display in difference colouration results.Nevertheless, due to the colour-neutral diffuse reflections on the inner walls of the housing as well as on that side of the partition which is towards the display (even in the presence of several sources of light) a homogeneous diffuse irradiation of the reverse side of the display over the entire area thereof still results without disturbing opposite colour influences, and there is still such a homogeneous diffuse irradiation even when a change over is made continuously from the colour on one side of the light-filtering partition to the colour on the other side thereof and in so doing there is mixed-coloured light operation. In this way, a seemingly optimum adaptation of the intensity and colour of the display background illumination (i.e. the contrast of the information representation of the display) with respect to the observer's ambient light conditions is possible.

Further developments and alternatives with further advantages will become apparent from the sub-claims. Advantageously use is more particularly made of the possibility of designing the partition with regionally different light transmittancy, in order in this way to deliberately compensate for higher light densities by reason of closer distances of some display regions to a source of light than other regions.

An embodiment of illumination equipment for a transmissively-operable passive display in accordance with the present invention will now be described by way of example only, with reference to the accompanying simplified drawings (not shown true to scale), in which: FIGURE I shows the illumination equipment in longitudinal section with the display arranged in front of a display aperture, and FIGURE 2 is a sectional plan view taken on line Il-Il of the illumination equipment shown in FIGURE 1.

The illumination equipment sketched in vertical cross-section in FIGURE 1 consists generally of a housing 1 with an aperture 2, in front of which is arranged a passive display 3 (preferably a liquid crystal display) that is to be operated transmissively. Arranged behind the display 3 (related to the direction of sight 4 thereof) in the housing 1 are at least two light sources 5, 6 preferably, as shown, in the form of electric light bulbs which project through a rearward housing lid 7 and are releasably fastened thereto by means of bulb holders 8. A circuit board 13 having a printed circuit surrounds a housing part 9 at the transition from upper and lower side walls 11, which part 9 extends inclined to the housing axis 10.A spigot 12 of the housing projects through the circuit board 13 and retaining pins 14 mounted on board 13 hold a blind diaphragm frame 1 5 (Blendrahmen) in front of the housing aperture 2 and in front of the display 3. The electrical connection between the circuit board 1 3 and the electrodes of the display 3 is effected by way of rubberized contact bridges 1 6.

The walls of the housing 1 are of metal or plastics material. Towards the interior of the housing 1 and situated behind the display aperture 2, the side walls 11 have an optically seiectively diffusely-reflecting effect, from example from the application of a matt white coating or from overlaying with a correspondingly acting white covering.

At least one light source 6 in the housing 1 is spaced from the aperture 2 and a light filter in the form of a transparent partition 1 7 is interposed between the aperture, at least from one other light source 5 in the housing 1. The light filter 1 7 - as a result of its choice of material, coating or covering -- has a white surface inclined towards the display aperture 2 and is thus also aselectively diffusely-reflecting in design; whereas its opposite surface, which is inclined towards the separated-off region of the housing 1, is equipped with a coloured covering or coating 18.The partition 1 7 is held between retaining ribs 1 9 on a side wall 11 and on the rearward lid 7 in such a way that a smaller volume (compartment) of the housing 1 is separated-off by the partition 1 7 for the first-mentioned light source 6 than for the housing part (compartment) having the (stronger) light source 5 and having the display aperture 2.

In daytime operation of the display 3, the information shown on the display (for instance by segmented symbol formation) must not be outshone or obscured by ambient brightness which falls in the direction of sight 4 onto the display 3. Therefore, in daytime operation of this transmissively-operating display 3 a light source 5 of very high intensity is to be provided behind the display, in other words in the housing 1. Light from source 5 is diffusely reflected (scattered) at the white or aselectively diffusely-reflecting surfaces (namely more particularly at the lower side wall 11 and at the partition 17) in order to emerge contrary to the direction of sight 4 through the aperture 2.If, in this part of the housing 1, several such light sources 5 are arranged, a light distribution follows as a result of superposition of its radiation constituents of all the diffuse (scattered) wall reflections; this leads to a uniform transillumination of the surface in question of the display 3 despite the presence of individual (more or less punctiform) light sources 5.

In dark ambient conditions an irradiation of the display 3 in a differing shade, for example redorange or yellow-green, is desired to represent display information, in order to compensate for sensitivity losses of the eye through such shadeoccasioned contrast changes. Moreover, a lower luminosity behind the display 3 is necessary.

Therefore, now, in such dark conditions, the other light source 6 is switched on. This light source 6 may be arranged in the smaller volume of the housing 1 because it consequently yields lower heat radiation losses. The light beams emanating from this smaller chamber (compartment) filtered by the partition 1 7 on the way to the display aperture 2 will have passed through the coloured coating 18 of the transparent partition 1 7 and appear, as light which is coloured in accordance with the coating 18, in the region of the space behind the display aperture 2. Light reflected at the coating 18 is reflected in a colour-neutral manner by the adjacent side wall 11 back towards partition 17 and also finally yields a contribution to the coloured transmission of the display 3 contrary to the direction of sight 4.

Similarly, those constituents of light which are coloured by the partition 1 7 and which do not directly reach the region of the display aperture 2 but are diffusely-reflected in a colour-neutral manner at the opposite side wall 11 also yield a contribution to the coloured display transmission.

Thus, there results an extremely homogeneous (now coloured) background illumination for the information representation by means of the display 3 by means of the light source 6. Light source 6 operates in principle in the same way (and more particularly does not have to be equipped with a coloured dome) as the daytime light source 5.

Additionally, it is of particular advantage with this arrangement that while using white light in accordance with operation with the daytime light source 5, by connecting up and controlling the brightness of further light source or sources 6 which is/are separated off by the light-filter partition 17, the optional transition between the colour tones is made possible; the individual sources of the mixed-colour background illumination do not mutually affect one another, but, as a result of the aselective wall reflections, yield an extremely homogeneous mixed colour behind the display 3. Thus, by simple intensity control of the light sources 5, 6, a smooth transition between background illumination upon operation is possible without information parts on the display 3 being shown with a different colour tone to other information parts.If, on the other hand, specific regions of the display 3 are to be transirradiated rather than other regions, by reason of different information content, then appropriate housings 1 can be provided appropriately by being distributed behind a largearea display 3; the housings 1 may be side-by-side or arranged within one another (not taken into consideration in the drawings). Also, depending upon the requirements for light source 6, further compartments or chambers may be defined inside the housing 1 by additional transparent colourfilter partitions having coatings of different colours as compared with the daytime light source 6, in order, depending on the given factors, to be able to select different night illumination colours or to be able to set mixed colours from several colour components.Also, the different colours can, depending on the information instantaneously displayed, be controlled by the same data processing equipment which brings about the information representation (by way of the segment-selecting control of the display 3).

In the sectional plan-view shown in FIGURE 2 account has been taken of the fact that, depending on geometrical factors behind the display aperture 2, it can be advantageous to vary the intensity and thus the darkening or shading effect of the coating 1 8 over different regions of the transparent partition 1 7 due to the different distances of the regions of the partition 1 7 from the display 3.In this way, for example, the coloured light component of the night light source 6 is prevented from becoming stronger at the upper region of the display 3 because of the closer distance of the upper display region to the partition 1 7 than the lower region; namely because the transparency (translucency) of the partition 1 7 is reduced by thicker application of the coating 1 8 (shown by the smaller distance of the lines, extending in rayshaped form, in FIGURE 2). Moreover, instead of a thicker coating in various regions of the piate or additionally to such thicker coating, an imprinted.

grating (network of lines) 20 of light-absorbing colour (for example black) may be provided; this yields stronger transmitted radiation through the coloured partition 1 7 in the rearward region of the housing 1 and thus aids homogeneous light mixing behind the display aperture 2.

Claims

1. Illumination equipment for a transmissively operable passive display, for example a liquid crystal display, comprising at least two light sources for coloured background illumination of the display from behind the display for coloured information representation, said at least two light sources being arranged in a housing behind an aperture provided for the reception of a display and being adjacent to reflecting parts of the housing, and the reflecting housing parts being inner walls of the housing which reflect light in a colour neutral diffuse manner, at least one of said at least two light sources being separated or partitioned off relative to at least the other of said at least two light sources and from said aperture by a light filter partition which, on its surface towards the display aperture is designed so as to be colour neutral diffusely-reflecting and is equipped on its opposite surface with a coloured coating or covering.

2. Illumination equipment as claimed in Claim 1 in which the coating or covering on the partition is designed with regionally-different light transmittancy.

3. Illumination equipment as claimed in Claim 2 in which the coloured coating or covering on the partition provides a regionally-different light absorbing intensity.

4. Illumination equipment as claimed in Claim 2 or Claim 3 in which the partition is equipped with a grating made of a light-absorbing material having regionally different line density.

5. Illumination equipment as claimed in one of the preceding claims, characterised in that by way of the partition compartments of different volume are defined inside the housing, the display aperture and one of said at least two light sources (the daytime-operative light source of greatest light density) being situated in the compartment of greatest volume.

6. Illumination equipment as claimed in one of the preceding claims, in which more than two light sources are provided and a plurality of light-filter partitions are arranged in the housing.

7. Illumination equipment as claimed in one of the preceding claims, in which behind a part of the said aperture a further similar piece of illumination equipment of smaller dimension is arranged in said housing.

8. Apparatus or device for illuminating a display, for example a liquid crystal display, comprising a housing having an aperture through which, in use, illuminating light is capable of being passed onto the display from at least two light sources, said at least two light sources in use being separated off from one another in the housing by a light-filter partition of the apparatus or device, said partition being in between said aperture and a compartment in the housing which in use receives one of said at least two light sources, the walls of the housing being light reflective, and the arrangement being such that, in a selected manner in use, light rays can travel from the light source in said compartment through the partition which imparts a colour to said light rays which are then transmitted through said aperture onto the display to illuminate the display in a particular colour mode in unfavourable ambient light conditions and/or light rays can travel from the other of said at least two light sources through said aperture without travelling through said partition.

9. Apparatus or device as claimed in Claim 8 in which different regions of the partition are graded in light transmittancy.

1 0. The combination of at least one passive display and one or more pieces of apparatus or devices as claimed in Claim 8 or Claim 9.

1 1. The combination as claimed in Claim 10 in which there is a plurality pieces of apparatus or devices as claimed in Claim 8 or Claim 9 which are arranged in parallel behind the display.

12. The combination as claimed in Claim 10 in which there is a plurality of pieces of apparatus or devices as claimed in Claim 8 or Claim 9 which are arranged within one another.

13. Illumination equipment, apparatus or device for a transmissively operable passive display substantially as herein described and illustrated with reference to the accompanying drawings.

14. The combination of illumination equipment, apparatus or device as claimed in Claim 13 and a liquid crystal display.