GB2135806A - Illumination equipment for a passive display - Google Patents

Abstract

Illumination equipment fore display (1), e.g. a LCD display (1), with an artificial-light source (7) provides that in addition to the light incidence from the ambient brightness in the direction of sight (2), light (15) can be radiated from the light source (7) into the display without thereby impairing the perceptibility of the information presented with respect to the observation visual angle or with respect to display contrast. For this, the display (1) is fixed (in the direction of sight (2)) behind a plane-parallel reflector plate (4), into which additional light (15) is introduced by means of deflecting angle pieces (5), offset laterally thereto, at such an angle that total reflection occurs at the outer surface (17) and in this way light (15) radiates without further refraction into the display (1). This light introduction from two opposite sides (8) of the display (1) yields upon rearward connection of the limbs (13) of the deflecting angle pieces (5) by means of a light distributor (6) a tubular construction. The illumination equipment (2) is suitable for displays with unfavourable ambient light conditions, e.g., dash-board of a motor vehicle. <IMAGE>

Description

SPECIFICATION Illumination equipment for a reflectively-operated passive display This invention relates to illumination equipment for a reflectively-operated passive display, more particularly a liquid crystal display, with an artificial light source.

It is known that passive displays can be operated reflectively, transmissively or transflectively (a combination of both transmission and reflection). In the case of transmissively operated displays, the region behind the display in the direction of sight (sight line) thereof is illuminated. In regions of the display which are switched on in a light-transmissive manner in order to present information, the observer thus sees the background light. Therefore, in this respect transmissive displays are particularly suitable for representing information in dark surroundings.Usually, however, it tends to be a problem that light from the surroundings of the observer also falls in the direction of sight onto the display and thereby outshines or obscures information represented on the display i.e. the contrast of the information represented against the background light is lessened and thus visibility or comprehension of the information being represented is also reduced. Basically, such adverse effects could be compensated for by the background brightness being increased; however, such a solution is not entirely practical because of the energy requirements of the system and also because of, more particularly with small-size display systems, heat radiation due to energy losses of the light source.

Therefore, in practice a transflective display has greater importance than a purely transmissive display. in transflective displays a partial light-transmissive mirror (transflector) is arranged between the display and the background light source. The display is operated transmissively by means of the background illumination and at the same time reflectively by means of the ambient brightness radiating in the direction of sight. Of course, the brightness of the transmissive operation is reduced as a result of the losses in the transflector that is to be irradiated, and similarly the transflector is prone to losses not incurred with purely reflective operation because it is a non-ideal mirror. Therefore, this 'mixed' operation yields poorer contrast than purely transmissive or purely reflective operation.Additionally, in the case of this mixed operation, optimisation of properties in the direction of purely transmissive or purely reflective operation is not possible because in the case of the transmissive operation, the optically blocked regions of the display are (because of the choice of high-blocking polarisation foils) supposed to be as impervious to light as possible, whilst the same polarisation foils, in the case of the relective operation reduce the reflective background light too severely by the double light passage through the display cell. The compromise of a transflective operation thus necessarily yields passive displays with only moderate contrast as compared with the one or other pure mode of operation because opposing modes of functioning are superimposed on one another.

A special kind of transmissive display is the so-called FLAD in which ambient light is collected in a body made from fluorescence-activatable light-conducting material (phosphorescent material). In accordance with the information to be represented light exit areas are provided on the surface of this material. in front of the light exit areas is arranged a purely transmissively working cell acting as a regionally controllable light valve. However, the replacement of the active light source behind the display by a body for collecting ambient light necessitates comparatively large dimensions in order to achieve a sufficiently high background brightness for the transmissive operation.Also, in order to ensure sufficient light radiation from the surroundings, open mounting of the light collecting body is necessary; installation into closed equipment or even only behind blind or diaphragm frames (light screen frame) such as for instance motor vehicle dash-boards is not feasible.

Passive displays of the kind in which stretched colour molecules as guest material are introduced or embedded into the material of a liquid-crystal field-effect cell as host material (so-called dichroic LCDs) will become of particular importance in the future. Indeed the low contrast of this kind of display can be improved by increasing the concentration of said colouring matter in the cell. Of course, as a result of such an increase in dye or colour concentration, the uniformity or stability (durability) of the material mixture, more particularly at low ambient temperatures as well as the electro-optical switch-over time constant are adversely affected. Therefore, under the limiting conditions of practical instances of use, the absorption properties of such a guest/host cell do not absolutely satisfy the requirements of a transmissively operated display.On the other hand, in the case of a reflectively operated display, a double light passage through the cell and thus doubled absorption leads to correspondingly increased contrast between regions of the display which are illuminated (energised) for the information representation and regions which are not illuminated (energised). Thus, for passive displays with a guest/host cell (which displays are becoming increasingly more interesting with respect to colour representation possibilities and also with respect to other factors, such as large permissible viewing angle) pure reflective operation is of particular practical interest, insofar as it succeeds in ensuring adequate display contrast under all lighting conditions such as bright daylight, twilight, and even total darkness.This is because, contrary to the factors in the case of transflective operation the mode of operation of the cell does not change. The passive display cell can thus appear to be optimised for a single (namely the reflective) mode of operation.

In recognition of these factors, an object of the present invention is to provide illumination equipment which allows ambient brightness to fall in the direction or line of sight onto the display, and additionally allows if necessary, depending on the ambient factors, artificial light to be introduced from a light source without such introduction markedly impairing the visibility of the displayed information with respect to contrast, angle dependence and parallax.

According to the present invention there is provided illumination equipment for a reflectively operated passive display, for example a liquid crystal display, which equipment is to receive artificial-light light source, the light of which is, in use, conductable through a frame of the equipment comprising or including a part of generally L-shaped cross-section made from light-conducting material; one limb of said L-shaped cross section is a light-reflective plate and an outer surface or boundary of said plate is to face the direction of sight, in use, whilst an inner surface or boundary of said plate is for fastening the display thereto; the other limb of said L-shaped cross section is connected or joined by way of a deflecting angle piece to the plate and in the transitional region between the deflecting angle piece and the plate a deflecting surface of said angle piece is inclined relative to the plate outer surface or boundary so that, in use, light travelling from the deflecting angle piece incident on the plate strikes the plate outer surface or boundary at a smaller light incidence angle than the critical or limiting angle for total reflection and is reflected into the display, the outer surface or boundary extends, in use, in a plane parallel to the display and is connected or joined at one end edge to the deflecting angle piece and the other limb of the frame is laterally offset from the plate.

By the present invention, a mechanically-stable small-size illumination device adaptable to the ambient brightness may be provided, which device can also be incorporated into equipment which is shielded (against ambient light) for additional illumination of a purely reflectively operable display. The cell structure of the display is disposed directly, namely without an optically effective boundary layer, behind a plate which is plane-parallel and flat in design. Therefore, the plate is not excessively bulky with respect to the overall volume of the illumination equipment and does not adversely affect the angle dependency of the information representation. The ambient light can pass through this plate unhindered in the direction of sight towards the display.Since the plate is of crystal-clear material, there is no occurrence of either a weakening of the illumination of the display with ambient light or of impairment of the contrast of the information represented on the display. On the other hand, by way of this plate, and by way of light beams laterally adjacent to the display, additional light can be radiated into the display from a separate artificial light source if the ambient light should no longer be adequate for the illumination of the display or, for example, in order to compensate for reduced contrast as a result of diffuse illumination in the evening twilight, when an illumination of the display with a specific colour tone is desirable.In this respect, this plate is dimensioned in such a way that, as a result of the mathematical interrelationships of total reflection, light supplied from regions laterally adjacent to the display does not exit contrary to the direction of sight from the plate (in other words does not lead to a reduction in contrast as a result of glare effects). The enlargement, afforded by this plate, of the effective dimensions of the display in the direction of sight is, within certain constructional limits, variable by lateral displacement of the light entering into this plate away from the adjacent edge of the display.

Advantageously the configuration of the illumination equipment is selected in such a way that the additional light intensity of the artificial light source is conducted laterally around the display to the plate. In this way, the light source can be arranged behind the display, whereby a comparatively compact construction emerges.

For uniform distribution of the additional illumination over the plate and more particularly for its parallax-free radiation into the display, advantageously a light feed is provided at two opposite boundaries of the display and preferably along its two longitudinal edges. Bringing together of the deflecting angle pieces, serving for this light feed, at the location of the light source behind the display yields in this respect a stable frame-shaped or tubular construction; the sensitive display itself (for example the liquid crystal cell) is secured in a well-protected manner in the interior thereof by an inner wall of the illumination equipment.

Still further according to the present invention there is provided apparatus or device for illuminating a reflectively operated passive display, for example a liquid crystal display, said apparatus or device comprising or including a frame of generally L-shaped cross section, one limb of the frame being a "transflector" plate (i.e. a plate which allows light through from one side thereof - namely the side facing the line of sight direction in use of the display - and reflects light travelling towards the plate from the other side) defining an outer boundary and an inner bondary, the inner boundary being for fixing said passive display thereto, the other limb of the frame being joined to the transflector plate by the interpolation of an individual angle piece, said angle piece presenting an outer boundary which is inclined to the plate, one edge of the plate adjoining a first face of the angle piece and a second face of the angle piece adjoining an edge of said other limb, said other limb being laterally offset from said plate and said inclined outer boundary being defined by a third face of the angle piece, the arrangement being such that, in use, the outer boundary of the plate is parallel to the plane of the display and light from an artificial light source is capable of travelling along the said other limb into the angle piece where it is totally internally reflected by said outer boundary of the angle piece towards said outer boundary of the plate where it is reflected onto the display, and ambient light is capable of being transmitted through the plate along the line of sight of the display.

Still further according to the present invention there is provided apparatus or device for illuminating a reflectively operated passive display, for example a liquid crystal display, said apparatus or device providing, in use, a generally closed frame around the display, which frame is for directing light from an artificial light source, arranged, in use, behind the display but shielded directly therefrom, around the sides of the display onto an outer boundary of a transflector plate of the frame, which plate is in a plane parallel to the display, said directed light being totally reflected at said outer boundary onto the display while ambient light can travel through the plate onto the display.

An embodiment of illumination in accordance with the present example will now be described, by way of example only, with reference to the following much simplified schematic drawings (shown not true to scale) in which: Figure 1 shows, in cross-section, a complete piece of illumination equipment with a display installed therein and a schematically indicated arrangement of an artificial light source in the region behind the display; Figure 2 shows a rear view of the illumination equipment in accordance with Figure 1; and Figure 3 shows a plan view of the illumination equipment in accordance with Figure 1.

The display 1 shown in chain-dotted lines and in cross-section in Figure lisa reflectively operated liquid crystal display, more particularly having a dichroic cell. Such a display is built up in the usual way (not shown in more detail in the drawings) from two transparent panes, between which a thin layer of liquid-crystalline host (receiving) material is enclosed and into which host material a guest material having stretched colourizing molecules is introduced.In accordance with the pattern of electrodes on the panes and of electrical fields between these electrodes, the thin layer of liquid-crystalline material is influenced in such a way that light incident in the direction of sight 2 is reflected behind ("behind" looking in the direction of sight) the rearward pane of the display cell and thus displays, in accordance with the control of the electrodes, for example, alphanumerical information.

Where light is incident in the direction of sight 2 which is to be reflected behind the display 1 the ambient light will be sufficient to illuminate the display but where the ambient conditions are unfavourable or, in the event of a colour representation of the information displayed differing from that with ambient light an artificial illumination of the display 1 in the direction of sight 2 can also be provided.

For an additional illumination of this kind, the display 1 is incorporated into a piece of illumination equipment 3. This consists of a material which has good light conducting properties and good processing possibilities; the material is preferably acrylic glass.

With the illumination equipment 3, three functioning groups or portions 4to 6 can be distinguished from one another; there is a flat reflector plate 4 (it is bounded by surfaces which are parallel to one another transversely to the direction of sight) which is adjoined on (at least) one side by a deflecting angle piece 5 to form an L-shaped frame with limbs 13, to which by way of a beam splitter or light distributor 6 a light source 7 is optically coupled. Each member of these function groups can be composed for reasons of production technique (as indicated in the cross-sectional representation of Figure 1) of several separate parts of simple geometrical construction; the parts may be bonded together by means of a colourless adhesive (of same refractive index as the material) in a manner so that the product is free from air bubbles.The adhesive may, for example, be that commercially available under the name "Acrifix 90". All the surfaces of said parts are highly polished.

Advantageously, in the interests of maintaining a uniform and parallax-free illumination of the display 1 from the plate 4 two such deflecting angle pieces 5 are connected to the plate lying opposite one another; namely preferably at the longitudinal edges 8 of the display 1. In cross-section the two L-shaped regions thus formed complement one another to form a U-shaped frame, with the plate 4 as the yoke between the limbs 13 thereof. The deflecting angle pieces 5 extend into a region beyond the display 1 i.e. beyond the inner side of the yoke of the U-shaped frame. The display 1 is connected to the inner surface of the plate 9 in such a way (preferably also bonded) that (by reason of identical refractive indices) no optically effective boundary surface or interface with regard to the plate 4 occurs.

In the interests of keeping the thickness 23 of the plate 4 small and maintaining symmetrical and thereby extensively parallax-free radiating of the additional light into the display 1,the illumination equipment 3 is designed as a whole symmetrically with respect to the centre plane 10 through the display 1, which plane 10 is orientated parallel to the longitudinal edges 8 thereof. Accordingly, also the light distributor 6, connecting the two limbs 13 rearwardly of the display 1, is designed so as to be symmetrical thereto and symmetrical to at least one aperture 11 into which projects a light source 7, for example a glow lamp or light bulb. Generally, the illumination equipment 3 is a substantially tubular frame design, composed at its inclined end surfaces from several plate-shaped parts.The display 1 is arranged in the interior of that part of the tube walling which is defined by the plate 4, and thus is relatively protected in a compact inherently stable frame structure.

The limbs 13 preferably extend parallel to the direction of sight 2 and perpendicularly to the main plane of the display 1, in other words perpendicularly to the plate inner surface 9; whilst the light distributor 6 is preferably similarly designed as a flat plate which in turn extends perpendicularly to the limbs 13 and thus parallel to the display 1. This results in simple geometrical conditions for the design of the edges at the transitions between the function groups/portions.

Disposed between the light distributor 6 and the linking deflecting angle piece 5 is, in orderto make possible a more compact construction than in the case of angle construction in accordance with the laws of total reflection, a flat end surface 14 inclined at 45o. The rays of light 15 conducted substantially parallel to the plane of the light distributor are deflected at end surface 14. To avoid light loss, these end surfaces 14 can be mirror-coated or silvered on the outside.

However, the mirror-coating vapour-deposition, necessary in the region of the plate 4 and defined exactly at the front thereof, would be too complex or expensive in production technique respects to be provided on the angle pieces 5. Therefore, in any event towards the adjoining reflection plate 4, each deflecting angle piece 5 is edged on the outside with a deflecting surface 16 which is inclined in such a way that both at surface 16 and at the plate outer surface 17 total reflection occurs for the deflected light beams 15. In this way, in this deflection region light losses are similarly avoided; and also no light constituent emerges contrary to the direction of sight 2 from the illumination equipment 3, so that no glare effects occur for the observer of the display 1.Instead, the light travelling from the deflection surface 16 is deflected in practice completely towards the inner surface 9 of the plate 4 where it enters without refraction phenomena into the display 1 and yields the additional display illumination for the reflective operation thereof.

The choice of inclination of the inner boundary 18 (situated towards the interior of the illumination equipment 3) of the deflecting angle piece 5 to the display 1 is in itself optional; nevertheless boundary 18 should not project into the path of the light beams 15 deflected at the opposite surface 16. Geometrical conditions which are the simplest in production technique respects emerge if, as shown, also this inner boundary 18 is designed as a flat surface which extends at an angle with respect to the main plane of the display 1 which is the same as the angle of incidence of the light beams 15 onto the plate outer surface 17.

As a result of this incoming light radiation, offset laterally relative to the display 1, entering the plate 4, the inner dimensions of the illumination equipment 3 parallel to the main panel of the display 1 are somewhat greater than the corresponding dimensions of the display 1 itself. Convenient or appropriate thicknesses of material result if the projecting distance 19 (measured from a lateral edge 8 of the display 1 to the inner wall 20 of the adjacent deflecting limb 13) is selected to be approximately the same as the limb material thickness 21 measured in this direction; also this distance may at the same time be selected to be in the order of magnitude of half the height extent of the display 1 which is irradiated by light for illumination by way of said adjacent deflecting angle piece 5.If, thus, the deflecting angle pieces 5 extend parallel to the upper and lower longitudinal edges 8 of the display, and the display 1, in the interests of parallax-free visibility is to be radiated with uniform light distribution throughout the full height of the display, from each side (in other words from top and from bottom as shown in Figure 1) then the projecting distance 19 and the material thickness 21 are to be approximately 50% of the height of the display 1 between its longitudinal edges 8-8.

For materials of practical consideration having light conducting properties of acrylic glass (with regard to refractive index relative to air and thus the total reflection angle) there results for the plate 4 at its outer surface or boundary 17 a light incidence angle 22 which is at all times somewhat smaller than the ideal angle for total reflection provided the plate has a thickness 23 (measured in the direction of sight 2) in the range from 50% up to just under 60% (preferably 56%) of the projection distance 19. Even under unfavourable circumstances, for instance by reason of the light beams in the deflecting limb 13 being non-ideally parallel it is nevertheless ensured that in practice no stray light which could disturb the readabiiity of the display emerges from the plate 4 contrary to the direction of sight 2.

An undisturbed transition of the light beams 15 from the respective deflecting angle piece 5 into plate 4 is provided for if (as taken into consideration in Figure 1) the boundary surface 24 between those two function groups in the case of joining together from separately produced parts is orientated generally perpendicularly to the light beams running through here.

In the interests of uniform illumination over the entire extent of the deflecting angles 5 (thus, in the exemplified instance shown in the drawings over the longitudinal sides 8 of the display 1) with, at most, minimum light losses occurring in the light distributor 6 thereof, the distributor 6 tapers - as is evident from the rearward view in accordance with Figure 2 - along a boundary 12 extending in a curved manner from the region of the end surface 14 to the plane in which the aperture 11 lies. This boundary 12 is, in accordance with the dimensions and arrangement of the light source 7, to be so selected that as much as possible total reflection occurs allround; in other words practically all light 15 is conducted onto the end surfaces 14.

In Figure 1 it is symbolically represented that the aperture 11 into which the light source 7 projects is closed by a screen 25 on account of reflective operation of the display 1 opposite the light source 7 and thus contrary to the direction of sight 2, which in practical realisation, however, already results by way of a corresponding screening effect of a reflector situated on the reverse side of the display 1 (not taken into account in the drawing).

It can be advantageous to apply a dereflection coating 26 on the outer surface 17, facing the direction of sight 2, of the plate 4, in order to prevent possibly disturbing ambient light reflecting contrary to the direction of sight 2. Of course, this coating 26 is to be selected taking into account the fact that the reflection properties from the interior of the plate 4 to this outer surface 17 are not to be varied if possible. Otherwise, for the projection distance 19 or the material thickness 21 and the plate thickness 23 respectively, a greater dimension would have to be selected in order that light 15 does not leave the plate 4 contrary to the direction of sight 2.

The following is a key to the reference numbers used in the drawings: 1 Display 2 Direction of sight (towards 1) 3 Illumination equipment (for 1) 4-6 Function groups (of 3) 4 Reflector plate (in front of 1 in 2) 5 Deflecting angle pieces (between 2 and 6) 6 Light distributor (for 7) 7 Light source (in 6/11) 8 Longitudinal edges (of 1 along 5) 9 Inner surface (of 4, receiving 1) 10 Centre plane (in direction of 2 through 1/3 11 Aperture (in 6 for 7) 12 Boundary (of 6) 13 Limbs (of 5, remote from 4 and connected to 6) 14 End surface (of 6, for connection to 5) 15 Light (beams along 6-5 towards 4) 16 Deflecting surface (in the case of the outside angle of 5 beside 4) 17 Outer surface (of 4, situated opposite 9/1 towards 2) 18 Inner boundary (of 5 opposite 16) 19 Projection distance (of 5 beside 1 in the direction of 13) 20 Inner wall (of 13 beside 18) 21 Material thickness (of 13) 22 Light incidence angle (on 17 from 16) 23 Thickness (of 4 for 1) 24 Boundary suface (of 4 towards 5) 25 Screen (between 1 and 11/7) 26 Coating (on 17)

Claims (17)

1. Illumination equipment for a reflectively operated passive display, for example a liquid crystal display, which equipment is to receive an artificial-light light source, the light of which is, in use, conductable through a frame of the equipment comprising or including a part of generally L-shaped cross-section made from light-conducting material; one limb of said L-shaped cross section is a light-reflective plate and an outer surface or boundary of said plate is to face the direction of sight, in use, whilst an inner surface or boundary of said plate is for fastening the display thereto; the other limb of said L-shaped cross section is connected or joined by way of a deflecting angle piece to the plate and in the transitional region between the deflecting angle piece and the plate a deflecting surface of said angle piece is inclined relative to the plate outer surface or boundary so that, in use, light travelling from the deflecting angle piece incident on the plate strikes the plate outer surface or boundary at a smaller light incidence angle than the critical or limiting angle for total reflection and is reflected into the display, the outer surface or boundary extends, in use, in a plane parallel to the display and is connected or joined at one end edge to the deflecting angle piece and the other limb of the frame is laterally offset from the plate.

2. Illumination equipment as claimed in Claim 1 in which a second deflecting angle piece is provided which adjoins a second edge of the plate, said second edge being arranged opposite said one edge of the plate, the second deflecting angle piece being connected to a further, third limb.

3. Illumination equipment as claimed in Claim 1 or 2 in which the or each deflecting angle piece extends into a region beyond the inner surface or boundary of the plate, remote from the direction of sight, where the free ends of said other limb and of the third limb, respectively, are connected together by a light distributor (beam splitter).

4. Illumination equipment as claimed in Claim 3 in which in the light distributor (beam splitter) at least one aperture is provided to receive a light source.

5. Illumination equipment as claimed as Claim 4, in which the at least one aperture is provided in the centre of the light distributor (beam splitter) in a plane extending parallel to the plate.

6. Illumination equipment as claimed in Claim 4 or 5, in which the light distributor (beam splitter) widens from the region of the aperture in the direction of the connection of the ends of the deflecting limbs.

7. Illumination equipment as claimed in one of the preceding claims, characterised in that an inner wall of the or each angle piece, lying generally opposite the associated deflecting surface has, at a transition from the plate inner surface to the associated limb, such an orientation that it does not project into or cross the path of light beams reflected from the associated deflecting surface.

8. Illumination equipment as claimed in one of the preceding claims, consisting of material with a light refractive index in the order of magnitude of that of acrylic glass and in which the or each limb connected to the associated deflecting angle piece is laterally offset by a projection distance to be arranged behind the plate inner surface relative to an adjacent edge of the boundary of the display, which projection distance is about 50% of the height extent of the display that is to be illuminated from this adjacent limb.

9. Illumination equipment as claimed in Claim 8, in which the material thickness of the or each limb measured parallel to the plane of the display, lies in the same order of magnitude as the projection distance; and the thickness of the plate, measured transversely to the plane of the display, lies approximately between 50% and 60% of the limb material thickness.

10. Illumination equipment as claimed in Claim 9, in which the angle between the deflecting surface and the plate outer surface is twice the light incidence angle from the associated angle piece to the plate (for example 22) and does not exceed the total reflection angle, for beams of the light at the plate outer surface, when the light in the or each limb is conducted substantially parallel to the direction of sight against the deflecting surface and then onto the display.

11. Apparatus or device for illuminating a reflectively operated passive display, for example a liquid crystal display, said apparatus or device comprising or including a frame of generally L-shaped cross section, one limb of the frame being a 'transflector' plate (i.e. a plate which allows light through from one side thereof - the side facing the line of sight direction in use of the display - and reflects light travelling towards the plate from the other side thereof) defining an outer boundary and an inner boundary, the inner boundary being for fixing said passive display thereto, the other limb of the frame being joined to the transflector plate by the interpolation of an individual angle piece, said angle piece presenting an outer boundary which is inclined to the plate, one edge of the plate adjoining a first face of the angle piece and a second face of the angle piece adjoining an edge of said other limb, said other limb being laterally offset from said plate and said inclined outer boundary being defined by a third face of the angle piece, the arrangement being such that, in use, the outer boundary of the plate is parallel to the plane of the display and light from an artificial light source is capable of travelling along the said other limb into the angle piece where it is totally internally reflected by said outer boundary of the angle piece towards said outer boundary of the plate where it is reflected onto the display, and ambient light is capable of being transmitted through the plate along the line of sight of the display.

12. Apparatus or device as claimed in Claim 11 arranged so that light from the deflecting angle piece entering into the plate strikes the plate outer boundary at a slightly smaller incidence angle (e.g. 22) than the critical angle for total internal reflection.

13. Apparatus or device as claimed in Claim 11 or 12 in which the frame is substantially U-shaped and defines a further, third limb opposite and generally parallel to said other limb and a second angle piece is arranged between a second edge of the plate (opposite said first mentioned edge) and the third limb.

14. Apparatus as claimed in Claim 13 in which the U-shaped frame is generally symmetrical about the axis of the plate.

15. Apparatus or device for illuminating a reflectively operated passive display, for example a liquid crystal display, said apparatus or device providing, in use, a generally closed frame around the display, which frame is for directing light from an artificial light source arranged, in use, behind the display but shielded directly therefrom, around the sides of the display onto an outer boundary of a transflector plate of the frame, which plate is in a plane parallel to the display, said directed light being totally reflected at said outer boundary onto the display while ambient light can travel through the plate onto the display.

16. Illumination equipment for a reflectively operated passive display, substantially as herein described with reference to the accompanying drawings.

17. The combination of illumination equipment, apparatus or device as claimed in any one of the preceding claims and a liquid crystal display.