More particularly, where such transparent glass or plastics plate presents a generally vertical reflective surface, the location of the display, (determined by such considerations as the need to be out of physical reach of members of the public and/or out of the way of passing vehicles, trolleys, etc. ) frequently mean that the typical observer will be located in front of and somewhat below the display whilst sources of ambient light will typically be located above and in front of the display, creating viewing conditions in which it is all too likely that any contrast between light-transmitting and light-occluding portions of the information-bearing part of the display-i. e. between light transmitting portions and light-occluding portions of the liquid crystal display, will be totally swamped by reflected ambient light reflected from the shiny outer surface of the glass or plastics front pane. Measures which have in the past been adopted to minimise this disadvantage include the provision of hoods or light shields around the borders of such displays and/or the provision of anti-reflective coatings on the front panes of such displays. However, these measures have not solved the problem entirely.

It is an object of the present invention to provide an improved visual display arrangement in which the above-noted disadvantage of known arrangements is mitigated to a greater degree than has hitherto been economically possible.

According to the invention there is provided a visual display arrangement comprising a panel having an image-providing part and a light-transmitting sheet arranged over the exposed front part of the display, the last-noted sheet having surface relief structure whereby image information-bearing light from the image-providing part can pass through the sheet to the observer with relatively small deviation, whilst light emanating from the region above and to the front of the display, from a range of angles relative to the display, upon striking the surface relief will be reflected thereby, such that a significant proportion of the ambient light will be redirected away from the line of sight of the observer.

Preferably the light-transmitting element is a prismatic sheet.

An embodiment of the invention is described below by way of example with reference to the accompanying drawings in which: Figure 1 is a schematic perspective view illustrating a display arrangement in accordance with the invention; and Figure 2 is a fragmentary view, to a much enlarged scale, in vertical section through a front panel of a display arrangement embodying the invention, and Figures 3 and 4 are views similar to Figure 2, of variants.

Referring to Figure 1, a visual display arrangement 10 is illustrated as comprising a rectangular casing or frame having a window 12 at the front through which an LCD display is visible. (The casing 10 may, for example, incorporate electronic drive circuitry, etc. for the display). Referring to Figure 2, the display arrangement 10 has a conventional glass or plastics pane 14 extending vertically thereon. The pane 14 has, in the normal way, opposite smooth shiny surfaces facing respectively inwardly towards the LCD elements and outwardly towards the viewer. (Only the outer surface is shown in Figure 2). It will be understood that if the smooth vertical outer surface of the pane 14 formed the outer surface of the display, a certain proportion of any ambient light falling on the display from the position in front of and above the display, at, for example, an angle of 50° to the horizontal, would be reflected forward and downwards from the display at a corresponding angle of 50° to the horizontal and so on. Light so reflected may be in the line of sight of an observer of the display and easily swamp the display making it effectively unreadable.

In accordance with the invention, in order to avoid light thus reflected having this effect, there is provided, on the front of the pane 14, a light-transmitting layer 16 having an anti-reflective surface relief. The layer 16 may typically take the form of a thin flexible transparent plastics film adhered to the front surface of the glass or plastics pane 14. The surface relief, in the illustrated embodiment taking the form of an array of parallel prismatic ribs, with intervening grooves. Preferably the reflective index of the film is comparable with that of the pane 14 and is stuck to the pane 14 using a transparent, refractive index-matching adhesive so as to avoid or minimise reflections at the interface between the film 16 and the pane 14.

As shown in Figure 2, the prismatic film or layer 16 has a flat rear surface which is in intimate contact with the co-planar front surface of pane 14 and has a front surface formed with an array of parallel horizontal V-section grooves and ribs, such that, in vertical section perpendicular to the plane of the rear surface of the layer the front surface presents a saw-tooth profile defined by alternating minor and major rib faces. Thus, each horizontal rib has a major, upper face 18 inclined downwardly and outwardly from the display at an acute angle, e. g. of 25°, as shown, with respect to the vertical, (and thus with respect to the plane of pane 14) and a minor, lower face 20 extending (in the arrangement shown) from the lower outer edge of the major face rearwardly and downwardly at a small angle to the horizontal, (to assist in release of the prismatic film from the mould or roll surface by means of which it may typically be formed). From the point of view of the effectiveness of the sheet 16 in minimising unwanted reflection, the precise orientation of this minor face is not of crucial importance-but would be engineered to optimise the output of the display. Ideally it should be generally perpendicular to the plane of the structure.

Figure 2 illustrates the effect of the prismatic screen in reflection and transmission. As illustrated in Figure 2, where as illustrated, the major face 18 of each rib is inclined at an angle of 25° to the vertical, a ray Rl of ambient light striking the screen, more particularly the inclined major face of one rib, at an angle of 50° with respect to the horizontal, (from above and from the front of the screen), will, by the normal rules of refraction, be partly transmitted (not shown) through the film 16 and pane 14, and partly reflected away from the screen along the horizontal. Rays of ambient light (such as R2) striking the sheet 16 from above at a lesser angle to the horizontal will be reflected at an angle upwardly with respect to the horizontal. On the other hand, a ray R3 emanating from the LCD elements behind the pane 14 and prismatic film 16 and shown emerging horizontally in Figure 2, is refracted downwardly, (typically through 15°), as it passes through the inclined major face 18 of the respective rib. Accordingly, not only does the prismatic screen 16 tend to deflect the light emerging from the LCD display elements downwardly somewhat, which is advantageous where the display is mounted somewhat above the viewer's eye level, but even ambient light striking the display from as much as 50° above the display will be so reflected as not to reach the eyes of the observer and thus not impede the observer from reading the display.

Ideally, with a view to avoiding or minimising the reflection towards the viewer of ambient light reflected at the interface between the prismatic film 16 and the pane 14, the prismatic film is bonded to the pane 14 by a transparent adhesive of a refractive index close to that of the pane 14 and prismatic film. Ideally, if the prismatic film and pane have the same refractive index, such adhesive should be also of the same refractive index whereas if they are of different refractive indices, the refractive index of the adhesive should be intermediate the refractive indices of the prismatic film and the pane, although clearly an adhesive of a refractive index is markedly different from that of the pane 14 and prismatic film may reduce unwanted reflections significantly as compared with the situation where an air gap exists between the prismatic film and the pane.

In some variants of the invention, (not shown) the pane 14 may be dispensed with and the functions of the pane 14 and sheet 16 both performed by a unitary, (for example rigid) light transmitting prismatic sheet forming the front wall of the display housing and containing the LCD elements, etc.

It will be appreciated that Figure 2 illustrates the triangular or saw-tooth ribs and grooves of the prismatic film 16 to a much greater scale than will normally be the case in practice. Typically, for small scale displays, the pitch between adjacent triangular ribs (i. e. the vertical spacing D as indicated in Figure 2) may be in the region lOp. (micrometers) to 100 so that the individual ribs are barely discernible to the human eye and are not normally discernible from the normal viewing distance for the display. However, for large scale displays, for example displays in which the size of the individual LCD pixels or segments is large, the pitch between the ribs may be much greater than 100p, but still small in relation to the size of the pixels or segments.

It should be appreciated that whilst the angle of the major face of each rib with respect to the plane of the rear face of the prismatic screen, (i. e. with respect to the plane of the pane 14 to which it is applied) -and which angle is herein referred to, for convenience, as the prism angle,-is 25° in the example illustrated in Figure 2, prismatic layers with other prism angles may be used, depending upon requirements. For example, with an arrangement as described with reference to Figure 2, but with a prism angle of 10°, no ambient light arriving at the prism surface less than 20° above the normal to the plane of the display will be reflected below the normal. The prisms will then typically deflect light passing through the display by 5° and towards the viewer.

By contrast, with a 25° prism angle, as noted above, no light from less than 50° above the normal can be reflected below the normal whilst transmitted light is typically deflected 15'towards the viewer.

Thus, as noted above, the use of the prism structure directs the (transmitted) light from the display towards the viewer and reduces glare by redirecting ambient light away from the viewer. The conventional way to reduce glare in a display whether mounted substantially vertically such as a workstation, horizontally such as a lap-top, or in a hand held device such as a mobile'phone, is to attach an anti-reflecting film to the surface of the display. By comparison with a non-treated surface (e. g. glass), an anti-reflecting coating can reduce the intensity of reflected light by a factor of 5. The prism structures of the invention in addition to redirecting ambient light, also have the ability to reduce glare because the surface is broken up into a series of segments. In variants of the invention, (cf. Figures 3 and 4), the major surface of each rib is deliberately made curved (Fig. 3) or slightly rough (Fig. 4). Thus, in an application where glare can occur, in some direction of concern, using a prismatic layer in accordance with the invention, the prism structure can be adapted by using a curved or textured surface such that the glare can be less than that from an anti-reflective surface.

The following table compares reflection characteristics of glass (reflection intensity 100) with anti-reflective (AR) coatings and typical prism structure MATERIAL REFLECTION INTENSITY Glass 100 AR coating 21 (moth eye) AR coating * 1 (multi-layer coating + circular polariser) 10° prism 36 (smooth facet) 10° prism 29 (textured facet) 15° prism 6 (curved facet) 25° prism 6 (textured facet) * Note: This is amongst the most effective anti-glare coatings, but due to the use of the circular polariser, significantly reduces light transmission from the display and thus display brightness.