GB2056150A

GB2056150A - Display device

Info

Publication number: GB2056150A
Application number: GB8024320A
Authority: GB
Original assignee: International Standard Electric Corp
Current assignee: International Standard Electric Corp
Priority date: 1979-08-02
Filing date: 1980-07-24
Publication date: 1981-03-11
Also published as: FR2463471B1; DE2931328A1; DE2931328C2; GB2056150B; FR2463471A1

Abstract

A liquid display cell switchable between transparent and light- scattering states is back-lit through a louvered (e.g. at 60 DEG ) layer (5) to brighten scattering areas. Layer 5 is provided with apertures (6) through which selected regions of the cell are more strongly illuminated via separate switched light sources (9). The separately illuminated regions may be provided with louvers (71) parallel to view (21), colour filter (7) and possibly with light guide fibre bundles between sources (9) and apertures (6). <IMAGE>

Description

SPECIFICATION Display device The present invention relates to a display device comprising a liquid display cell, wherein a liquid sandwiched between transparent electrodes is switchable between a state in which it is transparent and one in which it is scattering, and wherein at the rear of the liquid cell there is provided a light source and, between the light source and the liquid cell, a light-control film which prevents direct passage of light though the liquid cell to a viewer, so that the areas switched to the scattering state are visible as bright characters on a dark background.

A display device of this kind is described, for example, in German Auslegeschrift 20 42 1 80. It provides a monochromatic display which is sufficiently bright for many applications and has a uniform luminance distribution.

However, there are applications, such as in automotive engineering, which require a display to present given information with particularly high brightness and frequently with different colours.

With the conventional display devices of the above kind, this requirement cannot be met.

According to the present invention there is provided a display device comprising a liquid cell, wherein a liquid sandwiched between transparent electrodes is switchable between a state in which it is transparent and one in which it is scattering, and wherein at the rear of the liquid cell there is provided a light source and, between the light source and the liquid ceil, a light-control film which prevents direct passage of light through the liquid cell to a viewer, so that the areas switched to the scattering state are visible as bright characters on a dark background, wherein the light-control film is provided with openings, and that each of these openings is illuminated by an additional, switched light source associated with that opening.

In this way there is provided a display device of a kind which permits individual characters to be displayed with especially high brightness and, if required, with different colours.

Light spillage from the area to be illuminated by one light source into the area to be illuminated by another light source is minimised to give good contrast if in the light-control film, which consists of a plurality of louvers, the louver surfaces are inclined to a preferred direction of view at an angle of more than 40 , and if in the regions of the openings between the additional light sources and the viewer there are provided other control films consisting of a plurality of louvers whose surfaces are approximately parallel to the preferred direction of view.If in a preferred direction of view normal to the visible surface of the liquid cell, the louver surfaces of the light-control film make an angle of less than 60O with the visible surface of the liquid cell, and if the louver surfaces of the additional light-control film are approximately normal to the visible surface of the liquid cell. This also is found to militate towards the achievement of good contrast.

Contrast is enhanced if the additional lightcontrol films are inserted directly into the openings.

A coloured display is obtained in a simple manner if colour filters are disposed in the regions of the openings between the additional light sources and the viewer, and particularly if the additional light-control films are embedded in a material acting as a colour filter.

Gaod utilization of the emitted light and great freedom in positioning the light sources are provided if light-guiding means are disposed between the openings and the additional light sources to illuminate the openings.

Embodiments of the invention will now be described in detail with reference to the accompanying drawing, in which: Fig. 1 is a perspective front view of a schematic display device according to the invention; Fig. 2 shows a section of the display device of Fig. 1, and Fig. 3 shows a modified embodiment in the section of Fig. 2.

Figs. 1 and 2 show the liquid cell, consisting of glass plates 1 and 2 with the liquid 3 sandwiched between. The electrodes 4 serve to switch the liquid from highly transparent to highly scattering.

Bonded to the rear of the liquid cell is a lightcontrol film 5 with openings 6. The light-control film 5 is illuminated from behind by a light source 8, and the openings 6 are illuminated from behind by light sources 9. The light sources 8 and 9 are optically separated by a screen 10. Another lightcontrol film 7, whose louvers are embedded in a material acting as a colour filter, is bonded to the front surface 23. The viewer shown is looking at the display from the direction 21.

The liquid 3 may be a liquid crystal or any other liquid, such as certain colloids, which can be switched between highly transparent and highly scattering states by applying an electric field or an electric current.

The light-control film 5 is formed by louvers 51, shown in the sectional view of Fig. 2. These louvers allow light from the light source 8 to pass through only within a limited angular range, so that a viewer 22 looking at the display from outside this angular range cannot directly see the light source 8. If, however, an area between the electrodes 4 in the shape of a particular character is switched to the hgihly scattering state, the viewer 22 will see a bright character on a dark background.

As the light from the additional light sources 9 passes through the openings 6 to the viewer 22 nearly unobstructed, the viewer sees a character with a brightness as would be achievable by known means in the area of the light-control film 5 only with a candlepower of a light source which would be prohibitively high for practical applications.

A coloured display is provided in a simple manner by bonding colour filters 7 to the front surface 23 in the regions of the openings 6.

Despite the light attenuation by a colour filters 7, such a display has high brightness.

The optical screen 10 sufficiently prevents light of the individual light sources 8 and 9 from entering the region of the respective other light source and thus reducing the contrast of the display.

By providing the filter 7 with louvers 71 arranged approximately parallel to the direction of .view 21, the contrast of the display is further enhanced.

The device of Fig. 3 shows even better contrast.

Here louvers, forming another light-control film 16, fill the opening 6. These louvers, too, are embedded in a material acting as a colour filter if required.

By disposing light-guiding means, such as an optical-fibre bundle 20, between the additional light-control film 1 7 and the light source 9, the utilization of the light emitted by the light source 9 is improved, and there is greater scope for positioning the light source 9, because an opticalfibre bundle may be curved.

Claims

1. Display device comprising a liquid cell, wherein a liquid sandwiched between transparent electrodes is switchable between a state in which it is transparent and one in which it is scattering, and wherein at the rear of the liquid cell there is provided a light source and, between the light source and the liquid cell, a light-control film which prevents direct passage of light through the liquid cell to a viewer, so that the areas switched to the scattering state are visible as bright characters on a dark background, wherein the light-control film is provided with openings, and that each of these openings is illuminated by an additional, switched light source associated with that opening.

2. A display device as claimed in claim 1, wherein the light-control film consists of a plurality of louvers, the louver survaces of which are inclined to a preferred direction of view at an angle of more than 400, and wherein in the region of the openings between the additional light sources and the viewer there are provided other light-control films consisting of a plurality of louvers whose surfaces are approximately parallel to the preferred direction of view.

3. A display device as claimed in claim 2, wherein the louver surfaces of the light-control film make an angle of 600 with the visible surface of the liquid cell, and wherein the louver surfaces of the other light-control films are approximately normal to the visible surface of the liquid cell.

4. A display device as claimed in claim 2 or 3, wherein said other light-control films are inserted in the openings.

5. A display device as claimed in any one of the preceding claims, wherein colour filters are disposed in the regions of the openings between the additional light sources and the viewer.

6. A display device as claimed in claim 2, 3 or 4, wherein said other light-control films are embedded in a material acting as a colour filter.

7. A display device as claimed in any one of the preceding claims, wherein light-guiding means are disposed between the openings and the additional light sources associated with the openings.

8. A display device as claimed in claim 7, wherein said light-guiding means is provided by one or more optical fibre bundles.

9. A display device substantially as hereinbefore described with reference to the accompanying drawing.