GB2269928A

GB2269928A - Display

Info

Publication number: GB2269928A
Application number: GB9316785A
Authority: GB
Inventors: Anssi Saarikko
Original assignee: Nokia Mobile Phones Ltd
Current assignee: Nokia Oyj
Priority date: 1992-08-18
Filing date: 1993-08-12
Publication date: 1994-02-23
Also published as: FI923695A; FI91810B; FI91810C; GB9316785D0; FI923695A0

Abstract

A device for directing light from a light source (12) to a photoconductor (10) of a liquid crystal display, said device comprising a material having a substantially non light-absorbent reflective surface partially surrounding the light source (12) and adapted to direct light into said photoconductor (10). The material of the light guide may be either rigid or flexible. Separate light guides in one and the same liquid crystal display may be interconnected by intermediate bars. The light source is preferably an LED. <IMAGE>

Description

Light guide The invention relates to a device for directing light tin a liquid crystal display.

In a liquid crystal display the light-producing means, typically light emitting diodes(LEDs), are usually placed at or in the vicinity of the edges of the display. Above the LEDs, or above the entire display, there is fitted a so-called photoconductor, which is usually a means consisting of one or more parallel transparent plates of which the bottom plate is usually white so as to reflect light and the top or upper surface is often made diffuse in order to direct light towards a liquid crystal layer.

Thereby, the photoconductor distributes the light produced by the LEDs evenly over the entire area of the display. On top of the photoconductor there is placed an information transmitting means and on top of this a protective glass or the like.

It is necessary to direct the light produced by the LEDs to the center of the display, since otherwise the light will "escape" to the sides and the display itself will remain almost unlit. The escape of light has so far been prevented by coating with some suitable material, for example by painting, those parts of the photoconductor which surround the LEDs. Such coating of the surrounding of the LEDs has indeed served to prevent the escape of light, but there has also been the disadvantage that the coating has a light-absorbing property, whereby the intensity of the light of the display is weakened.

The present invention addresses the said disadvantage and provides a device for directing light from a light source to a photoconductor of a liquid crystal display, said device comprising a material having a substantially non light-absorbent reflective surface partially surrounding the light source and adapted to direct light into said photoconductor.

The advantage of the present invention is that, light can be aimed with precision at a specific area, whereby the quality of the display is improved and its power requirement is reduced. Materials suitable for the light guide include materials which are themselves reflective and non-absorbing, such as metals, or materials which are themselves non-reflective, such as various plastics and which have the surface facing the source of light coated with a reflective non light-absorbing coating agent. The said material may be either rigid or flexible. If the material is flexible it can be attached using, for example, tape.

In a preferred embodiment the device for directing light is separably coupled to the photoconductor. This has the advantage that it aids manufacture and assembly of a liquid crystal display apparatus.

Suitably, the light guide is made of a rigid material, and if the LEDs are grouped at different edges in the liquid crystal display and constitute areas separate from each other, and are thus protected by separate light guides.

Such light guides may be interconnected by intermediate bars made of a rigid material, to form a continuous piece.

Preferably such light guides and their intermediate bars are from the very beginning machined as one piece. When this piece is attached to the bottom of the display, which usually corresponds to a circuit board, a stable light display without vibration is obtained.

The structure of the light guide according to the invention is shown in greater detail in the following figures.

Figure 1 depicts a top view of the photoconductor.

Figure 2 is a perspective representation of the photoconductor.

Figure 3 depicts a top view of the photoconductor, protected by two light guides.

Figure 4 is a perspective representation of one light guide.

Figure 5 depicts a top view of a continuous piece which comprises two light guides interconnected by an intermediate bar.

Figure 6 depicts a side view of the intermediate bar according to Figure 5.

Figure 7 depicts a side view of a continuous piece according to Figure 5.

In Figure 1, depicting a photoconductor 10, the sites in which the LEDs are embedded are indicated by reference numeral 12. At points 13 the plate 11 is attached to the bottom of the display.

In Figure 3, the plate 11 of the photoconductor is seen protected by two separate light guides 20. Figure 4 shows in greater detail a light guide in which surface 21 is a curved surface protecting the LEDs 12, and 22 is a level means which can be attached to the plate 11. The LEDs 12 are, of course, not visible through the surface 21 in the devices according Figures 3 and 4; they have been indicated as visible in the figures only for the purpose of elucidating the structure of the light guide. In Figure 4 light is directed downwards into a photoconductor 10 (not shown) from a side of the photoconductor 10. The surfaces enclosing the light source 12, i.e. the curved surface 21, the side surfaces and the front surface of the light guide 20 in Figure 4 are of reflecting and non light-absorbing material.

Figure 5 depicts a top view of one preferred embodiment of the invention, in which two light guides 20 are interconnected by an intermediate bar 23 to form one piece. The piece can be attached at points 24 to the bottom of the display by, for example, soldering. This piece is preferably made of a continuous, reflective metal sheet. Structures made of sheet metal are economical to manufacture and easy to install.

In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

The scope of the present disclosure includes any novel feature or combination of features disclosed therein either explicitly or implicitly or any generalisation thereof irrespective of whether or not it relates to the claimed invention or mitigates any or all of the problems addressed by the present invention. The applicant hereby gives notice that new claims may be formulated to such features during prosecution of this application or of any such further application derived therefrom.

Claims

1. A device for directing light from a light source-to a photoconductor of a liquid crystal display, said device comprising a material having a substantially non lightabsorbent reflective surface partially surrounding the light source and adapted to direct light into said photoconductor.

2. A device according to claim 1, separably coupled to the photo conductor.

3. A device according to claim 1 or claim 2, wherein the material is rigid.

4. A device according to any preceding claim, wherein the material comprises a reflective metal.

5. A device according to claim 1, 2 or 3, wherein the material is a metal, a plastics or the like, coated with a substantially non light-absorbent reflective coating.

6. A device according to claim 1 or claim 2, wherein the material is a flexible material, such as tape, ribbon or the like, coated with a substantially non light-absorbent reflective coating.

7. A device according to any of claims 1-4, wherein the device is connected to another light directing device in the same liquid crystal display by means of at least one intermediate bar made of a rigid material, whereupon the separate light directing devices with their at least one intermediate bar constitute a continuous piece which can be attached to the bottom of a liquid crystal display.

8. A device according to claim 7, wherein the intermediate bar comprises a continuous reflective metal sheet.

9. A liquid crystal display apparatus comprising light directing devices according to any of claims 1-4 and at least one intermediate bar interconnecting the light directing devices such that the interconnected light directing devices are capable of being attached as a whole to the liquid crystal display apparatus.

10. A liquid crystal display apparatus according to claim 9, wherein the light directing device and the intermediate bars are made of a continuous, reflective non lightabsorbent metal sheet.

11. A device substantially as hereinbefore described and with reference to the accompanying drawings.