GB2274191A

GB2274191A - Displays

Info

Publication number: GB2274191A
Application number: GB9325437A
Authority: GB
Inventors: Neil Anthony Fox
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1993-01-09
Filing date: 1993-12-13
Publication date: 1994-07-13
Also published as: GB9325437D0; GB9300361D0; FR2700408A1; JPH06242726A; DE4344730A1

Description

2274191 DISPLAYS This invention relates to displays.

The invention is more particularly concerned with multi-colour matrix displays.

There are various ways in which a liquid crystal display (LCD) or other matrix display can provide a multi-colour image. In one arrangement, the display is illun-dnated from the rear with white light and individual colour filters are positioned in alignment with the individual elements of the matrix. By energizing, for example, those elements aligned with red filters, a red image can be produced. The problem with this arrangement is that the filters reduce the amount of light transmitted and reduce the efficiency of the display.

It is an object of the present invention to provide an improved display.

According to one aspect of the present invention there is provided a display including a first matrix array of a plurality of electricallyenergizable elements that can be individually energized to vary the amount of radiation transmitted through the element, a source of radiation located on one side of the display, and an intermediate optical assembly located between the first matrix array and the radiation source, the radiation source being a source of ultra-violet radiation, and the intermediate optical assembly including a second matrix array of fluorescent regions aligned with the first matrix, different ones of the fluorescent regions being of at least two different materials arranged to emit visible radiation of two different colours when illuminated by ultraviolet radiation from the source, and a third matrix array of lens elements located between the second and first matrices such that light emitted by the fluorescent regions is focussed by the lens elements towards the electrically-energizable elements of the first matrix.

The fluorescent regions may be formed on a surface of the lens elements or on a surface of a plate between the lens elements and the source of radiation. The fluorescent regions preferably have a layer of ultraviolet reflective material formed on a surface remote from the source of ultra-violet radiation. The display may include a support for the lens elements, the support preventing passage of radiation except through the lens elements. The display may include three different fluorescent regions that emit three different colours predominantly red, green and blue. The electrically-energizable elements are preferably LCD elements. The lens elements may be convex lenses and may be of a material that absorbs ultra-violet radiation.

A three-colour LCD matrix display according to the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a sectional side elevation of the display; Figure 2 is a plan view of the display; and Figure 3 is a sectional side elevation of a part of an alternative display.

With reference to Figures 1 and 2, the display includes an LCD unit 1, an ultra-violet light source 2 and an intermediate optical unit 3 located between the LCD unit and the ultraviolet light source.

The LCD unit 1 may be entirely conventional and comprise a matrix array of elements or pixels 10 that are normally transparent but can be rendered opaque, or partially opaque, by applying a voltage across the elements from an address and energization unit 11. Any one or more of the elements 10 can be energized by selecting the appropriate x and y addresses of electrodes for that element. The elements may be addressed by conventional multiplexing techniques or by use of an active matrix addressing technique such as incorporating thin film diode- or transistorswitched pixels. In this way, an image can be represented by rendering some of the elements opaque. The pixels are typically arranged as parallel rows and columns with pixels in adjacent rows being staggered from one another by half the spacing between the pixels. Typically, each pixel is about 0. 12 ram across and a unit might have an array of 2048 by 2048 pixels.

The ultra-violet light source 2 may be of a conventional kind comprising several gasdischarge tubes arranged side-by-side. Alternatively, the source may be a flat panel discharge lamp similar to that described in WO 90/09676, GB 2244855, GB 2247563 or GB 2261320 but without any phosphor coating, so that the radiation emitted by the panel is primarily in the ultra-violet part of the spectrum. The light source 2 preferably has a reflector 20 on its lower surface so that light is reflected upwardly towards the LCD unit 1.

The optical unit 3 includes a matrix array of converging lenses 30 mounted in a support 3 1. The array of lenses corresponds with the array of elements 10 in the LCD unit 1 so that each lens 30 is located directly below and is in alignment with a corresponding LCD element or pixel. Each lens is of a bi-convex form and is made from a glass or plastics which absorbs ultra-violet radiation. Alternatively, a holographic lens array could be used. The lower, curved surface 32 of each lens 30 is coated with a layer 34 of a material that is reflective of ultra-violet radiation but transparent to visible radiation. On top of this layer 34 is a thick film 33 of a fluorescent material, such as a phosphor. Three different phosphors are used, one of which emits visible light with a predominantly red colour when illuminated by ultra-violet radiation and the others of which emit predominantly green and blue light. As illustrated, the elements along each row of lenses 30 are coated with different colour phosphors: red R, green G or blue B. Various other configurations and combinations are possible, for example, in some arrangements it might be desirable to have a greater number of green phosphor regions than red andblueregions. The diameter of the lenses 30 is substantially the same as the dimensions of the LCI) elements 10.

The support 3 1 has a lower plate 3 5 of a plastics or glass material that is transparent to ultra-violet radiation. An upper plate 36 also of a plastics material, extends around the lenses 30 and has apertures 37 through which the lenses project. The upper plate 36 could be of a uvabsorbing material such as a glass. Between the upper and lower plates 36 and 35, there is a masking film 38 of a material that is opaque to ultra-violet and visible radiation, this could be an etched mesh of a glass or ceramic. The masking film 38 has an array of circular apertures 39 in alignment with the lenses 30, the mask extending between the lenses to prevent passage of radiation through the optical unit 3 except via the lenses.

Although Figure 1 shows the LCI) unit 1, the uv source 2 and the optical unit 3 as being spaced from one another, it will be appreciated that they could be butted against one another for a more compact configuration.

In operation, the energization unit 11 applies a voltage to render the LC1) unit 1 opaque apart from those elements 30 to be illun-dnated with red, green or blue light. Ultra-violet radiation from the light source 2 passes upwardly into the optical unit 3, the lower plate 35 providing little attenuation to the radiation. The uv radiation falls on the underside of the phosphor coatings 33 on the lenses 30. The thickness of the phosphor layers 33 is chosen for maximum efficiency with each uv photon making a number of elastic collisions with the phosphor before being absorbed. Typically the layers 33 are about 15 micron thick and can vary for the different red, green and blue phosphors. The visible light produced by each phosphor layer 33 is emitted in all directions, some travelling upwardly into the lens 310 where it is focussed onto the overlying element of the LCI) unit 1.

Because the lenses 30 are of a uv-absorbing material they provide a barrier preventing illumination of the LCD unit 1 by any tiv radiation that might pass through the phosphor 33. The layer 34 of uv-reflecting material on the lower surface of the lenses, between the phosphor layer 33 and the lens, further reduces the amount of uv radiation emerging from the intermediate unit 3. This is an advantage because uv radiation over time can cause polymerization or cross linking of the liquid crystal material and lead to failure of the LCD unit 1. Also, because the lenses 30 are opaque to uv radiation, the lower surface of the lenses will provide a reflective surface to any tiv radiation that passes through the phosphor. In this way, the escaping tiv radiation is reflected back down to the phosphor so that it can cause further fluorescence and an increase in the production of visible light.

Each lens 30 produces a focussed beam of red, green or blue light incident on respective elements 10 in the LCI) unit 1. Those of the elements 10 rendered opaque will block further passage of light; those of the elements that are transparent will allow to pass the appropriate beam of red, blue or green light. Different colours are produced by combinations of red, blue and green, the size of the elements being small enough that, when viewed from a distance, the colours merge and mix together in the same manner as in colour cathode ray tube television screens.

The present invention avoids the use of filters so that there is maximum efficiency in the utilization of the light emitted by the phosphors. This is increased by the array of lenses, giving a high level of radiation transmission through each LCI) pixel and a low cross-talk between adjacent pixels. It also enables conventional LCI) displays to be used, thereby avoiding the need to fabricate the LCD from special materials.

Various modifications are possible. For example, in some display applications it may only be necessary to have two different colour phosphors. It is not essential that the phosphors be coated on the lenses themselves but could instead be coated on the lower plate 35; this has an advantage in that it is easier to deposit a phophor layer on a flat surface. An example of an intermediate unit Tin which the phosphor layer 33'is deposited on a flat surface is shown in Figure 3. In this arrangement the lenses 3 0' are provided by a micro lens array of the kind made from Fotofonn glass by Coming and sold under the trade mark Smile. The lenses 30, are formed integrally within the thickness of an opaque glass substrate 3 6. The lens array is spaced above the phosphor layer 33'which is deposited on the upper surface of the lower plate 3Y. A uv-reflecting coating 34' is formed on the lower surface of the lens array 3 0% 3 6' so that any ultra-violet radiation passing through the phosphor 3 3' is reflected back to the phosphor.

11 7 Chkinis 1. A display including a first matrix array of a plurality of electrically-energizable elements that can be individually energized to vary the amount of radiation transmitted through the element, a source of radiation located on one side of the display, and an intermediate optical assembly located between the first matrix array and the radiation source, wherein the radiation source is a source of ultra-violet radiation, and wherein the intermediate optical assembly includes a second matrix array of fluorescent regions aligned with the first matrix, different ones of the fluorescent regions being of at least two different materials arranged to emit visible radiation of two different colours when illuminated by ultra-violet radiation from the source, and a third matrix array of lens elements located between the second and first matrices such that light emitted by the fluorescent regions is focussed by the lens elements towards the electrically-energizable elements of the first matrix.

Claims

2. A display according to Claim 1, wherein the fluorescent regions are

formed on a surface of the lens elements.

3. A display according to Claim 1, wherein the fluorescent regions are formed on a surface of a plate between the lens elements and the source of radiation.

4. A display according to any one of the preceding claims, wherein the fluorescent regions have a layer of ultra-violet reflective material formed on a surface remote from the source of ultra-violet radiation.

5. A display according to any one of the preceding claims including a support for the lens elements and wherein the support prevents passage of radiation except through the lens elements.

8 6. A display according to any one of the preceding claims including three different fluorescent regions that emit three different colours predominantly red, green and blue.

7. A display according to any one of the preceding claims, wherein the electricallyenergizable elements are LCD elements.

8. A display according to any one of the preceding claims, wherein the lens elements are convex lenses.

9. A display according to any one of the preceding claims, wherein the lens elements are of a material that absorbs ultra-violet radiation.

10. A display substantially as hereinbefore described with reference to Figures land 2 of the accompanying drawings.

11. A display substantially as hereinbefore described with reference to Figures 1 and 2 as modified by Figure 3 of the accompanying drawings.

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