Title of Invention

"EDGE-LIT ILLUMINATION SYSTEM"

Abstract

An edge-lit illumination system comprising a light transmitting sheet (10) and a light source (13. 14): the light source (13, 14) being positioned in proximity to and adjacent to an edge of said light transmitting sheet (10). characterised in that at leasl tane of the two opposing surfaces (11, 12) of said light transmitting sheet (10) carries markings such that said markings are disposed randomly within each of at least one nominal area of said at least one surface. If this novel surface treatment is disturbed or disrupted, for example by staining or abrasion, the disruption to the illumination of the system is less than would be expected.

Full Text

Edge-Lit illumination System The present Invention relates to an edge-it illumination system Edge-lit illumination systems which have as a basic feature a light source positoned alongside an edge of a light transmitting shest are well known. The state of the an is typified by the Bgnt transmitting sheet being treated on at least one of its surfaces such that the light entering the edge of this sheet Is irregularty reflected or acattered Therefore this Hgnt is spread evenly across the illuminated surface. One of the ways of treating the surface Is by application of a matrbc of fight reflecting and scattering malarial either directly to the surfaca or to a transparent fltm which Is then adhered to the surface as dtsdosed In EP- A- 0549679. In this application the light transmitting sheet a treated on both of its surfaces The light reflecting material is In the form of dots. These dote may be etched, painted or screen printed directly on to the surfaca of the light transmitting sheet or that of the transparent film adhered to the surface. The densty of these dots may be Increased In the direction away from the edge at which the lignt source is fixed by increasing the number of dots per unit area end decreasing the geps between them or by keeping the gaps between the dots the same and Increasing the site of the dots. One disadvantage of the above system la that if this dot pattern across the light transmitting sheet is disturbed or disrupted in some way then correspondingly visually the illumination of the system appears to be disturbed. Far example if a section of the dot pattern is abraded or stained then the flumination may appear to be disrupted corresponding to where the abrasion or staining has occurred on the surface of the light transmitting sheet A further disadvantage of the above system Is a feature of the light transmitting tried being treated on both of Its surfaces- Therefore there may be complete overlap of some at the dots on the upper surface of the sheet with some on the lower surface of ths sheet This causes fringing patterns which are apparent to an observer of such on edge-lit aunineted sign as slight dark patches on the surface of the sign. By fringing ws mean bands, rings or other patterns of ettamata light or dark It is an object of ths present invention to provide an adge-ltt Illumination system which overcomes some of these problems. Accordingly the precent invention provides an edge-lit Illumination system comprising a light transmitting sheet and a light source; the light source being positioned in pronnvty to and adjacent to an edge of and light transmitting sheet, characterised In that at least one of the two opposing surface of said light transmitting sheet cames markings such that said markings are disposed randomly within each of at least one normal area of said at least one surface The light transmitting sheet Is a transparent material. It may be glass or plastic but is preferably plastic and more specifically a clear acrylic inset. The sheet may be of any shape, for example round, square, rectangular, triangular, cylindrical Irregular. Preferably it is rectangular Many types of light source ere available but preferably fluorescent tubing is used The diameter of the fluorescent tube may vary from typically 6mm, commonly referred to as T2, to 25mm. T8. The distance from the edge of the light transmitting panel to the crast of the tube is preferably between 1 and 2mm. In an alternative embodiment the fluorescent tube is an aperture tube. This type of tube has coatod on the Inside wall of the glass a reflective coating with a fluorescent coating on top of it The aperture Is a part of this tube, for example 30* of the 360* around the nside of the tube, with no coating. This opening nuns the length of the tube and Is arranged so a a directing light from the light source at the edge of the light transmitting sheet. A reflector Is typically positioned behind each fluorescent tube and may be any material capable of reflecting light, for example mirrored aluminium. Preferably the light transmitting sheet Is in a fixed relationship to the Hght source. The surface of at least one side of the hght transmitting sheet may comprise a single nominal area or it may be comprised of a plurality of nominal areas. The angle nominal area or the plurality of nominal areas may cover part of the surface of the light transmitting sheet or the total area of the surface of the sheet Each of these nominal areas maybe of an equal acre or alternatively they may bo of different sizes. For example, where the light transmitting sheet is rectangular, the length of each nominal area may be epproximataly equal to the length of the edge of the sheet adjacent the light source and the width of each nominal area may bo the same or a varied distance along the length of the light transmitting sheet, moving away from the light source. Each of tho normal areas has markings which era disposed randomly within It The markings may be of any shape, for example square, round, rectangular, triangular or irregular, or a combination of different shapes Preferably they are of an Irregular shape, for example irregularly shaped generally elongated structures based on squares and/or rectangles. The markings may be of equal sae or a variety of sizes preferably ranging from 0.1mm to 10mm in length, more preferably 0.3 to 3mm. Preferably the width of tho markings ranges from 0 5 to 1mm. The makings can be translucont or opaqua and are preferably light coloured. By translucent the mean capable of transmuting rays of light with diffusion also. By opaque we moan substantially Incapable of transmitting light but with trie ability to softer IfghL These markings may be etched, painted or screen printed directly on to the surface of the Ight transmlttJns sheet or to that of a transparent film which is itself then adhered to the surface. Preferably the markings ore screen printed directly on to the lurfaca of the light transmitting sheet An example of Ink screen printing stochastic screen printing. One single way of defining stochastic screen printing is to compere it with the screen printing of the regular dot matrix, for example as illustraled in Figure 1 in EP- A-0649876. For a chosen nominal area of the regular dot matrix there to an associated coverage of link on the light transmitting sheet. For tha stochastic screen printing each dot in This link coverage is broken down, using a computer programme, Into many smaller random markings (these smaller markings are the markings of (he present application). These gmaller markings are randomly distributed in a pattern in the designated nominal area They may be of aqual size or a variety of aizes. This is as disclosed in Semen Process. July 1995. page 14 by J Mulvey. Tha area of coverage of ths marktings, for example as ink coverage if treatment of the surface is by ink screen printing is preferably 0.1 to 99%. more preferably 1 to 40% and espodaly 5 to 30% for the random markings within each nominal area. The ansa of coverage of tha markings on the surface of the light transmitting sheet may remain the same for each nominal area across the sheet. For example a sheet may have a number of nominel areas, which may be of equal or a variety of sizes, each nominal area having 10% markings coverage in a further embodiment ths density of markings within each nominal area is Increased in a direction away from the edge of the light transmitting sheet at which the fight source is positioned. The tensity of markings can be increased by increasing the size of tha markings and/or the number of markups for eech nominal area in tha direction away from the tight source For example for an edge iit system with a single light source there may be a number of nominal areas, each having a length approximately equal to the length of the edge of the sheet adjacent the light source and each heving a width, which may be the same or a varied distance along the length of the light transmitting sheet moving away from the light source The first area has a markings coverage of 3% and the coverage gradually increases with each nominal area until the nominal area which is furthest away from tha edge of the light trenamltting sheet at which the light source Is positioned has an area of markings coverags of 20% The overall illumination achieved may be similar or greater than that achieved when the dot matrix is regular, for example as flustratsd in Rgure 1 in EP- A- 0549679 Edge-lit llumlnation systems described in the present Invention can be used as lighting devices or light sources, for example for backIt displays and also may be modified for use as IDumlnBtad shelving, for example in refrigerators. Specific ambodimants of the Invention will now be further described In the following examples and with reference to the accompanying Figures. Figure 11s a sectional view through an llluminatad display system according to the Invention. Rgure 2 is an embodiment of the random markings pattern on one surface of the light transmiting sheet Figure 3 is a plan view of an abraded alluminated light transmitting sheet, treated on both surfaces according to the Invention. Rgure 4 is a plan view of an abraded Illuminated light transmitting sheet treated on both surfaces for comparative purposes. In Figure 1 the light transmitting sheet (10) is a 420 x 610 x 10mm clear cast polymethylrnethacrylare (PMMA) which has been treated by screen printing while Ink markings directly on to both Its opposing surfaces (11.12). The markings are printed on to each surface as shown in Figure 2 and range from 0.3 to 3mm in length. The light sources are Sytvanla Luxline Plus Daylight Delux fluorescent tubes (13,14) which both have a power output of 18 Watts, a colour rendering value (Ra) of 86 a colour temperature of 6500 Kalvin and a diameter of 25mm. These are each placsd adjacent to an edge of the light transmitting sheet and surrounded by a mirrored aluminium reflector (16.18) Example 2 The treated light transmittng sheet of Example 1 has been abraded on its upper surface (11). The abrasion is m the form of 6 marktings (17-22 Inciusive) fn a triangular configuration. Figure 3 illustrates the abraded illuminated sheet viewed from above the upper surface. Example 3 - Comparative Ths light transmitting shset of Example 1 has been replaced by a light transmitting sheet of the same damansions treated by screen printing a regular matrix of white Ink dots dlrectiy on to both its surfaces The level of Ink coverage ranges from about 3% In creeling to 16% along the light path length of 210mm , away from each of two fluorescent tube light sources (13,14). (By light path length we mean for a single light source the furthest distance, along (he length of the surface of one side of this sheet, through which light a emitted- For two light sources. adjacent to opposite edges of this sheet, then the light path length It half the distance between the two tubes.) The dots are circular and a regular distance apart, such that each nearest neighbour is 1.9mm away. The light transmitting sheet has been abraded as In Example 2. Figure 4 illustrates the abraded (23-2B inclusive) illuminated sheet viewed from above the upper surface. It can be readily seen from Figures 3 and 4 that the vieual disruption to illumination caused by tho abrasion is much easier to Identify in the comparative example in Figure 4 There is no evidence of the pres once of any dark patches in Figure 3 which could be attributed to fringing patterns. We claim: 1. An edge-lit illumination system comprising a light transmitting sheet and a light source; the light source being positioned in proximity to and adjacent to an edge of said light transmitting sheet, characterized in that at least one of the two opposing surfaces of said light transmitting sheet carries markings ranging from 0.1 to 10 mm in length such that said markings are disposed randomly within each of at least one nominal area of said at least one surface. 2. An edge-lit illumination system as claimed in claim 1, wherein both of the opposing surfaces of the light transmitting sheet carry markings. 3. An edge-lit illumination system as claimed in either of claim 1 or 2, wherein the area of markings coverage in each nominal area is between 0.1 to 99%. an edge-lit illumination system as claimed in claim 3, wherein the area of markings coverage in each nominal area is between 1 to 40%. An edge-lit illumination system as claimed in any of claims 1 to 4, wherein each nominal area is of an equal size. An edge-lit illumination system as claimed in any of claim 1 to 4, wherein each nominal area is of a different size. An edge-lit illumination system as claimed in any of claims 1 to 6, wherein the area of markings coverage is the same in each nominal area. 8. An edge-lit illumination system as claimed in any of claims 1 to 6, wherein the area of markings coverage is different in each nominal area. 9. An edge-lit illumination system as claimed in claim 1, wherein the markings range from 0.3 to 3mm in length. '.0. An edge-lit illumination system as claimed in any of claims 1 to 9, wherein the markings are of an irregular shape. An edge-lit illumination system as claimed in any of claims 1 to 10, wherein the markings are screen printed directly on to the surface of the light transmitting sheet. An edge-lit illumination system substantially as herein described with reference to the accompanying drawings.

Documents:

in-pct-2001-90-del-abstract.pdf

in-pct-2001-90-del-claims.pdf

in-pct-2001-90-del-correspondence-others.pdf

in-pct-2001-90-del-correspondence-po.pdf

in-pct-2001-90-del-description (complete).pdf

in-pct-2001-90-del-drawings.pdf

in-pct-2001-90-del-form-1.pdf

in-pct-2001-90-del-form-13.pdf

in-pct-2001-90-del-form-19.pdf

in-pct-2001-90-del-form-2.pdf

in-pct-2001-90-del-form-3.pdf

in-pct-2001-90-del-form-5.pdf

in-pct-2001-90-del-gpa.pdf