AU737722B2 - A method for extracting and distributing light from solid transparent light guides - Google Patents

Description

*4 IP0 AUSTRALIAw P100/tiln3 AMN mom Patents Act 1990 8tReuao3.

Original 7 i t 4Complete Specification Standard Patent Invention T1itle 6T# 4>4 D R E (4 C 41, AN 'Di ~i6 FRO rvj S OLAl3 TaA,%SPArR-.-r7 C-147- CuiDc3s ~The following statement is a full descniption of this invention, including the best method of performning~s~ W kow to me:-t a- 4 1 A METHOD FOR EXTRACTING AND DISTRIBUTING LIGHT FROM SOLID TRANSPARENT LIGHT GUIDES BACKGROUND OF THE INVENTION Conventional light distribution systems comprise discrete luminaires connected and supplied by electrical power cables.

The luminaires are generally distributed evenly over the ceiling of the room or space to be illuminated. This type of system has the disadvantage of a large number of relatively expensive individual light sources in the ceiling of the room. Each individual light source must be maintained or replaced at regular intervals requiring access to the light source which may, for example, be in a high ceiling. Each individual light source requires a considerable expense in electric cabling, switching and control.

In remote source electrical lighting a small number of highly 1 5 efficient and high output light sources may be linked by a light piping system incorporating light extraction and distribution devices. The advantages of such a system are that once installed dn the ceiling of a building the light piping system requires little maintenance and the remote electrical light sources may be S 20 located at a position much more readily accessible than the ceiling. This is particularly the case in high ceiling buildings such as theatres, sport stadiums, swimming pools or lecture :theatres.

However methods for extracting and distributing the light from 25 such light piping systems are poorly developed. Light piping systems are usually based on hollow light guides in the form of a cylindrical metallic reflector, or, on light guides formed from Ssolid transparent material in which the transmission of light occurs by the highly efficient phenomenon of total internal reflection at the solid dielectric to air interface. However the means of extracting and distributing the light from hollow light guides and, more particularly, from solid transparent light guides are very poorly developed. The reason for this is that the light is transported through the volume of the solid light guide and, to extract light efficiently it is desirable the extraction of light occurs from elements inside the solid light guide. However it is not obvious how light extraction means may be easily 2.

incorporated within the volume of a solid transparent light guide.

A method for making light deflecting window panels for the improved illumination of rooms by forming an array of laser cuts in a transparent acrylic sheet has been described previously, (Edmonds, AU 601634 (1990) "A window panel for improved daylighting of room interiors"; US 4,989,952 (1991) "Transparent light deflecting panel for daylighting rooms"). With the objective of deflecting light as it is being transmitted through a window panel the laser cuts are made at angles near normal to the surface of the panel so as to produce an array of reflecting surfaces within the panel which serve to deflect light transmitted from one side of the panel to the other. However the present invention differs both in objective and in method from this previous invention.

1 5 It is an objective of the present invention to provide a simple and versatile method for the production of reflecting elements within a transparent solid light guide for the extraction and distribution of light from said light guide.

The discussion above relates to remote source lighting in which light from a remote source is piped to a location where it is extracted and distributed for the purpose of illumination. The same concepts of light guiding, light extraction and light ':distribution may also be applied to the production of novel forms of luminaires in which light is guided from a source which is not 25 remote from, but adjoins the light extraction and distribution system. In this case the source, the solid transparent light guide, and the means of extraction and distribution of light form a localised system which serves the same function as systems generally referred to as luminaires. Light sources used in luminaires emit light with substantially radial or spherical symmetry if the source is point like (for example high intensity o discharge lamps) or with substantially cylindrical symmetry if source is tubular (for example fluorescent tubes). In a conventional form of luminaire light from an essentially radial or 35 cylindrical source travels directly through space to a reflective or diffusive element which serves to distribute the light in some desired manner. In the form of luminaire envisaged here a solid light guide and the associated extraction and distribution means serve to distribute light from essentially radial or cylindrical light sources in some desired manner.

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Therefore another objective of the present invention is to provide a simple and versatile method for extracting and distributing light from solid light guides for the purpose of producing novel and useful forms of luminaires.

It is desirable to produce a display which can be readily switched to display multiple messages to the front or to the rear of the display.

Displays in which light is admitted to a transparent panel and then extracted from the panel in a specified pattern have been 1 0 described previously. The methods of extracting the light include producing a sandblasted surface pattern which diffuses some light out of the panel and laminating a diffusing surface to the panel which also diffuses some light out of the panel. Both methods suffer from low efficiency due to the fact that diffusing surfaces generally diffuse light both in the forward and backward direction and thereby lower the efficiency of producing forwardly diffused light. Also as the visual display originates from diffuse light the brightness of the display falls rapidly with distance from the display. Therefore if light could be extracted from a solid transparent panel in a direction primarily normal to the face of the panel the brightness of the display when viewed from a distance would be much greater.

Therefore it is another object of this invention to provide a ".:simple and versatile method of extracting light from a 25 transparent light guiding panels at defined positions on the panel so as to produce a bright and useful form of display which can be readily switched to display, alternately, up to four different messages from the same panel.

SUMMARY OF THE INVENTION 30 This invention provides a method for extracting and distributing light from a solid transparent acrylic light guide by making laser cuts into the acrylic material at an angle approximating 450 relative to the normal to the surface of the acrylic light guide, the laser cuts extending right through, or partly through, the solid light guide such that highly reflecting surfaces are produced inside the solid light guide which reflect light propagating in the light guide out of the light guide and into directions approximately normal to the surface of the light guide.

BRIEF DESCRIPTION OF THE DRAWINGS.

The invention is illustrated in the drawings of which: FIG 1 illustrates the method of this invention of making angled laser cuts in a solid transparent light guide to extract light propagating in the light guide; FIG 2 is a cross section view of a light guide with light being extracted from the light guide by angled laser cuts according to the method of this invention; FIG 3 shows the manner of distributing angled laser cuts in a light guide so as to extract equal quantities of light at each section of guide so as to produce a source of constant luminance; FIG 4 shows an arrangement whereby a light guide with angled laser cuts to extract and distribute light is connected via solid light guide to a remote source of light; FIG 5 illustrates how multiple light guides with angled laser cuts extracting light according to the method of this invention may be linked via conventional light guiding elements to a single intense and remote source; 20 FIG 6 illustrates how a point like light source may be coupled to a ".disc like light guide; FIG 7 illustrates how light propagating in a disc like light guide may be extracted from the guide by making angled laser cuts in the guide according to the method of this invention; FIG 8 illustrates how light may be refracted upwards or downwards at the outer edge of a light guide by cutting or milling the outer face to some appropriate angle; FIG 9 illustrates how light from a tubular light source may be coupled to a planar solid transparent light guide provided with the angled laser cuts of this invention in order to extract light from the guide for the purpose of room illumination; FIG 10 illustrates how a light source emitting a substantially parallel beam may be coupled to a light guide so that light propagates radially in the guide and may be extracted at angled laser cuts for the purpose of room illumination; FIG 11 shows how multiple light guides provided with angled laser cuts for light extraction may be coupled through a ceiling aperture to a light source located within the ceiling cavity; FIG 12 shows how a pattern of angled laser cuts may be made in a large solid transparent panel so that the large panel may subsequently be sub divided into a set of smaller panels with an approximation of a radial pattern of angled laser cuts in each sub divided panel; FIG 13 illustrates how light propagating in a transparent solid light guide may be extracted to one face or the other face of the guide by an angled laser cut depending on the direction of light propagation in the guide; FIG 14 illustrates how a pattern of angled laser cuts in a solid transparent panel may produce a pattern of luminance to one side or the other side of the panel dependant on the switching of tubular light sources at different edges of the panel; FIG 15 illustrates how two patterns of angled laser cuts encoding two different messages in a panel may be alternately illuminated by sources at the edges of the panel to display the messages to .the front or the back of the panel; 25 FIG 16 illustrates how a dense pattern of small angled laser cuts may be made in a panel to encode a symbolic message in a panel which may be illuminated by lights at the edges of the panel; FIG 17 shows how a dense pattern of small angled laser cuts may be made in a panel to encode two messages in a panel which may be alternately illuminated by light sources at two edges of the panel; FIG 18 shows how a dense pattern of small angled laser cuts may be made in a panel to encode four messages in a panel which may be alternately illuminated by light sources at the four edges of the panel.

DETAILED DESCRIPTION OF THE INVENTION The basic form of light distribution system to which the present invention relates comprises a source of light, a means of injecting light from the source into a transparent solid light guide and a means of extracting the light from the light guide such that some desired light distribution may be obtained.

Referring to FIG. 1, light from a cylindrical source 1 is coupled into a solid transparent light guide 3 by a reflector 2.

The light extraction and distribution method of this invention is obtained by making laser cuts 4 in the material of the guide with a programmable laser cutting machine. The laser cuts extend from the surface of the guide into the material at an angle to the normal to the surface such that light rays 6 propagating inside the guide are reflected at the acrylic to air interfaces so 1 5 produced by the laser cuts and are reflected through the surface of the light guide and out of the light guide in a direction substantially normal to the surface of the light guide.

The geometry of this method of light extraction is shown in Fig 2.

where a longitudinal cross section of a solid light guide of rectangular profile with light propagating from the left toward the right is illustrated. When light 6 propagating parallel to the surface of the solid light guide 3 meets a thin laser cut 4 made in the material at an angle of 450 to the normal to the surface the light is total internally reflected at the air material interface 25 so created and is reflected out through the surface of the material in a direction normal to the surface of the material. The angle of incidence on the internal surface produced by laser cutting is, in this case, 450 which exceeds the critical angle for total internal reflection ic at an air to acrylic interface (ic S 30 arcsin(1/n)) where n is the refractive index of the material in the wavelength region of visible light (n 1.5 and ic 420 for acrylic plastic). Thus in this case all light incident on the laser cuts is *extracted from the guide. More generally light propagating within the solid light guide by total internal reflection lies within an 35 angular range of 420 of the longitudinal axis of the guide.

Some of this light will be incident on the surface of the laser cuts at angles of incidence ic and will not be totally reflected.

Thus, in general, only some fraction of the light incident on the laser cuts will be totally internally reflected with the remainder being partially reflected and partially transmitted. Additionally if the laser cuts do not extend right through the guide and/or if the laser cuts do not extend all the way across the guide then some light propagating in the guide will not intercept the laser cuts. Thus in general some fraction fl will be reflected out of the guide at the location of laser cuts with the remainder (1 fl) transmitted further along the guide. At a location further along the guide a different fraction f 2 may be extracted by laser cuts of appropriate extent.

Depending on the angle and extent of the laser cuts there are many light distributions possible with this system. However one practical form of light distribution from a guide would require that equal amounts of light be extracted from all parts of the light guide. In this case the luminous energy propagating in the light guide would decrease progressively along the length of the light guide and to obtain equal emission from all parts of the guide the laser cuts would need to be such that progressively larger fractions of the luminous energy were extracted at progressively larger distances along the light guide. It may be shown, (Edmonds et al, Extractors and emitters for light distribution from hollow light guides, Lighting RESEACH and Technology, 29(1) 23-32 (1997), Corrigenda 29(2) 88 (1997)) that equal emission may be obtained if the fractions extracted per unit length of the guide, fi, are related by the expression fi fi+/(1 fi+l).

25 It follows that the fraction of light extracted out of the guide must follow the inverse ratio of (1 x) where x is the distance from the end of the guide. For example, the fraction of light extracted at the end of the guide should equal 1 and at progressive unit distances, x, towards the input to the guide the fraction of light extracted should decrease as 1/(1 That is as 1, 1/2, 1/3, 1/4, 1/5, etc. This fractional extraction and even distribution of luminance can be achieved by spacing the laser cuts across the guide as illustrated in Fig 3. Fig 3 shows a rectangular light guide 3 which is unit distance wide and 5 unit distances long. The third dimension,the thickness of the guide, would be about 1/100 of a unit distance in a practical guide. For example if the unit distance is one metre the thickness of transparent acrylic sheet used for the guide would be 1 cm. The laser cuts 4 are made such that in the first unit section the cuts extend over 1/5 of the width of the guide, and in the next section over 1/4 of the width etc. In practice the cuts would be made smaller and more numerous so that the required fraction extracted is obtained with a much more even distribution of extraction points than illustrated in Fig 3. Also account must be made of the fact that not all light propagating in the guide suffers total internal reflection at the laser cuts. However this example illustrates the general principle by which desired distributions may be obtained. When a light guide with laser cuts made in this manner is coupled to a thin cylindrical light source by a collimation device as illustrated in FIG. 1 then the light guide becomes an extended source of constant luminance.

As one of the desirable features of remote source lighting systems is easy access to the light source it may be desirable to couple a light guide 3 with laser cuts 4 for extraction and distribution via a connecting light guide 7 to a source 1 at some convenient location as illustrated in FIG. 4.

A light distribution system as illustrated in FIG. 5 may be made to provide for light transport from a single intense light source via a solid acrylic guide connected via right angle bends to multiple light guides with light extracting laser cuts as in FIG. 1, 2 or 3 to provide an extended light distribution system capable of illuminating large rooms.

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Another objective of the present invention is to provide a simple and versatile method for extracting and distributing light from 25 solid light guides for the purpose of producing novel and useful forms of luminaires. In luminaires the light guide is used to transfer light away from a high intensity source to a position from where it may be extracted and distributed, at much lower .:.luminance, into some desired angular range. The specific form of 30 the light guide used and the specific form of the light extraction method of this invention depends on the type of light source.

There are three types of common light sources; point-like sources, line-like sources and sources which deliver a near parallel distribution of light from an associated parabolic 35 reflector.

Where the light source is point like, for example a short axial filament enclosed in a narrow glass cylinder as in high intensity discharge lamps the light is emitted primarily around the plane perpendicular to the axis of the filament. The effective form of light guide to match a source of this type is a flat disc of transparent solid material located in the radial plane as illustrated in FIG 6. Referring to FIG 6 the source 1 is centred in a central circular hole in a transparent solid disc 3. Light which enters the transparent disc 3 from the central source 1 is guided out radially from the centre by total internal reflection within the solid material of the disc. According to the method of this invention light may be extracted and distributed from transparent guide 3 by making angled laser cuts 4 in the guide at angles substantially at 450 to the face of the disc of material as shown in cross section in FIG 7. Any light not reflected out of the guide at a laser cut passes through the laser cut or bypasses the laser cut without change of direction and is retained within the guide.

The spacing and slope of the angled cuts may be adjusted to obtain a suitable output distribution of the light with a suitably low output luminance. The laser cuts may be placed at angles in the upper or lower surface of the light guide suited to distribute proportions of light upwards or downwards so as to achieve an uplighter or downlighter effect. The outer edge of the disc may be laser cut or milled to a slope which refracts light reaching the outer edge either upwards or downwards as appropriate, as illustrated in Fig 8.

Where the light source consists of a long tubular element (for example as in a conventional fluorescent tube), the light guides 25 best suited are in the form of flat rectangular panels the edges of S. which abut the tubular source as in Fig 9. According to the method of this invention the light may be extracted from the light guides by angled laser cuts made at appropriate positions across the guide. Any light which traverses the entire guide may be extracted from the edge of the guide by milling the edge to a slope which refracts the light in the desired direction as in Fig 8.

Where the light source 1 consists of a point like filament enclosed in a light directing reflector as in reflector lamps or quartz halogen lamps the essentially parallel light emitted may be directed into a solid transparent guide 3 perpendicular to the emitted beam of light and the light admitted into the guide by milling a conical bevel 9 in the guide at a slope of approximately 450 which deflects light from the source into the guide by total internal reflection, as in Fig 10. Once captured in the guide the light may, according to the method of this invention, be extracted by angled laser cuts 4 placed in appropriate radial sequence /0.

across the guide. This type of light guiding luminaire would normally be fixed against the ceiling with the lamp and parabolic reflector set in the ceiling as shown in Fig 11. If necessary it is possible to achieve a better match between the aperture of the source and the guide by using two or more overlapping guides as shown in Fig 11.

If the light extraction is to be uniformly distributed over the surface of the guide so as to produce a luminaire of constant luminance then the density of the laser cuts should become greater as the distance from the source increases. In this way extracting a small fraction of the intense light near the source provides about the same luminosity as extracting a larger fraction of the weaker light further from the source. When the guide is linear in form so that the light is guided in one direction only the fractional density of cuts follows the simple relation fi fi+i/(1 fi+ 1 given above. However when light is guided radially within a guide the extraction ratios required should account for this different geometry.

The method of extracting and distributing light from solid light guides by making angled laser cuts in the guide varies in detail with the type of guide to be produced. For a luminaire in which the light is guided substantially in one direction from the source as, for example a tubular source as in Fig 7, the method is to make angled laser cuts to some specified depth through a large 25 area panel (typically about 3/4 way through) at specified intervals across the panel. Subsequently the large area panel may then be laser cut into narrow rectangular panels with the required cross section. However, for a light guide in the form of a circular disc the method of placing laser cuts in the disc is o 30 more complicated. On laser cutting machines provided with an angled head the head cannot conveniently be rotated during the cutting process. Thus, to cut an angled laser cut around a circular path on a planar disc by moving the laser cutting head is not possible. In this case it is more appropriate to keep the angled 35 laser cutting head stationary and to rotate the disc of acrylic below the laser beam. The procedure is as follows. The disc of clear acrylic plastic is mounted centrally on a rotatable platform.

0 The laser beam is directed at the surface of the disc at the **"desired angle to the normal to the disc and at some specified 40 distance from the centre of the disc and the axis of the rotating platform. The platform is set rotating at a specified angular velocity and the laser is switched on and off for specified intervals of time such that angled laser cuts are made around a circular arc centred on the centre of the disc. The cut made may be continuous or may be broken at intervals depending on the required aesthetics of the luminaire. When one arc is complete the laser is moved inward or outwards and a second series of laser cuts are made about this second circular arc, and so on.

Ideally the angular speed of the rotating platform and disc would be varied so that the laser, at constant power, makes cuts of the 1 0 appropriate depth through the acrylic disc.

A second alternative to make angled laser cuts of essentially radial form in a disc like guide is to make a series of linear angled laser cuts across a large flat panel. When one series of cuts is made as shown in FIG 12a the large panel is rotated through some finite angle (for example 600) then another series of cuts made across the panel which is then rotated again and another series of cuts made, and so on, until the panel has been rotated through 3600. Then the large panel may be subdivided into smaller disc like panels in which the combination of the series of laser cuts has produced a essentially radial or circular pattern of angled laser cuts as illustrated in FIG 12b.

It is another object of this invention to provide a simple and versatile method of extracting light from a transparent light guiding panels at defined positions on the panel so as to produce a bright and useful form of display which can be readily switched to display, alternately, up to four different messages from the same panel.

o The present invention describes a method by which up to different messages, including no message, can be alternately displayed. The type of display is novel and has not been described S: before. It provides for an illuminated sign in which words of variable size and colour can be alternately displayed. The sign may be in any size from small less than 0.1 metre square in size to extremely large greater than 100 metres square. Where the display can be viewed from the front and the back then two different displays, for example STOP and GO, can be alternately switched between the front and back views. The multiple messages would include the state of no message when the 0 display or sign would carry no message. Ideally in this state the display sign would disappear from view so entirely that viewers

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would not be aware that the display exists in some location.

The basis of the invention is a method of extracting light perpendicular to a panel which is internally illuminated by light admitted into the panel (6mm to 15 mm thick) from standard thin fluorescent light tubes at the sides of the panel. The method of this invention is to make laser cuts at an angle of 450 to the face of the panel which penetrate right through or partly through the panel. The angled laser cuts are made at specified positions on the panel and in specified quantities such that letters or symbols of a message are encoded in the panel by the angled laser cuts.

The regions of the panel encoded by angled laser cuts become strongly visible to a person viewing the panel when light is extracted from the panel at the laser cuts into a direction substantially normal to the face of the panel. The novel aspect of 1 5 the invention is the method of extracting the light from the panel by using angled laser cuts made in the panel at specified locations on the panel. The advantages are that the light is admitted primarily in a direction normal to the face of the panel and that it is possible to overlap messages by altering the direction of the angled laser cutting and to alternately display these messages by switching light sources located at the four edges of the panel in order to alternately display up to four messages.

Displays in which light is admitted to a transparent panel and 25 then extracted from a panel in a specified pattern have been described previously. The methods of extracting the light include o producing a sandblasted surface pattern which diffuses some light out of the panel and laminating a diffusing surface to S"the panel which also diffuses some light out of the panel. The 30 advantage and novelty of the present invention is in the method of extracting light by making angled laser cuts into the panel.

Angled laser cuts extract light by total internal reflection. The .advantages of the present method relative to previous methods are, firstly, that with angled laser cuts the light is reflected out 35 of the panel and not diffused. This allows for a much brighter luminance and allows the display to be seen at much greater distance. The second advantage is that multiple displays (up to 4 in number) may be made in the same area of panel with each particular display having its pattern of angled laser cuts sloping ;40 at directions at 900 to the each other. By placing tubular light sources at each edge of the panel up to 4 different displays can be /3.

alternately displayed from the face of the panel by switching alternately between the 4 light sources.

The principle of the method is illustrated in FIG 13. Light which passes into a transparent prism as in FIG 13a may be total internally reflected at a surface at approximately 450 and extracted from the prism of material. If the light entering the prism of material is spread over some angular range then some of the light may be extracted and some of the light may be refracted through the 450 surface as shown in Fig 13b. However, if the reflecting surface is produced internally to the material of the panel by making a parallel sided laser cut into the material at approximately 450 with a laser then some light may be extracted while some light may pass through the laser cut undeviated as shown in FIG 13c. Such light as passes through the laser cut will be retained inside the transparent material by total internal reflection and may subsequently be extracted at other laser cuts.

If light enters the transparent material from the right hand side as shown in FIG 13d this light will be extracted by total internal reflection into the opposite direction as light entering from the left hand side (FIG 13c). This is illustrated in Fig 14 which shows in cross section how tubular fluorescent light sources 1 and 2 may be coupled to the edges of a solid transparent panel 3. For efficient use of light the sources would require a reflective arrangement 12 around the light source as shown in Fig 14 to couple more of the light from the source into the transparent panel edge. Note that when source 1 is on light is extracted by the laser cut 4 to the front and when source 2 is on light is extracted by the laser cut 4 to the back of the panel. By making a number of laser cuts in specified regions of the panel a pattern S 30 may be formed on the surface of the panel which would appear o bright from the front when light source 1 is on and would appear bright when viewed from the back when light source 2 is on. A pattern of laser cuts may be made in the panel with the laser cuts S"sloping upwards to the left and another overlapping pattern of laser cuts sloping upwards to the right as in Fig 15. When *.***light source 1 is on pattern A appears to the front and pattern B appears to the back as illustrated by the full lines in Fig 15. When light source 2 is on the patterns of light displayed to the front and the back are reversed, (broken lines in Fig 15). Fig 16 illustrates how a pattern may be made on the panel by placing a large number of evenly spaced small angled laser cuts in the panel. This pattern becomes luminous when one of the light lisources is switched on. When two patterns of small angled laser cuts are made in the panel such that one pattern of laser cuts slopes to the right towards source 2 and the other slopes to the left towards source 1 the patterns can be alternately illuminated by switching between source 1 and 2 as illustrated in Fig 17. If sources are placed at all 4 edges of the panel then four different patterns may be illuminated and alternately displayed by switching alternately between each of the 4 sources as illustrated in Fig 18. Note that the four patterns may be overlapping on the panel. However in Fig 18 the patterns are shown separated for clarity.

It should be noted that where the surface of the panel is perforated by a pattern of angled laser cuts it is possible for moisture and dust to enter the laser cuts and degrade performance. Thus where such panels are used in exposed environments the side of the panel on which the laser cuts are made would be protected by lamination of a thin solid sheet of clear plastic or glass to the panel.

This new type of illuminated display panel would have application in traffic and pedestrian control and also in advertising. It is useful to note that automatic laser cutting machines can be programmed to execute very complex patterns automatically. The mode of production envisaged is that a particular pattern of laser cuts would be programmed and cut in an acrylic panel by a laser 25 cutting beam angled at approximately 450. The panel would then S: be rotated through 900 and another pattern (possibly overlapping the first) cut in the panel. The panel is then rotated again through 900 and another pattern cut and so on to produce four patterns.

Four light sources fitted to the four edges of the panel could then 30 be switched to alternately make each pattern luminous to a viewer.

.While the method of this invention for extracting and distributing light from solid transparent light guides has been described in detail in relation to the production of remote source lighting 35 systems and to the production of luminaire systems and to the production of illuminated displays it is not limited in application to these systems.

Claims (1)

1. 6.000. approximately 450 with the radius extending from the centre of the disc to the point at which the laser cut is being made thereby 0. producing concentric conical interfaces inside the material of the 25 disc whereby light propagating radially outwards from the centre S. of said disc and falling on said laser cuts is extracted by internal reflection at the surface of said laser cuts and distributed through the surface of said disc for illumination purposes. Claim 6. An illuminating system comprising two flat, horizontal, rectangular panels of solid transparent material positioned such that one long edge of one transparent panel is separated from a long edge of the other transparent panel by a short distance thereby forming a narrow parallel sided gap between the long edges of each panel; a thin cylindrical light source located in the gap between said panels and lying in the horizontal plane formed by said two panels such that a high proportion of the light emitted by said light source passes through the edges of said two panels proximate to said light source and enters into and is ,4 guided by total internal reflection through the interior of said 17 panels, said transparent panels having a plurality of linear laser cuts made through the lower or the upper surfaces of said transparent panels at specified distances from the axis of said cylindrical light source with said laser cuts being cut through the surface of the transparent panels such that the planar air to solid material interfaces produced inside the material of said transparent panels by said laser cuts are parallel the axis of said cylindrical light source and make an angle of approximately 450 to the upper and lower surfaces of said transparent panels whereby light propagating in said transparent panels which falls on said laser cuts is extracted by total internal reflection at the surface of said laser cuts and distributed through the lower surfaces of said transparent panels for illumination purposes. Claim 7. An illuminating system comprising a circular disc of 15 solid transparent material with a small conical volume of material removed from the central region of said circular disc such that the apex of the conical surface so formed is on the central axis of the disc and contingent with the upper surface of said circular disc; a light source in a parabolic reflector which 20 produces a near parallel beam of output light, said light source being located on the central axis of said circular disc such that the near parallel light emanating from the source is directed o along the direction of the central axis of said circular disc so that the light enters the top surface of said circular disc and S 25 impinges on the conical transparent material to air interface and is thereby reflected by the process of total internal reflection to flow radially outward through the interior of said circular disc; said transparent disc having a plurality of concentric laser cuts made through the lower or upper surface or both surfaces of said transparent disc at specified radii from the centre of said transparent disc with said laser cuts being cut through the surface of the disc such that the direction of the laser cut makes an angle of approximately 450 with the radius extending from the centre of the disc to the point where the laser cut is being made, whereby light propagating radially outward through said circular disc and incident on the laser cuts is extracted from the disc by total internal reflection at the laser cuts and distributed through the surface of said disc for illumination purposes. Claim 8. An illuminating system substantially as herein described with reference to the accompanying drawings. Claim 9. A luminous display comprising a vertical rectangular panel of transparent material having a front face, a rear face, a left vertical edge and a right vertical edge, an upper edge and a lower edge; said vertical transparent panel of material having a thin vertical source of light positioned adjacent to the left vertical edge such that light from the source enters the left vertical edge of the panel and is guided within the panel through the interior of the panel from left to right; said panel having a pattern of vertical laser cuts made across the front face of the panel from right to left, said laser cuts being made in a pattern on the front surface of said panel such that the pattern of laser cuts represents the form of specific letters, numbers or shapes; said laser cuts extending through or partly through said panel with said laser cuts being made at an angle of approximately 450 to the front face of said panel such that light propagating from left to right in the interior of said panel and falling on said laser cuts is reflected by total internal reflection at the surface of said laser cuts out of the front face of said panel in directions near normal to the front face of said panel 20 thereby making the pattern of laser cuts luminous and visible to a person looking towards the front face of said panel. 0 Claim 10. A luminous display providing a front directed and a rear directed display comprising a vertical rectangular panel o f transparent material having a front face, a rear face, a left S 25 vertical edge and a right vertical edge, an upper edge and a lower edge; said vertical transparent panel of material having a thin vertical source of light positioned adjacent to the left vertical edge such that light from the source enters the left vertical edge of the panel and is guided within the panel through the interior of the panel from left to right; said panel having a first pattern of vertical laser cuts made across the front face of the panel from right to left, said laser cuts being made in a pattern on the front surface of said panel such that the pattern of laser cuts represents the form of specific letters, numbers or shapes with said laser cuts extending through or partly through said panel and said laser cuts being made at an angle of approximately 450 to the front face of said panel such that light propagating from left to right in the interior of said panel and falling on said laser cuts is reflected by total internal reflection at the surface of said laser cuts out of the front face of said panel in directions near normal to the front face of said panel thereby making the first ,pattern of laser cuts luminous and visible to a person looking 1q. towards the front face of said panel; said panel having a second pattern of vertical laser cuts made across the rear face of the panel from right to left, said laser cuts being made .in a second pattern on the rear face of said panel such that said second pattern of laser cuts represents the form of specific letters, numbers or shapes with said laser cuts extending through or partly through said panel and said laser cuts being made at an angle of approximately 450 to the rear face of said panel such that light propagating from left to right in the interior of said panel and falling on said laser cuts is reflected by total internal reflection at the surface of said laser cuts out of the rear face of said panel in directions near normal to the rear face of said panel thereby making the second pattern of laser cuts luminous and visible to a person looking towards the rear face of said panel. Claim 11. A luminous display as in claim 10 wherein the thin vertical source of light comprises a fluorescent tube or comprises an linear array of light emitting diodes. Claim 12. A luminous display substantially as herein described 20 with reference to the accompanying drawings. :Claim 13. A switchable luminous display providing two different forwardly directed displays comprising a vertical rectangular panel of transparent material having a front face, a rear face, a left vertical edge and a right vertical edge, an upper edge and a 25 lower edge; said vertical transparent panel of material having a thin vertical source of light positioned adjacent to the left vertical edge such that light from the source enters the left vertical edge of the panel and is guided within the panel through the interior of the panel from left to right; said panel having a first pattern of vertical laser cuts made across the front face or the rear face of the panel from right to left, said first pattern of laser cuts being made in a pattern on the front surface of said panel such that the pattern of laser cuts represents the form of specific letters, numbers or shapes and said laser cuts extending through or partly through said panel with said laser cuts being made at an angle of approximately 450 to the front face of said panel such that light propagating from the left within the interior of said panel and falling on said first pattern laser cuts is reflected by total internal reflection at the surface of said laser cuts out of the front face of said panel in directions near normal to the front face of said panel thereby making the first pattern of laser cuts luminous and visible to a person looking towards the front face of said panel; said vertical transparent panel of material having a second thin vertical source of light positioned adjacent to the right vertical edge such that light from the source enters the right vertical edge of the panel and is guided within the panel through the interior of the panel from right to left; said panel having a second pattern of vertical laser cuts made across the front face or rear face of the panel from right to left, said second pattern of laser cuts being made in a pattern on the face of said panel such that the pattern of laser cuts represents the form of specific letters, numbers or shapes with said laser cuts extending through or partly through said panel and said second pattern of laser cuts being made at an angle of approximately 450 to the face of said panel such that light propagating from right to left in the interior of said panel and falling on said second pattern of laser cuts is reflected by total internal reflection at the surface of said laser cuts out of the front face of said panel in directions near normal to the front 20 face of said panel thereby making the second pattern of laser cuts .".luminous and visible to a person looking towards the front face of said panel; said left vertical light source and said right vertical light source being alternately switchable such that when the left vertical light source only is on the first pattern of laser cuts is made visible to a person looking towards the front face of said panel and when the right vertical light source only is on the second pattern of laser cuts is made luminous and visible to a person looking towards the front face of said panel. o*oo Claim 14. A switchable luminous display providing four different front directed displays comprising a vertical rectangular panel of transparent material having a front face, a rear face, a left vertical edge and a right vertical edge, an upper edge and a lower edge; said vertical transparent panel of material having a first thin source of light positioned vertically adjacent to the left vertical edge, a second thin source of light positioned vertically adjacent to the right vertical edge, a third thin source of light positioned horizontally adjacent to the upper edge and a fourth thin source of light positioned horizontally adjacent to the lower edge such that light from the first source enters the panel and is guided from left to right, light from the second source enters the panel and is guided from right to left, light from the third source S enters the panel and is guided from top to bottom and light from the fourth source enters the panel and is guided from bottom to top; said panel having four different patterns of laser cuts made across the surface of the panel, the first pattern of laser cuts comprised of vertical laser cuts made at an angle of approximately 450 to the face of the panel such that light from the first source falling on the laser cuts is reflected out of the front face of the panel, the second pattern of laser cuts comprised of vertical laser cuts made at an angle of approximately 450 to the face of the panel such that light from the second source falling on the laser cuts is reflected out of the front face of the panel, the third pattern of laser cuts comprised of laser cuts made horizontally across the panel at an angle of approximately 45' to the face of the panel such that light from the third source falling on the laser cuts is reflected out of the front face of the panel and the fourth pattern of laser cuts comprised of laser cuts made horizontally across the panel at an angle of approximately 450 to the face of the panel such that light from the fourth source falling on the laser cuts is reflected out of the front face of the panel; said first, second, third or fourth light sources being alternately switchable on such that said first, second, third or fourth pattern of laser cuts is alternately made luminous and visible to a person viewing the front of said panel. Claim 15. A switchable luminous display as in claim 13 and 14 wherein the thin sources of light comprise fluorescent tubes or comprise linear arrays of light emitting diodes. Claim 16. A switchable luminous display substantially as herein described with reference to the accompanying drawings. 4__ light guide 11/6/01 I H' t i-