GB2468353A

GB2468353A - A light guide device

Info

Publication number: GB2468353A
Application number: GB0903862A
Authority: GB
Inventors: James Gourlay
Original assignee: ITI Scotland Ltd
Current assignee: ITI Scotland Ltd
Priority date: 2009-03-05
Filing date: 2009-03-05
Publication date: 2010-09-08
Also published as: GB0903862D0

Abstract

A light guide device 1 comprises a base substrate 2 having a first refractive index. At least one light source e.g. and LED 3 is mounted on a surface of the base substrate. A guide layer 4 has a light output surface and a second refractive index that is less than or equal to the first refractive index. The guide layer encapsulates the light source(s). One or more reflective light scattering structures 11 and a heat sink plate 8 may be provided. The light guide device is suitable for use in a range of applications, particularly in connection with the backlighting of displays, for example, liquid crystal displays.

Description

INTELLECTUAL

. .... PROPERTY OFFICE Application No. GB0903862. 1 RTM Date:30 June 2009 The following terms are registered trademarks and should be read as such wherever they occur in this document: Stanley; Dymax; Shi Wa.

Intellectual Property Office is an operating name of the Patent Office www.ipo.gov.uk

LIGHT GUIDES

Field of the Invention

This invention relates to light guide layers, light guide devices and methods of manufacture. The light guide layers and devices are suitable for use in a range of applications, particularly in connection with the backlighting of displays, for example, liquid crystal displays.

Background of the Invention

A number of light guiding devices are known. These devices are employed for a range of functions including illumination, backlighting, signage and display purposes.

Typically, the devices are constructed from an injection moulded or machined transparent plastic component, where a light source, such as a fluorescent lamp or a plurality of light emitting diodes (LEDs), is integrated by means of mechanical attachment at the edge of the transparent plastic component.

Common to all of these devices is the fact that light from the light source is guided through a transparent guide, typically made of plastic, by total internal reflection. For backlighting applications, light is emitted in a substantially perpendicular direction to that of the direction of propagation of the light within the transparent guide. This is achieved through the light being directed so as to interact with scattering structures or films located within, or on the surface of, the transparent guide.

The integration of fluorescent lamps or LEDs to the edge of the transparent light guide is not a straightforward process and thus significantly increases the complexity of the production process for these devices. Achieving a good coupling is essential to the optical performance of the device. In addition, edge coupling of the light sources renders these components susceptible to mechanical damage during both the production process and the normal use of the device.

In seeking to provide thin direct lit backlights, it is preferable to have light emitted into the plane of the light guide. Further benefit may be obtained if the light sources are distributed across the panel, so minimising the length of guiding in the light guide. This has the benefit of creating a thin and efficient backlight but has the disadvantage of creating dark spots above the light source. Preferably, these dark spots should not be visible or, at least, reduced in appearance. Existing solutions to this problem tend to add considerable thickness to the backlight.

Many backlights fall into the categories of edge-lit" or direct-lit". These categories differ in the placement of the light sources relative to the output of the backlight, where the output area defines the viewable area of the display device. In edge-lit backlights, one or more light sources are disposed along an outer border or edge of the backlight construction outside the zone corresponding to the output area. The light sources typically emit light into a light guide, which has length and width dimensions of the order of the output area and from which light is extracted to illuminate the output area.

In direct-lit backlights, an array of light sources is disposed directly behind the output area, and a diffuser is placed in front of the light sources to provide a more uniform light output. Some direct-lit backlights also incorporate an edge-mounted light, and are thus illuminated with a combination of direct-lit and edge-lit illumination.

Other challenges facing display manufacturers, such as those incorporating large area LED Back Light Units (BLUs) includes producing a thin and efficient device which enables 2-d or 3-d spatial dimming to support high display performance and reduced power consumption. This has proved problematic for both edge-lit and direct lit devices and has typically resulted in thicker backlight devices.

It is an object of the present invention to provide a light guiding device that addresses one or more of the aforesaid issues.

Summary of the Invention

In a first aspect of the present invention, there is provided a light guide device comprising a base substrate having a first refractive index, upon a first surface of which are mounted one or more light sources and a first guide layer having a second refractive index that is optionally less than or equal to the first refractive index and which comprises a light output surface, the first guide layer being arranged so as to encapsulate the one or more light sources upon the first surface, wherein the base substrate and the guide layer form a composite structure for guiding light produced by the one or more light sources over the first surface and said one or more light sources are positioned directly behind the light output surface and direct light parallel to the plane of the base substrate.

The light guide device may further comprise one or more scattering and/or reflective structures arranged so as to direct light away from the first surface and in the direction of the light output surface. For example, the one or more further scattering and/or reflective structures may be located at the interface between the base substrate and the first light guide layer and/or on the lower surface of the substrate which is opposite the first surface.

The light guide device may comprise a diffuser located above the light output surface.

Upon the first guide layer there may be mounted a second guide layer having a third refractive index that is equal to or greater than the refractive index of the first guide layer and at the interface between the first and second guide layer and above the one or more sources of light may be located one or more light scattering and/or reflective structures. Specifically, the device may optionally not comprise one or more light scattering and/or reflective structures which are located between a first and second light guide layer and above the one or more sources of light. The concealment of the one or more light sources may be provided in the absence of such features. The concealment of the one or more light sources may be provided by only, or substantially only, light directed normal to the plane of the substrate in combination with the diffuser and optionally in combination with a single light guide layer.

The light guide device may further comprise thermal bonding material in contact with the lower surface of the base substrate wherein the lower surface is opposite and parallel or substantially parallel to the first surface, and wherein said thermal bonding material contacts a heat sink plate and forms an air gap between the lower surface of the base substrate and the heat sink plate. The thermal bonding material is present in discrete portions and positioned in line or substantially in line with the one or more sources of light. The non-continuous nature of the thermal bonding material means that an air gap or gaps are formed between the substrate and the heat sink plate thus facilitating efficient heat dissipation.

The one or more light sources direct at least some light parallel to the plane of the first substrate. Advantageously the one or more light sources comprise, or consist of, or consist essentially of side emitting LEDs. Preferably, the one or more light sources form an array of side-emitting LEDs across the base substrate in a direct-lit arrangement. Preferably, a portion of the light emitted by the one or more light sources is not coupled into the light guide but is directed normal to the base substrate and in the direction of the light output surface. Typically, this is about 2% or less of the light emitted from the one or more light sources.

According to a second aspect of the present invention, there is provided a method of producing a light guide device, the method comprising: i. mounting one or more light sources onto a first surface of a base substrate having a first refractive index; and ii. adding a first guide layer, having a second refractive index that is less than or equal to the first refractive index, to the first surface so as to encapsulate the one or more light sources upon the first surface; iii. applying one or more scattering and/or reflective structures on the first guide layer and/or the substrate before the substrate and the first guide layer are combined, such that said one or more scattering and/or reflective structures are located at the interface between the substrate and the first guide layer; or applying one or more scattering and/or reflective structures on the lower surface of the base substrate; iv. optionally adding a heat sink plate to the lower surface of the base substrate which is opposite the first surface of the base substrate, wherein the heat sink plate is in contact with said base substrate via discrete portions of thermal bonding material.

In the method according to the second aspect of the invention, further steps may be incorporated in order to mount a second guide layer having a third refractive index that is equal to or greater than the refractive index of the first guide layer and at the interface between the first and second guide layer and above the one or more sources of light may be located one or more light scattering and/or reflective structures.

The method according to the second aspect of the invention provides a means for guiding light produced by the one or more light sources over the first surface.

Preferably, the method of adding the first guide layer to the first surface of the base substrate and/or mounting the second guide layer onto the first guide layer comprises: i. applying a liquid polymer on the first surface and/or first guide layer; and ii. curing the liquid polymer on the first surface and/or first guide layer.

The method of applying the liquid polymer on the first surface and/or the first guide layer may comprise printing, stencilling or dispensing the liquid polymer.

The step of applying one or more scattering and/or reflecting structures so as to redirect light away from the first surface may comprise printing a patterned, reflecting ink layer.

The arrangement of the guide layer or layers in relation to the light sources provides a light guiding device that exhibits enhanced mechanical protection for the light sources.

Furthermore, a device is provided that is simple to produce and which exhibits enhanced optical coupling of the light within the device. With the refractive index of the base substrate and the optional second guide layer selected to be equal to or higher than that of the first guide layer, the generated light is guided within both the transparent base substrate and the guide layer or layers due to the effects of total internal reflection.

The base substrate and the first and second guide layers are light transmissive and preferably transparent to the light generated by the one or more light sources.

According to a third aspect of the present invention, there is provided a display device comprising a light guiding device according to the various aspects including the first aspect of the invention. The display device may be a liquid crystal display device and may therefore comprise a liquid crystal cell which may also be referred to as a liquid crystal panel.

According to a fourth aspect of the present invention there is provided a light guide device comprising a non-transparent base substrate, upon a first surface of which are mounted one or more light sources and a first light guide layer which comprises a light output surface, the first light guide layer being arranged so as to cover the one or more light sources upon the first surface, wherein said one or more light sources are positioned directly behind the light output surface and direct light parallel to the plane of the first substrate. The device according to this aspect of the invention is also suitable for use in a display device.

In an embodiment of this aspect a transparent base substrate may replace the non-transparent base substrate, however, the arrangement is such that the transparent base substrate is not optically coupled to the first light guide layer. This may be achieved by the use of a reflector.

The one or more light sources direct at least some light parallel to the plane of the first substrate. Advantageously the one or more light sources comprise, or consist of, or consist essentially of side emitting LEDs. Preferably the one or more light sources form an array of side-emitting LEDs across the base substrate in a direct-lit arrangement. Preferably a portion of the light emitted by the one or more light sources is not coupled into the light guide but is directed normal to the base substrate and in the direction of the light output surface. Typically this is about 2% or less of the light emitted from the one or more light sources.

The light guide layer suitable for use in the fourth aspect of the invention is a further aspect of the present invention. As such, according to a fifth aspect of the invention, a light guide layer comprising one or more cavities of a size and shape suitable to fit over the one or more light sources is provided. Upon the first guide layer there may be mounted a second guide layer having a third refractive index that is equal to or greater than the refractive index of the first guide layer and optionally at the interface between the first and second guide layer and positioned above the one or more cavities may be located one or more light scattering and/or reflective structures. The surface of the light guide layer which is in contact with the non transparent substrate may be coated with a modified film such as a modified brightness enhancement film (BEF). The BEF may be modified by contacting one or more of the microstructures of the BEF with ink.

Where the ink contacts the BEF the light which would otherwise escape from the light guide is prevented or substantially prevented. A suitable example of a BEF is BEF Ill Brightness Enhancement film which is commercially available from 3M. The ink may be light transmissive. Light transmissive ink has the effect of planarising or flattening the microstructures of the BEF and facilitates light guiding. The light transmissive or transparent ink reduces the amount of light escaping from the film at the microstructure on which it is deposited. The refractive indices of the ink and the microstructure may be substantially the same. For example, the difference in refractive indices may be about 2% or less.

The present invention seeks to provide one or more of the following advantages: a more uniform light guide device with reduced/no dark spots when viewed in use; efficient light distribution resulting in lower power requirements; a thinner, lighter structure; a device comprising a reduced number of system components. The devices according to the present invention may advantageously be used for 2-d and 3-d dimming.

Detailed Description of the Invention

Base substrate The base substrate may be formed from a transparent polymer sheet such as polyester or polycarbonate. The thickness of the transparent base substrate is typically of the order of about 0.1mm, for example in the range of about 0.1mm to about 0.2mm. The refractive index of the base substrate is typically greater than 1.5.

For those aspects of the invention which relate to the use of a non-transparent substrate, the substrate may be a printed circuit board.

Light sources The light source can be any of those known to those skilled in the art, including those which are suitable for use in backlighting. Such light sources include one or more LEDs. The light may be non-directional. The LEDs can be any of the designs known to those skilled in the art, including edge-emitting, side emitting, top emitting or bare die LEDs.

The light sources are arranged to direct substantially all of the light into the light guide.

Advantageously they are selected from side-emitting LEDs wherein the light is directed parallel to the plane of the substrate. Even more advantageously a proportion of the light is not coupled into the light guide but is allowed to propagate in the direction of the output surface. For example, about 2% of the light is allowed to propagate in such a manner. The effect of allowing this light to propagate towards the output surface is that the appearance of the light sources is concealed when viewed in normal use. In particular, this light allows a diffuser to be positioned more closely to the light guide layer than in other conventional backlights. Typically, an LED suitable for use in the present invention is of the order of about 1mm in each dimension.

Electrical tracks may be patterned onto the transparent base substrate, so forming electrical bonding pads for the one or more light sources and electrical connections for external electrical driving equipment. The electrical tracks may be patterned by etching methods, for example, using copper or gold, or by additive screen printing methods, for example, using silver loaded adhesive.

The LED light sources may be electrically and mechanically attached to the electrical bonding pads by soldering or conducting adhesive methods.

Guide layers The guide layer or layers (which may also be referred to as light guide layers) which are typically suitable for use in a backlight unit may comprise a transparent flexible plastic polymer layer, typically of about 1mm in thickness.

The refractive indices of the first and second guide layers may be substantially the same or the refractive index of the second guide layer may be higher than the first guide layer. For the situation where the second light guide layer has a higher refractive index, the difference in refractive indices may be as high as about 10%.

The guide layers may be made from a range of available polymers, including acrylics, urethanes or polycarbonates.

The guide layers may be combined using a standard lamination technique. Such a technique may require the use of a transparent adhesive which has a refractive index which is higher than both the first and second guide layers. The guide Jayers may be optically joined during manufacture. The method of combining the layers may comprise applying and curing a liquid polymer layer. Methods of curing may make use of one or more techniques including UV, thermal or two-part curing. The method may comprise printing, stencilling or dispensing the liquid polymer. Optically joined indicates the layers are combined in such a way that, optically, these layers are effectively indistinguishable. This technique may also be used for combining the first guide layer and the base substrate.

The light guide layer may be suitably modified before being combined with the non-transparent substrate such as a printed circuit board (PCB). When such a substrate is used the first light guide layer may be laser or press cut to size in order to create suitable openings so that the light guide layer may be used to cover the one or more light sources. The surface of the light guide layer which is contact with the substrate may have a modified brightness enhancement film (BEF). The BEF may be modified by contacting one or more of the microstructures of the BEF with ink. Where the ink contacts the BEF the light which would otherwise escape from the light guide is prevented or substantially prevented. A suitable example of a BEF is BEF Ill Brightness Enhancement film which is commercially available from 3M. The ink may be light transmissive. Light transmissive ink has the effect of planarising or flattening the microstructures of the BEF and facilitates light guiding. The light transmissive or transparent ink reduces the amount of light escaping from the film at the microstructure on which it is deposited. The refractive indices of the ink and the microstructure may be substantially the same. For example the difference in refractive indices may be about 2% or less. The first light guide layer may be an acrylic sheet. The modified BEF may be laminated with the first light guide layer.

For use in connection with either the non-transparent or transparent substrate, upon the first guide layer there may be mounted a second guide layer having a third refractive index that is equal to or greater than the refractive index of the first guide layer and at the interface between the first and second guide layer and above the one or more sources of light may be located one or more light scattering and/or reflective structures. The first and second light guide layers may be laminated together.

Lamination may be achieved using a uv curable clear polymer adhesive such as Dymax.

Light scattering and/or reflective structures The light scattering and/or reflective structures disturb the total internal reflection of the guided light. The application of the structures may be accomplished using standard printing, micromoulding, microstamping and microembossing techniques. Suitable scattering features include highly reflective white printed ink dots. In such an arrangement, each dot disturbs the total internal reflection of the guided light and causes the light to be scattered randomly and to escape from the light guide. The size and/or pitch of the dots may be varied to ensure uniform light scatter.

The ink, which may be a polymeric material, may be applied to a guide layer to form a thin pattern of features, according to any of a number of methods and may be referred to in general terms as an additive printing process. For example, conventional screen printing incorporates the use of a mesh screen with openings corresponding to the pattern required to be printed. This pattern facilitates the accurate delivery of a volume of ink to the required areas of the guide layer. Suitable inks for use in the present invention include those which may be UV or solvent cured. Other suitable examples of additive printing methods include stencil printing, ink jet printing, flexographic printing and other known lithographic techniques. The ink may be applied in varying amounts and shapes.

Other suitable structures include rnicrostructured surfaces which comprise a plurality of three dimensional features, or irregularities, which are proud of the surface and arranged on a scale of about 1 to about 1000 microns, independently, in width, depth and pitch, preferably about 5 to about 50 microns, more preferably about 20 to about 50 microns. Specific types of microstructures, or features, which are suitable for use in the present invention include prisms, pyramids, (micro)lenses, eg. cylindrical or circular shaped lenses and random diffusing structures.

Prism based rnicrostructures may have a saw tooth shape structure varying in one direction across the entirety of the surface with a pitch of about 50 microns, wherein the pitch is the distance between the centre of adjacent microstructures. (Micro)lenses have a regular or random distribution of lenses, which may be of a low focal length, distributed across the surface on a scale of about 10 to 20 microns. The diffusing structures may possess a random surface texture which is also on a scale (depth and pitch) of about 10 to 100 microns.

The light scattering and/or reflective features may also be referred to as light extraction features.

Heat sink plate The heat sink plate may be located behind and substantially parallel to the transparent base substrate and is connected to the substrate via discrete portions of thermal bonding material. The thermal bonding material is advantageously located in line with the one or more light sources. The positioning of the discrete portions of thermal bonding material means that there is an air gap located between the substrate and the heat sink plate and between the discrete portions of thermal bonding material. The air gap means that the heat sink plate does not interfere with the light guiding mechanism and ensures uniform light scattering from the scattering features. A backlight reflector film may be located in the vicinity of the air gap or gaps to improve optical efficiency.

For example, the backlight reflector film may be located on the lower surface of the substrate or on the upper surface of the heat sink plate.

The heat sink plate may be made from materials which assist in the dissipation of the heat. Suitable examples include metals such as aluminium. The heat sink plate is typically about 0.2mm to 10mm in thickness. The thermal bonding material may be an adhesive such as an epoxy or a silicone or it may be a pressure sensitive adhesive tape or screen/stencil printable polymer with high thermal conductivity. The adhesive may be applied using a needle or by using screen printing. The adhesive tape may be applied using a standard taping machine.

The use of the heat sink plate according to the present invention provides the means for operating at higher current at a wider temperature range. By running at higher current the light output can be increased thus reducing the number of light sources e.g. LEDs.

The substrate and heat sink may be combined using lamination techniques.

Diffuser The diffuser may be positioned more closely to the light guide layer when compared with more conventional light guide devices. For example, the distance from the top of the light guide layer to the bottom of the diffuser may be less than about 12mm. For example the distance may be as low as about 9mm.

The diffuser is kept separate from the light guide layer by means of a conventional spacing arrangement. For example, a spacing element is located around the edge of the light guide layer.

The diffuser may be chosen from conventional diffusers used in backlights.

Uses of the Liqht Guide Devices The light guide devices according to the present invention may be employed for a range of functions including illumination, backlighting, signage and display purposes.

Liquid crystal devices are well known in the art. A liquid crystal display device operating in a transmissive mode typically comprises a liquid crystal cell, which may also be referred to as a liquid crystal panel, a backlight unit incorporating a light guide device, and one or more polarisers. Liquid crystal cells are also well known devices.

In general, liquid crystal cells typically comprise two transparent substrates between which is disposed a layer of liquid crystal material. A liquid crystal display cell may comprise two transparent plates which may be coated on their internal faces respectively with transparent conducting electrodes. An alignment layer may be introduced onto the internal faces of the cell in order that the molecules making up the liquid crystalline material line up in a preferred direction. The transparent plates are separated by a spacer to a suitable distance, for example about 2 microns. The liquid crystal material is introduced between the transparent plates by filling the space in between them by flow filling. Polarisers may be arranged in front of and behind the cell. The backlight unit may be positioned behind the liquid crystal cell using conventional means. In operation, a liquid crystal cell, operating in a transmissive mode, modulates the light from a light source such as a backlight unit which may comprise a light guide device.

Brief Description of the Drawings

Embodiments of the invention will now be described, by way of example only and without limitation, with reference to the accompanying drawings and the following

Examples, in which:

Figure 1 illustrates a light guide device according to the present invention incorporating a heat sink plate; Figure 2 illustrates a light guide device according to the present invention.

In Figure 1, a light guide device (1) in side elevation comprises a transparent base substrate (2) made from a transparent polymer sheet such as polyester or polycarbonate and having a refractive index n2. On top of the transparent base substrate (2) are bonded a number of light sources (3) in the form of LEDs. Electrical bonds are indicated at (3a). The distance between the LEDs is typically about 10mm to about 200mm. The LEDs illustrated are side emitting LEDs and the direction of the light emitted from the LEDs is indicated at (5) and is directed parallel to the plane of the substrate. Covering the LEDs and the remaining area of the top surface of the transparent base substrate (2) is a first transparent guide layer (4) also formed from a plastic polymer and having a refractive index n4. Located on the lower surface of the transparent base substrate is a scattering structure (6) in the form of a patterned reflecting ink layer.

Optionally (not shown), and located on the upper surface of the first transparent guide layer may be a second transparent guide layer having a refractive index n6.

At the perimeter interface between the transparent base substrate (2) and the first transparent guide layer (4), a cavity layer structure (not shown) may be incorporated in order to form a suitable cavity in which the LEDs (3) may be embedded.

The refractive indices of the transparent base substrate and the first transparent guide layer may be such that they satisfy the inequality n2 �= n4.

When present, the refractive indices of the second transparent guide layer and the first transparent guide layer may be such that they satisfy the inequality n6 �= n4.

Light, generated by the LED light sources is initially coupled into the transparent guide layer so as to propagate in a direction substantially parallel to a plane defined by the transparent base substrate. The generated light is guided within both the transparent base substrate and the transparent guide layer or layers due to the effects of total internal reflection. Therefore, the transparent base substrate and the transparent guide layer or layers form a composite structure that acts as the guiding media for the light generated by the encapsulated LED light sources (3).

When the light has propagated as far as the scattering structure (6), it interacts with this structure so as to be redirected and so exit the device via the top surface of the transparent guide layer so providing a backlighting function.

The scattering and/or reflective structures (6) may comprise highly reflective white ink dots. Both the dot size and/or pitch may be varied in order to fine tune the scattering effects.

A heat sink plate (8) is contacted to the lower surface of the base substrate (2) via discrete portions of thermal bonding material (9). An air gap is formed through the use of discrete portions of thermal bonding material. A further light reflecting structure (11) may optionally be introduced on either the lower surface of the substrate (2) or on the upper surface of the heat sink plate (8).

As a result of the fact that there is no air gap between the output of the light sources and the light guiding media, the transparent guide layers provide a simpler, and enhanced means of optically coupling the light within the device.

In Figure 2, a light guide device (15) in side elevation comprises a non-transparent base substrate (16), e.g. a conventional printed circuit board (PCB). On top of the substrate are bonded a number of light sources (17) in the form of LEDs. A light scattering and/or reflecting feature (18) is located on a first surface of the base substrate (16). The light guide layer (or layers) structure (19) is formed independently of the base substrate. A first light guide layer (20) is modified by laser cutting or press cutting appropriate size cavities in for example a suitable polymer. A second light guide layer (21) may, optionally, be located on the first guide layer. Optionally, concealment features (22) e.g. scattering and/or reflecting features may be incorporated at the interface of the first and second light guide layers. Optionally, a BEE type structure (23) may be incorporated on to the surface of the light guide layer which is to contact the first substrate. The BEF may be suitably modified.

Examples

Example I

A device in accordance with the invention was constructed as follows. A 0.125mm thick sheet of transparent polyester was used as a base substrate. A scattering structure comprising white lines of ink was printed onto the underside of the polyester film. The ink used was a white acrylic based, UV curing polymer screen printable ink which is commercially available. On the opposite (or top) side of the polyester film was printed conducting tracks (silver particle loaded conducting epoxy) and conducting adhesive in order to mount a number of LEDs (Stanley Twi 1 451s-tr) onto the substrate and provide suitable electrical connections onto the conducting ink tracks. A cavity, about 0.7mm deep was formed around the perimeter of the base substrate using a cavity layer structure. The cavity was then filled with UV curing transparent polymer (Dymax 4-20688), thus forming a first light guide layer. A spacing element was positioned and secured on the first light guide layer and the diffuser (Shin Wha 97% haze film) was positioned on the spacing element. The distance of the diffuser to the light guide layer was 9mm The LEDs were concealed from observation from above, by the combination of light not coupled into the light guide layer and the diffuser. A thin aluminium heat sinking plate of 2mm thickness was fixed to the base substrate via discrete localised sections of thermal bonding material. Good uniformity of light was observed from the extracted light.

Claims

Claims 1. A light guide device comprising a base substrate having a first refractive index, upon a first surface of which are mounted one or more light sources and a first guide layer having a second refractive index that is less than or equal to the first refractive index and which comprises a light output surface, the first guide layer being arranged so as to encapsulate the one or more light sources upon the first surface, wherein the base substrate and the guide layer form a composite structure for guiding light produced by the one or more light sources over the first surface and said one or more light sources are positioned directly behind the light output surface and direct light parallel to the plane of the first substrate.
2. A light guide device according to claim 1, wherein the light guide device comprises one or more reflecting light scattering structures arranged so as to direct light away from the first surface of the base substrate.
3. A light guide device according to any one of the previous claims wherein the base substrate and light guide layer are formed from light transparent polymers.
4. A light guide device according to any one of the previous claims wherein the base substrate is about 0.1mm thick.
5. A light guide device according to any one of the previous claims wherein the light source is selected from one or more LEDs.
6. A light guide device according to the previous claim, wherein the one or more LEDs comprise, consist essentially of, or consist of side-emitting LEDs.
7. A light guide device according to the previous claim, wherein the one or more LEDs form an array of side-emitting LEDs across the base substrate in a direct-lit arrangement.
8. A light guide device according to any one of the previous claims, wherein a heat sink plate is attached to the lower surface of the first substrate.
9. A light guide device according to the previous claim, wherein the heat sink plate is attached to the lower surface of the base substrate via discrete portions of thermal bonding material and there are one or more air gaps formed between the heat sink plate and the substrate.
10. A display device comprising the light guide device according to any one of the previous claims.