CN101253442A - Edge-lit backlight with light-recycling cavity with concave transflector - Google Patents

Abstract

An edge-lit backlight having a light recycling cavity with a concave transflector is disclosed. The edge-lit backlight has an output area and includes a back reflector facing the output area of the backlight. The backlight also includes a transflector that partially transmits and partially reflects incident light, the transflector being shaped to form a concave structure facing the back reflector so as to form one or more recycling cavities between the transflector and the back reflector, wherein the one or more recycling cavities substantially fill an output area of the backlight. The backlight also includes at least one light source disposed proximate a first edge thereof. The at least one light source is operable to inject light into the one or more recycling cavities through an input surface of the one or more recycling cavities, wherein the input surface is substantially perpendicular to the output area, and the at least one concave structure converges with the back reflector in a direction away from the input surface.

Description

Edge-lit backlight with light-recycling cavity with concave transflector

Cross references to related patent applications

This application claims priority to US Provisional Patent Application No. 60/711,520, filed August 27, 2005, and US Patent Application No. 11/466,628, filed August 23, 2006.

technical field

The present invention relates to backlights, particularly edge-lit backlights, components used in the backlights, systems using the backlights, and methods of making and using the backlights. The invention is particularly suitable for backlights used in liquid crystal display (LCD) devices and similar displays, and backlights that use LEDs as illumination sources.

Background technique

The number and variety of display devices available to the public has grown tremendously in recent years. Computers (whether desktop, laptop or notebook), personal digital assistants (PDAs), mobile phones and thin LCD televisions are just a few examples. While some of these devices can also use normal ambient light to view the display, most have a light-emitting panel called a backlight to make the display visible.

Many of these backlights can be classified as either "edge-lit" or "direct-lit". The difference between the two types of backlights is the placement of the light sources relative to the output area of the backlight, where the output area defines the visible area of the display device. In an edge-lit backlight, one or more light sources are arranged along the outer edge or edge of the backlight construction, outside the area corresponding to the output area. The light source typically projects light into a light guide, the length and width of which approximates the length and width of the output area, from which light is extracted to illuminate the output area. In direct-lit backlights, the array of light sources is positioned directly behind the output area, with a diffuser plate placed in front of the light sources to produce a more uniform light output. Some direct-lit backlights also have edge-mounted light sources, providing a combination of direct-lit and edge-lit lighting.

An important aspect of edge-lit backlights is that the light illuminating the display should be uniform in brightness. The illumination uniformity problem is particularly prominent when point light sources such as light emitting diodes (LEDs) are used as light sources at the edges of the backlight. In such cases, the backlight is required to spread the light across the display panel so that there are no dark areas in the displayed image. Additionally, in some applications, the display is also illuminated with light from a number of different LEDs that produce light of different colors. Since changes in color are more easily discerned by the human eye than changes in brightness, it can be difficult to efficiently mix light sources emitting different colors to create the white light that illuminates the display. In this case, it is very important to mix the light of different LEDs so that the color and brightness of the displayed image are uniform.

Contents of the invention

In one aspect, the invention provides an edge-lit backlight having an output area. The edge-lit backlight includes: a back reflector facing an output area of the backlight; and a transflector partially transmitting and partially reflecting incident light and shaped to form at least one concave structure facing the back reflector so that One or more recycling cavities are formed between the transflector and the back reflector. The one or more recycling cavities substantially fill the output area of the backlight. The backlight also includes at least one light source disposed near the first edge thereof. The at least one light source is operable to inject light into the one or more recycling cavities through an input surface of the one or more recycling cavities, wherein the input surface is substantially perpendicular to an output area of the backlight. The at least one concave structure converges with the back reflector in a direction away from the input surface.

In another aspect, the present invention provides a display system including a display panel having an illuminated side and a viewing side, and an edge-lit backlight disposed on the illuminated side of the display panel. The backlight has an output area. The backlight comprises: a back reflector facing the output area of the backlight; and a transflector, which partially transmits and partially reflects incident light, shaped to form at least one concave structure facing the back reflector so that the transflector One or more recycling cavities are formed between the plate and the back reflector. The one or more recycling cavities substantially fill the output area of the backlight. The backlight also includes at least one light source disposed near the first edge thereof. The at least one light source is operable to inject light into the one or more recycling cavities through an input surface of the one or more recycling cavities, wherein the input surface is substantially perpendicular to an output area of the backlight. The at least one concave structure converges with the back reflector in a direction away from the input surface.

In another aspect, the present invention provides an edge-lit backlight having an output area. The backlight source includes a back reflector and a transflective device that partially transmits and partially reflects incident light. The transflector includes at least one concave structure facing the back reflector so as to form one or more recycling cavities between the transflector and the back reflector, wherein the one or more recycling cavities substantially fill the output of the panel area. The backlight also includes a light source device disposed near its first edge for injecting light into the one or more recycling cavities through an input surface of the one or more recycling cavities, wherein the input surface is in contact with the backlight The output area of is basically vertical. The at least one concave structure converges with the back reflector in a direction away from the input surface.

The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The Figures and Detailed Description that follow more particularly illustrate exemplary embodiments.

Description of drawings

FIG. 1 is an exploded perspective view of a display system with an edge-lit backlight.

2 is a schematic cross-sectional view of one embodiment of an edge-lit backlight including at least one light recycling cavity.

3 is a schematic cross-sectional view of another embodiment of an edge-lit backlight including at least one light recycling cavity.

4 is a schematic cross-sectional view of an embodiment of an edge-lit backlight including at least two light recycling cavities.

5 is a schematic cross-sectional view of an embodiment of a combined edge-lit and direct-lit backlight comprising at least three light recycling cavities.

6 is a perspective view of one embodiment of an edge-lit backlight including a light recycling cavity, the backlight having light sources disposed near its edge.

7 is a schematic plan view of one embodiment of an edge-lit backlight that includes four recycling cavities and light sources positioned near four edges of the backlight.

8-11 are schematic cross-sectional views of various packaged LEDs that may be used as light sources in the disclosed backlights.

Detailed ways

This disclosure describes an edge-lit backlight that includes a back reflector and a transflector that partially transmits and partially reflects incident light. The transflector is shaped to form at least one concave structure facing the back reflector so as to form one or more recycling cavities between the transflector and the back reflector. At least one light source, and in some cases an array of light sources, is positioned near an edge of the backlight to direct light into each recycling cavity. Advantageously, conventional packaged or unpackaged LEDs can be used as light sources.

Edge-lit backlights are well known for their presence in small displays such as mobile phones, personal digital assistants, and laptop computers. Typically, such backlights use solid lightguides to redistribute light (emitted by one or more light sources at one or more edges of the display) uniformly across the entire area of the display panel. Solid light guides work well for small displays; however, they are less effective for displays larger than about 20 inches. Because the larger the light guide, the heavier it is, and the more difficult it is to design it to output uniform light. They can also suffer from high transmission loss, which limits overall uniformity and system efficiency.

Hollow light guides have been proposed to create edge-lit backlights that are lighter in weight and more efficient than solid light guides. Typically, such light guides guide light within a hollow cavity between two films, at least one of which has a light extraction function to guide the light out of the light guide. While these designs did solve some of the problems with solid lightguides, they also introduced new ones, such as the need to provide mechanical support to keep the two films at the proper spacing.

Edge-lit backlights using single-color LEDs as light sources must have sufficient color mixing capability and provide sufficient brightness uniformity. Several designs of edge-lit backlights illuminated by single-color LEDs (eg, red, green, and blue LEDs) include "premix" regions to evenly mix the colors before introducing the light into the lightguide region behind the display. This mixing region increases the size and weight of the backlight, and may also reduce efficiency.

The edge-lit backlights described herein can provide uniform illumination over the output area of the backlight without the need for a premixed area. Because of the extremely high efficiency and much lower losses than solid light guides, this backlight can be used to illuminate large area displays.

It has been found that the concave nature of the transflector is particularly suitable for providing uniform illumination over the area of the recirculation cavity, even when using sparsely arranged discrete light sources such as LEDs. It has also been found that this concave property is also effective for color mixing of light produced by separate light sources of different colors, such as red/green/blue LED arrays.

To minimize the overall thickness of the backlight and the number of light sources required, the concave shape of the transflector and its relative position to the back reflector enables a relatively shallow and wide circulation cavity. In some embodiments, the circulation cavity is hollow to minimize panel weight.

The transflector may include various partially transmissive and partially reflective films or objects, and in order to improve panel efficiency, the transflector preferably has low absorption loss. Surface structured films, such as films with parallel grooves forming extended linear prisms, or films with pyramidal shapes such as cube corner arrays, are an example. Specular or diffuse reflective polarizers are another example. Reflective polarizers can have coextruded polymer multilayer constructions, cholesteric constructions, wire grid constructions or blended (continuous phase/disperse phase) thin film constructions, thus allowing specular or diffuse transmission and specular or diffuse reflection of light. An apertured specular or diffuse reflective film is another example of a suitable transflector.

One embodiment of an edge-lit backlight is schematically shown in the exploded perspective view of FIG. 1 . Among them, the display system 100 includes: a display panel 102, such as a liquid crystal display (LCD) panel; an edge-lit backlight 108, which provides large-area illumination sufficient for a viewer to easily view information contained in the display panel. Both the display panel 102 and the backlight 108 are shown in simplified block form, but the reader should understand that each block contains additional detail. The backlight 108 may also include a frame 110 . Backlight 108 projects light onto extended output area 118 . The output area 118 is generally rectangular, but may have other extended area shapes if desired, which may correspond to the outer surface of a film used in the backlight, or simply to an aperture in the frame 110 .

The display system 100 shown in FIG. 1 may employ any suitable edge-lit backlight described herein, such as the edge-lit backlight 200 of FIG. 2 .

The backlight 108 also includes one or more light sources 120 disposed near at least one edge 114 of the backlight 108 . The light sources 120 may both emit white light, or separately emit light of one color among red/yellow/green/cyan/blue (RYGCB) and then mix to provide a white light output or produce a single color output by matching.

In operation, the light source 120 illuminates the entire output area 118 . When illuminated, backlight 108 enables multiple viewers 130a and 130b to view images or graphics displayed by display panel 102 . When using an LCD panel, these images or graphics are typically dynamic and are produced by an array of typically thousands or millions of individual picture elements (pixels), which nearly completely fill the lateral dimensions of the display panel 102, Namely length and width. In other embodiments, the display panel 102 may include a film with a static graphic image printed thereon.

In some LCD embodiments, the backlight 108 continuously emits white light, and the pixel array of the display panel 102 is combined with a matrix of color filters to form groups of multicolor pixels (such as yellow/blue (YB) pixels, red/green/blue (RGB) ) pixels, red/green/blue/white (RGBW) pixels, red/yellow/green/blue (RYGB) pixels, red/yellow/green/cyan/blue (RYGCB) pixels, etc.), so that the displayed image is more color. Alternatively, a color sequential technique may be used to display multi-color images. Instead of continuously illuminating the display panel 102 from behind with white light and modulating groups of multi-color pixels in the display panel 102 to produce colors, instead, it Separate light sources for different colors of the edge 114 of the backlight 108 itself (e.g., red, orange, amber, yellow, green, cyan, blue (including royal blue), and white selected from combinations such as those described above) 120 modulates so that backlight 108 sequentially flashes spatially evenly distributed colored light output (eg, first red, then green, then blue) in a rapidly repeating fashion. This color-modulated backlight is then combined with a display panel that has only a single pixel array (without any color filter matrix) so that when the modulation is fast enough to produce a transient color mixing effect in the observer's visual system Next, the pixel array is modulated synchronously with the backlight 108 to produce all perceivable colors across the entire pixel array. In some cases, one may only wish to provide a monochrome display. In these cases, backlight 108 may include filters or special light sources that emit primarily one visible wavelength or color.

Although not shown, display system 100 may include other optical elements such as reflective polarizers, brightness enhancing layers or films, diffuser plates, and the like. See, for example, the U.S. patent application entitled "OPTICAL ELEMENT FOR LATERAL LIGHT SPREADING IN EDGE-LITDISPLAYS AND SYSTEMS USING SAME" to Epstein et al. Patent Application No. 11/167,003.

FIG. 2 is a schematic cross-sectional view of one embodiment of an edge-lit backlight 200 . As shown, the backlight 200 includes a frame 210 having an output area 218 and a back reflector 212 facing the output area 218 . The frame 210 has a first edge 214 and a second edge 216 opposite the first edge 214 . The backlight 200 also includes a transflector 232 that partially transmits and partially reflects incident light. The transflector 232 is shaped to form a concave structure facing the back reflector 212 . This concave structure forms the recycling cavity 230 between the transflector 232 and the back reflector 212 .

The backlight 200 also includes at least one light source 220 disposed near the first edge 214 of the backlight 200 . In the embodiment shown in FIG. 2 , the light source 220 is located in an edge reflective cavity 240 that includes side reflectors 242 . In some embodiments, edge reflective cavity 240 may also include a back reflector 244 . The back reflector 244 can be a part of the back reflector 212 of the backlight 200 or an independent reflector.

Side reflectors 242 may have any suitable shape, and may be curved (as shown) or flat. If the side reflectors 242 are curved, they may be of any suitable type of curvature, eg, elliptical or parabolic. In the illustrated embodiment, side reflectors 242 are curved in one dimension.

Side reflectors 242 may be any suitable type of reflector, for example, a metallized reflector, a multilayer dielectric reflector, or a multilayer polymer film (MOF) reflector. The space within edge reflective cavity 240 may be filled or empty. In embodiments where, for example, a transparent optical body is used to fill the space, the side reflectors 242 may be reflective coatings on the filling body. In embodiments where the space is empty, reflector 242 may be a front reflector. Different configurations of reflective cavities are further described in US Patent Application Nos. 10/701,201 and 10/949,892.

As shown in FIG. 2 , the light source 220 is disposed near the first edge 214 of the backlight 200 . The light source 220 is operable to inject light into the recycling cavity 230 through the input surface 234 of the recycling cavity 230 . Input surface 234 is an area (if the cavity is hollow) or a surface (if the cavity is solid) that is substantially perpendicular to output area 218 of backlight 200 . Furthermore, as shown, the concave structure formed by the transflector 232 and the back reflector 212 converges with the back reflector 212 in a direction away from the input surface 234 . In other words, over at least a portion of transflector 232 , the distance between transflector 232 and back reflector 212 decreases in a direction along the y-axis from input surface 234 to edge 216 of frame 210 .

Additionally, the backlight 200 may include an optional diffuser layer 250 disposed adjacent the output area 218 so as to receive light from the output area 218 . Diffusion layer 250 may be any suitable diffusion film or plate. For example, diffusing layer 250 may comprise any suitable diffusing material or materials. In some embodiments, diffusion layer 250 may comprise a polymer matrix of polymethyl methacrylate (PMMA) with various dispersed phases including glass, polystyrene beads, and CaCO ₃ particles. Exemplary diffusers include 3M ^™ Scotchcal ^™ diffuser sheet films, types 3635-30 and 3635-70, available from 3M Company of St. Paul, Minnesota.

The backlight 200 optionally includes a light management film arrangement 260 , or light control unit, arranged such that an optional diffuser layer 250 is located between the light management film arrangement 260 and the output region 218 . The light management film arrangement 260 affects the illumination light propagating from the backlight output area 218 . Light management film assembly 260 may include any suitable film or layer, such as a diffuser, reflective polarizer, brightness enhancing film, or the like.

Overall, the circulation cavity 230 substantially fills the output area 218 . Thus, if the output region 218 is shown in plan view (e.g., when viewed by a distant observer along an axis perpendicular to the output region), the total projected area of the concave recirculation cavity (even though the distant observer cannot see clearly These circulation chambers) will be greater than half the surface area of the output region 218, preferably at least 75%, 80% or 90% of the surface area of the output region 218, and more preferably will be approximately 100% of the surface area of the output region 218. Regardless of whether the backlight 200 has only one concave circulation chamber or multiple concave circulation chambers, the projected area of the one or more circulation chambers preferably accounts for at least 75%, 80% of the area of the backlight output area 218 when viewed in a plan view. %, 90% or 100%.

Fig. 2 shows how transflector 232 partially transmits and partially reflects the light emitted by light source 220, and how this partial transmission and partial reflection together with back reflector 212 generate light circulation in recycling cavity 230, and in the recycling cavity Light emission or leakage over the entire lateral dimension of 230. The concave configuration of the transflector 232 not only helps define the boundaries of the recycling cavity 230, but also tends to confine the recycled light within the boundaries and enlarge the angular wedge of emitted light through the varying geometry of the transflector. Confining light to specific circulation cavities is one of the functions of the design details.

As detailed below, a given light source can be (1) an active component such as an LED die or fluorescent lamp that converts electrical energy into light energy, or a phosphor that converts excitation light into emitted light, or (2) Passive elements, such as lenses, waveguides (such as fibers), or other optical elements that transmit and/or shape light emitted by active elements, or (3) a combination of one or more active and passive elements. For example, the light source 220 in FIG. 2 may be a packaged side-emitting LED, wherein the LED die is located behind the back reflector 244, next to the circuit board or heat sink, and the shaped envelope or lens portion of the packaged LED passes through the back reflector 244. A slot or aperture in reflector 244 extends within reflective cavity 240 . See below for more discussion on light sources.

In the embodiment of FIG. 2 , the circulation cavity 230 is substantially one-dimensional, extending across the output region 218 in the shape of a strip parallel to the x-axis. The shape of the transflector 232 is such that it has a concave configuration as shown in the y-z section, but in the perpendicular x-z section the transflector 232 is substantially flat. That is, the transflector exhibits simple curvature. In other embodiments, the transflector 232 may exhibit complex curvature, in which case the shape of the transflector has a concave structure in both the y-z and x-z sections.

For improved efficiency, the back reflector 212 preferably has a high reflectivity. For example, back reflector 212 may have an average reflectivity of at least 90%, 95%, 98%, or 99% or higher for visible light emitted by light source 220 . Whether spatially uniform or patterned, the back reflector 212 can be primarily a specular reflector, a diffuse reflector, or a combination of specular and diffuse reflectors. In some cases, back reflector 212 may be made from a rigid metal substrate with a high reflectivity coating, or from a high reflectivity film laminated to a support substrate. Suitable high reflectivity materials include, but are not limited to, Vikuiti ^™ Enhanced Specular Reflector (ESR) multilayer polymer film available from 3M Company; Polyethylene terephthalate film (2 mil thick) doped with barium sulfate was laminated to Vikuiti ^™ ESR film, referred to herein as "EDRII"film; available from Toray Industries, Inc.'s E-60 series Lumirror ^™ polyester film; porous polytetrafluoroethylene (PTFE) film (such as available from WL Gore & Associates, Inc.); available from Labsphere, Inc.'s Spectralon ^™ reflective material; Miro ^™ anodized aluminum films (including Miro ^™ 2 films) from Alanod Aluminum-Veredlung GmbH &Co.; MCPET high reflectivity foam sheets from Furukawa Electric Co., Ltd.; and Mitsui Chemicals, Inc. White Refstar ^TM film and MT film.

The back reflector 212 can be generally flat and smooth, or have a structured surface associated therewith to enhance light scattering or mixing. This structured surface can be: (a) applied to the reflective side of the back reflector, or (b) coated over a clear coating applied to the reflective side. In the former case, the high-reflectivity film can be laminated to a substrate with a pre-formed structured surface, or to a flat substrate (such as a metal foil, which is similar to Vikuiti ^TM available from 3M Company. Durable Enhanced Specular Reflector-Metal (DESR-M) reflector similar), and then form a structured surface such as by embossing operations. In the latter case, a transparent film with a structured surface can be laminated to the flat reflective surface, or a transparent film can be applied to the reflector 212 and the structured surface can then be formed on the transparent film.

The edges of the frame 210 along the outer boundary of the output region 218 (other than the first edge 214 containing the input surface 234) are preferably lined or otherwise provided with highly reflective vertical walls to reduce light loss and Improve cycle efficiency. These walls may use the same reflective material as the back reflector 212, or may use a different reflective material. In an exemplary embodiment, the sidewalls are diffusely reflective.

Transflector 232 is a structure (such as a film) that partially transmits, partially reflects incident light, or includes a structure (such as a film) in which the partial transmission is high enough to allow light to effectively pass through transflector 232, The partial reflectivity is also high enough to allow light recycling with the back reflector. As described herein, a variety of different films can be used, often with different optimum geometries and characteristics, and the light source and back reflector 212 capabilities used may also vary for optimum brightness, brightness uniformity ( light source concealment) and color mixing. In some cases, it may be possible for the backlight designer to come up with a certain recirculation chamber design (such as the recirculation chamber assembly discussed in this article) and then select the appropriate light source for a given recirculation chamber.

Several suitable films are discussed further below, but this discussion is not limiting, any of which may be used alone or in combination to produce the desired transmission and reflection properties. For combinations of films, the films may or may not be attached to each other. If attached to each other, any known attachment means may be used, and the films may be attached over the entire major surface, or only at discrete points or lines. If an adhesive is used, the adhesive can be transparent, diffuse and/or birefringent.

Some of the films suitable for use as transflectors fall into the types referred to herein as transflective films and polarizing films.

In general, a semi-reflective film is a film or the like that reflects approximately 30% to 90% of normally incident visible light, while having sufficiently low absorptivity to transmit the vast majority, preferably nearly all, of the remaining (unreflected) light. Reflection and transmission can be specular or diffuse, or a combination of specular and diffuse, whether spatially uniform or patterned. Diffuse reflection can be produced with surface diffusers (including holographic diffusers), bulk diffusers, or a combination of both. The appropriate level of reflectivity depends on several factors, including the number of light sources and their location near the edges of the backlight, the intensity and light distribution (angular distribution of light intensity) of one or more light sources, the depth of the recirculation cavity, the backlight output The ideal brightness and color uniformity of the backlight, and the presence of other components such as diffuser plates or light control units in the backlight. The higher reflectivity of the films used in transflectors tends to improve the brightness uniformity and color uniformity of the backlight at the expense of efficiency. The reduction in efficiency is due to the increase in the average number of reflections in the recycling cavity, each reflection being accompanied by at least some loss of light. As mentioned earlier, we want to minimize visible light absorption not only by the transflector, but also by the back reflector and any reflective sidewalls.

An example of a semi-reflective film suitable for use as a transflector is a thin metallized mirror with a metal coating thin enough to transmit some visible light. This thin metallic coating can be applied to films or substrates.

Another example of a semireflective film is known in the art as a controlled transmission mirror film (CTMF). Such films are made by coating both sides of a multilayer interference mirror stack (such as the ESR mirror film referred to herein) with a diffuse reflective coating or layer. Another example of a semireflective film is a multilayer polymer mirror film that has been flame embossed, ie, briefly burned with a flame to destroy the multilayer interference stack at certain locations.

Reflective polarizers are another example of semi-reflective films. Such polarizers include cholesteric polarizers, multilayer polymer polarizers made using coextrusion and stretching techniques, wire grid polarizers, and diffuse blend polarizers with continuous phase/disperse phase configurations, which A polarizer nominally transmits half of the light from an unpolarized source (corresponding to a first polarization state) and reflects the other half (corresponding to an orthogonal second polarization state). Examples of such reflective polarizers include any of the Vikuiti brand Double Brightness Enhancement Film (DBEF) products and Diffuse Reflective Polarizer Film (DRPF) products available from 3M Company. See also reflective films such as disclosed in US Patent Nos. 5,882,774 (Jonza et al.) and 6,111,696 (Allen et al.) and US Patent Publication 2002/0190406 (Merrill et al.). If one reflective polarizing film is not enough, two or more of these films can also be combined and shaped to form concave structures.

Non-polarizing diffuse reflectors are also examples of semi-reflective films. Such reflectors can be made by dispersing specularly reflective particles or flakes into a low-absorption transparent polymer matrix to form a film or other body. The reflective particles or flakes can be distributed throughout the thickness of a thick film, or disposed as a thin curable coating on the surface of a substrate. There are many known diffuse reflector structures and fabrication methods. The diffuse coating can be applied to the reflector or other body using inkjet printing, screen printing, and other known techniques. Diffusing adhesives can also be used, where the diffusion is created by particles or air gaps with different refractive indices. Diffuse reflectors used as transflectors preferably have low absorptivity and should have an average transmission of 20% to 80% for visible wavelengths.

Semi-reflective films also include reflective films that have a pattern of small holes or holes that act to increase transmission and reduce reflection. This kind of semi-reflective film can be made as long as a small hole with a desired pattern is punched on the reflective film. Virtually any of the reflective films discussed herein can be used as a raw material and then converted or processed to form perforations or other apertures. US Patent Application Publications US2004/0070100 (Strobel et al.) and US2005/0073070 (Getschel et al.) propose techniques suitable for flame perforating thin films. The pattern of holes or holes can be uniform or non-uniform, and when the pattern is non-uniform, the location and size of the holes can be random or pseudo-random. In one example, a Vikuiti ^™ ESR film sheet is perforated with equally spaced circular holes arranged in a hexagonal array with spacing equal to a multiple of the hole diameter.

In general, a polarizing film suitable as a transflector in the disclosed backlight refers to a film or the like having small structures arranged to form a structured surface or the like to follow light A change in the direction of incidence to reflect and transmit light. The film may have such a structured surface on one or both sides. Available structures include linear prisms, pyramids, cones, and ellipsoids, which can be convex protruding from the surface or pits concave into the surface. The size, shape, geometry, orientation and spacing of the structures can all be selected to optimize the performance of the transflector, recycling cavity and backlight, and the individual structures can be symmetrical or asymmetrical. A structured surface can be uniform or non-uniform, and when non-uniform, the location and size of the structures can be random or pseudo-random. The color and brightness uniformity of the backlight can be adjusted by disrupting the regularly arranged features with periodic or pseudo-random changes in size, shape, geometry, orientation, and/or spacing. In some cases, it may be advantageous to distribute small and large structures together.

Examples of suitable polarizing films include commercial one-dimensional (linear) prismatic polymer films such as Vikuiti ^™ Brightness Enhancement Film (BEF), Vikuiti ^™ Transmissive Right Angle Film (TRAF), Vikuiti ^™ Image Turning Film, all available from 3M Company (IDF) and Vikuiti ^TM Optical Lighting Film (OLF), as well as conventional lenticular linear lens arrays. If the one-dimensional prismatic film described above is employed, the prismatic structured surface preferably faces downwardly towards the back reflector.

In other examples of polarizing films, the structured surface has two-dimensional characteristics, these polarizing films include: cube corner surface configurations, such as U.S. Pat. Benson), 5,450,285 (Smith et al.) and 5,840,405 (Shusta et al.); unsealed cube corner sheeting such as 3M ^™ Scotchlite ^™ Reflective Material 6260 High Gloss Film and 3M ^™ Scotchlite™ Reflective Material available from 3M Company 6560 High GlossSparkle Film; inverse prism surface configurations such as those described in U.S. Patent Nos. 6,287,670 (Benson et al.) and 6,280,822 (Smith et al.); U.S. Patent 6,752,505 (Parker et al.) and Patent Publication US 2005/0024754 ( Epstein et al); and beaded retroreflective sheeting.

Polarizing films can be used alone or with other suitable transflectors. When used with different types of transflectors, the polarizing film can be placed inside the recirculation cavity (closest to the back reflector), and the other film can be a semi-reflective film such as a diffuser or another polarizing film , it can be placed outside the circulation cavity. When two or more linear prismatic polarizing films are used in combination, the films can be aligned, misaligned, or "crossed" such that the prismatic orientation of one film is perpendicular to that of the other film.

Returning now to FIG. 2 , one or more light sources 220 are schematically shown. In most cases, these light sources are compact light-emitting diodes (LEDs). In this case, "LED" refers to a diode that emits visible light, ultraviolet light, or infrared light. It includes enclosed or packaged incoherent semiconductor devices marketed as LEDs (whether conventional or superradiant). If the LED emits invisible light such as ultraviolet light, and in some cases where the LED emits visible light, it is packaged to contain a phosphor (or to illuminate a phosphor placed at a distance), so that the short-wavelength light Conversion to longer wavelength visible light, in some cases results in devices that emit white light. "LED die" is the most basic form of LED, that is, a single component or chip made by semiconductor processing. The component or chip may include electrical contacts for applying energy to drive the device. The individual layers and other functional elements of the component or chip are typically formed at the wafer level, and the processed wafer is diced into individual elements to produce a large number of LED dies. This article will discuss packaged LEDs in detail, including front-emitting and side-emitting LEDs.

If desired, other visible light emitters such as linear cold cathode fluorescent lamps (CCFL) or hot cathode fluorescent lamps (HCFL) can be used in place of or in addition to discrete LED light sources as illumination sources for the disclosed backlights. For example, in some applications it may be desirable to replace light source 220 with a different light source, such as an elongated cylindrical CCFL, or a linear surface-emitting light guide that emits light along its length and is connected to remote active elements, such as LEDs. Die or halogen lamps. Examples of such linear surface emitting lightguides are disclosed in US Patent Nos. 5,845,038 (Lundin et al.) and 6,367,941 (Lea et al.). Also known are fiber-coupled laser diodes and other semiconductor emitters in which, when placed in or otherwise close to the input surface of the disclosed edge reflective cavity, The output end of the fiber optic waveguide can be regarded as a light source. The same applies to other passive optical components with small light-emitting areas, such as lenses, deflectors, narrow light guides, and similar components that emit light received from active components such as light bulbs or LED dies. An example of such a passive component is a molded envelope or lens for a side-emitting packaged LED.

Returning to FIG. 2 , the circulation cavity 230 has a depth d as shown and a length L and a width W, wherein the length and width are substantially equal to the length and width of the output region 218 . In some embodiments, the width W of the recirculation cavity is at least 2.5 times its depth d; in other embodiments, W is at least 5 times d.

As mentioned earlier herein, any suitable type of edge reflective cavity may be used in the backlight of the present invention. For example, FIG. 3 is a schematic cross-sectional view of another embodiment of a backlight 300 . Backlight 300 includes a back reflector 312 , a recycling cavity 330 formed by transflector 332 and back reflector 312 , and one or more light sources 320 disposed near edge 314 of backlight 300 . All design considerations and possibilities of the back reflector 212, recycling cavity 230, transflector 232, and light source 220 of the embodiment shown in FIG. 2 apply equally to the back reflector 312, recycling cavity of the embodiment shown in FIG. 330 , a transflector 332 and a light source 320 . Backlight 300 may also include optional diffuser layer 350 and light management film 360 . Any suitable diffusion layer 350 may be used with backlight 300, such as those described with respect to diffusion layer 250 of FIG. 2 . Furthermore, any suitable layer or film can be used for optional light management film 360, such as those described with respect to light management film device 260 of FIG.

One or more light sources 320 are placed in the edge reflective cavity 340 so that the light sources 320 inject light into the recycling cavity 330 through the input surface 334 of the recycling cavity 330 . The edge reflective cavity 340 is configured such that the light emitting surface 322 of each light source 320 faces the input surface 334 of the recycling cavity 330 . Edge reflective cavity 340 may include sidewalls 342 that are preferably reflective. Such reflective sidewalls 342 can direct light from the light source 320 toward the input surface 334 . The reflective material used for the side reflectors 242 of the edge reflective cavity 240 shown in FIG. 2 may also be used for the reflective side walls 342 of the reflective cavity 340 in FIG. 3 . Although the edge reflective cavity is shown as having a rectangular shape, the edge reflective cavity 340 may take any suitable shape for directing light from the light source 320 into the recycling cavity 330 through the input surface 334 .

Turning now to Figures 4-5, some of the various examples of geometric configurations that may be used to construct a suitable edge-lit backlight are shown. These figures are all shown in cross-sectional view when viewed along the x-axis direction (perpendicular to the plane of the figures). However, these figures can also be understood as showing cross-sectional views when viewed along the orthogonal y-axis direction, therefore, these figures generally show two types of embodiments. In one type of embodiment, the transflector is in the y-z plane There are simple bends, and in another class of embodiments the transflector has complex bends in the y-z and x-z planes. For the above reasons, the term "curved" should be understood broadly and not limited to geometric arcs or even curved shapes.

FIG. 4 shows a direct-lit backlight 400 with two recycling cavities 430 and 470 formed by the combination of two concave structures in the transflector 432 and the back reflector 412 . The illustrated transflector 432 is divided into two parts: 432a and 432b, respectively corresponding to the two concave structures. The two parts may be connected by a part of the transflector 432 at the middle area 433, or may not be connected. The circulation chambers 430 and 470 are sized to substantially fill the output region 418, preferably 75%, 80%, 90% or more of the plan view area of the output region 418. The area behind the output area 418 that is not provided with a concave recirculation cavity accounts for only a small fraction (less than 25%, 20% or 10%, preferably about 0%) of the plan view area of the output area 418 in total. Due to the close proximity of the recirculation chambers, the angular distribution of the light emitted by the recirculation chambers and the placement of the output area above the recirculation chambers (e.g., the placement of an optional diffuser plate (not shown)), these areas without concave recirculation chambers may have a negative impact on Uniformity of brightness across output area 418 has little or no negative impact. As long as there are such areas not provided with concave recirculation chambers, in the exemplary embodiment, these areas should be distributed preferentially near or along the periphery of the output area 418 and away from the central portion of the output area 418 .

The backlight 400 also includes one or more light sources 420 disposed adjacent the first edge 414 of the frame 410 within an edge reflective cavity 440 having side reflectors 442 . Backlight 400 may employ any suitable light sources and edge reflective cavities described herein. The light source 420 is operable to inject light into the recycling cavity 430 through an input surface 434 of the recycling cavity 430 .

The backlight 400 also includes one or more light sources 422 disposed within an edge reflective cavity 480 having an edge reflector 482 adjacent the second edge 416 of the frame 410 . Any suitable light source and edge reflective cavity may be placed near second edge 416 . The light source 422 is operable to inject light into the recycling cavity 470 through the input surface 474 .

Backlight 400 may also include other layers or films configured to receive light emitted by output region 418 , such as diffusion layer 350 and/or light control unit 360 of FIG. 3 .

5 shows a combined edge-lit and direct-lit backlight 500 with three recycling cavities 530 , 570 and 590 formed by three concave structures in a transflector 532 in combination with a back reflector 512 . Transflector 532 is shown as having three portions corresponding to the three concave structures: 532a, 532b, and 532c, respectively. These three parts may be connected by a part of the transflector 532 at the middle area 592a and 592b, or may not be connected, and the area of the middle area is preferably minimized. Light sources 520 a , 520 b and 520 c are arranged to inject light into their respective recycling cavities 530 , 570 and 590 . The illustrated light sources 520a-c may each represent a single light source, or represent an array of light sources arranged along a direction parallel to the x-axis. Recirculation chambers 530 and 570 may take the same shape; alternatively, each recirculation chamber may take a different shape.

The backlight 500 may use any suitable direct-illuminated recycling cavity, such as the U.S. company DIRECT-LIT BACKLIGHT HAVING LIGHT RECYCLING CAVITY WITH CONCAVE TRANSFLECTOR (direct-lit backlight with light recycling cavity with concave transflector)" Directly illuminated recirculation chamber described in Patent Application No. 11/212,166.

In some embodiments of the invention, one or more light sources may be placed near two or more edges of the backlight frame. For example, FIG. 6 is a schematic perspective view of a backlight 600 . The backlight 600 includes a frame 610 and a back reflector 612 . Backlight 600 also includes an output area 618 facing back reflector 612 . The light source 620 is disposed near the first edge 614 of the backlight 600 and the light source 622 is disposed near the second edge 619 of the backlight 600 . Light sources 620 and 622 are operable to inject light into an input surface of a recycling cavity (not shown) formed by a transflector 632 shaped to have a concave structure facing back reflector 612 . All design considerations and possibilities of the frame 210, back reflector 212, light source 220, and transflector 232 of the embodiment shown in FIG. 2 apply equally to the frame 610, back reflector 612, Light sources 620 and 622 and transflector 632 .

In the embodiment shown in FIG. 6 , light source 620 is disposed near edge 614 such that light source 620 is operable to inject light into the input surface of the recycling cavity formed by transflector 632 and back reflector 612 . The concave structure formed by the transflector 632 converges with the back reflector 612 in a direction away from the input surface of the recycling cavity. In other words, the transflector 632 converges with the back reflector 612 along a direction from the first edge 614 where the light source 620 is disposed to the third edge 616 of the backlight 600 .

In general, the light source 620 is operable to inject light into the input surface of the recycling cavity along a direction parallel to the y-axis. In other words, the light emitted by the light source 620 is incident along a direction substantially perpendicular to at least a part of the transflector 632 .

Contrary to the light source 620, the light source 622 disposed adjacent to the second edge 619 is operable to inject light into the recycling cavity along the x-axis direction, which in this embodiment is the extending direction of the transflector. In other words, very little, if any, of the light incident on light source 622 will be perpendicular to the surface of the transflector.

7 is a plan view of an edge lit backlight showing multiple light recycling cavities positioned behind the output area of the panel. The output area of the backlight has an aspect ratio of 16:9, which is the ratio currently popular in LCD televisions. In FIG. 7, the backlight output area (not shown) is substantially filled by an array of four recycling cavities 730a-d. Each recycling cavity consists of a transflector forming a concave structure facing the back reflector. The shape of the transflector can define a concave structure in the x-z plane and another concave structure in the orthogonal y-z plane, the former defines the width W of each circulation cavity, and the latter defines the length of each circulation cavity L. Light sources 720 are positioned near four edges 702 , 704 , 706 , and 708 of backlight 700 .

Figure 7 can also be understood to represent an embodiment in which the transflector has a simple curved shape to define one or more linear tunnel-like structures, but between the transflector and the back reflector Vertical partitions are set to divide the circulation chamber into multiple independent areas or sub-circulation chambers. For example, the transflector can form a single concave structure in the x-z plane between the top and bottom ends of the output region 718 to form a loop cavity with a width of 2W and a length of 2L (where W and L are shown in FIG. 7 ), the difference is that, as shown by the dotted line in the x direction in the figure, a vertical partition (whether it is specular reflection or diffuse reflection, preferably made of high reflectivity material) is set between the transflector and the back reflector, to Two distinct regions or circulation chambers 730a/730c and 730b/730d are defined. As another example, the transflector can form two adjacent concave structures in the x-z plane to form two circulation cavities, the width of each circulation cavity is W and the length is 2L (W and L are shown in Figure 7 ), the difference is that in each concave structure, a vertical partition wall is set along the x direction between the transflector and the back reflector, so as to divide the first circulation cavity into two circulation cavities 730a/730b and divide the second circulation cavity The second circulation chamber is divided into two circulation chambers 730c/730d.

Also, for example, the transflector may be shaped to have a maximum depth at all four corners of the backlight 700 and a minimum depth along each of the dashed lines shown in FIG. 7 . This configuration will form a complex concave structure with curvature in both the x-z plane and the y-z plane. Such a structure would have the shape of an outdoor music stand, where the transflector converges with the back reflector along two orthogonal directions away from the two adjacent edges of the backlight 700 . For example, recycling cavity 730d is formed by a transflector and a back reflector converging in a positive x-direction away from edge 702 and a positive y-direction away from edge 704 .

In general, the recirculation cavity can take any suitable plan-view shape, whether simple or complex. Polygons (eg, triangles, rectangles, trapezoids, pentagons, hexagons, etc.), circles, ellipses, and any other desired shape are contemplated. The geometry can be custom designed to provide a backlight with high efficiency and good brightness uniformity and color uniformity.

Desirably, the recycling cavity formed by the concave transflector and the back reflector is relatively shallow in the z-axis direction (ie, the depth d is small), and relatively wide in the lateral direction. The depth d of a particular recycling cavity refers to the maximum separation between the back reflector and the transflector along an axis perpendicular to the output area (ie in the z-direction). The width (W) of the circulation chamber refers to the lateral dimension of the circulation chamber measured in the following manner: considering the shape of the circulation chamber in the plan view (as shown in Figure 7), the width of the circulation chamber refers to the smallest circumscribed rectangle of the circulation chamber plan view shape smaller size. In some embodiments, the width W of the circulation cavity disclosed in the present invention may be greater than 2d, preferably at least 2.5d, 5d or more. The length (L) of the circulation cavity refers to the larger dimension of the smallest circumscribed rectangle of the shape of the plan view of the circulation cavity. In special cases, the smallest rectangle may be a square, where L=W.

Backlights using more than one recycling cavity disclosed herein, especially those having zones or arrays of different recycling cavities (each zone or recycling cavity being controlled independently or independently relative to the light sources in adjacent recycling cavities) addressable own light source), can be used with suitable drive electronics to support dynamic contrast display techniques and color sequential display techniques in which the brightness and/or color distribution over the output area of the backlight is intentionally Designed to be uneven. Thus, different areas on the output area can be controlled to be brighter or darker than other areas, or different areas can be made to emit light of different colors simply by properly controlling different light sources in different recirculation cavities .

The disclosed concave circulation cavity for backlight can be fabricated using different assembly methods and techniques.

One approach is to place a single piece of transflective film across the entire width of the backlight housing, with the film edges inserted between or physically secured to the side walls of the housing to form a tunnel-like concave structure. This method is especially suitable for relatively small displays.

When the backlight unit is thin and wide, it may be advantageous to use multiple tunnel-like concave structures. Scribing the transflective film, ie, cutting along a line or lines part of the thickness of the film, has been found to be a convenient technique for defining the boundaries of the concave structure. Another useful technique is to create creases by folding the transflective film along one or several lines. The score and fold method facilitates turning a single sheet of film into a combination of multiple concave structures by providing defined locations for easy folding of the film. Any known scribing technique can be used for scribing, including laser methods, heat methods (eg, using a hot wire or a hot knife), and known kiss cutting techniques.

When using multiple tunnel-like structures formed from a single sheet of film, physically attaching the film to the floor, sidewalls, or floor and sidewalls of the backlight housing results in a stable and robust structure for the film. Examples of methods of physically attaching the concave film to the backlight include, but are not limited to, securing the scored portion of the film to the chassis by the following items or methods: rivets, screws, staples, thermal or ultrasonic spot welding, nailing Plastic nails for the base plate (which can also be used to support the diffuser plate), pins nailed into the side walls of the backlight and pins to secure the scribed area of the film to the base plate, adhesive tape on the base plate, etc.

The edges of the concave film can be attached to locations and slots molded into the sidewall reflectors of the backlight housing that help define the shape of the concave structure. Alternatively, the film may be made rigid enough to allow the recessed structures to be inserted into predetermined slots in the side walls or reflective floor. In general, embossing corrugations on at least a portion of the transflector can increase the rigidity or rigidity of the transflector. Transflectors that are not inherently rigid can also be used in combination with a transparent support with a suitable surface shape, for example by placing the transflector on the support.

Another method of securing the scored film within the backlight housing involves the use of support members, which may be molded into the structure of the side walls of the housing, or inserted into the side walls of the housing. The method may use transparent polymer rods inserted into the side walls of the housing at predetermined locations, the rods spanning the length or width of the backlight, thus providing guide rods that can weave the transflector through or through, while using the Technology fixes the edges of the film. Alternatively, a thin wire can be used instead of the rod. This approach is especially useful when making asymmetric concave structures, where films tend to be resistant to transitioning into asymmetric shapes.

Another method of forming a concave structure in the transflector is to place plastic pegs on the back of the front diffuser at predetermined locations corresponding to where the transflector will touch or nearly touch the back reflector. During assembly of the backlight, pins can be brought into contact with the flexible transflective film to form a transflector, which can be attached to the backlight housing at the edges to form one or more pins defined by the position of the pins. concave shape. Other suitable methods of forming the backlights described herein can be found, for example, at "METHODS OF FORMING DIRECT-LITBACKLIGHTS HAVING LIGHT RECYCLING CAVITY WITH CONCAVETRANS FLECTOR" " (Attorney Docket No. 61199US006) found in U.S. Patent Application No. XX/XXX,XXX.

8-11 show views of some of the light sources that may be used in the disclosed backlight, and these figures are not limiting. The illustrated light sources include packaged LEDs. The light sources of Figures 8, 9 and 11 show side-emitting LED packages in which the light emitted by the LED die is reflected and/or refracted by an integral encapsulant or lens element to propagate generally laterally rather than along the source's axis of symmetry. The peak light propagated before. The light source of Figure 10 can be front emitting or side emitting, depending on whether an optional deflector is included.

In FIG. 8 , light source 800 includes LED die 810 mounted on frame 812 and electrically connected to leads 814 . Leads 814 are used to electrically and physically connect light source 800 to a circuit board or the like. The lens 820 is attached to the frame 812 . The lens 820 is designed so that all light rays entering the upper half of the lens are totally internally reflected on the upper surface 822 so that the light is incident on the lower surface 824 of the upper half and refracted outside the device. Light entering the lower half 826 of the lens is also refracted out of the device. Light source 800 may also include an optional diverter 830 , such as a sheet of reflective material, mounted over lens 820 or attached to upper surface 822 . See also US Patent Application Publication US2004/0233665 (West et al.).

In FIG. 9 , light source 900 includes LED die (not shown) mounted on lead frame 910 . The transparent encapsulant 920 encapsulates the LED die, the lead frame 910 and some wires. Encapsulation 920 has reflective symmetry with respect to a plane containing the normal to the surface of the LED die. The enclosure has a recess 924 defined by a curved surface 922 . The depression 924 is substantially linear, centered at the center of the plane of symmetry, and is coated with a reflective coating 926 on at least a portion of the surface 922 . The light emitted from the LED die is reflected by the reflective coating 926 to form reflected rays, which are refracted by the refractive surface 928 of the package to form a plurality of refracted rays 930 . See also US Patent 6,674,096 (Sommers).

In FIG. 10 , light source 1000 includes LED die 1010 within recessed reflector region 1018 of lead frame 1012 . Power is supplied to the light source by the lead frame 1012 and the other lead frame 1014 through the wire bonding between the LED die 1010 . The LED die 1010 has a fluorescent material layer 1016 on its surface, and the entire assembly is embedded in an epoxy resin transparent package 1020 with a lens on its front surface. When powered on, the top surface of the LED die 1010 will emit blue light. Some of this blue light passes through the phosphor layer and mixes with the yellow light from the phosphor to create a white output light. Alternatively, the phosphor layer can be omitted so that the light source only emits blue light (or another desired color) from the LED die 1010 . In both cases above, white light or colored light is emitted substantially forward so as to emit peak light in a direction along the axis of symmetry of the light source 1000 . However, if desired, light source 1000 may also include an optional deflector 1030, the reflective surface of which is capable of redirecting light in a generally lateral or lateral direction, thereby converting light source 1000 into a side light. The deflector 1030 may be mirror-symmetrical about a plane perpendicular to the paper, or rotationally symmetrical about a vertical axis coincident with the axis of symmetry of the resin package 1020 . See also US Patent 5,959,316 (Lowery).

In FIG. 11 , light source 1100 has LED die 1112 supported by package backplane 1116 . Lens 1120 is attached to base plate 1116 , and enclosure axis 1126 passes through the center of base plate 1116 and lens 1120 . The shape of the lens 1120 defines a space 1114 between the LED die 1112 and the lens 1120 . The space 1114 may be filled and sealed with silicone or other suitable medium such as resin, air or gas, or vacuum. Lens 1120 includes a sawtooth refractive portion 1122 and a total internal reflection (TIR) funnel portion 1124 . The sawtooth portion 1122 is designed to refract and bend light so that the angle between the light emitted from the lens 1120 and the package axis 1126 is as close to 90 degrees as possible. See also US Patent 6,598,998 (West et al.).

In addition to the diverters shown in Figures 8 and 10, other diverters may be used with the light sources, including those with the designation "DIRECT-LIT BACKLIGHT HAVING LIGHT SOURCES WITH BIFUNCTIONAL DIVERTERS" A dual function diverter is described in commonly assigned US Patent Application No. 11/458,891.

Whether used to generate white light or not, polychromatic light sources can take many forms in a backlight and have different effects on the color and brightness uniformity of the output area of the backlight. In one approach, multiple LED dies (for example, red, green, and blue emitting dies) are all mounted in close proximity to each other on a lead frame or other substrate, and then packed together into a single encapsulant to form a single LED die. The package body may further include a single lens element. Such a light source can be controlled to emit any individual color, or all colors simultaneously. In another approach, individually packaged LEDs can be integrated into a bundle for a given recirculation cavity, where each package has only one LED die and emits one color of light, and the LED bundle contains LEDs that emit different colors. A combination of packaged LEDs of color (such as blue/yellow or red/green/blue). In another approach, such individually packaged multicolor LEDs may be arranged in one or more lines, arrays, or other patterns.

Depending on the light source selected, the amount of UV radiation received by the back reflector, transflector, and other components of the backlight will vary, with CCFL and HCFL light sources generally emitting more UV light than LED light sources. Therefore, components of the backlight may contain UV absorbers or stabilizers, or may use materials selected to minimize UV degradation. If a light source with a lower UV output, such as an LED, is used to illuminate the backlight, the use of UV absorbers and similar substances may not be necessary, and the choice of materials will be wider. In addition to UV absorbers and stabilizers, the transflector may contain dyes and/or pigments to adjust the transmissivity, color and other optical properties of the transflector, recycling cavity and backlight.

Exemplary embodiments of this invention have been discussed herein and reference has been made to possible variations within the scope of this invention. These and other variations and modifications of the present invention will be apparent to those skilled in the art without departing from the scope of the present invention, and it should be understood that the present invention is not limited to the exemplary embodiments provided herein. Example. Accordingly, the invention is to be limited only by the claims provided below.

Claims (21)

1. An edge-lit backlight having an output area, comprising: a back reflector facing the output area of the backlight; a transflector partially transmitting, partially reflecting incident light and shaped to form at least one concave structure facing said back reflector so as to form one or more a circulation cavity, the one or more circulation cavities substantially filling the output area of the backlight; and at least one light source disposed adjacent the first edge of the backlight, the at least one light source operable to inject light into the one or more recycling cavities through an input surface of the one or more recycling cavities , the input surface is substantially perpendicular to the output area of the backlight source, and the at least one concave structure converges with the back reflector along a direction away from the input surface. 2. The backlight of claim 1, further comprising an edge reflective cavity disposed adjacent the first edge of the backlight, wherein the at least one light source is configured to emit light within the edge reflective cavity. 3. The backlight of claim 1, wherein each recycling cavity has a depth d and a width W, and W is at least 2.5 times d. 4. The backlight of claim 1, wherein each recycling cavity has a depth d and a width W, and W is at least 5 times d. 5. The backlight of claim 1, wherein at least one recycling cavity is hollow. 6. The backlight of claim 1, wherein the at least one concave structure consists essentially of a single concave structure, and the one or more recycling cavities consist essentially of a single recycling cavity. 7. The backlight of claim 1, wherein the at least one concave structure comprises a plurality of concave structures and the one or more recycling cavities comprises a plurality of recycling cavities. 8. The backlight of claim 7 , wherein each concave structure has a concave cross-sectional profile in a first plane and a substantially flat cross-sectional profile in a second plane perpendicular to the first plane. section profile. 9. The backlight of claim 7, wherein each concave structure has a concave cross-sectional profile in first and second mutually perpendicular planes. 10. The backlight of claim 7, wherein each recycling cavity extends across a certain dimension of the output area. 11. The backlight of claim 1, wherein the at least one light source comprises a plurality of LEDs. 12. The backlight of claim 11, wherein the plurality of LEDs includes LEDs that emit light of different colors. 13. The backlight of claim 11 , wherein the transflector is shaped to form a plurality of concave structures facing the back reflector so as to form a plurality of recycling cavities, each recycling cavity having an input surface, And for each recycling cavity, at least one LED is positioned near the edge of the backlight to direct light into the input surface of the recycling cavity. 14. The backlight of claim 1, wherein the transflector consists essentially of a thin film selected from the group consisting of a semi-reflective film and a polarizing film. 15. The backlight of claim 1, wherein the transflector comprises two films selected from the group consisting of semi-reflective films, polarizing films, and combinations thereof. 16. The backlight of claim 1, wherein the transflector comprises a scored film. 17. The backlight of claim 1, wherein the transflector comprises a film held in compression. 18. A display system comprising: a display panel having an illuminated side and a viewing side; and an edge-lit backlight disposed on the illuminated side of the display panel and having an output area, The edge-lit backlight includes: a back reflector facing the output area of the backlight; a transflector partially transmitting, partially reflecting incident light and shaped to form at least one concave structure facing said back reflector so as to form one or more a circulation cavity, the one or more circulation cavities substantially filling the output area of the backlight; and at least one light source disposed adjacent the first edge of the backlight, the at least one light source operable to inject light into the one or more recycling cavities through an input surface of the one or more recycling cavities , the input surface is substantially perpendicular to the output area of the backlight source, and the at least one concave structure converges with the back reflector along a direction away from the input surface. 19. The system of claim 18, wherein the display panel is comprised of a liquid crystal display (LCD). 20. The system of claim 19, wherein the system comprises a liquid crystal display television. 21. An edge-lit backlight having an output area, comprising: back reflector; a transflector partially transmitting, partially reflecting incident light and comprising at least one concave structure facing said back reflector so as to form one or more recycling cavities between said transflector and said back reflector , the one or more circulation chambers substantially fill the output area of the panel; and A light source device, which is arranged near the first edge of the backlight source, and is used to inject light into the one or more recycling cavities through the input surface of the one or more recycling cavities, the input surface and the one or more recycling cavities The output area of the backlight is substantially vertical, and the input surface is substantially perpendicular to the output area; Wherein the at least one concave structure converges with the back reflector in a direction away from the input surface.

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