WO2008083018A1

WO2008083018A1 - Illumination light unit and display using same

Info

Publication number: WO2008083018A1
Application number: PCT/US2007/088270
Authority: WO
Inventors: Kenneth A. Epstein; Simon Magarill
Original assignee: 3M Innovative Properties Company
Priority date: 2006-12-29
Filing date: 2007-12-20
Publication date: 2008-07-10
Also published as: TW200837457A

Abstract

An illumination light unit (210) is disclosed that includes a substrate (218), and at least a first light source (216) positioned proximate the substrate (218). The first light source (216) is capable of producing illumination light generally along an illumination axis (217) that is substantially orthogonal to the substrate (218). The illumination light unit (210) also includes an elongated reflecting cavity (212) including a curved reflector (214) that is concave down facing the substrate (218). The curved reflector (214) includes an elliptical cross-section in a plane substantially orthogonal to the substrate (218). The first light source (216) is positioned proximate a first line focus (222) of the reflecting cavity (212) and an output surface (220) ' of the reflecting cavity (212) is positioned proximate a second line focus (224) of the reflecting cavity (212).

Description

ILLUMINATION LIGHT UNIT AND DISPLAY USING SAME

Related Applications

This application claims the benefit of U.S. Provisional Patent Application No. 60/882,803, filed on December 29, 2006, the disclosure of which is incorporated by reference herein in its entirety.

Background

Recent years have seen tremendous growth in the number and variety of display devices available to the public. Computers (whether desktop, laptop, or notebook), personal digital assistants (PDAs), mobile phones, and thin LCD TVs are but a few examples. Although some of these devices can use ordinary ambient light to illuminate the display, most include a light panel referred to as a backlight to make the display visible.

Many such 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 area 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 on 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. In some applications, a display is illuminated with light from a number of different light sources that produce light of different colors. Because the human eye more easily discerns variations in color than in brightness, it can be difficult to effectively mix light sources that produce different colors to provide white illumination light to the display. It is important in these situations that the light from the different light sources be mixed so that the color, as well as the brightness, are uniform across the displayed image. Summary

In one aspect, the present disclosures provides an illumination light unit that includes a substrate, and at least a first light source positioned proximate the substrate. The first light source is capable of producing illumination light generally along an illumination axis that is substantially orthogonal to the substrate. The illumination light unit also includes an elongated reflecting cavity including a curved reflector that is concave down facing the substrate. The curved reflector includes an elliptical cross- section in a plane substantially orthogonal to the substrate. The first light source is positioned proximate a first line focus of the reflecting cavity and an output surface of the reflecting cavity is positioned proximate a second line focus of the reflecting cavity.

In another aspect, the present disclosure provides a display that includes an image- forming panel having an illumination side, and a backlight unit disposed to the illumination side of the image-forming panel. The backlight unit includes a light guide including a first input surface and at least one illumination light unit including an output surface. The output surface is positioned proximate the first input surface of the light guide. The illumination light unit includes a substrate, and at least a first light source positioned proximate the substrate. The first light source is capable of producing illumination light generally along an illumination axis that is substantially orthogonal to the substrate. The illumination light unit also includes an elongated reflecting cavity including a curved reflector that is concave down facing the substrate. The curved reflector includes an elliptical cross-section in a plane substantially orthogonal to the substrate. The first light source is positioned proximate a first line focus of the reflecting cavity and the output surface of the reflecting cavity is positioned proximate a second line focus of the reflecting cavity. In another aspect, the present disclosure provides a backlight that includes a light guide including a first input surface, and at least one illumination light unit including an output surface positioned proximate a first input surface of the light guide. The illumination light unit further includes a substrate, and at least a first light source positioned proximate the substrate. The first light source is capable of producing illumination light generally along an illumination axis that is substantially orthogonal to the substrate. The illumination light unit further includes an elongated reflecting cavity including a curved reflector that is concave down facing the substrate. The curved reflector includes an elliptical cross-section in a plane substantially orthogonal to the substrate. The first light source is positioned proximate a first line focus of the reflecting cavity and the output surface of the reflecting cavity is positioned proximate a second line focus of the reflecting cavity.

These and other aspects of the present disclosure will be apparent from the detailed description below. In no event, however, should the above summaries be construed as limitations on the claimed subject matter, which subject matter is defined solely by the attached claims, as may be amended during prosecution.

Brief Description of the Drawings

FIG. 1 is a schematic cross-section view of one embodiment of an edge-lit liquid crystal display system.

FIGS. 2A-B are schematic cross-section views of one embodiment of a backlight that includes an illumination light unit and a light guide.

FIG. 3 is a schematic cross-section view of one embodiment of a reflecting cavity having a curved reflector with an elliptical cross-sectional shape.

FIG. 4 is a schematic cross-sectional view of another embodiment of a backlight that includes an illumination light unit and a light guide. FIG. 5 is a schematic cross-section view of an embodiment of a backlight that includes two illumination light units proximate an input surface of a light guide.

Detailed Description

The present disclosure is applicable to illuminated signs and displays, such as liquid crystal displays (LCDs, or LC displays), and is also applicable to displays that are illuminated using light sources positioned to the side of the display panel, known as edge- lit displays. The disclosure is believed to be particularly useful for displays that are illuminated by light sources of different colors. The disclosure is believed also to be applicable to systems that provide space lighting. In general, the present disclosure provides an illumination light unit that includes an elongated reflecting cavity having a curved reflector. In some embodiments, the curved reflector has an elliptical cross-section that forms a first line focus and a second line focus. One or more light sources can be placed proximate the first line focus such that light produced by the light sources is directed by the curved reflector to the second line focus. The elongated reflecting cavity also includes an output surface that is positioned proximate the second line focus. In embodiments where the one or more light sources include sources that produce different wavelengths of light, such light is allowed to expand within the cavity in a direction substantially parallel to the first and second line focuses such that the various wavelengths can be mixed, thereby providing uniform white light to a display, sign, etc.

In some embodiments, the output surface of the illumination light unit can be positioned proximate an input surface of a light guide to provide a backlight, e.g., for displays, signs, etc. In such embodiments, the second line focus is positioned proximate the input surface of the light guide. Because a substantial portion of the light emitted by the light sources is directed by the curved reflector to the second line focus, this substantial portion of the light is directed into the light guide. Further, placing the input surface of the light guide at the second line focus allows for thin light guides because the light being transmitted through the output surface should include its narrowest profile in the thickness direction of the light guide. In other words, positioning the input surface at the second line focus allows the light guide to capture nearly all of the light emitted by the illumination light unit. The illumination light units of the present disclosure can be used to provide light for displays, area illumination, signage, etc. For example, FIG. 1 illustrates one embodiment of an edge-lit display 100 that includes a backlight 112 including illumination light units 120. Such a display 100 can be used, for example, in an LCD monitor or LCD-TV. In this exemplary embodiment, the display 100 uses a liquid crystal (LC) image-forming panel 150, which typically includes a layer of LC 152 disposed between panel plates 154. The plates 154 are often formed of glass, and may include electrode structures and alignment layers on their inner surfaces for controlling the orientation of the liquid crystals in the LC layer 152. The electrode structures are commonly arranged so as to define LC panel pixels, i.e., areas of the LC layer 152 where the orientation of the liquid crystals can be controlled independently of adjacent pixels. A color filter may also be included with one or more of the plates 154 for imposing color on the displayed image. An upper absorbing polarizer 156 is positioned above the LC layer 152 and a lower absorbing polarizer 160 is positioned below the LC layer 152. In the illustrated embodiment, the upper and lower absorbing polarizers 156, 160 are located outside the display panel 150. The absorbing polarizers 156, 160 and the display panel 150, in combination, control the transmission of light from a backlight 112 through the display panel 150 to the viewer. In some exemplary embodiments, when a pixel of the LC layer 152 is not activated, it does not change the polarization of light passing therethrough. Accordingly, light that passes through the lower absorbing polarizer 160 is absorbed by the upper absorbing polarizer 156, when the absorbing polarizers 156, 160 are aligned perpendicularly. When the pixel is activated, the polarization of the light passing therethrough is rotated, so that at least some of the light that is transmitted through the lower absorbing polarizer 160 is also transmitted through the upper absorbing polarizer 156. Selective activation of the different pixels of the LC layer 152, for example, using a controller 180, results in the light passing out of the display 100 at certain desired locations, thus forming an image seen by the viewer. The controller 180 may include, for example, a computer or a television controller that receives and displays television images. One or more optional layers 158 may be provided over the upper absorbing polarizer 156, for example, to provide mechanical and/or environmental protection to the display surface. In one exemplary embodiment, the layer 158 may include a hardcoat over the absorbing polarizer 156.

Some types of LC displays may operate in a manner different from that described herein and, therefore, differ in detail from the described system. For example, the absorbing polarizers may be aligned parallel and the LC panel may rotate the polarization of the light when in an unactivated state. Regardless, the basic structure of such displays remains similar to that described herein.

The backlight 112 includes a light guide 130 and one or more illumination light units 120 that produce the illumination light and direct the illumination light into the light guide 130. The illumination light units 120 include one or more light sources 124 to produce the illumination light. The light sources 124 are shown schematically. In most cases, these sources 124 are compact light emitting diodes (LEDs). In this regard, "LED" refers to a diode that emits light, whether visible, ultraviolet, or infrared. It includes incoherent encased or encapsulated semiconductor devices marketed as "LEDs," whether of the conventional or super radiant variety. If the LED emits non- visible light such as ultraviolet light, and in some cases where it emits visible light, it is packaged to include a phosphor (or it may illuminate a remotely disposed phosphor) to convert short wavelength light to longer wavelength visible light, in some cases yielding a device that emits white light. An "LED die" is an LED in its most basic form, i.e., in the form of an individual component or chip made by semiconductor processing procedures. The component or chip can include electrical contacts suitable for application of power to energize the device. The individual layers and other functional elements of the component or chip are typically formed on the wafer scale, and the finished wafer can then be diced into individual piece parts to yield a multiplicity of LED dies.

If desired, other visible light emitters such as linear cold cathode fluorescent lamps (CCFLs) or hot cathode fluorescent lamps (HCFLs) can be used instead of or in addition to discrete LED sources as illumination sources for the disclosed backlights. In addition, hybrid systems such as, for example, (CCFL/LED), including cool white and warm white, CCFL/HCFL, such as those that emit different spectra, may be used. The combinations of light emitters may vary widely, and include LEDs and CCFLs, and pluralities such as, for example, multiple CCFLs, multiple CCFLs of different colors, and LEDs and CCFLs.

For example, in some applications it may be desirable to replace the row of discrete light sources 124 with a different light source such as a long cylindrical CCFL, or with a linear surface emitting light guide emitting light along its length and coupled to a remote active component (such as an LED die or halogen bulb), and to do likewise with other rows of sources. Examples of such linear surface emitting light guides are disclosed in U.S. Patent Nos. 5,845,038 (Lundin et al.) and 6,367,941 (Lea et al). Fiber-coupled laser diode and other semiconductor emitters are also known, and in those cases the output end of the fiber optic waveguide can be considered to be a light source with respect to its placement in the disclosed illumination light units. The same is also true of other passive optical components having small emitting areas such as lenses, deflectors, narrow light guides, and the like that give off light received from an active component such as a bulb or LED die. One example of such a passive component is a molded encapsulant or lens of a side-emitting packaged LED.

In some embodiments, the backlight 112 continuously emits white light, and the image-forming panel 150 is combined with a color filter matrix to form groups of multicolored 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, or the like) so that the displayed image is polychromatic. Alternatively, polychromatic images can be displayed using color sequential techniques, where, instead of continuously back-illuminating the panel 150 with white light and modulating groups of multicolored pixels in the panel 150 to produce color, separate differently colored light sources within the backlight 112 itself (selected, for example, from red, orange, amber, yellow, green, cyan, blue (including royal blue), and white in combinations such as those mentioned above) are modulated such that the backlight flashes a spatially uniform colored light output (such as, for example, red, then green, then blue) in rapid repeating succession. This color-modulated backlight is then combined with a display module that has only one pixel array (without any color filter matrix), the pixel array being modulated synchronously with the backlight to produce the whole gamut of achievable colors (given the light sources used in the backlight) over the entire pixel array, provided the modulation is fast enough to yield temporal color-mixing in the visual system of the observer. Examples of color sequential displays, also known as field sequential displays, are described in U.S. Patent No. 5,337,068 (Stewart et al.) and U.S. Patent No. 6,762,743 (Yoshihara et al.). In some cases, it may be desirable to provide only a monochrome display. In those cases the backlight 112 can include filters or specific sources that emit predominantly in one visible wavelength or color.

The illumination light unit 120 may include an elongated reflecting cavity 120 that is used to collect and direct light from the light sources 124 to the light guide 130. The light guide 130 guides illumination light from the light sources 124 to an area behind the panel 150, and directs the light to the panel 150. The light guide 130 may receive illumination light through a single edge, or through multiple edges. In other embodiments, not illustrated, the light may be coupled into the light guide 130 through a light coupling mechanism other than the edge of the light guide 130. A base reflector 114 may be positioned on the other side of the light guide 130 from the display panel 150. The light guide 130 may include light extraction features 132 that are used to extract the light from the light guide 130 for illuminating the display panel 150. For example, the light extraction features 132 may include diffusing spots on the surface of the light guide 130 that direct light either directly towards the display panel 150 or towards the base reflector 114. Other approaches may be used to extract the light from the light guide 130. The base reflector 114 is preferably highly reflective for enhanced panel efficiency. For example, the base reflector 114 may have an average reflectivity for visible light emitted by the light sources of at least 90%, 95%, 98%, 99%, or more. The base reflector 114 can be a predominantly specular, diffuse, or combination specular/diffuse reflector, whether spatially uniform or patterned. In some cases, the base reflector 114 can be made from a stiff metal substrate with a high reflectivity coating, or a high reflectivity film laminated to a supporting substrate. Suitable high reflectivity materials include Vikuiti™ Enhanced Specular Reflector (ESR) multilayer polymeric film available from 3M Company; a film made by laminating a barium sulfate-loaded polyethylene terephthalate film (2 mils thick) to Vikuiti™ ESR film using a 0.4 mil thick isooctylacrylate acrylic acid pressure sensitive adhesive, the resulting laminate film referred to herein as "EDR II" film; E-60 series Lumirror™ polyester film available from Toray Industries, Inc.; porous polytetrafluoroethylene (PTFE) films, such as those available from W. L. Gore & Associates, Inc.; Spectralon™ reflectance material available from Labsphere, Inc.; Miro™ anodized aluminum films (including Miro™ 2 film) available from Alanod Aluminum-Veredlung GmbH & Co.; MCPET high reflectivity foamed sheeting from Furukawa Electric Co., Ltd.; and White Refstar™ films and MT films available from Mitsui Chemicals, Inc.

The base reflector 114 may be substantially flat and smooth, or it may have a structured surface associated with it to enhance light scattering or mixing. Such a structured surface can be imparted (a) on the reflective surface of the base reflector 114, or (b) on a transparent coating applied to the reflective surface. In the former case, a highly reflecting film may be laminated to a substrate in which a structured surface was previously formed, or a highly reflecting film may be laminated to a flat substrate (such as a thin metal sheet, as with Vikuiti™ Durable Enhanced Specular Reflector-Metal (DESR- M) reflector available from 3M Company) followed by forming the structured surface, such as with a stamping operation. In the latter case, a transparent film having a structured surface can be laminated to a flat reflective surface, or a transparent film can be applied to the reflector and then afterwards a structured surface imparted to the top of the transparent film. The backlight 112 can also include sides and ends (not shown) located along the outer boundary of the backlight 112 along edges that do not include an illumination light unit. Such sides are preferably lined or otherwise provided with high reflectivity vertical walls to reduce light loss and improve recycling efficiency. The same reflective material used for the base reflector 114 can be used to form these walls, or a different reflective material can be used. In exemplary embodiments, the side walls are diffusely reflective.

An arrangement 170 of light management films, which may also be referred to as a light management unit, is positioned between the backlight 112 and the image-forming panel 150. The light management films 170 affect the illumination light propagating from the backlight 112 so as to improve the operation of the display system 100. For example, the arrangement 170 of light management films may include a diffuser 172. The diffuser 172 is used to diffuse the light received from the light sources 124, which results in increased uniformity of the illumination light incident on the panel 150. Consequently, this results in an image perceived by the viewer to be more uniformly bright. The diffuser layer 172 may be any suitable diffuser film or plate. For example, the diffuser layer 172 can include any suitable diffusing material or materials. In some embodiments, the diffuser layer 172 may include a polymeric matrix of polymethyl methacrylate (PMMA) with a variety of dispersed phases that include glass, polystyrene beads, and CaCO₃ particles. Exemplary diffusers can include 3M™ Scotchcal™ Diffuser Film, types 3635-30 and 3635-70, available from 3M Company, St. Paul, Minnesota.

The light management unit 170 may also include a reflective polarizer 174. The light sources 124 typically produce unpolarized light, but the lower absorbing polarizer 160 only transmits a single polarization state; therefore, about half of the light generated by the light sources 124 is not transmitted through to the LC layer 152. The reflective polarizer 174, however, may be used to reflect the light that would otherwise be absorbed in the lower absorbing polarizer 160. Consequently, this light may be recycled by reflection between the reflective polarizer 174 and the reflective substrate 102. At least some of the light reflected by the reflective polarizer 174 may be depolarized and subsequently returned to the reflective polarizer 174 in a polarization state that is transmitted through the reflective polarizer 174 and the lower absorbing polarizer 160 to the LC layer 152. In this manner, the reflective polarizer 174 may be used to increase the fraction of light emitted by the light sources 124 that reaches the LC layer 152, thereby providing a brighter display output.

Any suitable type of reflective polarizer may be used for the reflective polarizer 174, e.g., multilayer optical film (MOF) reflective polarizers, diffusely reflective polarizing film (DRPF), such as continuous/disperse phase polarizers, wire grid reflective polarizers, or cholesteric reflective polarizers.

Both the MOF and continuous/disperse phase reflective polarizers rely on the difference in refractive index between at least two materials, usually polymeric materials, to selectively reflect light of one polarization state while transmitting light in an orthogonal polarization state. Some examples of MOF reflective polarizers are described in co-owned U.S. Patent Nos. 5,882,774 (Jonza et al.). Commercially available examples of MOF reflective polarizers include Vikuiti™ DBEF-D200 and DBEF-D440 multilayer reflective polarizers that include diffusive surfaces, available from 3M Company.

Examples of DRPF useful in connection with the present disclosure include continuous/disperse phase reflective polarizers as described, e.g., in co-owned U.S. Patent No. 5,825,543 (Ouderkirk et al.), and diffusely reflecting multilayer polarizers as described, e.g., in co-owned U.S. Patent No. 5,867,316 (Carlson et al.). Other suitable types of DRPF are described in U.S. Patent No. 5,751,388 (Larson).

Some examples of wire grid polarizers useful in connection with the present disclosure include those described, e.g., in U.S. Patent No. 6,122,103 (Perkins et al.).

Wire grid polarizers are commercially available from, inter alia, Moxtek Inc., Orem, Utah.

Some examples of cholesteric polarizers useful in connection with the present disclosure include those described, e.g., in U.S. Patent No. 5,793,456 (Broer et al.), and U.S. Patent Publication No. 2002/0159019 (Pokorny et al.). Cholesteric polarizers are often provided along with a quarter wave retarding layer on the output side so that the light transmitted through the cholesteric polarizer is converted to linearly polarized light. In some embodiments, a polarization control layer 178 may be provided between the diffuser 172 and the reflective polarizer 174. Examples of polarization control layers include a quarter wave retarding layer and a polarization rotating layer such as a liquid crystal polarization rotating layer. The polarization control layer 178 may be used to change the polarization of light that is reflected from the reflective polarizer 174 so that an increased fraction of the recycled light is transmitted through the reflective polarizer 174. The arrangement 170 of light management films may also include one or more brightness enhancing layers. A brightness enhancing layer is one that includes a surface structure that redirects off-axis light in a direction closer to the axis of the display. This increases the amount of light propagating on-axis through the LC layer 152, thus increasing the brightness of the image seen by the viewer. One example of a brightness enhancing layer is a prismatic brightness enhancing layer, which has a number of prismatic ridges that redirect the illumination light through refraction and reflection. Examples of prismatic brightness enhancing layers that may be used in the display 100 include the Vikuiti™ BEF II and BEF III family of prismatic films available from 3M Company, including BEF II 90/24, BEF II 90/50, BEF HIM 90/50, and BEF HIT. The exemplary embodiment illustrated in FIG. 1 shows a first brightness enhancing layer 176a disposed between the reflective polarizer 174 and the image-forming panel 150. A prismatic brightness enhancing layer typically provides optical gain in one dimension. An optional second brightness enhancing layer 176b may also be included in the arrangement 170 of light management layers, having its prismatic structure oriented orthogonally to the prismatic structure of the first brightness enhancing layer 176a. Such a configuration provides an increase in the optical gain of the display 100 in two dimensions. In other exemplary embodiments, the brightness enhancing layers 176a, 176b may be positioned between the backlight 112 and the reflective polarizer 174. The different layers in the light management unit 170 may be free standing. In other embodiments, two or more of the layers in the light management unit 170 may be laminated together, for example as discussed in co-owned U.S. Patent Application Publication No. 2006/0082698 (Ko et al.). In other exemplary embodiments, the light management unit 170 may include two subassemblies separated by a gap, for example, as described in co-owned U.S. Patent Application Publication No. 2006/0082700 (Gehlsen et al.).

One embodiment of a backlight 200 that may be used with a display (e.g., display 100 of FIG. 1) is illustrated in FIGS. 2A-B. Backlight 200 includes an illumination light unit 210 that includes an output surface 220, and a light guide 230 that includes a first input surface 232. The output surface 220 of the illumination light unit 210 is positioned proximate the first input surface 232 of the light guide 230. Although depicted as including one illumination light unit 210, the backlight 200 can include two or more illumination light units positioned along the same or other edges of the light guide 230.

The illumination light unit 210 includes a substrate 218 and one or more light sources 216 positioned proximate the substrate 218. Each light source 216 is capable of producing illumination light generally along an illumination axis 217 that is substantially orthogonal to the substrate 218. The unit 210 further includes an elongated reflecting cavity 212 that includes a curved reflector 214 that is concave down facing the substrate 218.

The substrate 218 may be any suitable material or materials. In some embodiments, the substrate 218 may be reflective for reflecting light from the light sources 216 propagating in a direction toward the substrate 218. The reflective substrate 218 may have an average reflectivity for visible light emitted by the light sources 216 of at least 90%, 95%, 98%, 99%, or more. The reflective substrate 218 can be a predominantly specular, diffuse, or combination specular/diffuse reflector, whether spatially uniform or patterned. In some cases, the reflective substrate 218 can be made from a stiff metal substrate with a high reflectivity coating, or a high reflectivity film laminated to a supporting substrate. Suitable high reflectivity materials include Vikuiti™ Enhanced Specular Reflector (ESR) multilayer polymeric film available from 3M Company; a film made by laminating a barium sulfate-loaded polyethylene terephthalate film (2 mils thick) to Vikuiti™ ESR film using a 0.4 mil thick isooctylacrylate acrylic acid pressure sensitive adhesive, the resulting laminate film referred to herein as "EDR II" film; E-60 series Lumirror™ polyester film available from Toray Industries, Inc.; porous polytetrafluoroethylene (PTFE) films, such as those available from W. L. Gore & Associates, Inc.; Spectralon™ reflectance material available from Labsphere, Inc.; Miro™ anodized aluminum films (including Miro™ 2 film) available from Alanod Aluminum-

Veredlung GmbH & Co.; MCPET high reflectivity foamed sheeting from Furukawa Electric Co., Ltd.; and White Refstar™ films and MT films available from Mitsui Chemicals, Inc.

The reflective substrate 218 may be substantially flat and smooth, or it may have a structured surface associated with it to enhance light scattering or mixing. Such a structured surface can be imparted (a) on the reflective surface of the substrate 218, or (b) on a transparent coating applied to the reflective surface. In the former case, a highly reflecting film may be laminated to a substrate in which a structured surface was previously formed, or a highly reflecting film may be laminated to a flat substrate (such as a thin metal sheet, as with Vikuiti™ Durable Enhanced Specular Reflector-Metal (DESR- M) reflector available from 3M Company) followed by forming the structured surface, such as with a stamping operation. In the latter case, a transparent film having a structured surface can be laminated to a flat reflective surface, or a transparent film can be applied to the reflector and then afterwards a structured surface imparted to the top of the transparent film.

The light sources 216 may be positioned proximate the substrate 218 such that the light sources 216 are on, embedded in, or below the substrate 218. For example, the light sources 216 and conductors for providing current to the light sources 216 may be positioned on the substrate 218. In other embodiments, the light sources 216 may be positioned proximate a flexible substrate such as those described in U.S. Patent Publication No. 2005/0116235 (Schultz et al), entitled ILLUMINATION ASSEMBLY. The illumination light unit 210 can also include sides and ends (not shown) located along the outer boundary of the unit 210 that are preferably lined or otherwise provided with high reflectivity vertical walls to reduce light loss and improve recycling efficiency. The same reflective material used for the reflective substrate 218 can be used to form these walls, or a different reflective material can be used. In exemplary embodiments, the side walls are diffusely reflective. The ends can also include other reflectors, e.g., turning mirrors, tilted mirror film, etc.

Positioned proximate the substrate 218 is one or more light sources 216. Light sources 216 can include any suitable light source or combination of sources, e.g., those light sources described in regard to light sources 124 of FIG. 1. The illumination light unit 210 also includes the elongated reflecting cavity 212 that includes the curved reflector 214. In some embodiments, the curved reflector 214 is concave down facing the substrate 218. The curved reflector 214 can take any suitable cross-sectional shape, e.g., cylindrical, spherical, rectangular, etc. In some embodiments, the curved reflector 214 includes an elliptical cross-section in a plane substantially orthogonal to the substrate 218. For example, in the embodiment illustrated in FIG. 2B, the curved reflector 214 has an elliptical cross-section in the x-z plane. In general, an ellipse is defined as a closed geometric figure shaped like an elongated circle and symmetric about two axes of different lengths, i.e., the major and minor axes. For example, FIG. 3 illustrates a cross-section view of a curved reflector 314 that has an elliptical cross-section in the plane of the drawing. FIG. 3 also includes the outline of an ellipse 302 superimposed on the curved reflector 314 for illustration purposes. The ellipse 302 includes a major axis 350 and a minor axis 352. The ellipse also includes a first focus 354 and a second focus 356. For a light source placed at the first focus 354 of the curved reflector 314, light from the source that is incident on the curved reflector 314 will be reflected through the second focus 356. Returning to FIGS. 2A-B, the reflecting cavity 212 is elongated along an axis that is coincident with the y-axis. In other words, the reflecting cavity 212 can be thought of as being formed by projecting the elliptical cross-section of the curved reflector 214 along the y-axis. The curved reflector 214 converges with the substrate 218 in a direction away from the output surface 220. The output surface 220 can take any suitable shape. Further, the output surface 220 can be substantially orthogonal to the substrate 218; alternatively, the output surface 220 can be canted at an angle to the substrate 218.

In embodiments where the curved reflector 214 has an elliptical cross-section, the curved reflector 214 forms a first line focus 222 that, in the illustrated embodiment, is substantially parallel with the y-axis. The first line focus 222 refers to the collection of first foci of the elliptical cross-sections of the curved reflector 214. The reflecting cavity 212 also includes a second line focus 224 that refers to the collection of second foci of the elliptical cross-sections of the curved reflector 214. As illustrated, the light sources 216 are positioned proximate the first line focus 222. Further, the output surface 220 of the reflecting cavity 212 is positioned proximate the second line focus 224. Because the input surface 232 of the light guide 230 is positioned proximate the output surface 220 of the reflecting cavity 212, the input surface 232 is also positioned proximate the second line focus 224.

The curved reflector 214 may be any suitable type of reflector, for example a metalized reflector, or a multilayer dielectric reflector, which includes polymer multilayer optical film (MOF) reflectors. For example, the reflector 214 may include ESR. In other embodiments, the reflecting cavity 212 can include a solid optical body having a surface 214 that totally internally reflects at least a portion of light from the light sources 216. The curved reflector 214 may be positioned such that the major axis of the ellipse formed in part by the curved reflector 214 is parallel to the substrate 218. In other embodiments, the major axis may be positioned at an angle to the substrate 218 such that the curved reflector's second line focus 224 is proximate a central region of the input surface 232 of the light guide 230.

The curved reflector 214 and the substrate 218 form a space 226. The space 226 may be filled or may be empty. In embodiments where the space 226 is filled, for example, with a transparent optical body, then the reflector 214 may be attached to the outer surface of the body. The space 226 can be filled using any suitable transparent material or materials, e.g., glass; acrylates, including polymethylmethacrylate, polystyrene, fluoropolymers; polyesters including polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and copolymers containing PET or PEN or both; polyolefms including polyethylene, polypropylene, polynorborene, polyolefins in isotactic, atactic, and syndiotactic sterioisomers, and polyolefins produced by metallocene polymerization. Other suitable polymers include polyetheretherketones and polyetherimides. Different configurations of reflective cavities are described further in U.S. Patent No. 7,070,301 (Magarill).

In general, at least a portion of illumination light from a light source 216 is emitted generally along the illumination axis 217 toward the reflector 214. Because the light source 216 is positioned proximate the first line focus 222 of the reflector 214, a portion of the illumination light is reflected by the reflector 214 toward the second line focus 224. The input surface 232 of the light guide 230, which is positioned proximate the second line focus 224 of the reflector 214, receives the reflected light. The light guide 230 can include extraction features (e.g., extraction features 132 of FIG. 1) that redirect the light from the illumination light unit 210 out of the light guide 230.

In embodiments where the light sources 216 include sources that produce different wavelengths of light, the reflecting cavity 212 allows the illumination light to expand in a direction substantially parallel with the y-axis of FIGS. 2A-B, thereby providing mixing of the various wavelengths of light. In other words, illumination light within the reflecting cavity 212 is generally constrained in the x-z plane and allowed to expand in the x-y plane, and, therefore, various wavelengths of light can be mixed to provide white light to the light guide 230. For example, light sources 216 may include a first light source capable of producing illumination light at a first wavelength, and a second light source capable of producing light at a second wavelength different from the first wavelength. Further, for example, the first wavelength may be in the blue region, and the second wavelength may be in the yellow region. The blue and yellow light can then be mixed within the reflecting cavity 212 to provide white light to the light guide 230.

In some embodiments, the light sources 216 can include a third light source capable of producing illumination light at a third wavelength different from the first and second wavelengths. For example, the first wavelength can be in the red region, the second wavelength in the green region, and the third wavelength in the blue region. The red, green, and blue light can then be mixed within the reflecting cavity 212 to provide white light to the light guide 230. Any number of different wavelength-emitting light sources can be provided in reflecting cavity 212.

The output surface 220 of the illumination light unit 210 is positioned proximate the input surface 232 of the light guide 230. In some embodiments, the unit 210 and the light guide 230 may be a unitary whole such that the output surface 220 and the input surface 232 are the same surface. In other embodiments, one or more optical elements can be positioned between the output surface 220 and the input surface 232. The one or more optical elements can include any suitable optical element or elements, e.g., optical coupling agents such as adhesives or index matching fluids or gels, optical brightness enhancing films such as BEF (available from 3M Company), and short-wavelength absorbing materials such as ultraviolet light absorbing dyes and pigments, reflective polarizing films such as DBEF (also available from 3M Company), diffusers, lenses, controlled transmission films, and combinations thereof. See, e.g., U.S. Patent Application Publication No. 2006/0291238 (Epstein et al.).

The light guide 230 can include any suitable light guide, e.g., hollow or solid light guide. Although the light guide 230 is illustrated as being planar in shape, the light guide 230 may take any suitable shape, e.g., wedge, cylindrical, planar, conical, complex molded shapes, etc. Further, the light guide 230 can include any suitable material or materials. For example, the light guide 230 may include glass; acrylates, including polymethylmethacrylate, polystyrene, fluoropolymers; polyesters including polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and copolymers containing PET or PEN or both; polyolefϊns including polyethylene, polypropylene, polynorborene, polyolefms in isotactic, atactic, and syndiotactic sterioisomers, and polyolefϊns produced by metallocene polymerization. Other suitable polymers include polyetheretherketones and polyetherimides. In some embodiments, the light guide 230 may be made of the same materials as are used for the illumination light unit 210. In other embodiments, the light guide 230 may be hollow.

FIG. 4 illustrates another embodiment of a backlight 400. The backlight 400 includes a light guide 430 that includes a first input surface 432, and an illumination light unit 410 that includes an output surface 420 positioned proximate the input surface 432 of the light guide 430. All of the design possibilities and considerations in regard to the light guide 230 and the illumination light unit 210 of the embodiment illustrated in FIGS. 2A-B apply equally to the light guide 430 and illumination light unit 410 of the embodiment illustrated in FIG. 4.

The illumination light unit 410 of backlight 400 is similar in may regards to the unit 210 of backlight 200 of FIG. 2. The unit 410 includes a substrate 418, and one or more light sources 416 positioned proximate the substrate 418. Each light source 416 is capable of generating illumination light generally along an illumination axis 417 that is substantially orthogonal to the substrate 418. The unit 410 also includes an elongated reflecting cavity 412 that includes a curved reflector 414 that is concave down facing the substrate 418. In some embodiments, the curved reflector 414 includes an elliptical cross- section in a plane substantially orthogonal to the substrate 418 (e.g., in FIG. 4, the x-z plane). The light sources 416 are positioned proximate a first line focus 454 of the reflecting cavity 412, and the output surface 420 of the cavity 412 is positioned proximate a second line focus 456 of the cavity 412. One difference between the unit 410 and unit 210 of FIGS . 2 A-B is that the reflecting cavity 412 includes at least one facet 424 positioned between the light sources 416 and the output surface 420 of the reflecting cavity 412. The facet 424 may be formed of any suitable reflective material or materials, e.g., metal, polymeric, etc. In some embodiments, facet 424 may include a polymeric multilayer optical film, e.g., ESR. In other embodiments, the reflecting cavity 412 can include a solid optical body having the facet 424 formed therein. Such a facet 424 can be shaped so that it provides a surface that reflects incident light. The facet 424 may be formed in the reflecting cavity, on the substrate, attached to the substrate, etc.

The facet 424 can include any suitable shape or shapes such that incident light is directed toward the output surface 420. Although the embodiment illustrated in FIG. 4 has only one facet, two or more facets may be included two direct incident light as described herein.

Another difference between the unit 410 and the unit 210 of FIGS. 2A-B is that the elliptical curved reflector 414 is tilted at an angle to the input surface 432 of the light guide 430 such that the second line focus 456 is positioned proximate a central region of the input surface 432. In other words, a major axis 458 of the elliptical curved reflector 414 is not orthogonal to the input surface 432 of the light guide 430. The major axis 458 can be tilted at any suitable angle to the input surface 432 of the light guide 430. Because the light from the light source 416 that is positioned proximate the first line focus 454 is directed to the second line focus 456, the cone of light directed by the curved reflector 414 will be at its most narrow profile in the x-z plane at the second line focus 456. By placing the input surface 432 of the light guide 430 at the second line focus 456, a width d of the light guide 430 can be reduced while still allowing the light guide 430 to capture a substantial portion of the light leaving the illumination light unit 410. Reducing the thickness d of the light guide 430 can also reduce the weight and cost of the backlight 400. FIG. 5 illustrates another embodiment of a backlight 500. The backlight 500 includes a light guide 530 that includes a first input surface 532, a first illumination light unit 510 having the output surface 520 positioned proximate an input surface 532 of the light guide 530, and a second illumination light unit 540 having an output surface 550 positioned proximate the input surface 532. All of the design considerations and possibilities regarding the light guide 230 and the illumination light unit 210 of the embodiment illustrated in FIGS. 2A-B apply equally to the light guide 530, the first illumination light unit 510, and the second illumination light unit 540 of the embodiment illustrated in FIG. 5.

The first unit 510 and second unit 540 are positioned proximate the same input surface 532 of the light guide 530. As illustrated in FIG. 5, the second unit 540 is rotated in relation to the first unit 510 such that electrical connections to light sources 546 can more easily be provided. The second unit 540 can be positioned in any suitable orientation or relationship to the first unit 510 such that both the first unit 510 and the second unit 540 are positioned proximate the same input surface 532 of the light guide 530. Although depicted in FIG. 5 as having illumination light units 510, 540 positioned proximate input surface 532 of light guide 530, the backlight 500 can include one or more additional illumination light units positioned along other edges of the light guide 530.

The backlights described herein can be manufactured using any suitable technique. For example, backlight 200 of FIGS. 2A-B can be manufactured by first providing light sources 216 on substrate 218. The reflecting cavity 212 can then be formed on the substrate 218 using any suitable technique. In one exemplary embodiment, a solid reflecting cavity 212 can be formed onto the light sources 216 and substrate 218, e.g., by molding, such that the light sources are encased within the reflecting cavity 212. Such a configuration can provide protection for the light sources 216 as the reflecting cavity 212 in essence encapsulates the light sources 216. The illumination light unit 210 can then be positioned proximate the input surface 232 of the light guide 230 using any suitable technique. For example, the unit 210 can be attached to the input surface 232, held in place next to or in contact with the input surface 232, etc. In some embodiments, the unit 210 can be attached to the input surface 232 using a suitable adhesive, e.g., Norland OP29, OP21, OP40, or Summers SK9. Alternatively, the reflecting cavity 212 and light guide 230 can be a unitary piece that is molded onto the light sources 216 and substrate 218. The curved reflector 214 can then be positioned on or adjacent the reflecting cavity

212 using any suitable technique. For example, a metal coating can be applied to or deposited onto the outer surface of the reflecting cavity 212. If the curved reflector 214 includes a polymeric multilayer optical film, then such film can be attached to the reflective cavity 212 using any suitable technique, e.g., attached using an optical adhesive. If the reflecting cavity 212 is hollow (i.e., space 226 is not filled using a liquid or solid material), then the curved reflector 214 can be positioned proximate the light sources 216 and light guide 230 using any suitable technique. For example, one end of the curved reflector 214 can be attached to or otherwise held in place on the substrate 218, and another end of the curved reflector 214 can be attached to or otherwise held in place on or adjacent the input surface 232 of the light guide 230. If the curved reflector 214 includes a polymeric multilayer optical film, e.g., ESR, then the film can be formed using any suitable technique into the desired cross-sectional shape, e.g., thermoforming. Suitable techniques for forming polymeric multilayer optical films are further described, e.g., in U.S. Patent No. 6,788,463 (Merrill et al), entitled POST-FORMABLE MULTILAYER OPTICAL FILMS AND METHODS OF FORMING.

All references and publications cited herein are expressly incorporated herein by reference in their entirety into this disclosure, except to the extent they may directly contradict this disclosure. Illustrative embodiments of this disclosure are discussed and reference has been made to possible variations within the scope of this disclosure. These and other variations and modifications in the disclosure will be apparent to those skilled in the art without departing from the scope of the disclosure, and it should be understood that this disclosure is not limited to the illustrative embodiments set forth herein. Accordingly, the disclosure is to be limited only by the claims provided below.

Claims

What is claimed is:

1. An illumination light unit, comprising: a substrate; at least a first light source positioned proximate the substrate, wherein the first light source is capable of producing illumination light generally along an illumination axis that is substantially orthogonal to the substrate; and an elongated reflecting cavity comprising a curved reflector that is concave down facing the substrate, wherein the curved reflector comprises an elliptical cross-section in a plane substantially orthogonal to the substrate, and further wherein the first light source is positioned proximate a first line focus of the reflecting cavity and an output surface of the reflecting cavity is positioned proximate a second line focus of the reflecting cavity.

2. The unit of claim 1 , wherein the reflecting cavity is operable to direct at least some of the illumination light from the first light source through the output surface of the reflecting cavity.

3. The unit of claim 1 , wherein the first light source comprises an LED.

4. The unit of claim 1 , wherein the curved reflector converges with the substrate in a direction away from the output surface of the reflecting cavity.

5. The unit of claim 1 , wherein the substrate comprises a reflective surface facing the curved reflector.

6. The unit of claim 5, wherein the reflective surface of the substrate comprises a specularly reflective polymeric multilayer optical film.

7. The unit of claim 1 , wherein the curved reflector comprises a polymeric multilayer optical film.

8. The unit of claim 7, wherein the reflecting cavity further comprises a molded optical element, wherein the polymeric multilayer optical film is positioned on the molded optical element.

9. The unit of claim 8, wherein the molded optical element is formed on the first light source and the substrate.

10. The unit of claim 1 , wherein the reflecting cavity is hollow.

11. The unit of claim 1 , wherein the first light source is capable of producing illumination light at a first wavelength, wherein the unit further comprises a second light source positioned proximate the substrate and the first line focus of the reflecting cavity, wherein the second light source is capable of producing illumination light at a second wavelength different from the first wavelength.

12. The unit of claim 11 , wherein the first light source and the second light source comprise LEDs.

13. The unit of claim 11 , further comprising a third light source positioned proximate the substrate and the first line focus of the reflecting cavity, wherein the third light source is capable of producing illumination light at a third wavelength different from the first and second wavelengths.

14. The unit of claim 13, wherein the first, second, and third wavelengths are red, green, and blue wavelengths respectively.

15. The unit of claim 1, wherein the first light source is capable of producing white illumination light.

16. A display, comprising: an image-forming panel having an illumination side; and a backlight unit disposed to the illumination side of the image-forming panel, wherein the backlight unit comprises a light guide comprising a first input surface and at least one illumination light unit comprising an output surface, wherein the output surface is positioned proximate the first input surface of the light guide, wherein the illumination light unit comprises: a substrate; at least a first light source positioned proximate the substrate, wherein the first light source is capable of producing illumination light generally along an illumination axis that is substantially orthogonal to the substrate; and an elongated reflecting cavity comprising a curved reflector that is concave down facing the substrate, wherein the curved reflector comprises an elliptical cross-section in a plane substantially orthogonal to the substrate, and further wherein the first light source is positioned proximate a first line focus of the reflecting cavity and the output surface of the reflecting cavity is positioned proximate a second line focus of the reflecting cavity.

17. The display of claim 16, wherein the image-forming panel comprises an LCD panel.

18. The display of claim 16, further comprising one or more light management films disposed between the backlight unit and the image-forming panel.

19. The display of claim 18, wherein the one or more light management films comprise at least one of a reflective polarizer and a prismatic brightness enhancing film.

20. The display of claim 16, wherein the first light source is capable of producing illumination light at a first wavelength, wherein the system further comprises a second light source positioned proximate the substrate and the first line focus of the reflecting cavity, wherein the second light source is capable of producing illumination light at a second wavelength different from the first wavelength.

21. The display of claim 16, wherein the first light source is capable of producing white illumination light.

22. The display of claim 16, wherein the curved reflector comprises a polymeric multilayer optical film.

23. A backlight, comprising: a light guide comprising a first input surface; and at least one illumination light unit comprising an output surface positioned proximate the first input surface of the light guide, wherein the illumination light unit further comprises: a substrate; at least a first light source positioned proximate the substrate, wherein the first light source is capable of producing illumination light generally along an illumination axis that is substantially orthogonal to the substrate; and an elongated reflecting cavity comprising a curved reflector that is concave down facing the substrate, wherein the curved reflector comprises an elliptical cross-section in a plane substantially orthogonal to the substrate, and further wherein the first light source is positioned proximate a first line focus of the reflecting cavity and the output surface of the reflecting cavity is positioned proximate a second line focus of the reflecting cavity.