Light emitting diode arrays for direct backlighting of liquid crystal displays

A display panel for a flat panel display includes a planar array of LCD devices and a planar array of LED devices that is closely spaced apart from the planar array of LCD devices, at least some of the LED devices being disposed within a periphery of the array of LCD devices such that, in operation, the planar array of LED devices provides backlighting for the planar array of LCD devices. The planar array of LED devices can include at least one solid metal block having first and second opposing metal faces. The first metal face includes therein an array of reflector cavities, and the second metal face includes therein heat sink fins that are exposed at the back face of the flat panel display.

FIELD OF THE INVENTION

This invention relates to Liquid Crystal Display (LCD) devices, and more particularly, to backlighting of LCD devices.

BACKGROUND OF THE INVENTION

LCD devices are widely used in flat panel displays for monitors, televisions and/or other displays. As is well known to those having skill in the art, an LCD display generally includes a planar array of LCD devices that act as an array of optical shutters. Transmissive LCD displays employ backlighting using fluorescent tubes above, beside and sometimes behind the array of LCD devices. A diffusion panel behind the LCD devices can be used to redirect and scatter the light evenly to provide a more uniform display.

For example, it is known to use one or more fluorescent cold cathode tubes adjacent one or more edges of the planar array of LCD devices, and a light guide or light pipe that directs the light from the fluorescent cold cathode tubes, to illuminate the face of the planar array of LCD devices. Unfortunately, such edge lighting may be inefficient, with up to 50% or more of the light being lost.

It is also known to provide an array of fluorescent cold cathode tubes behind and facing the planar array of LCD devices. Unfortunately, an array of fluorescent cold cathode tubes may increase the thickness of the LCD display and/or increase the power consumption thereof. It also may be difficult to uniformly illuminate the planar array of LCD devices with the array of fluorescent cold cathode tubes.

Semiconductor light emitting devices, such as Light Emitting Diode (LED) devices, also may be used for edge illumination of a planar array of LCD devices. For example, U.S. patent application Ser. No. 10/898,608, filed Jul. 23, 2004, entitled Reflective Optical Elements for Semiconductor Light Emitting Devices, to coinventor Negley, and assigned to the assignee of the present invention, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein, describes side emission LEDs that may be used for large area LCD and/or television backlighting.

SUMMARY OF THE INVENTION

Some embodiments of the present invention provide a display panel for a flat panel display that includes a planar (i.e., a two dimensional) array of LCD devices and a planar array of LED devices that is closely spaced apart from the planar array of LCD devices, at least some of the LED devices being disposed within a periphery of the array of LCD devices such that, in operation, the planar array of LED devices provides backlighting for the planar array of LCD devices. In some embodiments, the planar arrays of LCD and LED devices are at least 17 inches in size along a diagonal thereof. In other embodiments, the planar array of LED devices is configured to emit light that appears as white light. In still other embodiments of the present invention, the LED devices in the planar array of LED devices are spaced sufficiently close to one another so as to provide uniform backlighting of the planar array of LCD devices.

In some embodiments, the planar array of LED devices is configured to transmit light from the planar array of LED devices through the planar array of LCD devices, along a light path that extends generally perpendicular to the planar arrays of LCD and LED devices. In other embodiments, the light path does not redirect the light to be parallel to the planar arrays of LCD and LED devices. In still other embodiments, a reflector-free light path is provided between the planar array of LED devices and the planar array of LCD devices. In yet other embodiments, the planar array of LED devices is configured to emit light generally parallel to the planar array of LCD devices. In these embodiments, an array of reflectors may be configured to redirect the light that is emitted generally parallel to the planar array of LCD devices along a light path that extends generally perpendicular to the planar arrays of LCD and LED devices.

In other embodiments, a planar optical film is located between the planar array of LCD devices and the planar array of LED devices, such that, in operation, the planar array of LED devices transmits light through the planar optical film and to the planar array of LCD devices. The planar optical film may include polarizers, scatterers and/or other optical elements.

In some embodiments of the invention, the planar array of LED devices includes at least one solid metal block having first and second opposing metal faces that extend parallel to the array of LCD devices. The first metal face is facing toward the array of LCD devices, and the second metal face is facing away from the array of LCD devices. The first metal face includes therein an array of reflector cavities, and the second metal face includes therein a plurality of heat sink fins. At least one LED device is mounted in a respective reflector cavity such that, in operation, the reflector cavity reflects light that is emitted by the at least one LED device that is mounted therein away from the reflector cavity. In some embodiments, the at least one LED device that is mounted in the respective reflector cavity is configured to emit light that appears as white light in operation. In other embodiments, the at least one LED device that is mounted in the respective reflector cavity consists of a red LED device, a blue LED device and two green LED devices. In some embodiments, the two green LED devices emit green light at different frequencies.

It will be understood that embodiments of the invention have been described above in connection with display panels for flat panel displays. However, other embodiments of the invention can provide an LED-based backlighting system for an LCD display, according to any of the embodiments that were described above. Moreover, still other embodiments of the invention can add other components such as a frame and/or electronics to provide a flat panel display. Analogous backlighting methods also may be provided.

Other embodiments of the present invention provide a flat panel display that includes a front face comprising a planar (i.e., two dimensional) array of LCD devices, and a back face comprising at least one solid metal block. The solid metal block includes first and second opposing metal faces that extend parallel to the array of LCD devices. The first metal face is facing toward the array of LCD devices, and the second metal face is facing away from the array of LCD devices. The first metal face includes therein an array of reflector cavities and the second metal face includes therein a plurality of heat sink fins that are exposed at the back face of the flat panel display. At least one LED device is mounted in a respective reflector cavity such that, in operation, the reflector cavity reflects light that is emitted by the at least one LED device that is mounted therein away from the reflector cavity.

In some embodiments, the solid metal block is a single solid metal block that is congruent to the planar array of LCD devices. In other embodiments, the at least one solid metal block includes a plurality of solid metal block tiles that are arranged in an array that is congruent to the planar array of LCD devices. In still other embodiments, the at least one solid metal block includes a plurality of solid metal block bars that are arranged face-to-face to be congruent to the planar array of LCD devices.

In still other embodiments, a frame is provided that is configured to surround the front and back faces of the flat panel displays. The planar array of LCD devices may be at least 17 inches diagonal, the LED devices may be configured to emit light that appears as white light, the at least one LED device can include a red LED, a blue LED and two green LEDs, and/or an electronics module may be provided that is supported by the frame and is configured to control the LCD and LED devices, according to any of the embodiments that were described above.

DETAILED DESCRIPTION

Furthermore, relative terms, such as “lower”, “base”, or “horizontal”, and “upper”, “top”, or “vertical” may be used herein to describe one element's relationship to another element as illustrated in the Figures. It will be understood that relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. For example, if the device in the Figures is turned over, elements described as being on the “lower” side of other elements would then be oriented on “upper” sides of the other elements. The exemplary term “lower”, can therefore, encompasses both an orientation of “lower” and “upper,” depending on the particular orientation of the figure. Similarly, if the device in one of the figures is turned over, elements described as “below” or “beneath” other elements would then be oriented “above” the other elements. The exemplary terms “below” or “beneath” can, therefore, encompass both an orientation of above and below. Moreover, the terms “front” and “back” are used herein to describe opposing outward faces of a flat panel display. Conventionally, the viewing face is deemed the front, but the viewing face may also be deemed the back, depending on orientation.

FIG. 1is a cross-sectional view of display panels for flat panel displays according to various embodiments of the present invention. As shown inFIG. 1, these display panels100according to various embodiments of the present invention, include a planar (i.e., two dimensional) array110of LCD devices, and a planar array120of LED devices130that is closely spaced apart from the planar array110of LCD devices, at least some of the LED devices130being disposed within a periphery110aof the array110of LCD devices such that, in operation, the planar array120of LED devices130provides backlighting for the planar array110of LCD devices.

FIG. 2is a perspective view of flat panel displays ofFIG. 1according to various embodiments of the present invention. As shown inFIG. 2, the LED devices130in the planar array120may be spaced apart from one another so as to provide substantially uniform backlighting of the planar array of LCD devices110. The LED devices130may be packed in a random array, a grid array, and/or using hexagonal packing, as shown inFIG. 2. Uniform and/or non-uniform packing may be provided.

Embodiments of the present invention may provide uniform backlighting for large area display panels. The display panels may be combined with other electrical and/or mechanical elements to provide computer monitors, televisions and/or other flat panel displays. As used herein, “uniform” backlighting means that an ordinary viewer, who views the display at a conventional viewing distance, is not aware of any variation in backlighting intensity. In some embodiments, variations of less than about 25% may provide uniform intensity, whereas, in other embodiments, variations of less than 5% may provide uniform intensity. In some embodiments, these displays are rectangular and, in some embodiments, may be square. As used herein, a large area display has a diagonal size D of at least 17″. However, other embodiments of the invention may be used with displays that are smaller than 17″ diagonal. Moreover, the pitch P between adjacent LED devices130in the array also may be arranged to allow a uniform backlighting of the planar array of LCD devices, according to some embodiments of the invention, as will be described in detail below.

Embodiments of the present invention that are described inFIGS. 1 and 2can provide direct backlighting of flat panel liquid crystal displays. In particular, as shown inFIG. 1, the planar array120of LED devices130is configured to transmit light from the planar array120of LED devices130to the planar array110of LCD devices along a light path140that extend generally perpendicular to the planar arrays110,120of LCD and LED devices. In some embodiments, the light path140does not redirect the light to be parallel to the planar arrays110,120of LCD and LED devices. In other embodiments, the light path between the planar array120of LED devices130and the planar array110of LCD devices is reflector-free. In yet other embodiments, at least some of the LED devices130are disposed within a periphery of the array110of LCD devices.

By providing direct backlighting, the thickness of the display panel100may be reduced and/or the optical efficiency may be enhanced compared to edge backlighting. Moreover, in some embodiments, the need for diffusing and/or light guide elements between the planar array110of LCD devices and the planar array120of LED devices130also may be reduced or eliminated.

As was described above, in some embodiments of the present invention, the LED devices130in the planar array120of LED devices130are spaced sufficiently close to one another, so as to provide uniform backlighting of the planar array110of LCD devices. In particular, the light path140ofFIG. 1is illustrated by showing the half angle of illumination, i.e., the angle of illumination wherein the light output falls by one half the light output on the optical axis. By placing the LEDs sufficiently close so that the half angles of illumination just overlap, as shown inFIG. 1, uniform illumination of the array110of LCD devices may be provided, according to some embodiments of the present invention.

FIG. 3is an exploded view of a portion of the display panel for the flat panel display ofFIG. 1, illustrating geometries that can provide uniform direct illumination according to various embodiments of the present invention. As shown inFIG. 3, the half angle of illumination is denoted by θ, the spacing between the planar array110of LCD devices and the planar array120of LED devices130is denoted by x, and the pitch between adjacent LED devices130is2y. It will be understood by those having skill in the art that smaller pitches than2ymay be used, but may not be needed to provide uniform illumination. Moreover, larger pitches may provide non-uniform illumination or may provide uniform illumination using diffusers and/or other optical elements in the light path.

As was described above, some embodiments of the present invention can eliminate the need for at least some optical films that are conventionally used in some flat panel displays. Conventionally, these optical films may include polarizers, light scattering films, light guide films, etc. In other embodiments of the invention, some of these optical films may be eliminated, but other optical films may still be used. For example, a polarizing film still may be used. Accordingly, as shown inFIG. 4, an optical film410may be placed between the array110of LCD devices and the array120of LED devices130.

FIG. 5is a cross-sectional view of flat panel displays600according to other embodiments of the present invention. In these embodiments, the planar array120of LED devices130includes at least one solid metal block500including first and second opposing metal faces500a,500b, respectively, that extend parallel to the array110of LCD devices. The first metal face500afaces toward the array110of LCD devices, and the second metal face500bfaces away from the array110of LCD devices. The first metal face500aincludes therein an array of reflector cavities510, and the second metal face500bincludes therein a plurality of heat sink fins530. At least one LED device130is mounted in a respective reflector cavity510such that, in operation, the reflector cavity510reflects light that is emitted by the at least one LED device130that is mounted therein from the reflector cavity510along the optical path140, as shown inFIG. 5.

In some embodiments, the reflector cavity510includes at least one sidewall502that is configured to reflect light that is emitted from the LED130in the cavity510along the optical path140. Moreover, in some embodiments, a flexible film1420also may be provided that extends across one or more of the cavities510. The flexible film560may include therein optical elements such as lenses, phosphor and/or other optical elements therein.

Many different embodiments of planar arrays120of LED devices130may be provided according to various embodiments of the present invention, as are described, for example, in U.S. Publication No. 2006/0097385, published May 11, 2006, entitled Solid Metal Block Semiconductor Light Emitting Device Mounting Substrates and Packages Including Cavities and Heat Sinks, and Methods of Packaging Same, to coinventor Negley, and U.S. Publication No. 2006/0124953, published Jun. 15, 2006, entitled Semiconductor Light Emitting Device Mounting Substrates and Packages Including Cavities and Cover Plates, and Methods Of Packaging Same, to coinventor Negley, both of which are assigned to the assignee of the present invention, the disclosures of both which are hereby incorporated herein by reference in their entirety as if set forth fully herein.

In particular, as described in the abstract of U.S. Publication No. 2006/0097385, published May 11, 2006, a mounting substrate for a semiconductor light emitting device includes a solid metal block having first and second opposing metal faces. The first metal face includes a cavity that is configured to mount at least one semiconductor light emitting device therein, and to reflect light that is emitted by at least one semiconductor light emitting device that is mounted therein away from the cavity. The second metal face includes heat sink fins therein. One or more semiconductor light emitting devices are mounted in the cavity. Reflective coatings, conductive traces, insulating layers, pedestals, through holes, lenses, flexible films, optical elements, phosphor, integrated circuits and/or optical coupling media also may be provided in the package. Related packaging methods also may be provided.

Moreover, as described in the abstract of U.S. Publication No. 2006/0124953, published Jun. 15, 2006, a mounting substrate for a semiconductor light emitting device includes a solid metal block having first and second opposing metal faces. The first metal face includes a cavity that is configured to mount at least one semiconductor light emitting device therein, and to reflect light that is emitted by at least one semiconductor light emitting device that is mounted therein away from the cavity. One or more semiconductor light emitting devices are mounted in the cavity. A cap having an aperture is configured to matingly attach to the solid metal block adjacent the first metal face such that the aperture is aligned to the cavity. Reflective coatings, conductive traces, insulating layers, pedestals, through holes, lenses, flexible films, optical elements, phosphor, integrated circuits, optical coupling media, recesses and/or meniscus control regions also may be provided in the package. Related packaging methods also may be provided.

Still referring toFIG. 5, the planar array120of LED devices130may be configured to act as the back face of a flat panel display600according to various embodiments of the present invention. More particularly, the display600ofFIG. 5includes a front face570athat comprises the planar array110of LCD devices. A back face570bcomprises the at least one solid metal block500including the first and second opposing metal faces500a,500b, respectively, that extend parallel to the array110of LCD devices. The first metal face500ais facing toward the array110of LCD devices, and the second metal face120bis facing away from the array110of LCD devices. The first metal face500aincludes therein an array of reflective cavities510, and the second metal face500bincludes therein a plurality of heat sink fins530that are exposed at the back face570bof the flat panel display600. At least one LED device130is mounted in a respective reflector cavity510such that, in operation, the reflector cavity510reflects light that is emitted by the at least one LED device130that is mounted therein away from the reflector cavity510. Accordingly, the at least one solid metal block500forms an exposed back face of the flat panel display100. An electronics module550also may be included that is electrically connected to the LED devices130and the LCD devices110. A frame540and/or other mechanical elements may be used to maintain the array of LCD devices110and the array120of LED devices130in closely spaced apart relation facing one another. The electronics module550also may be supported by the frame540.

Various configurations of solid metal blocks500may be used according to various embodiments of the present invention. For example, as shown inFIG. 5, the solid metal block500may be a single solid metal block that is congruent to the planar array of LCD devices110. In other embodiments, as shown inFIG. 6, a plurality of solid metal block bars600are arranged face-to-face, to be congruent to the planar array110of LCD devices. In still other embodiments, as shown inFIG. 7, a plurality of solid metal block tiles700are arranged in an array that is congruent to the planar array110of LCD devices. The solid metal block bars600and/or tiles700may be maintained in place by the frame540and/or by various interconnection schemes, including mating surfaces and/or fasteners on the bars and/or tiles that can provide mechanical and/or electrical interconnection of the LED devices130on the various bars600and/or tiles700.

FIG. 8is a plan view of a portion of the first face500aof a solid metal block500according to various embodiments of the present invention, illustrating how multiple LEDs may be placed in a single cavity according to various embodiments of the present invention. In particular, as shown inFIG. 8, a semiconductor white light pixel800includes a red LED device810R, a blue LED device810B, a first green LED device810G1and a second green LED device810G2. The first and second green LED devices810G1and810G2, respectively, emit light at different green frequencies. For example, in some embodiments, the first green LED device810G1can emit at 534 nm and the second green LED device810G2can emit at 528 nm. The red LED device810R can emit at 625 nm and the blue LED device810B can emit at 460 nm. The red, blue, first green and second green LED devices810R,810B,810G1,810G2, respectively, are configured to emit light that appears as a pixel of white light in operation.

In other embodiments, a single red, green and blue LED device may be configured to emit light that appears as a pixel of white light in operation. For example, in some embodiments, the die size of the red, green and/or blue LED devices may be selected to meet a desired brightness and/or intensity balancing. In one embodiment, standard LEDs marketed by the assignee of the present invention may be used wherein, for example, a C460XT290-Sxx00-A blue LED (290 μm×290 μm), a green C527XB500-S0100-A LED and a conventional red LED may be used. The larger green LED die can provide sufficient optical brightness and may reduce assembly costs compared to a pixel that includes, red, blue, first green and second green LED devices. Other configurations may be used to provide a desired lumen requirements using properly sized die.

FIG. 9is a cross-sectional view of display panels for flat panel displays according to other embodiments of the present invention. As shown inFIG. 9, these display panels900according to other embodiments of the present invention include at least one solid metal block500including first and second opposing faces500a,500b, respectively, that extend generally parallel to the array110of LCD devices. The first metal face500aincludes therein an array of reflector cavities510and the second metal face500bincludes therein a plurality of heat sink fins530. At least one LED device130is mounted in a respective reflector cavity510such that, in operation, the reflector cavity510reflects light that is emitted by the at least one LED device130that is mounted therein from the reflector cavity along an optical path140, as shown inFIG. 9.

In embodiments ofFIG. 9, the planar array of LED devices130is configured to emit light generally parallel to the planar array of LCD devices110. Moreover, an array of reflectors910also is provided. The reflectors910are generally oblique with respect to the first space500a, and are configured to redirect the light that is emitted generally parallel to the planar array of LCD devices110along the light path140that extends generally perpendicular to the planar arrays of LCD and LED devices. Accordingly, some geometries according to embodiments of the present invention can provide optical cavities that are generally perpendicular or oblique to the first face500aand can use a secondary optical reflector910to move the photons from generally parallel to the first face500ato generally orthogonal to the first face500a. In some embodiments, a flexible film including optical elements may extend parallel to the arrays of LCD and LED devices, similar to the flexible film560ofFIG. 5. In other embodiments, separate flexible films may be provided across the cavities510, extending generally orthogonal to the arrays of LCD and LED devices.

It also will be understood by those having skill in the art that various combinations and subcombinations of embodiments ofFIGS. 1-9may be provided according to other embodiments of the present invention. Thus, for example, embodiments ofFIG. 9may be combined with embodiments ofFIGS. 5,6,7and/or8.