The present techniques relate generally to video display systems. More specifically, the present techniques relate to backlight illumination of video display systems, such as liquid crystal displays (LCDs).
This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present embodiments that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present embodiments. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Backlit displays, such as liquid crystal display (LCD) panels, are employed in a variety of display systems. Such systems may include, for example, flat screen computer monitors, portable computers, digital cameras, cellular telephones, hand-held devices, flat screen television sets (TVs), digital watches, and so forth. The LCD panel incorporated in such systems may include a matrix of transistors or other micro-devices acting as electrical switches that modulate light. In cooperation with other components, such as polarizing filters, the modulation of the light may be used to generate an image.
The light used to generate the image may be reflected light, transmitted through the front surface of the LCD and reflected from a mirror behind the LCD, e.g., in LCD watches. In other LCDs, the light may be provided by a light source from the back side of the panel, e.g., a backlight. Generally, color LCDs require a backlight, since reflected light may not adequately illuminate the display. For example, the light used for illuminating an LCD may be provided by a plurality of fluorescent tubes, which are disposed behind the LCD panel.
However, because light generated by such fluorescent tubes is generally emitted uniformly, the LCD panel may receive only a portion of the emitted light. Furthermore, the components of the display that are used to generate the image may block a substantial portion of the light. For example, a polarizing film that may be used in the generation of an image may block as much as 50%, or more, of the light from a backlight. Other components used to improve image quality, such as a diffuser plate, may decrease the light even more.
Various techniques may be employed to increase the overall amount of the backlight emitted by the LCD and, thus, provide a brighter image. For example, a reflective white surface may be placed behind the fluorescent tubes to direct more light to the front of the device. Further, an increased number of fluorescent tubes may be used in the display. However, an increase in the number of fluorescent tubes increases the power consumption of a device, which may decrease the battery life in a portable device. An increase in the number of fluorescent tubes may also increase the heat generated by the device, which may increase the stress on components and decrease the lifespan of the display.
Advantages of embodiments of the present techniques may become apparent upon reading the following detailed description and upon reference to the drawings in which:
One or more specific embodiments of the present techniques will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. Further, as used herein, terms describing geometric shapes, such as triangular, pyramidal, and point, should be understood to indicate that the shapes are not ideal shapes, but are substantially as described, e.g., substantially triangular, substantially pyramidal, and substantially small in area.
Embodiments of the present techniques provide a backlit display, such as a liquid crystal display (LCD), having an improved reflector for backlighting. The improved reflector may include beveled, e.g., triangular, reflectors under each fluorescent tube in a display backlight, which may direct the light from each of two adjoining tubes to form a composite image of a fluorescent tube. In effect, the composite image forms a virtual tube located between the two adjoining fluorescent tubes. Such a virtual tube may, for example, improve the amount and the alignments of the light reaching other components in the display. This may lower the number of fluorescent tubes required for effective illumination of a display and, thus, lower the power requirements of the display.
An overview of an LCD system 10 in accordance with an embodiment is provided in the block diagram shown in
In some embodiments, the LCD system 10 may comprise an LCD monitor such as those used in computers, TVs or the like. The LCD system 10 includes an illumination system 12. As discussed in detail below, the illumination system 12 may include fluorescent tubes or other light producing devices configured to generate white or colored light 13 for providing backlight illumination for the LCD system 10.
The illumination system 12 may include additional components, such as the beveled mirror discussed with respect to
The LCD system 10 may include a diffusing and polarizing element 14. The diffusing and polarizing element 14 may include a diffusing component 14A and a polarizing component 14B. The diffusing and polarizing element 14 may be adapted to diffuse the light 13 emanating from the illumination source 12. For example, the diffusing component 14A of the diffusing and polarizing element 14 may act to smooth or smear the light 13 to create a uniform backlight distribution. Further the diffusing component 14A may scatter light 13 towards the polarizing component 14B. The polarizing component 14B may function to linearly polarize the light 13 generated by the illumination source 12. Thus, the diffusing and polarizing element 14 may produce diffused and polarized light 15.
During operation of the LCD system 10, the diffused and polarized light 15 from the diffusing and polarizing element 14 passes through an LCD panel 16. In other embodiments, the LCD panel 16 may be replaced by different types of backlit panels. In the LCD panel 16, active micro-devices may modulate the light 15, for example, by changing the polarization axis of the light 15 in response to applied current, as discussed in detail with respect to
During operation of the LCD system 10, the modulated light 17 from the LCD panel 16 is directed to a polarizing screen 18 to facilitate producing an image 19. The image 19 may be formed when the modulated light 17 at each pixel is either blocked to some degree or passed by the polarizing screen 18. The brightness of the image 19 may be determined by the degree of alignment of the polarization axis of the modulated light 17 with the polarization axis of the polarizing screen 18.
As illustrated by
As discussed in further detail with respect to
In an embodiment, the LCD system 20 may include a diffuser 34. In embodiments, the diffuser 34 may be an opaque or translucent plastic film or glass sheet. The diffuser 34 may smooth or smear light from the fluorescent tubes 26 and virtual tubes 30 and, thus, more uniformly distribute the light. Further, proper image generation may depend on the extent to which the light from the light source 24 is polarized before reaching an LCD panel 36. The ability of the LCD system 20 to polarize the light may depend on the angular distribution of the light when it impinges on a polarizing filter. Accordingly, if the angular distribution of the light is too wide, this may result in backlight illumination that is only partially polarized. This may result in decreased image contrast, with the dark hues of an image being too light. The diffuser plate 34 may compensate for the wide angular distribution of light, for example, by scattering light towards the image 25 formed by the unit when the light is received by the diffuser plate 34 at a shallow angle, as represented by light beam 38. In various embodiments, scattered light 40 from the diffuser plate 34 may impinge a fiber optic screen 42 which may be placed between the diffuser 34 and a polarizer 44, as illustrated in
The fiber optic screen 42 may, for example, be made from a large number of optical fibers joined in a longitudinal fashion (e.g., aligned with the image 25) to form a plate or screen. The fibers may be formed from any number of materials, including, for example, glass, plastic, or clear ceramics. The fiber optic screen 42 may substantially block scattered light, such as that represented by light beams 46, that is not adequately aligned with the component optical fibers. Further, the fiber optic screen 42 may pass light, such as that represented by light beams 48, that has an angular incidence on the fiber optic screen 42 within a few degrees (e.g., about 5°, 10°, or 15°) of perpendicular to the fiber optic screen 44. Thus, the fiber optic screen 42 may produce angularly aligned light 50. This may significantly improve the contrast of the image 25 produced by the LCD system 20 by lowering the amount of partially polarized light transmitted from the polarizer 40. The angularly aligned light 50 may then impinge on the polarizer 44.
The polarizer 44 may be formed of a polarizing material, such as a doped polymer or a similar material. Further, the polarizer 44 may be disposed within the LCD system 20 such that its polarization axis is oriented along a preferred direction relative to the LCD system 20, for example, vertically, as indicated by arrows 52. In this manner, the polarizer 44 polarizes the angularly aligned light 50 from the fiber optic screen 42 along the preferred direction to produce polarized light 54. The polarized light 54 may then be modulated by the LCD panel 36 to create the image.
The LCD panel 36 may be made up of active or passive micro-devices that include liquid crystal materials. For example, in one embodiment, the LCD panel 32 may comprise a matrix of active micro-devices that utilize thin film transistors (TFTs) disposed along pixel intersections of a grid comprising the display matrix. The luminance of the pixels of the LCD panel 36 may be controlled by the current applied by the TFTs. In another embodiment, the LCD panel 36 may comprise a passive matrix employing a grid of conductors, whereby the pixels are disposed along intersections of the display matrix. In such an embodiment, the pixels may be controlled by current driven across two conductors disposed along the grid comprising the matrix of pixels. As for the active matrix TFTs the luminance of an individual pixel may be controlled by the current applied.
In an embodiment of the LCD system 20, twisted nematic liquid crystals may be controlled by the micro-devices in the LCD panel 36 to form the image. One of ordinary skill in the art will recognize that any number of other technologies used to generate an image, both existing and not yet developed, may benefit from the reflectors of the present techniques.
Generally, in a twisted nematic liquid crystal display, the LCD panel 36 is located between two polarizing filters, for example the polarizer 44 and a polarizing screen 56. The polarization axis 52 of the polarizer 44 and a polarization axis 58 of the polarizing screen 56 may generally be perpendicularly aligned. For example, the polarization axis 58 of the polarizing screen 56 may be horizontally aligned if the polarization axis 52 of the polarizer 44 is vertically aligned.
In the LCD panel 36, the liquid crystal molecules in a non-energized cell 60 may rotate the polarization of the light from the polarizer 44 by 90°, such as from a vertical orientation to a horizontal orientation, to produce rotated light 62. If the polarizing screen 56 has a polarization axis 58 that is perpendicular to the polarizer 44, the rotated light 62 from the LCD panel may pass through the polarizing screen 56 and may form the image 25. In contrast, the liquid crystal molecules in an energized cell 66 may be aligned, thus allowing light 54 to pass through the energized cell 66 without rotating the polarization axis to produce light 68. Since, in this embodiment, the polarization of the emitted light 54 from the polarizer 44 has not been rotated, it is essentially perpendicular to the polarizing screen 56 and substantially blocked. Thus, light 70, which passed through the polarizing screen 56 and forms the image 25 seen by a viewer, has generally passed through a non-energized cell 60.
One of ordinary skill in the art will recognize that this is not the only configuration that may be used in an LCD. For example, in another embodiment, the polarization axis 52 for the polarizer 44 and the polarization axis 58 for the polarized screen 56 may be aligned. In this embodiment, rotated light from a non-energized cell 66 may be blocked by the polarizing screen 56.
As illustrated by
A backlight illumination system 73, in accordance with present embodiments, is illustrated in
As illustrated in
The shapes of each of the beveled reflectors 28 may be controlled to adjust the angle of light reflected and, thus, control the appearance of the virtual tube 30. For example, the sharpness of the virtual tube 30 may be adjusted by the angles of a surface 78 of each of the beveled reflectors 28. For example, a first intersection angle 80 of the surface 78 of the beveled reflectors 28 with the mirror 22 may be between about 10° and 80° or about 45°. A second intersection angle 82 may generally be about the same as the first intersection angle 80. Alternatively, the intersection angles 80 and 82 may differ to enhance the light reflection. For example, the intersection angles 80 and 82 may be different at the edges of the mirror 22. In one embodiment, the first intersection angle 80 may be set to 90° if the first intersection angle 80 is proximate to a side of the LCD. One of ordinary skill in the art will recognize that an apex angle 84 will be equal to 180° minus the sum of the intersection angles 80 and 82. For example, if the intersection angles 80 and 82 are equivalent at about 45°, the apex angle will equal about 90°.
The height of the beveled reflectors 28 may be adjusted relative to the positions of the fluorescent tubes 26 with respect to the mirror 22. In some embodiments, the beveled reflectors 28 may project from the mirror 22 about 10% to about 90% of the distance to the fluorescent tubes 26 or about 50% of the distance to the fluorescent tubes 26. In some embodiments, the distance between the mirror 22 and the fluorescent tubes 26 may be between about 2 millimeters (mm) and about 10 mm. In one embodiment, the distance between the mirror 22 and the fluorescent tubes is about 5 mm.
One of ordinary skill in the art will recognize that not all of the reflected light is reflected from the beveled reflectors 28. For example, light 86 may be reflected from the mirror 22 between the beveled reflectors 28. This reflected light, as represented by light beam 88, may not pass through the location of the virtual tube 30. Accordingly, the image of the virtual tube 30 may not be sharp or focused. In embodiments in which a sharper image is desired, the beveled reflectors 28 may be raised parabolic shapes formed into the mirror 22, with a focal point at the desired location for defining the virtual tubes 30.
The mirror 22 and beveled reflectors 28 may be formed from any number of materials including glass, metal, ceramic, or plastic. These materials do not need to be transparent as light will generally be reflected from them. The choice of materials may be made on the basis of functional properties, including, for example, stiffness, heat resistance, and weight, among others. Plastics that may used in embodiments include, for example, high impact polystyrene (HIPS), polycarbonate (PC), polyacrylate, polyphenylene sulfide, and polyvinylchloride (PVC), among others.
The beveled reflectors 28 may be formed on the surface of the mirror 22 using any number of techniques. Generally, the shapes may be formed prior to coating with a reflective surface, such as a mirror coating. For example, the beveled reflectors 28 may be formed as an integral part of the mirror 22 by molding, etching, photolithography, or any other suitable technique known in the art. Alternatively, the bevel reflectors 28 may be formed separately and joined to the surface of the mirror 22 by adhesive, ultrasonic welding, heat fusion, or any similar techniques used to join surfaces. After the mirror 22 with the beveled reflectors 28 has been formed, the reflective surfaces of the beveled reflectors 28 and of the mirror 22 will generally be coated (e.g., silvered) to increase the total amount of light reflected along the axis 74, toward the front of the LCD.
Next, the method 100 proceeds to block 108, where the beveled reflectors and mirror reflect the back-propagating portion of the light forward. This forward reflection may generally be along the display axis of the LCD, e.g., towards a polarizer and LCD panel. Accordingly, in one embodiment, at block 108, a portion of the light is reflected from the beveled reflectors aligned with each fluorescent tube to form a composite image of the adjoining fluorescent tubes, e.g., a virtual tube. Thereafter, at block 110, the emitted light of block 104 and the reflected light of block 108 propagate forward toward the LCD panel where the light is modulated to form an image. The use of such beveled reflectors to form virtual tubes may decrease the number of fluorescent tubes required and, thus, decrease the power requirements of a display. This may help to extend the battery life in portable devices.
While the present disclosure may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, it should be understood that the present disclosure is not intended to be limited to the particular forms disclosed. Rather, the present disclosure is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present disclosure as defined by the following appended claims.
Number | Date | Country | Kind |
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200810172781.7 | Dec 2008 | CN | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US2009/051037 | 7/17/2009 | WO | 00 | 5/3/2011 |