Abstract:
An LCD TV includes a housing, an LCD screen panel disposed on the front side of the housing, a first mirror disposed on the back side of the housing and a projection-based backlight system disposed in a lower cabinet of the housing, wherein the projection-based backlight system provides polarized light for the LCD screen panel through the first mirror. The projection-based backlight system can provide uniformly polarized light and increase polarization efficiency as well as be easily achieved by using low-cost optical components.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention generally relates to an LCD TV, and more particularly to an LCD TV using a projection-based backlight system. 
   2. Description of the Related Art 
   In recent years, liquid crystal displays (LCDs) have been widely used in a variety of applications, including LCD televisions (LCD TVs), portable computers, and vehicle, ship and aircraft instrumentation, due to the advantage of a thin profile and brilliant display. Most LCDs require an illumination source or backlight unit for backlighting LCD panels so that the image displayed on the LCD can be seen by a viewer. 
   In those applications, LCD TVs are gradually gaining in popularity due to their thin, light features and low power consumption in comparison with conventional cathode ray tube televisions (CRT TVs). An LCD TV comprises an LCD screen panel and a backlight unit placed at the back of the LCD screen panel and configured to light the LCD screen panel so that an image can be formed on the LCD screen panel. In the backlight unit, cold cathode fluorescent lamps (CCFLs) are generally adopted as the light source to provide a uniform backlighting of the LCD screen panel. It is necessary to illuminate the whole surface of the LCD screen panel with the light from a so-called linear light source by such a fluorescent lamp. 
   In general, as to features of a cold cathode fluorescent lamp (CCFL) used for a light source in an LCD screen panel, its luminance is inversely proportional to its lifetime. That is, if the CCFL is driven with a high current to increase the luminance, its lifespan is reduced, and if the CCFL is driven at a low current to increase its lifetime, it is difficult to obtain high luminance. However, actual commercial products generally require high luminance and a long lifetime concurrently. 
   Further, when an LCD TV, particularly over 40 inches, is to be manufactured, it is necessary to have a large backlight unit with more numbers of CCFL tubes for supplying sufficient light to the LCD screen panel of the LCD TV. However, the yield for such a large backlight unit having more numbers of CCFL tubes not only has lower yield rate but also has even higher cost. In additions, a more uniformly bright and effectively polarized light for such an LCD TV is not easy to be achieved by these CCFL tubes. 
   Due to the above shortcomings of the CCFL and its use in an LCD TV, it is needed to provide an LCD TV using a projection-based backlight system so as to solve the above-mentioned problems in the prior art. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide an LCD TV using a projection-based backlight system which can supply a uniformly bright and effectively polarized light. 
   It is another object of the present invention to provide a projection-based backlight system which not only has uncomplicated structural design but also has high efficiency polarization. 
   In order to achieve the above objects, the present invention provides an LCD TV comprises a housing, an LCD screen panel disposed on the front side of the housing, a first mirror disposed on the back side of the housing and a projection-based backlight system disposed in a lower cabinet of the housing, wherein the projection-based backlight system supplies uniformly polarized light to the LCD screen panel through the first mirror. The projection-based backlight system comprises a light source for supplying light, polarizing means for polarizing the light supplied by the light source and a projection lens for receiving the polarized light from the polarizing means and projecting the polarized light to the LCD screen panel. 
   According to one aspect of the present invention, the polarizing means comprises two lens arrays, a polarization conversion element, a condenser lens, a relay lens and a polarizer. The two lens arrays have a plurality of lenses respectively disposed opposite to each other, adjacent to the light source and configured to receive the light from the light source to compensate the light. The polarization conversion element is disposed adjacent to the lens arrays and configured to convert the compensated light into polarized light. The condenser lens is disposed adjacent to the polarization conversion element and configured to condense the polarized light. The relay lens is disposed adjacent to the condenser lens and configured to direct the condensed light. The polarizer is disposed adjacent to the relay lens and configured to further polarize the directed light. A first projection lens directly receives the polarized light from the polarizer and projects the polarized light to the LCD screen panel. An illuminating light almost like natural color, supplied from the arc lamp, is reflected back by the elliptical reflector and emitted to the lens arrays. When the illuminating light travels through the two lens arrays, the two lens arrays will compensate the illuminating light so that it can be perpendicularly incident on the incident surface of the polarization conversion element. The compensated light passes through the polarization conversion element and is converted into polarized light. The polarized light then passes through the condenser lens and relay lens to reach the polarizer and is further polarized by the polarizer. The light passing through the polarizer becomes polarized light and then enters the projection lens so that a uniformly polarized light can be emitted to the LCD screen panel. 
   According to another aspect of the present invention, the polarizing means comprises an integrating sphere, a reflective polarizer, an integrating rod, a condenser lens, and a relay lens. The integrating sphere has an entrance aperture and an exit aperture defined thereon. The integrating sphere is disposed adjacent to the light source with the entrance aperture facing the light source and configured to receive the light through the entrance aperture. The reflective polarizer is disposed adjacent to the exit aperture and configured to allow a specific polarization light pass therethrough and to reflect other polarization lights back into the integrating sphere. The integrating rod has an entrance-side end surface and an exit-side end surface. The integrating rod is disposed adjacent to the reflective polarizer and configured to receive the specific polarization light and to direct it out through the exit-side end surface. The condenser lens is disposed adjacent to the exit-side end surface of the integrating rod and configured to condense the specific polarization light. The relay lens is disposed adjacent to the condenser lens and configured to direct the condensed specific polarization light from the condenser lens. The first projection lens receives the specific polarization light from the relay lens and projects the specific polarization light to the LCD screen panel. The integrating sphere and the reflective polarizer are used so that a specific polarization light, e.g. S-polarization light or P-polarization light, can be provided, and others will be reflected back to the integrating sphere and be de-polarized by the integrating sphere. In such a manner, the light can be effectively used and the polarization efficiency can be increased. 
   According to a further aspect of the present invention, the polarizing means comprises two lens arrays, a condenser lens, a relay lens, a polarizing beam splitter, a second mirror, a half waveplate, and a second projection lens. The two lens arrays have a plurality of lenses respectively disposed opposite to each other, and adjacent to the light source to receive the light from the light source to compensate the light. The condenser lens is disposed adjacent to the lens arrays and configured to condense the compensated light. A relay lens is disposed adjacent to the condenser lens and configured to direct the condensed light. The polarizing beam splitter has a light input side facing the relay lens for receiving the directed light. A first split-light side is adjacent to the light input side, a second split-light side is opposite to the light input side, and a light output side is opposite to the first split-light side. The polarizing beam splitter is configured to split the directed light into first P-polarization light to pass directly through the second split-light side and S-polarization light to be directed toward the first split-light side. The second mirror is disposed adjacent to the first split-light side and configured to reflect the S-polarization light. The half waveplate is disposed adjacent to the second mirror and configured to receive the S-polarization light from the second mirror and to convert the S-polarization light into second P-polarization light. The second projection lens is disposed adjacent to the half waveplate and configured to receive the second P-polarized light from the half waveplate and to project the second P-polarized light to the LCD screen panel. The first projection lens receives the first P-polarized light from the second split-light side of the polarizing beam splitter and projects the first P-polarized light to the LCD screen panel. The second projection lens can be appropriately aligned so as to project the same polarization light as projected by the first projection lens on the same LCD screen panel, so that the light provided by the light source can be effectively used and polarization efficiency can be increased. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, advantages, and novel features of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
       FIGS. 1   a  and  1   b  respectively shows a front view and a side view of an internal structure of an LCD TV according to an embodiment of the present invention. 
       FIG. 2  illustrates a structure of a projection-based backlight system according to one embodiment of the present invention. 
       FIG. 3  illustrates a structure of a projection-based backlight system according to another embodiment of the present invention. 
       FIG. 4  illustrates a structure of a projection-based backlight system according to another embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1   a  and  1   b  respectively show a front view and a side view of an internal structure of a liquid crystal display television (LCD TV)  100  according to an embodiment of the present invention. The LCD TV  100  comprises a housing  102 , an LCD screen panel  104 , a first mirror  106  and a projection-based backlight system  108 . The LCD screen panel  104  is disposed on the front side  102   a  of the housing  102  and produces an image to a viewer. The first mirror  106  is disposed on the back side  102   b  of the housing  102 . The projection-based backlight system  108  is disposed in a lower cabinet  110  of the housing  102  and is configured to supply uniformly polarized light to the LCD screen panel  104 . 
   When the LCD TV  100  is in “ON” state, the projection-based backlight system  108  emits uniformly polarized light  112  toward the first mirror  106  by a projection lens  108   a , and then the first mirror  106  reflects the uniformly polarized light  112  toward the LCD screen panel  104 . When the uniformly polarized light  112  reflected from the first mirror  106  reaches the LCD screen panel  104 , it will be modulated in accordance with the operation of the pixels of the LCD screen panel  104  which are driven in accordance with corresponding red, green and blue signals derived from a video signal. Finally, the modulated light passes through a color filter (not shown) disposed within the LCD screen panel  104  so as to produce a color image to a viewer. Preferably, a Fresnel lens  114  is disposed at the light incident side  104   a  of the LCD screen panel  104  for collimating the uniformly polarized light  112  reflected from the first mirror  106 . 
   According to the LCD TV of the present invention, the backlight provided to the LCD screen panel  104  is supplied by the projection-based backlight system  108 , not a backlight module with cold cathode fluorescent lights (CCFL), which can not only increase polarization efficiency but also supply more uniform backlight to the LCD screen panel  104 . Further, since the LCD screen panel  104  receives a uniformly polarized light supplied by the projection-based backlight system  108 , the LCD screen panel  104  can eliminate the usage of polarizer on the surfaces so as to reduce the manufacturing cost of the LCD screen panel. In the following paragraphs, three different structures for forming the projection-based backlight system  108  will be described in greater detail. 
     FIG. 2  illustrates a structure of a projection-based backlight system  200  according to one embodiment of the present invention. The projection-based backlight system  200  includes a light source  202 , two lens arrays  204 ,  206 , a polarization conversion element  208 , a condenser lens  210 , a relay lens  212 , a polarizer  214  and a projection lens  216 . The light source  202  further includes an arc lamp  202   a  and an elliptical reflector  202   b . The lens arrays  204  and  206  have a plurality of lenses  204   a  and  206   a  respectively and are disposed opposite to each other. Further, they are disposed adjacent to the light source  202  and configured to receive light provided by the light source  202 . The polarization conversion element  208  is disposed adjacent to the lens arrays  204  and  206  and converts the light passing therethrough into polarized light. The condenser lens  210  is disposed adjacent to the polarization conversion element  208  and configured to condense the polarized light received from the polarization conversion element  208 . The polarization conversion element  208  is preferably a P-S converter. The relay lens  212  is disposed opposite to the condenser lens  210 , and configured to receive the condensed light from the condenser lens  210  and to direct it to the polarizer  214 . The polarizer  214  is disposed adjacent to the relay lens  212  and configured to polarize light passing therethrough. The projection lens  216  is disposed adjacent to the polarizer  214 , and configured to receive the polarized light from the polarizer  214  and to project it to an LCD screen panel (not shown). 
   In projection-based backlight system  200 , an illuminating light almost like natural color, supplied from the arc lamp  202   a , is reflected back by the elliptical reflector  202   b  and emitted to the lens arrays  204 . When the illuminating light travels through the two lens arrays  204  and  206 , the two lens arrays  204  and  206  will compensate the illuminating light so that it can be perpendicularly incident on the incident surface of the polarization conversion element  208 . The compensated light passes through the polarization conversion element  208  and is converted into polarized light. The polarized light then passes through the condenser lens  210  and relay lens  212  to reach the polarizer  214  and is further polarized by the polarizer  214 . The light passing through the polarizer  214  becomes polarized light  218  and then enters the projection lens  216  so that a uniformly polarized light can be emitted to an LCD screen panel (not shown). 
     FIG. 3  illustrates a structure of a projection-based backlight system  300  according to another embodiment of the present invention. The projection-based backlight system  300  includes a light source  302 , an integrating sphere  304 , a reflective polarizer  306 , an integrating rod  308 , a condenser lens  310 , a relay lens  312  and a projection lens  314 . The light source  302  further includes an arc lamp  302   a  and an elliptical reflector  302   b , and the integrating sphere  304  further has an entrance aperture  304   a  and an exit aperture  304   b  defined thereon. The integrating sphere  304  is disposed adjacent to the light source  302  with the entrance aperture  304   a  facing the light source  302 . The reflective polarizer  306  is disposed adjacent to the exit aperture  304   b  of the integrating sphere  304 . The integrating rod  308  is disposed at one side of the reflective polarizer  306 , opposite to that facing the integrating sphere  304 , with its entrance-side end surface  308   a  aligning with the exit aperture  304   b  and its exit-side end surface  308   b  pointing toward the condenser lens  310 . The condenser lens  310  is disposed adjacent to the integrating rod  308  and configured to condense the light therethough. The relay lens  312  is disposed opposite to the condenser lens  310 , and configured to receive the condensed light from the condenser lens  310  and to direct it to the projection lens  314 . The projection lens  314  is disposed adjacent to relay lens  312 , and configured to receive the light from the relay lens  312  and to project the light to an LCD screen panel (not shown). 
   In projection-based backlight system  300 , an illuminating light from the arc lamp  302   a  is reflected back by the elliptical reflector  302   b  and then enters the inside of the integrating sphere  304 . The inner surface of the integrating sphere  304  has a coating of a material with a Lambertian quality; that is, the surface has the directional characteristic of distributing reflected light uniformly over the entire sphere&#39;s inner surface. Thus, once the illuminating light enters the integrating sphere  304  through its entrance aperture  304   a , the light is evenly distributed over the entire inner sphere surface, including the exit aperture  304   b . Since the reflective polarizer  306  is disposed adjacent to the exit aperture  304   b , only a specific polarization light, e.g. S-polarization light or P-polarization light, can pass through the reflective polarizer  306  and others will be reflected back into the integrating sphere  304 . The specific polarization light then enters the integrating rod  308 . The integrating rod  308  is a rod having a rectangular cross section, and is arranged in such a way that the entrance-side end surface  308   a  is disposed adjacent to the reflective polarizer  306 . The specific polarization light passing through the reflective polarizer  306  enters the integrating rod  308  from the entrance-side end surface  308   a , and then reaches the exit-side end surface  308   b  by being totally reflected from the side surfaces of the integrating rod  308 . The specific polarization light emitted from the exit-side end surface  308   b  then passes through the condenser lens  310  and relay lens  312  to reach the projection lens  314  so that the specific polarization light can be emitted to an LCD screen panel (not shown). 
   According to the projection-based backlight system  300  of the present invention, the integrating sphere  304  and the reflective polarizer  306  are used so that a specific polarization light, e.g. S-polarization light or P-polarization light, can be provided, and others will be reflected back to the integrating sphere  304  and be de-polarized by the integrating sphere  304 . In such a manner, the light can be effectively used and the polarization efficiency can be increased. 
     FIG. 4  illustrates a structure of a projection-based backlight system  400  according to another embodiment of the present invention. The projection-based backlight system  400  includes a light source  402 , two lens arrays  404 ,  406 , a condenser lens  408 , a relay lens  410 , a polarizing beam splitter  412 , a second mirror  414 , a half waveplate  416 , a first projection lens  418  and a second projection lens  420 . The light source  402  further includes an arc lamp  402   a  and an elliptical reflector  402   b . The lens arrays  404  and  406  have a plurality of lenses  404   a  and  406   a  respectively and are disposed opposite to each other. Further, they are disposed adjacent to the light source  402  and configured to receive the light provided by the light source  402 . The condenser lens  408  is disposed adjacent to the lens arrays  404  and  406  and configured to condense the light received from the lens arrays  404  and  406 . The relay lens  410  is disposed opposite to the condenser lens  408 , and configured to receive the condensed light from the condenser lens  408  and to direct it to the polarizing beam splitter  412 . The polarizing beam splitter  412  is disposed adjacent to the relay lens  410  and configured to reflect S-polarization light in a transverse direction and allow P-polarization light to pass directly therethrough. The polarizing beam splitter  412  has a light input side  412   a , a first split-light side  412   b  adjacent to the light input side  412   a , a second split-light side  412   c  opposite to the light input side  412   a  and a light output side  412   d  opposite to the first split-light side  412   b . The first projection lens  418  is disposed adjacent to the second split-light side  412   c  and configured to receive P-polarization light passing through the second split-light side  412   c  and to project the P-polarization light to an LCD screen panel (not shown). The second mirror  414  is disposed adjacent to the first split-light side  412   b  and configured to receive S-polarization light passing through the first split-light side  412   b  and to reflect it toward the half waveplate  416 . The half waveplate  416  is disposed adjacent to the second mirror  414  and configured to receive the S-polarization light from the second mirror  414  and to convert it into second P-polarization light. The second projection lens  420  is disposed adjacent to the half waveplate  416  and the first projection lens  418 , and configured to receive the second P-Polarization light and to project the second P-Polarization light to the LCD screen panel (not shown). 
   In projection-based backlight system  400 , an illuminating light supplied from the arc lamp  402   a  is reflected back by the elliptical reflector  402   b  and emitted to the lens arrays  404 . When the illuminating light travels through the two lens arrays  404  and  406 , the two lens arrays  404  and  406  will compensate the illuminating light so that it can be perpendicularly incident on the incident surface of the condenser lens  408 . The compensated light then passes through the condenser lens  408  and relay lens  410  to reach the polarizing beam splitter  412 . When the light  421  enters the polarizing beam splitter  412 , it is split by the polarizing beam splitter  412  into first P-polarization light  422  which will pass directly through the second split-light side  412   c  and S-polarization light  424  which will be directed toward the first split-light side  412   b . The first P-polarization light  422  then enters the first projection lens  418  and is emitted to an LCD screen panel (not shown) by the first projection lens  418 . In addition, the S-polarization light  424  reaches the second mirror  414  and is reflected toward the half waveplate  416  by the second mirror  414 , and then converted into second P-polarization light  426  by the half waveplate  416 . The second P-polarization light  426  then enters the second projection lens  420  and is emitted to the same LCD screen panel (not shown) by the second projection lens  420 . 
   According to the projection-based backlight system  400  of the present invention, the second projection lens  420  can be appropriately aligned so as to project the same polarization light as projected by the first projection lens  418  on the same LCD screen panel, so that the light provided by the light source  402  can be effectively used and polarization efficiency can be increased. 
   While the foregoing descriptions and drawings represent the preferred embodiments of the present invention, it should be understood that various additions, modifications and substitutions may be made therein without departing from the spirit and scope of the principles of the present invention as defined in the accompanying claims. One skilled in the art will appreciate that the invention may be used with many modifications of form, structure, arrangement, elements, and components. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, and the scope of the invention should be defined by the appended claims and their legal equivalents, not limited to the foregoing descriptions.