Abstract:
A display device is disclosed. The display device includes a lamp emitting light, a plurality of filters dividing the emitted light into a red light, a green light, and a blue light, an additional light source unit compensating a light having a lowest light intensity among the divided red, green, and blue light, and a red liquid crystal display, a green liquid crystal display, and a blue liquid crystal displaying an image by using the light emitted from the lamp and the light emitted from the additional light source unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims the benefit of Korean Application No. P2003-027198, filed on Apr. 29, 2003, which is hereby incorporated by reference as if fully set forth herein.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a display device, and more particularly, to a display device using a supplementary light source for enhancing brightness.  
           [0004]    2. Discussion of the Related Art  
           [0005]    As satellite broadcasting and digital broadcasting are being extensively introduced and provided, the demand and interest for wide screen displays are increasing, and with such increase, the expectations on projectors and their importance as a display device are also on the rise. Accordingly, many technologies for high luminance projectors are recently being developed.  
           [0006]    For example, a liquid crystal display (LCD) projector divides a light emitted from a lamp, which is used as a light source herein, by using a plurality of color filters and combines the divided colors so as to represent a color image. However, in this case, there lies a problem in that a light intensity rate of each of the colors of red, green, and blue, which form the color image, should be controlled in accordance with the specific characteristic of the lamp.  
           [0007]    In other words, in a spectrum of the lamp used in the LCD projector, the green region has the highest light intensity, whereas the blue region and the red region have relatively low light intensities. More specifically, due to the low light intensity of the blue region, which has the lowest luminosity factor, the brightness shown from the projector is seen to be relatively weak through the eyes of a viewer. Such phenomenon results in a decrease in the brightness of the LCD projector.  
           [0008]    Therefore, in the related art LCD projector, in order to represent a color image corresponding to an input video signal, the light intensities of the red and green regions should be reduced in accordance with that of the blue region, which has the lowest light intensity, thereby controlling the white balance.  
           [0009]    As described above, the related art LCD projector does not use all of the light emitted from the lamp. Instead, the related art LCD projector should control the color combination rate of red, green, and blue based on the color having the lowest light intensity, thereby causing the problem of decreasing the brightness of the entire screen.  
         SUMMARY OF THE INVENTION  
         [0010]    Accordingly, the present invention is directed to a display device that substantially obviates one or more problems due to limitations and disadvantages of the related art.  
           [0011]    An object of the present invention is to provide a display device that uses an additional light source to enhance the brightness of a displayed color image.  
           [0012]    Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
           [0013]    To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a display device includes a lamp emitting light, a plurality of filters dividing the emitted light into a red light, a green light, and a blue light, an additional light source unit compensating a light having a lowest light intensity among the divided red, green, and blue light, and a red liquid crystal display, a green liquid crystal display, and a blue liquid crystal displaying an image by using the light emitted from the lamp and the light emitted from the additional light source unit.  
           [0014]    Herein, the additional light source unit includes a supplementary light source, and a lightguide with mirror combining the light emitted from the supplementary light source and the light emitted from the lamp, and transmitting the combined light to the liquid crystal display. And, the supplementary light source is formed of a light emitting diode.  
           [0015]    Also, the lightguide with mirror includes a light incident surface having the light emitted from the supplementary light source incident thereon, an inclined surface inclined at a predetermined angle from the light incident surface, and reflecting the light incident on the light incident surface, and a reflective surface reflecting the light reflected from the inclined surface to a direction identical to the light emitted from the lamp.  
           [0016]    Herein, an inclination angle of the inclined surface of the lightguide with mirror can be controlled in accordance with the direction of the light emitted from the lamp.  
           [0017]    In another aspect of the present invention, a display device includes a lamp emitting light, a plurality of filters dividing the emitted light into a red light, a green light, and a blue light, a supplementary light source compensating a light having a lowest light intensity among the divided red, green, and blue light, a plurality of polarizers polarizing the light emitted from one of the lamp and the supplementary light source, and a red liquid crystal display, a green liquid crystal display, and a blue liquid crystal displaying an image by using the light transmitted through the polarizer.  
           [0018]    Herein, the polarizer includes a first polarizing unit polarizing the light emitted from the lamp, and a second polarizing unit polarizing the light emitted from the light emitting diode array.  
           [0019]    The polarizer further includes a third polarizing unit selectively transmitting or reflecting the light transmitted through the first and second polarizing units depending upon the direction factor of the transmitting light, and a fourth polarizing unit polarizing the light transmitted or reflected by the third polarizing unit.  
           [0020]    The polarizing unit is a polarizing beam splitter, wherein the polarizing beam splitter is formed of a plurality of micro polarizing beam splitters. Herein, the polarizing beam splitter includes alternately formed half-wave plates.  
           [0021]    The supplementary light source is formed of a light emitting diode array.  
           [0022]    And, the light emitting diode array includes a half-wave plate formed at an end portion of each light emitting diode.  
           [0023]    It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and together with the description serve to explain the principle of the invention. In the drawings;  
         [0025]    [0025]FIG. 1 illustrates block diagram showing a structure of a display device according to a first embodiment of the present invention;  
         [0026]    [0026]FIG. 2 illustrates a graph showing a light intensity spectrum of a general lamp;  
         [0027]    [0027]FIGS. 3A and 3B illustrate a detailed view showing the principle of a lightguide with mirror of the display device according to the first embodiment of the present invention;  
         [0028]    [0028]FIG. 4 illustrates a block diagram of a display device according to a second embodiment of the present invention;  
         [0029]    [0029]FIG. 5 illustrates the principle of a polarizing beam splitter of the display device according to the second embodiment of the present invention; and  
         [0030]    [0030]FIG. 6 illustrates a block diagram of a light emitting diode according to the second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0031]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
         [0032]    [0032]FIG. 1 illustrates block diagram showing a structure of a display device according to a first embodiment of the present invention.  
         [0033]    Referring to FIG. 1, the display device includes a lamp being a light source, and red and blue filters  2  and  4  dividing the light and transmitting only the light of the corresponding color. The display device also includes red and blue mirrors  3  and  5  reflecting the light of the corresponding color, a light emitting diode (LED)  15  used as a supplementary light source, and a lightguide with mirror  14  combining and transmitting the light emitted from the LED  15  and the light emitted from the light source.  
         [0034]    In addition, the display device according to the present invention further includes red, green, and blue liquid crystal displays (LCDs)  7 ,  8 , and  9  displaying images of the corresponding colors based on electrical signals, a prism  10  combining the images displayed by the LCDs and processing the images to a constant direction, a projection optical part  11  enlarging the combined image, and a screen  12  displaying the enlarged image.  
         [0035]    The operations of the display device according to the present invention having the above-described structure will now be described in detail.  
         [0036]    The light generated from the lamp  1  is passed forward towards the front surface through a reflector. Among the light passed forward, only the red light is transmitted by the red filter  2 , whereas the green light and the blue light are reflected.  
         [0037]    Subsequently, the transmitted red light is reflected by the red mirror  3 , which is then irradiated to the red LCD  7 . Meanwhile, the blue filter transmits the blue light reflected by the red filter  2  and reflects the green light. The reflected green light is then irradiated to the green LCD  8 .  
         [0038]    In addition, after the blue light transmitted through the blue filter  4  is reflected by the blue mirror  5 , the lightguide with mirror  14  changes the path of the reflected blue light, which is then irradiated to the blue LCD  9 .  
         [0039]    [0039]FIG. 2 illustrates a graph showing a light intensity spectrum of a general lamp.  
         [0040]    Generally, as shown in FIG. 2, in a spectrum of the lamp used in the LCD projector, the light intensity of the green region is the highest, and the light intensities of the red and blue regions are relatively low. More specifically, the luminosity factor of the blue region is the lowest, which causes the blue region to become the darkest region.  
         [0041]    In other words, in order to correctly display a color image with the adequate colors, the light intensity of the color having the lowest light intensity should be increased.  
         [0042]    Accordingly, the light emitting diode (LED)  15  emitting blue light is formed on a side of the lightguide with mirror  14  as a supplementary light source. The blue light emitted from the LED  15  is reflected by the lightguide with mirror  14  and then irradiated to the blue LCD  9 . Similarly, the blue light emitted from the lamp and the blue light generated from the LED  15  are combined, and then irradiated to the blue LCD  9 .  
         [0043]    [0043]FIGS. 3A and 3B illustrate a detailed view showing the principle of a lightguide with mirror of the display device according to the first embodiment of the present invention.  
         [0044]    Referring to FIGS. 3A and 3B, the lightguide with mirror  14  is formed of an inclined surface  16 , a reflective surface  17 , and a light incident surface  18 . The light generated from the LED  15  is incident on the light incident surface  18 .  
         [0045]    The blue light  19  reflected by the blue mirror  5  is passed through to be parallel to the optical path of the lamp, and the blue light  19  is then reflected to the inclined surface  16  of the lightguide with mirror  14 .  
         [0046]    Meanwhile, the blue light emitted from the LED  15  is incident on the light incident surface  18  of the lightguide with mirror  14 . Thereafter, the blue light is totally reflected from the inclined surface  16 , and the totally reflected light is reflected once again from the reflective surface  17  to be parallel to the optical path of the lamp.  
         [0047]    At this point, when the inclination angle of the inclined surface  16  is controlled, the direction of the blue light generated from the LED  15  can be parallel to the blue light emitted from the lamp.  
         [0048]    Herein, the lightguide with mirror  14  can be formed in various shapes, such as a right triangle, a parallelogram, a semi-circle, and so on.  
         [0049]    As described above, by increasing the light intensity of the blue light, each of the red, green, and blue lights emitted from the lamp can be used without any loss.  
         [0050]    [0050]FIG. 4 illustrates a block diagram of a display device according to a second embodiment of the present invention. And, FIG. 5 illustrates the principle of a polarizing beam splitter of the display device according to the second embodiment of the present invention.  
         [0051]    Referring to FIG. 4, the display device according to the second embodiment of the present invention includes a lamp  101  being a light source, a first micro polarizing beam splitter  113  changing the light emitted from the lamp into a constant polarized light, a red filter  102 , a blue filter  104 , a red mirror  103 , and first and second blue mirrors  105  and  106 .  
         [0052]    The display device also includes a light emitting diode (LED) array  124  acting as a supplementary light source, and a second micro polarizing beam splitter  121  changing the light emitted from the LED array  124  into a constant polarized light.  
         [0053]    Additionally, the display device further includes a third micro polarizing beam splitter  123  selectively reflecting and transmitting the polarized lights passing through the first and second polarizing beam splitters  113  and  121 , a fourth micro polarizing beam splitter changing the reflected and transmitted polarized lights into a single polarized light, a red liquid crystal display  107 , a green liquid crystal display  108 , and a blue liquid crystal display  109 , a prism  110 , an projection optical part  111 , and a screen  112 .  
         [0054]    The light emitted from the lamp is reflected by the reflector and passed forwards towards the front surface. Thereafter, the first polarizing beam splitter  113  changes the light into a constant polarized light.  
         [0055]    The principle of the polarizing beam splitter will now be described with reference to FIG. 5.  
         [0056]    The light  125  emitted from the lamp  101  and incident on the polarizing beam splitter includes a combination of P-waves and S-waves.  
         [0057]    The incident light  125  is focused to a coating surface  127  of the polarizing beam splitter by a micro lens  126 . Among the incident light  125 , the P-wave light  128  is transmitted and passes through the coating surface  127  of the polarizing beam splitter. The polarizing direction of the P-wave light  128  is then rotated by 90 degrees (90°) by a half-wave plate  130 , so as to be changed into the S-wave light  129 .  
         [0058]    Meanwhile, among the incident light  125 , the S-wave light  129  is reflected by the coating surface  127  of the polarizing beam splitter, which is then reflected once again by the coating surface of an adjacent polarizing beam splitter in a direction parallel to the P-wave light.  
         [0059]    As described above, all of the light incident on the micro polarizing beam splitter  113  is changed into S-wave light.  
         [0060]    On the other hand, when the half-wave plates  130  are positioned at the front surface of the coating material of the even-numbered polarizing beam splitters, as opposed to FIG. 5, the incident light can all be changed into P-wave light.  
         [0061]    Referring to FIG. 4, among the polarized light formed by the first polarizing beam splitter, the red filter  102  transmits only the red light and reflects the green light and the blue light. Subsequently, the transmitted red light is reflected by the red mirror  103 , which is then irradiated on the red liquid crystal display (LCD)  107 .  
         [0062]    Meanwhile, among the light reflected by the red filter  102 , the blue light is transmitted by the blue filter  104 , and the green light is reflected. The reflected green light is irradiated on the green LCD  108 .  
         [0063]    In addition, the blue light transmitted through the blue filter  104  is sequentially reflected by the first blue mirror  105  and the second blue mirror  106 . The reflected blue light then passes through in the same direction as the blue LCD  109 .  
         [0064]    As described above, in order to accurately represent the color image, the light intensity of the color blue having the lowest light intensity should be increased.  
         [0065]    Therefore, the display device of the present invention uses a flat light emitting diode (LED)  124  as a supplementary light source of the blue light.  
         [0066]    [0066]FIG. 6 illustrates a block diagram of a light emitting diode according to the second embodiment of the present invention.  
         [0067]    Referring to FIG. 6, an LED p-layer  132  and an LED n-layer  134  are serially deposited on the substrate  131 . Then, an LED emission layer  133  is formed between the LED p-layer  132  and the LED n-layer  134 . And, each of the LED p-layer  132  and the LED n-layer is adjacent to an indium tin oxide (ITO) layer  135 , which is a transparent electrode.  
         [0068]    The ITO layer  135  receives an external electrical signal so as to apply a voltage to the LED p-layer  132  and the LED n-layer  134 , thereby generating light from the LED emission layer  133 .  
         [0069]    Herein, the light passes through in both directions of the emission layer  133 . However, since the light passing through the right side of the emission layer  133  is reflected to the left side by the reflective surface  136 , the entire light is passed through to the left side of the emission layer  133 .  
         [0070]    Subsequently, after the light is transmitted through the LED substrate  131 , the micro lens  126  focuses the transmitted light to the coating surface  127  of the second micro polarizing beam splitter. Herein, the coating surface  127  is formed to transmit a wave having a constant vibration direction and to reflect a wave that does not have a constant vibration direction.  
         [0071]    For example, after being transmitted through the coating surface  127  of the polarizing beam, the direction of the polarized light of the S-wave light  129  is rotated by 90 degrees (90°) by the half-wave plate  130 , so as to be modified to a P-wave light  128 . Meanwhile, the P-wave light  128  is reflected downwards in a perpendicular direction at 90 degrees (90°) by the coating surface  127  of the polarizing beam splitter, which is then reflected once again towards the left side in a horizontal direction at 90 degrees (90°) by the coating surface  127  of an adjacent polarizing beam splitter.  
         [0072]    Similarly, the light emitted from the LED is polarized as a P-wave light  128  by the second micro polarizing beam splitter  121 .  
         [0073]    In other words, the first micro polarizing beam splitter  113  polarizes the light emitted from the lamp as a S-wave, and the second micro polarizing beam splitter  121  polarized the light emitted from the LED as a P-wave.  
         [0074]    Referring back to FIG. 4, the S-wave blue light emitted from the lamp and the P-wave blue light emitted from the LED are combined at the third micro polarizing beam splitter  123 , so as to be passed through towards the blue LCD.  
         [0075]    The third micro polarizing beam splitter  123  is controlled to transmit the S-wave light and to reflect the P-wave light, as shown in FIG. 4. Thereafter, the S-wave blue light emitted from the lamp is transmitted through the third micro polarizing beam splitter  123 , and the P-wave blue light emitted from the LED is reflected by the third micro polarizing beam splitter  123 .  
         [0076]    The combined blue light is then polarized as one of a P-wave and a S-wave by the fourth micro polarizing beam splitter  122 , so as to be irradiated to the blue LCD. Accordingly, the light intensity of the blue light irradiated to the blue LCD can be increased.  
         [0077]    Meanwhile, the direction of the final polarized light passing through the fourth micro polarizing beam splitter is set to have the polarizing direction of the LCD, thereby enhancing the light efficiency of the LCD.  
         [0078]    Subsequently, due to an electrical signal, each of the red LCD  107 , the green LCD  108 , and the blue LCD  109  displays an image of the corresponding color. Then, the images displayed from each of the red, green, and blue LCDs are combined at the prism  110 , so as to form a single color image.  
         [0079]    The projection optical part enlarges the color image and projects the enlarged color image to the screen. The viewer is then able to view the displayed image in front of or from behind the screen.  
         [0080]    However, when the light intensity of other colors other than the color of blue is relatively lower, depending upon the characteristics of the lamp, the supplementary light source corresponding to the color having the lowest light intensity can be used instead.  
         [0081]    The above-described display device according to the present invention has the following advantages.  
         [0082]    By using a light emitting diode (LED), the color having the lowest light intensity among the R, G, and B lights emitted from the lamp being the light source can be compensated, thereby increasing the brightness of the screen without any light loss by color regions.  
         [0083]    Moreover, the polarizing beam splitter polarizes the light emitted from the lamp as a constant polarized light, thereby enhancing the optical efficiency of the LCD.  
         [0084]    It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.