Abstract:
A projector is equipped with: a light emitting diode for emitting light; an image display element to which the light emitted from the light emitting diode is incident and which modulates the incident light and emits the light as image light; and an ultraviolet light incidence preventing member disposed between the light emitting diode and the image display element for preventing ultraviolet light from being incident to the image display element.

Description:
[0001]     This application is based on Japanese Patent application JP 2004-087876, filed Mar. 24, 2004, the entire content of which is hereby incorporated by reference. This claim for priority benefit is being filed concurrently with the filing of this application.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Technical Field of the Invention  
         [0003]     The present invention relates to a projector for projecting light supplied with information such as an image or the like onto a screen to display the image on the screen.  
         [0004]     2. Description of the Related Art  
         [0005]     A projector using a liquid crystal panel or DMD (digital micro-mirror device) has been known as a projector for projecting light supplied with information such as an image or the like to a screen to display the image on the screen. According to a liquid crystal projector using a liquid crystal panel, light irradiated to the liquid crystal panel is transmitted through the liquid crystal panel or light irradiated to the liquid crystal panel is reflected by the liquid crystal panel, whereby image information displayed on the liquid crystal panel is projected to the screen. The image information displayed on the liquid crystal panel is displayed on the screen while being enlarged.  
         [0006]     The liquid crystal projector is equipped with an illumination device for illuminating light to the liquid crystal panel, and an illumination optical system for uniformly irradiating light from the illumination device onto the liquid crystal panel is provided in front of the illumination device. The illumination optical system contains a lens, a polarization converting element, etc., and the light irradiated from the illumination device is irradiated through the illumination optical system to the liquid crystal panel. It is preferable that the liquid crystal panel is illuminated with bright and uniform light, and thus it is desired that the light irradiated from the illumination device has high brightness and the light flux thereof is uniform. Accordingly, it has been general to use as the illumination device a high-luminance discharge lamp which can light having brightness (high luminance) needed to project an image on the liquid crystal panel such as an ultra-high pressure mercury lamp, a metal halide lamp, a xenon lamp or the like.  
         [0007]     The high-luminance discharge lamp is heated, and thus it is necessary to provided a large-scale cooling device for cooling the lamp. However, when the cooling device is provided, there is a problem that the illumination device must be designed in a large size and further the manufacturing cost of the projector is increased. Furthermore, it has been required to reduce the cost when the projector is used, for example, to reduce the power to be consumed to irradiate high-brightness light and further to lengthen the period for which the high-luminance discharge lamp can be used.  
         [0008]     Therefore, it has been recently considered that a light emitting diode (hereinafter referred to as “LED”) is used as an illumination device in place of the ultra-high discharge lamp. LED has advantages that it is more compact in size, lighter in weight, smaller in power consumption and longer in lifetime, it can be driven with a low voltage and it has a high response speed when it is subjected to turn-on control as compared with the ultra-high discharge lamp described above. However, light emitted from LED is diffused over a broad range, and thus JP-A-2003-186110 has proposed a method of focusing light emitted from LED by a lens. Furthermore, awhile-color LED for emitting white light is used as LED used for the illumination device.  
         [0009]     There are some types of LEDs for emitting white light. One of these types of LEDs comprises a combination of an element for generating ultraviolet light and a white fluorescent material for emitting light upon reception of ultraviolet light (a mixture of plural kinds of primary color fluorescent materials). With this type, the whole ultraviolet light thus generated is not necessarily converted to white light, and a part of the light may leak to the outside. Even in other types of LEDs, leakage of ultraviolet light is unavoidable in some constructions. Furthermore, orientation film of the liquid crystal panel is weak to ultraviolet light, and the lifetime of the present liquid crystal panel is greatly affected by a total irradiation amount of ultraviolet light. Accordingly, when a liquid crystal projector is constructed by using LED as an illumination device, it is important to treat ultraviolet light thus leaking, and the JP-A-2003-186110 and other techniques have hardly paid attention to the above matter.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention has an object to provide a projector which can prevent ultraviolet light leaking from a white light emitting diode from being irradiated to a liquid crystal panel although the white light emitting diode is used.  
         [0011]     A projector according to the present invention is characterized by comprising: a light emitting diode for emitting light; an image display element to which the light emitted from the light emitting diode is incident and which modulates the incident light and emits the light as image light; and an ultraviolet light incidence preventing member disposed between the light emitting diode and the image display element for preventing ultraviolet light from being incident to the image display element.  
         [0012]     The ultraviolet light incidence preventing member is preferably constructed by a member for absorbing or reflecting the ultraviolet light.  
         [0013]     According to the projector of the present invention, it is equipped with the light emitting diode for emitting light, the image display element to which the light emitted from the light emitting diode is incident and which modulates the incident light and emits the light as image light, and the ultraviolet light incidence preventing member disposed between the light emitting diode and the image display element for preventing ultraviolet light from being incident to the image display element. Therefore, the ultraviolet light leaking from the light emitting diode is irradiated forwardly although the light emitting diode is used, and thus the ultraviolet light is prevented from being incident to the image display element.  
         [0014]     The ultraviolet light incidence preventing member is constructed by the member for absorbing or reflecting ultraviolet light, so that ultraviolet light leaking from the light emitting diode can be irradiated forwardly and prevented from being incident to the image display element. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  is a diagram showing the construction of one embodiment of a projector used for the invention.  
         [0016]      FIG. 2  is a perspective view showing one embodiment of the outlook of an illumination light source device of the invention.  
         [0017]      FIG. 3  is a cross-sectional view showing one embodiment of a light source of the invention.  
         [0018]      FIG. 4  is a diagram showing an irradiation direction of light irradiated from the white LEDs.  
         [0019]      FIG. 5  is a diagram showing the intensity of light irradiated from the white LEDs. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]     In  FIG. 1 , a liquid crystal projector  10  is equipped with an illumination optical system  11 , a mirror  12  for varying an irradiation direction of irradiated light, dichroic mirrors  13 ,  14 , three transmission type liquid crystal panels (image display elements)  15 R,  15 G,  15 B, a cross dichroic prism  16 , a projection lens  17 , a screen  18  and an illumination device  19 .  
         [0021]     The illumination optical system  11  is equipped with a lens  20  and a polarization converting element  21 . White light containing red light (R light), green light (G light) and blue light (B light) are irradiated from the illumination device  19  to the downstream side thereof. The light irradiated from the illumination device  19  is incident to the lens  20 . The light incident to the lens  20  is collimated and then irradiated to the downstream side of the lens  20 . The polarization converting element  21  is disposed at the downstream side of the lens  20 . The polarization converting element  21  transmits light irradiated from the illumination device  19  therethrough to convert the light to R light, G light and B light having no specific polarization plane to S-polarized light. Each color light transmitted through the polarization converting element  21  is reflected by the mirror  12  and then incident to the dichroic mirror  13 .  
         [0022]     The dichroic mirror  13  transmits B light contained in white light and reflects R light and G light to separate the B light. The B light thus separated is reflected by the mirror  12  and incident to the liquid crystal panel  15 B. The R light and the G light reflected by the diachronic mirror  13  are incident to the diachronic mirror  14 . The diachronic mirror  14  transmits the R light therethrough and reflects the G light to separate the R light and the G light from each other. The R light transmitted through the dichroic mirror  14  is reflected from the mirror  12 , and incident to the liquid crystal panel  15 R. The G light reflected by the dichroic mirror  14  is incident to the liquid crystal panel  15 G.  
         [0023]     In the liquid crystal panels  15 R,  15 G,  15 B, the R light, the G light and the B light incident thereto are supplied with image information. The light flux of the R light, the G light and the B light transmitted through the liquid crystal panels  15 R,  15 G,  15 B is incident to the cross dichroic prism  16 . The cross dichroic prism  16  comprises a combination of four rectangular prisms. The cross dichroic prism  16  has two kinds of dichroic faces of a R light reflection face  16   a  for reflecting R light and a B light reflection face  16   b  for reflecting B light, and the orthogonal prisms thereof are arranged so that the R light reflection face  16   a  and the B light reflection face  16 B are orthogonal to each other.  
         [0024]     When the R light transmitted through the liquid crystal panel  15 R is reflected by the R light reflection face  16   a , the irradiation direction of the R light is varied so as to be orthogonal to the transmission direction of the R light through the liquid crystal panel  15 R so that the reflected R light is directed to the projection lens  17 , and thus the R light is incident to the projection lens  17 . The G light transmitted through the liquid crystal panel  15 G is transmitted through the R light reflection face  16   a  and the B light reflection face  16   b , straightly travel and then are incident to the projection lens  17 . When the B light transmitted through the liquid crystal panel  15 B is reflected by the B light reflection face  16   b , the irradiation direction of the B light is varied so as to be orthogonal to the transmission direction of the B light through the liquid crystal panel  15 B so that the reflected B light is directed to the projection lens  17 , and thus the B light is incident to the projection lens  17 . The projection lens  17  projects the light flux of the respective color light combined by the cross dichroic prism  16  while enlarging each color light flux, and focuses them onto the screen  18  (not shown), whereby the image information is displayed on the screen  18 .  
         [0025]     As shown in  FIGS. 2 and 3 , the illumination device  19  is equipped with a light source  29 , a rod integrator  30  and an ultraviolet light absorbing plate (ultraviolet light incidence preventing member)  31 .  
         [0026]     The light source  29  comprises plural white LEDs (light emitting diodes)  32  for emitting white light, a base member  33  to which the white LEDs  32  are mounted, and a lens array  35  having plural condensing lens  34  for condensing light emitted from the white LEDs.  
         [0027]     Each of the white LEDs  32  has a fixing portion  32   a  to be fixed to the base member  33  and an irradiation portion  32   b  for irradiating light. The base member  33  is designed in a semispherical shape having a hollow portion therein, and plural holes  33   a  are formed in the outer peripheral surface of the base member  33  so as to be spaced from one another at predetermined intervals. The fixing portion  32   a  is engagedly fitted in each hole  33   a  so that the irradiation portion  32   b  faces the inside of the base member  33 , whereby the white LEDs  32  are fixed to the base member  33 .  
         [0028]     The plural condensing lenses  34  are fixed to the lens array  35  so as to be arranged in the same interval as the holes  33   a . An opening portion  33   b  is formed at the flat front surface of the base member  33  so as to intercommunicate with the hollow portion in the base member  33 . The lens array  35  is inserted from the opening portion  33   b  and fixed in the base member  33 . When the lens array  35  is fixed, each of the plural condensing lenses  34  faces each of the irradiation portions  32   b  of the while LEDs  32  fixed to the base member  33 . The heating amount of the while LEDs is set to a level that resin can be used as the material of the condensing lenses  34 , and thus it is preferable that the condensing lenses  34  may be formed integrally with the lens array  35 . Accordingly, even when the lens array  35  is designed in a complicated shape, the light source can be simply manufactured.  
         [0029]     The rod integrator  30  is formed of transparent material to have a quadratic-prism shape. A surface of the rod integrator  30  which is located at one end side thereof in the longitudinal direction and faces the opening portion  33   a  serves as an incidence face  30  to which light irradiated from white LEDs  32  is incident, and a surface of the rod integrator  30  which is located at the opposite side to the incidence face  30   a  serves as an irradiation face  30   b  from which light incident from the incidence face  30   a  is irradiated to the outside.  
         [0030]     The ultraviolet absorbing plate (ultraviolet light incidence preventing member)  31  is fixed to the incidence  30   a  of the rod integrator  30 . The ultraviolet light absorbing plate  31  absorbs ultraviolet light (light of substantially 430 nm or less in wavelength) out of light irradiated from the white LEDs  32 , and it is formed of material through which white light is transmitted. Accordingly, it prevent incidence of ultraviolet light to the rod integrator  30 , the lens  20 , the liquid crystal panels  15 R,  15 G,  15 B, etc. which are located at the downstream side thereof.  
         [0031]     As shown in  FIG. 4 , when light is irradiated from the white LEDs  32  under the state that the white LEDs  32  are fixed to the base member  33 , the irradiation axes  32   c  each of which serves as the center axis of an irradiation range of light emitted from each white LED  32  extend radially, and also cross one another in a fixed range. The rod integrator  30  is located in front of the opening portion  33   a  of the base member  33  so that the incidence face  30   a  thereof is located in the cross range of the irradiation axes  32   c.    
         [0032]     When light which is irradiated from the white LEDs  32  and then from which ultraviolet light is absorbed by the ultraviolet light absorbing plate  31  is incident to the incidence face  30   a , the incident light is totally reflected by the inner surface and then irradiated as substantially uniformly collimated light flux from the irradiation face  30   b  to the outside. Accordingly, the irradiation of the light irradiated from the white LEDs  32  is varied, and the light is irradiated to a predetermined range with substantially uniform brightness.  
         [0033]     Here, as shown in  FIG. 5 , the light irradiated from the white LEDs  32  has a characteristic in that the brightness thereof is highest on the irradiation axis  32   c  and it is gradually reduced toward the periphery of the light. Therefore, if the light irradiated from the white LEDs  32  is used without using any rod integrator  30 , the image information on the screen  18  is bright at the center portion thereof and is gradually darkened toward the peripheral portion thereof. Accordingly, the liquid crystal projector  10  can achieve uniformly bright image information by using the rod integrator  30 .  
         [0034]     Suitable material such as glass, transparent resin such as acrylic resin or the like may be used as the material for the rod integrator  30  insofar as it is transparent material having a refractive index different from air. Furthermore, the shape of the rod integrator  30  is not limited to the quadratic prism, but it may be any suitable shape. It may be designed to have a hollow cylindrical shape. When the inside of the rod integrator  30  is designed to have a hollow portion therein, the light reflection frequency at the inner surface is increased, so that more uniformly collimated light flux can be achieved.  
         [0035]     Next, the operation of the liquid crystal projector thus constructed will be described. When light is irradiated from the white LEDs  32 , the light thus irradiated is condensed by the condensing lens  34 , and irradiated to the incidence face  30   a  of the rod integrator  30 . The ultraviolet light contained in the light irradiated to the incidence face  30   a  of the rod integrator  30  is absorbed by the ultraviolet light absorbing plate  31 , and then the light is incident to the incidence face  30   a , whereby ultraviolet light can be prevented from being incident to the rod integrator  30 , the lens  20 , the liquid crystal panels  15 R,  15 G,  15 R, etc. located at the downstream side of the ultraviolet light absorbing plate  31 . Since the white LEDs  32  are arranged so that the irradiation axes  32   c  of light irradiated from the respective white LEDs  32  cross one another in a fixed range, light having high brightness can be made incident from the incidence face  30   a.    
         [0036]     The light incident from the incidence face  30   a  is totally reflected by the inner surface of the rod integrator  30 , and then irradiated as substantially uniformly collimated light flux from the irradiation face  30   b  to the outside. Accordingly, the light irradiated from the white LEDs  32  is irradiated with substantially uniform brightness in a predetermined range while the irradiation direction thereof is varied. The light irradiated from the rod integrator  30  is passed through the cross dichroic prism  16  and the projection lens  17  and then projected onto the screen  18 .  
         [0037]     As described above, the ultraviolet light of the light irradiated to the incidence face  30   a  of the rod integrator  30  is absorbed by the ultraviolet light absorbing plate  31 , and then the light concerned is incident to the incidence face  30   a . Therefore, ultraviolet light can be prevented from being incident to the rod integrator  30 , the lens  20 , the liquid crystal panels  15 R,  15 G,  15 B, etc. located at the downstream side of the ultraviolet light absorbing plate  31 . Accordingly, the liquid crystal panels  15 R,  15 G,  15 B whose orientation films would be liable to be broken if ultraviolet light is incident thereto can be protected.  
         [0038]     In the above embodiment, the ultraviolet light absorbing plate  31  is secured to the incidence face  30   a  of the rod integrator  30 , however, the present invention is not limited to this embodiment. It is merely required only to prevent the ultraviolet light of the light irradiated from the white LEDs  32  from being incident to the liquid crystal panels  15 R,  15 G,  15 B. For example, the ultraviolet light absorbing plate  31  may be secured to the irradiation face  30   b  of the rod integrator  30 , the incidence face of the lens  20  or the like. In addition, the position at which the ultraviolet light absorbing plate  31  is secured may be suitably changed.  
         [0039]     Furthermore, in the above embodiment, as the ultraviolet light incidence preventing member is used an ultraviolet light absorbing plate  31  formed of a material which absorbs ultraviolet light out of light irradiated from the white LEDs  32  and through which white light is transmitted. However, the present invention is not limited to this embodiment, and it is merely required only to prevent ultraviolet light out of light irradiated from the white LEDs  32  from being incident to the liquid crystal panels  15 R,  15 G,  15 B, and as the ultraviolet light incidence preventing member may be used an ultraviolet light reflecting plate formed of a material which reflects ultraviolet light out of light irradiated from the white LEDs  32  and through which white light is transmitted.  
         [0040]     Furthermore, the LEDs serving as the light source are not limited to the white LEDs, and for example, a combination of three color LEDs of R, G and B may be used as a light source of the projector.  
         [0041]     Still furthermore, the present invention is not limited to the transmission type liquid crystal projector  10  in which light irradiated to the liquid crystal panel is transmitted therethrough, but it may be applied to a reflection type projector in which light irradiated to a liquid crystal panel is reflected therefrom, a projector using DMD or other projectors.