Surface light source capable of changing range of spread angle of exit light, and liquid crystal display apparatus using this surface light source

Abstract

A surface light source includes first and second light sources that emit lights, and an optical deflection element. The optical deflection element changes light emitted from the first light source into first illumination light having a maximum value of an exit light intensity present in a direction parallel to a normal line of the surface light source, a spread angle range, and high directivity in a direction of the normal line and allows the changed light to exit therefrom. The optical deflection element also changes light emitted from the second light source into second illumination light having a maximum value of an exit light intensity in an oblique direction inclined at an angle with respect to the normal line and a spread angle range wider than that of the first illumination light and allows the changed light to exit therefrom.

1 . A surface light source comprising: 
 a first light source and at least one second light source that emit lights; and    an optical deflection element that changes light emitted from the first light source into first illumination light having a maximum value of an exit light intensity present in a direction parallel to a normal line of the surface light source, a predetermined spread angle range, and high directivity in a direction of the normal line and allows the changed light to exit therefrom; and that changes light emitted from the second light source into second illumination light having a maximum value of an exit light intensity in an oblique direction inclined at a predetermined angle with respect to the normal line of the surface light source and a spread angle range wider than that of the first illumination light and allows the changed light to exit therefrom.    
   
   
       2 . The surface light source according to  claim 1 , 
 wherein the optical deflection element comprise a light guide plate including:    a light incidence facet that is provided on one facet of the light guide plate and allows lights emitted from the first light source and the second light source arranged with a predetermined distance therebetween to enter therefrom;    a light exit surface which is provided on a plate surface crossing the light incidence facet of the light guide plate, and allows light that has entered from the light incidence facet and has been led into the light guide plate to exit therefrom in a predetermine direction;    an opposed surface provided on the other plate surface facing the light exit surface; and    at least one reflection surface which is provided on one of the light exit surface and the opposed surface, changes a direction of light emitted from the first light source to allow the light to exit from the light exit surface as the first illumination light, and changes a direction of light emitted from the second light source to allow the light to exit from the light exit surface as the second illumination light.    
   
   
       3 . The surface light source according to  claim 2 , 
 wherein the first light source is arranged at a substantially central position of the light incidence facet of the light guide plate in a length direction of a side thereof crossing the light exit surface,    said at least one second light source includes two second light sources, each of which is respectively arranged at each of at least two positions separated from the central position of the incidence facet on both sides thereof by a predetermined distance, and    the reflection surface of the light guide plate includes a plurality of concentrically arranged arc-like inclined surfaces that form an arc shape along a part of a circle having the central position of the light incidence facet where the first light source is arranged at the center, reflect light from the first light source that has entered from the central position of the light incidence facet to a direction substantially parallel to a normal line of the light exit surface, and reflect two lights from the second light sources that have entered from two positions separated from the central position of the incidence facet on both sides thereof by a predetermined distance to directions parallel to respective planes inclined with respect to a vertical reference plane at each angle corresponding to the distance from the central position and perpendicular to a horizontal reference plane when a plane perpendicular to each of the light exit surface and the light incidence facet is determined as the vertical reference plane and a plane that includes the normal line of the light exit surface and is perpendicular to the vertical reference plane is determined as the horizontal reference plane.    
   
   
       4 . The surface light source according to  claim 3 , 
 wherein the arc-like inclined surfaces are formed on the opposed surface of the light guide plate.    
   
   
       5 . The surface light source according to  claim 3 , 
 wherein the arc-like inclined surfaces are formed on the light exit surface of the light guide plate, and which further comprises a prism sheet that is arranged to face the outer side of the light exit surface and condenses light exiting from the light exit surface.    
   
   
       6 . The surface light source according to  claim 1 , 
 wherein the optical deflection element comprises a light guide plate having:    a light incidence facet that is provided on one facet of the light guide plate, and allows lights emitted from the first light source and the second light source arranged with a predetermined distance provided therebetween to enter therefrom;    a light exit surface that is provided on a plate surface crossing the light incidence facet of the light guide plate, and allows light that has entered from the light incidence facet and has been led into the light guide plate to exit therefrom in a predetermined direction;    an opposed surface provided on the other plate surface facing the light exit surface; and    a plurality of arc-like inclined surfaces that are provided on one of the light exit surface and the opposed surface, form an arc shape along a part of a circle having a substantially central position of the light incidence facet where the first light source is arranged in a length direction of a side thereof crossing the light exit surface at the center, are concentrically arranged with the central position at the center, and reflect light from the first light source toward a direction substantially parallel with the normal line of the light exit surface.    
   
   
       7 . The surface light source according to  claim 1 , further comprising, on the outer side of the opposed surface of the light guide plate, a reflection plate that reflects light which has been transmitted through the light guide plate to exit from the opposed surface toward the opposed surface and returns the light to the inside of the light guide plate.  
   
   
       8 . The surface light source according to  claim 1 , further comprising an anisotropic diffusion plate that is arranged to face the outer side of the light exit surface of the light guide plate, and diffuses light exiting from the light exit surface in a predetermined angle range in a direction inclined at each predetermined angle with respect to the vertical reference plane on the horizontal reference plane.  
   
   
       9 . The surface light source according to  claim 1 , 
 wherein the optical deflection element changes light emitted from the first light source into first illumination light having high directivity by which an intensity of exit light in each of oblique directions inclined on both sides of the normal line of the surface light source at an angle of 20° becomes 10% or below of an intensity of exit light in a direction parallel to the normal line, and allows the first illumination light to exit therefrom.    
   
   
       10 . The surface light source according to  claim 1 , 
 wherein the optical deflection element changes light emitted from the second light source into second illumination light having an intensity distribution in which a maximum value of an exit light intensity exists in an oblique direction having an inclination angle with which an exit light intensity of the first illumination light becomes 10% or below of a maximum value thereof with respect to the normal line of the surface light source, and allows the second illumination light to exit therefrom.    
   
   
       11 . A liquid crystal display apparatus comprising: 
 a liquid crystal display device that includes a screen region in which a plurality of pixels that control transmission of light are arranged in a matrix form, an image signal being applied to each of the plurality of pixels, thereby displaying an image corresponding to the image signal;    a first light source and at least one second light source that emit lights; and    a surface light source including an optical deflection element that changes light emitted from the first light source into first illumination light having a maximum value of an exit light intensity present in a direction parallel to a normal line of the surface light source, a predetermined spread angle range, and high directivity in a direction of the normal line and allows the first illumination light to exit therefrom; and that changes light emitted from the second light source into second illumination light having a maximum value of an exit light intensity present in an oblique direction inclined at a predetermined angle with respect to the normal line of the surface light source and a spread angle range wider than that of the first illumination light and allows the second illumination light to exit therefrom,    the surface light source being arranged on an opposite side of an observation side of the liquid crystal display device.    
   
   
       12 . The liquid crystal display apparatus according to  claim 11 , 
 wherein the optical deflection element comprises a light guide plate having:    a light incidence facet that is provided on one facet of the light guide plate, and allows lights emitted from the first light source and the second light source arranged with a predetermined distance provided therebetween to enter therefrom;    a light exit surface that is provided on a plate surface crossing the light incidence facet of the light guide plate, and allows light that has entered from the light incidence facet and has been led into the light guide plate to exit therefrom in a predetermined direction;    an opposed surface provided on the other plate surface facing the light exit surface; and    a plurality of arc-like inclined surfaces that are provided on one of the light exit surface and the opposed surface, form an arc shape along a part of a circle having a substantially central position of the light incidence facet where the first light source is arranged in a length direction of a side thereof crossing the light exit surface at the center, are concentrically arranged with the central position at the center, and reflect light from the first light source toward a direction substantially parallel with a normal line of the light exit surface,    the first light source being arranged at the central position of the light incidence facet of the light guide plate, and    the second light source being arranged at least one of two positions separated from the central position of the incidence facet on both sides by a predetermined distance.    
   
   
       13 . The liquid crystal display apparatus according to  claim 12 , 
 wherein, when a plane perpendicular to each of the light exit surface and the light incidence facet is determined as a vertical reference plane and a plane that includes the normal line of the light exit surface and is perpendicular to the vertical reference plane is a horizontal reference plane, the arc-like inclined surfaces of the light guide plate have an inclination angle with which light from the first light source that has entered from the central position of the light incidence facet is reflected in a direction substantially parallel with the normal line of the light exit surface, and light from the second light source that has entered from the at least one of two positions separated from the central position of the incidence facet on both sides by a predetermined distance are reflected in a direction substantially parallel with respective planes inclined with respect to the vertical reference surface at each angle corresponding to the distance from the center and perpendicular to the horizontal reference plane.    
   
   
       14 . The liquid crystal display apparatus according to  claim 11 , 
 wherein the optical deflection element changes light emitted from the first light source into first illumination light having high directivity by which an exit light intensity in an oblique direction inclined with respect to the normal line of the surface light source on each of both sides at an angle of 20° becomes 10% of an exit light intensity in a direction parallel to the normal line and allows the first illumination light to exit therefrom; and that changes light emitted from the second light source into second illumination light having an intensity distribution in which a maximum value of an exit light intensity exists in an oblique direction having an inclination angle with which an exit light intensity of the first illumination light becomes 10% or below of a maximum value thereof with respect to the normal line of the surface light source and allows the second illumination light to exit therefrom.    
   
   
       15 . A liquid crystal display apparatus comprising: 
 a liquid crystal display device that has a screen region in which a plurality of pixels that control transmission of light are arranged in a matrix form, an image signal being applied to each of the plurality of pixels, thereby displaying an image corresponding to the image signal;    a surface light source arranged on an opposite side of an observation side of the liquid crystal display device,    the surface light source including: 
 a first light source and at least one second light sources that emit lights; and  
 an optical deflection element that changes light emitted from the first light source into first illumination light having a maximum value of an exit light intensity present in a direction parallel to a normal line of the surface light source, a predetermined spread angle range, and high directivity in the normal line direction and allows the first illumination light to exit therefrom; and that changes light emitted from the second light source into second illumination light having a maximum value of an exit light intensity present in an oblique direction inclined at a predetermined angle with respect to the normal line of the surface light source and a spread angle range wider than that of the first illumination light and allows the second illumination light to exit therefrom; and  
   a controller including a display drive circuit that supplies the image signal to each pixel in the liquid crystal display device to display an image in the liquid crystal display device, and a light source drive circuit that controls lighting states of the first and the second light sources in accordance with an image displayed in the liquid crystal display device.    
   
   
       16 . The liquid crystal display apparatus according to  claim 15 , 
 wherein the light source drive circuit selectively controls a lighting state of the first light source alone and a simultaneous lighting state of the first and the second light sources in accordance with a viewing angle selection signal supplied from the outside.    
   
   
       17 . The liquid crystal display apparatus according to  claim 15 , 
 wherein the display drive circuit selectively supplies to the liquid crystal display device a display image signal corresponding to image data supplied from the outside and a fixed image signal corresponding to a predetermined fixed image to display each image, and    the light source drive circuit turns on the first light source in accordance with display of a display image corresponding to the display image signal of the liquid crystal display device and turns on the second light source in accordance with display of a fixed image corresponding to the fixed image signal of the liquid crystal display device based on the viewing angle selection signal supplied from the outside.    
   
   
       18 . The liquid crystal display apparatus according to  claim 15 , 
 wherein, when wide-viewing angle display is selected based on the viewing angle selection signal supplied from the outside,    the controller uses the display drive circuit to supply the display image signal corresponding to image data to each pixel in the liquid crystal display device, thereby displaying a display image in the liquid crystal display device, and    the controller uses the light source drive circuit to alternately turn on the first light source and the second light source at an equal rate in synchronization with supply of the display image signal to each pixel; and    when narrow-viewing angle display is selected based on the viewing angle selection signal,    the controller uses the display drive circuit to alternately supply the display image signal corresponding to image data and the fixed image signal corresponding to a fixed image having a predetermined pattern to each pixel in the liquid crystal display device, thereby displaying each image in the liquid crystal display device, and    the controller uses the light source circuit to turn on the first light source in synchronization with supply of the display image signal to each pixel and turn on the second light source in synchronization with supply of the fixed image signal to each pixel.    
   
   
       19 . The liquid crystal display apparatus according to  claim 15 , 
 wherein the display drive circuit supplies the display image signal required to display the display image to each pixel in the liquid crystal display device during a first sub-frame obtained by dividing one frame constituted of a period in which an image signal required to display one image is supplied into two, and selectively supplies the display image signal and the fixed image signal formed of an image having the predetermined pattern to each pixel in the liquid crystal display device in accordance with the viewing angle selection signal supplied from the outside during a second sub-frame obtained by dividing the one frame into two, and    the light source drive circuit turns on the first light source in synchronization with supply of the display image signal to each pixel during the first sub-frame, and turns on the first light source in synchronization with supply of the display image signal to each pixel and turns on the second light source in synchronization with supply of the fixed image signal to each pixel during the second sub-frame.    
   
   
       20 . The liquid crystal display apparatus according to  claim 19 , 
 wherein the liquid crystal display device includes a field sequential drive liquid crystal display panel that controls a transmission factor of light without having color filters,    each of the first and the second light sources includes a plurality of first and second light-emitting elements that selectively emit respective color lights of, red, green, and blue,    the controller supplies a display image signal corresponding to each color, i.e., red, green, or blue in the display image to each pixel in the liquid crystal display device in accordance with each field obtained by dividing the first sub-frame into three, and supplies a fixed image signal corresponding to each color, i.e., red, green, or blue in one of the display image signal and the fixed image signal selected based on the viewing angle selection signal in accordance with each field obtained by dividing the second sub-frame into three, and    the light source drive circuit generates light having a corresponding color from the first light-emitting element in synchronization with supply of the display image signal of each color to each pixel in accordance with each field in the first sub-frame, and generates light having a corresponding color from the first light-elements in synchronization with supply of the display image signal of each color to each pixel and generates light having a corresponding color from the second light-emitting element in synchronization with supply of the fixed image signal of each color to each pixel in accordance with each field in the second sub-frame.