Area light source and lightguide used therefor

Abstract

An area light source comprises an LED ( 2 ), a plate-like light guide ( 4 ) adapted to guide the light emitted from the LED ( 2 ) and having a light incident end face ( 41 ) and a light emerging face ( 43 ), and a light deflecting element ( 6 ). Continuously arranged on the light emerging face ( 43 ) are lens arrays extending generally perpendicularly to the direction of the directivity of the light entering the light guide ( 4 ) from the LED ( 2 ) in a plane along the light emerging face ( 43 ) and having an average angle of inclination of 0.5° to 60°. On each surface of the lens arrays a coarse surface having an average angle of inclination of 0.1° to 8° is formed. Continuously arranged on the back ( 44 ) of the light guide are lens arrays extending generally parallel to the direction of the directivity of the light entering the light guide ( 4 ) from the LED ( 2 ) in the plane along the light emerging face ( 43 ) and having an average angle of inclination of 8° to 60°. Formed on a light entering surface ( 61 ) of the light deflecting element ( 6 ) are prism arrays ( 61 a ) parallel to one another and parallel to the light incident end face ( 41 ) of the light guide. A light reflecting element ( 8 ) is so disposed as to be opposed to the back ( 44 ) of the light guide.

1 . A plate-like light guide for planar light source device which guides a light emitted from a primary light source in a point state, and has a light incident end face on which the light emitted from the primary light source is incident and a light emitting face through which the guided light is emitted, 
 characterized in that on one of the light emitting face and a back surface on the opposite side thereto, a plurality of elongated lenses having an average slant angle of 0.5 to 60° are continuously or intermittently formed, and a rough surface of an average slant angle of 0.1 to 8° is formed on at least a part of a surface of each of the elongated lenses and/or at least a part of a surface on the opposite side to the surface on which the elongated lenses are formed.    
     
     
         2 . The light guide for the planar light source device according to  claim 1 , wherein each of the elongated lenses extends in a direction substantially orthogonal to a direction of a directivity of the light emitted from the primary light source and entered into the light guide in a plane along the light emitting face.  
     
     
         3 . The light guide for the planar light source device according to  claim 2 , wherein each of the elongated lenses extends in a direction substantially orthogonal to a propagation direction of the light emitted from the primary light source and entered into the light guide in the plane along the light emitting face.  
     
     
         4 . The light guide for the planar light source device according to  claim 2  or  3 , wherein an average slant angle of the elongated lenses is in a range of 0.5 to 25°.  
     
     
         5 . The light guide for the planar light source device according to  claim 2 , wherein the surface on the opposite side to the surface on which the elongated lenses are formed, a plurality of elongated lenses are formed to extend substantially along the direction of the directivity of the light emitted from the primary light source and entered into the light guide in the plane along the light emitting face.  
     
     
         6 . The light guide for the planar light source device according to  claim 2 , wherein on the surface on the opposite side to the surface on which the elongated lenses are formed, a plurality of elongated lenses are formed to extend substantially along the propagation direction of the light emitted from the primary light source and entered into the light guide in the plane along the light emitting face.  
     
     
         7 . The light guide for the planar light source device according to  claim 5  or  6 , wherein each of the elongated lenses extending substantially along the direction of the directivity of the light entered into the light guide is an elongated prism or an elongated lenticular lens.  
     
     
         8 . The light guide for the planar light source device according to  claim 5  or  6 , wherein the average slant angle of the elongated lenses extending substantially along the direction of the directivity of the light entered into the light guide is in a range of 8 to 60°.  
     
     
         9 . The light guide for the planar light source device according to  claim 1 , wherein each of the elongated lenses extends substantially along the direction of the directivity of the light emitted from the primary light source and entered into the light guide in the plane along the light emitting face.  
     
     
         10 . The light guide for the planar light source device according to  claim 9 , wherein each of the elongated lenses extends substantially along the propagation direction of the light emitted from the primary light source and entered into the light guide in the plane along the light emitting face.  
     
     
         11 . The light guide for the planar light source device according to  claim 1 , wherein the average slant angle of the rough surface is in a range of 0.5 to 6°.  
     
     
         12 . The light guide for the planar light source device according to  claim 1 , wherein each of the elongated lenses is an elongated prism or an elongated lenticular lens.  
     
     
         13 . The light guide for the planar light source device according to  claim 1 , wherein the average slant angle of the elongated lenses is in a range of 8 to 60°.  
     
     
         14 . The light guide for the planar light source device according to  claim 1 , wherein a flat part is formed in a valley between adjacent elongated lenses.  
     
     
         15 . The light guide for the planar light source device according to  claim 1 , wherein a pitch of the elongated lenses is changed according to a distance from the primary light source.  
     
     
         16 . The light guide for the planar light source device according to  claim 1 , wherein the average slant angle of the rough surface varies from place to place.  
     
     
         17 . The light guide for the planar light source device according to  claim 16 , wherein the average slant angle of the rough surface is larger in a second region near the light incident end face than that in a first region which is the other region.  
     
     
         18 . The light guide for the planar light source device according to  claim 17 , wherein the average slant angle of the rough surface in the second region is in a range of 2 to 8°.  
     
     
         19 . The light guide for the planar light source device according to  claim 18 , wherein the average slant angle of the rough surface in the first region is in a range of 0.5 to 4°.  
     
     
         20 . The light guide for the planar light source device according to  claim 1 , wherein the rough surface is formed on both of the surface of the elongated lenses and the surface on the opposite side to the surface on which the elongated lenses are formed, the average slant angle of the rough surface varies from place to place, and the average slant angle of the rough surface on the surface of the elongated lenses is smaller in a region in which the average slant angle of the rough surface of the surface on the opposite side to the surface on which the elongated lenses are formed is larger.  
     
     
         21 . A planar light source device comprising: the light guide described  claim 1;  the primary light source arranged adjacently to the light incident end face of the light guide; and a light deflecting device arranged adjacently to the light emitting face of the light guide, 
 wherein the light deflecting device has a light entering surface positioned so as to confront the light emitting face of the light guide and a light going-out surface on the opposite side to the light entering surface, and a plurality of elongated lenses are disposed on the light entering surface.  
 
     
     
         22 . The planar light source device according to  claim 21 , wherein each of the plurality of elongated lenses of the light deflecting device extends in a direction substantially orthogonal to the direction of the directivity of the light emitted from the primary light source and entered into the light guide in the plane along the light emitting face.  
     
     
         23 . The planar light source device according to  claim 21 , wherein each of the plurality of elongated lenses of the light deflecting device extends in a direction substantially orthogonal to the propagation direction of the light emitted from the primary light source and entered into the light guide in the plane along the light emitting face.  
     
     
         24 . The planar light source device according to  claim 21 , wherein each of the plurality of elongated lenses of the light deflecting device is an elongated prism, and at least one of prism surfaces that form the elongated prism is a convex curved surface.  
     
     
         25 . The planar light source device according to  claim 21 , wherein the light deflecting device includes at least one light deflection sheet, the light deflection sheet has a light entering surface through which a light based on the emitted light from the light emitting face of the light guide is entered into the light deflection sheet and a light going-out surface on the opposite side to the light entering surface, a plurality of elongated lenses are formed on a light entering surface of a first light deflection sheet positioned closest to the light guide so as to extend in a direction substantially parallel to the light incident end face, each of the elongated lenses of the first light deflection sheet forms a substantially triangular sectional shape of an apex angle of 50 to 80°, a plurality of linear structures each having concave or convex cross-section are formed on a light going-out surface of the first light deflection sheet, or a light entering surface or a light going-out surface of the other light deflection sheet so as to extend in a direction substantially orthogonal to the light incident end face, and an average slant angle of the surface on which the linear structures are formed is in a range of 5 to 40°.  
     
     
         26 . The planar light source device according to  claim 25 , wherein each of the linear structures comprises an elongated lens.  
     
     
         27 . The planar light source device according to  claim 25 , wherein each of the linear structures is formed by hairline processing and is a range of 0.1 to 200 μm in height.  
     
     
         28 . The planar light source device according to  claim 25 , wherein the light deflecting device includes the first light deflection sheet and the other second light deflection sheet, and the linear structures are formed on a light entering surface of the second light deflection sheet.  
     
     
         29 . The planar light source device according to  claim 25 , wherein the light deflecting device includes the first light deflection sheet and the other second light deflection sheet, and the linear structures are formed on a light going-out surface of the second light deflection sheet.  
     
     
         30 . The planar light source device according to  claim 29 , wherein adhesion prevention means is disposed to prevent adhesion between the first light deflection sheet and the second light deflection sheet.  
     
     
         31 . The planar light source device according to  claim 30 , wherein the adhesion prevention means is a spacer which forms a gap between the first light deflection sheet and the second light deflection sheet.  
     
     
         32 . The planar light source device according to  claim 30 , wherein the adhesion prevention means is a light diffusion sheet arranged between the first light deflection sheet and the second light deflection sheet.  
     
     
         33 . The planar light source device according to  claim 25 , wherein the light deflecting device is constituted of the first light deflection sheet, and the linear structures are formed on the light going-out surface of the first light deflection sheet.  
     
     
         34 . The planar light source device according to any one of  claims 21  to  33 , wherein the primary light source is an LED or an aggregate of LED's.  
     
     
         35 . A planar light source device comprising: a primary light source in a point state; a plate-like light guide arranged adjacently to the primary light source to guide a light emitted from the primary light source and having a light incident end face on which the light emitted from the primary light source is incident and a light emitting face through which the guided light is emitted; and a light deflecting device arranged adjacently to the light emitting face of the light guide, 
 wherein the light deflecting device includes at least one light deflection sheet, the light deflection sheet has a light entering surface through which a light based on the emitted light from the light emitting face of the light guide is entered into the light deflection sheet and a light going-out surface on the opposite side to the light entering surface, a plurality of elongated lenses are formed on a light entering surface of a first light deflection sheet positioned closest to the light guide so as to extend in a direction substantially parallel to the light incident end face, each of the elongated lenses of the first light deflection sheet forms a substantially triangular sectional shape of an apex angle of 50 to 80°, a plurality of linear structures each having concave or convex cross-section are formed on a light going-out surface of the first light deflection sheet, or a light entering surface or a light going-out surface of the other light deflection sheet so as to extend in a direction substantially orthogonal to the light incident end face, and an average slant angle of the surface on which the linear structures are formed is in a range of 5 to 40°.    
     
     
         36 . The planar light source device according to  claim 35 , wherein each of the linear structures comprises an elongated lens.  
     
     
         37 . The planar light source device according to  claim 35 , wherein each of the linear structures is formed by hairline processing and is a range of 0.1 to 200 μm in height.  
     
     
         38 . The planar light source device according to  claim 35 , wherein the light deflecting device includes the first light deflection sheet and the other second light deflection sheet, and the linear structures are formed on a light entering surface of the second light deflection sheet.  
     
     
         39 . The planar light source device according to  claim 35 , wherein the light deflecting device includes the first light deflection sheet and the other second light deflection sheet, and the linear structures are formed on a light going-out surface of the second light deflection sheet.  
     
     
         40 . The planar light source device according to  claim 39 , wherein adhesion prevention means is disposed to prevent adhesion between the first light deflection sheet and the second light deflection sheet.  
     
     
         41 . The planar light source device according to  claim 40 , wherein the adhesion prevention means is a spacer which forms a gap between the first light deflection sheet and the second light deflection sheet.  
     
     
         42 . The planar light source device according to  claim 40 , wherein the adhesion prevention means is a light diffusion sheet arranged between the first light deflection sheet and the second light deflection sheet.  
     
     
         43 . The planar light source device according to  claim 35 , wherein the light deflecting device is, constituted of the first light-deflection sheet, and the linear structures are formed on the light going-out surface of the first light deflection sheet.