Back lighting device for a panel

• US 5,093,765 A
• Filed: 02/14/1991
• Issued: 03/03/1992
• Est. Priority Date: 02/16/1990
• Status: Expired due to Term

• Current Assignee: Tosoh Corporation
• Original Assignee: Tosoh Corporation
• Inventors: Kashima, Keiji, Yoshida, Naoki, Yanagi, Eiichi, Shoji, Osamu, Fukunishi, Takumi
• Primary Examiner(s): Dority, Carroll B.
• Application Number:
  US07/655,520
• Time in Patent Office: 383 Days
• Field of Search: 362/31, 362/26
• US Class Current: 362/622
• CPC Class Codes: G02B 6/0051 Diffusing sheet or layer

Abstract

An improved backlighting device for liquid-crystal display panels comprising a linear light source the length of which is equal to or less than the length of an end portion of a light conducting plate at which light is admitted from the linear light source placed adjacent to it, the linear light source being enclosed with a light diffusing reflector that has a slit formed in the surface through which incident light is admitted into the light conducting plate and which is provided in such a way as to form a clearance from the surface of the linear light source, one major surface of the light conducting plate being partially covered with a light diffusing material under specified conditions that has a higher refractive index than the material of which the light conducting plate is made, the major surface being further covered with a specular or light diffusing/reflecting plate, with a plurality of light diffusing plates being provided on the other major (light emerging) surface of the light conducting plate.

Claims

1. A back lighting device for a liquid-crystal panel comprising:

a light conducting plate made of alight-transmissive material;

a linear light source provided at an end portion of at least one side of said light conducting plate, at least a portion of said inner light source which is capable of uniform light emission being equal to or less than a length of said end portion, said linear light source being enclosed with a light diffusing reflector having a slit through which light emitted from said linear light source is admitted into one side of the light conducting plate and providing a clearance between an outer surface of the linear light source and an opposing surface of said reflector;

a coating of a light diffusing material having a refractive index greater than said light-transmissive material, said coating being provided in a dot pattern on one major surface of said light conducting plate such that an area of coverage (Y) of said coating satisfies the functional relationship Y=aXⁿ or Y=a^x or the approximate relationship thereof (where X or x represents the distance from the linear light source;

n=1.7-3.5; and

a is a constant determined by regression of a mathematical expression) and such that an area of coverage (Y'"'"')of said coating which is provided on said major surface of the light conducting plate in an increasing amount towards both ends of a line parallel to the axis of said linear light source satisfies the functional relationship Y'"'"'=a'"'"'X'"'"'ⁿ or Y'"'"'=a'"'"'^x'"'"' or the approximate relationship thereof (where X'"'"' or x'"'"' represents the distance the coating departs from a line vertical to the center of the linear light source towards both ends thereof;

n=1.7-3.5; and

a'"'"' is a constant determined by regression of a mathematical expression) over the range from the area that is nearest to the linear light source and where X'"'"' is at maximum (each end of the light conducting plate) to the area where Y=Y'"'"' with Y'"'"' decreasing or increasing gradually, and is constant with increasing X along said both ends of the light conducting plate;

a specular or light diffusing/replacing plate for covering said coated surface; and

at least one light scattering plate provided on the other major and light emerging surface of said light conducting plate.

2. A back lighting device for a liquid-crystal panel according to claim 1 further comprising:

a specular reflecting member for covering an end face of said light conducting plate which is farthest from said linear light source.

3. A back lighting device for a liquid-crystal panel comprising:

a light conducting plate made of a light-transmissive material;

a linear light source provided in close proximity to an end portion of at least one side of said light conducting plate;

a coating of a light diffusing material having a refractive index greater than said light-transmissive material and is provided on one surface of said light conducting plate such that the coverage of said coating increases with the distance from the linear light source;

a specular reflecting plate or a light diffusing/reflecting plate for covering said one surface; and

a plurality of light scattering plates provided on the other and surface of said light conducting plate.

4. A back lighting device for a liquid-crystal panel according to claim 3 further comprising:

a specular reflecting member for covering an end face of said light conducting plate which is farthest from said linear light source.

5. A back lighting device for a liquid-crystal panel according to claim 3, in which the coverage of the light conducting plate with said light diffusing material increases in proportion to a power of the distance from the linear light source, said power being in the range of 1.7-3.5 or with the approximate relationship thereof.

6. A back lighting device for a liquid-crystal panel according to claim 3, in which at least a portion of said linear light source which is capable of uniform light emission is equal to or less than the length of said end portion, said linear light source being enclosed within a light diffusing reflector having a slit through which light emitted from said linear light source is admitted into one side of the light conducting plate and providing a clearance between an outer surface of the linear light source and an opposing inner surface of said reflector.

7. A back lighting device for a liquid-crystal panel according to claim 6, in which said coating of a light diffusing material is provided in a dot pattern on said one surface of said light conducting plate such that an area of coverage (Y) of said coating satisfies the functional relationship Y=aXⁿ or Y=a^x or the approximate relationship thereof (where X or x represents the distance from the linear light source;

n=1.7-3.5; and

a is a constant determined by regression of a mathematical expression) and such that an area of coverage (Y'"'"') of said coating which is provided on said surface of the light conducting plate in an increasing amount toward both ends of a line parallel to the axis of said linear light source satisfying the functional relationship Y'"'"'=a'"'"'X'"'"'ⁿ or Y'"'"'=a'"'"'^x'"'"' or the approximate relationship thereof (where X'"'"' or x'"'"' represents the distance the coating departs from a line vertical to the center of the linear light source towards both ends thereof;

n=1.7-3.5; and

a'"'"' is a constant determined by regression of a mathematical expression) over a range of an area that is nearest to the linear light source and where X'"'"' is at a maximum (each end of the light conducting plate) to the area where Y=Y'"'"' with Y'"'"' decreasing or increasing gradually and is constant with increasing X along said both ends of the light conductive plate.

8. A back lighting device for a liquid-crystal panel comprising:

a light conducting plate made of a light-transmissive material;

a linear light source provided in close proximity to the end portion of one side of said light conducting plate;

a first coating of alight diffusing material having a refractive index greater than said light-transmissive material and providing on one major surface of said light conducting plate such that a coverage of said first coating increases with the distance from an end portion of said one side of said light conducting plate which faces said linear light source; and

a specular reflecting member for covering an end face of said light conducting plate which is farthest from said linear light source.

9. A back lighting device for a liquid-crystal panel according to claim 8 further comprising:

a second coating of a light diffusing material having a refractive index greater than said light-transmissive material and providing on one major surface of said light conducting plate such that the area near the end portion of said light conducting plate which is farthest from said linear light source has an area in which the coverage of said second coating is equal to that in the other area or an area in which the coverage of said coating is greater than that in the other areas in which the rate of increase of said coverage is smaller than that in the other area.

10. A back lighting device for a liquid-crystal panel according to claim 8 further comprising:

a specular or light diffusing/replacing plate for covering said coated surface; and

at least one light scattering plate provided on another major and light emerging surface of said light conducting plate.

11. A back lighting device for a liquid-crystal panel according to claim 8, in which the coverage of said first coating of the light conducting plate with said light diffusing material increases in proportion to a power of the distance from the linear light source, said power being in the range of 1.7-3.5.

12. A back lighting device for a liquid-crystal panel according to claim 8, in which at least a portion of said linear light source which is capable of uniform light emission is equal to or less than the length of said end portion, said linear light source being enclosed with a light diffusing reflector having a slit through which light emitted from said linear light source is admitted into one side of the light conducting plate and providing a clearance between an outer surface of the linear light source and an opposing inner surface of said reflector.

13. A back lighting device for a liquid-crystal panel according to claim 12, in which said coating of a light diffusing material is provided in a dot pattern on said one surface of said light conducting plate providing an area of coverage (Y) of said coating which satisfies the functional relationship Y=aXⁿ or Y=a^x or the approximate relationship (where X or x represents the distance from the linear light source;

n-1.7-3.5; and

a is a constant determined by regression of a mathematical expression).