Surface light emission device, method of manufacturing the same, and liquid crystal display device

• US 20020114150A1
• Filed: 12/11/2001
• Published: 08/22/2002
• Est. Priority Date: 12/14/2000
• Status: Active Grant

• Current Assignee: ALPS Electric Company Limited (Alps Alpine Co., Ltd.)
• Original Assignee: ALPS Electric Company Limited (Alps Alpine Co., Ltd.)
• Inventors: Nakamura, Sadao
• Granted Patent: US 6,652,109 B2
• Time in Patent Office: Days
• US Class Current: 362/31
• CPC Class Codes: G02B 6/0036 2-D arrangement of prisms, protrusions, indentations or roughened surfaces
• CPC Class Codes: G02B 6/0065 Manufacturing aspects; Material aspects
• CPC Class Codes: G02F 1/133616 Front illuminating devices

Abstract

A surface light emitting device includes a light source and a light introduction plate having a structure for causing the light from the light source to be incident from a side end surface and to outgo from a light outgoing surface. Grooves are formed in a stripe shape on an opposing surface opposite to the light outgoing surface, and the grooves are formed deeper as they have a longer distance from the light source, and the difference between the depths of adjacent grooves is made larger as they have a distance longer from the light source. A method of manufacturing the surface light emitting device and a liquid crystal device including the surface light emitting device are also disclosed. With this arrangement, the surface light emitting device can obtain a sufficiently quantity of light at any position and the liquid crystal device can display an image in uniform brightness.

Claims

1. A surface light emitting device, characterized by comprising a light source and a light introduction plate having a structure for causing the light from the light source to be incident from a side end surface and causing the light to outgo from a light outgoing surface, wherein a plurality of grooves each composed of a gentle slanting surface and a steep slanting surface having a slanting angle steeper than that of the gentle surface are periodically formed in a stripe shape on the opposing surface of the light introduction plate opposite to the light outgoing surface, and a groove having a larger distance from the light source of the grooves is formed deeper as well as the difference between the depths of adjacent grooves is made larger as they have a distance longer from the light source.

2. A surface light emitting device according to claim 1, characterized in that the depth H_n+1 of a (n+1)-th groove from the light source of the plurality of grooves is formed to satisfy a formula H_n+1=H_n×

T/(T−

H_n) using the depth H_n of a n-th groove and the thickness T of the light introduction plate.

3. A surface light emitting device according to claim 1, characterized in that the depth H_n (μ

m) of a n-th groove from the light source of the plurality of grooves is shown by a formula H_n=an²T+H₁ using the number n of the groove, a coefficient a, the depth H₁ (em) of a first groove, and the thickness T (μ

m) of the light introduction plate and that the coefficient a is from 1.0×

10<sup>−

8</sup> or more to 5.0×

10<sup>−

8</sup> or less.

4. A surface light emitting device according to claim 1, characterized in that the depth H_n (μ

m) of a n-th groove from the light source of the plurality of grooves is shown by a formula

H₂=(an²+bn)×

T +H₁ using the number n of the groove, coefficients a and b, the depth H₁ (μ

m) of a first groove, and the thickness T (μ

m) of the light introduction plate and that the coefficient a is from 1.0×

10<sup>−

8</sup> or more to 5.0×

10<sup>−

8</sup> or less and the coefficient b is from 1.0×

10<sup>−

6</sup> or more to 3.0×

10<sup>−

6</sup> or less.

5. A surface light emitting device according to claim 1, characterized in that the depth F_n of a n-th groove from the light source of the plurality of grooves is shown by (H_n+d) which is the sum of an effective portion H_n of the depth F_n that contributes to outgoing of light and an ineffective portion other than the effective portion H_n and that the depth F_n+1 of a (n+1)-th groove from the light source is shown by a formula F_n+1=((F_n−

d)×

T/(T−

F_n+d))+d using the depth F_n of the n-th groove, the thickness T of the light introduction plate, and the ineffective portion d.

6. A surface light emitting device according to claim 1, characterized in that the reflection surface of the light introduction plate has flat portions formed between the grooves which are adjacent to each other.

7. A surface light emitting device according to claim 1, characterized in that the reflection surface of the light introduction plate has flat portions formed on the bottoms of the grooves.

8. A surface light emitting device according to claim 6, characterized in that the flat portions are formed to have a smaller area as they have a larger distance from the light source.

16. A liquid crystal display device, characterized by comprising the surface light emitting device according to claim 1.

9. A method of manufacturing a surface light emitting device, characterized by comprising a step of producing a casting mold by flatly machining one surface of a casting mold substrate at a predetermined pitch and by forming a plurality of grooves in a stripe shape to the step portions formed on the surface of the casting mold substrate by the flat machining at the pitch;

a step of producing a metal mold from the casting mold;

a step of producing a light introduction plate by injection molding using the metal mold; and

a step of disposing a light source to the light introduction plate, wherein a groove having a larger distance from the light source of the plurality of grooves is formed deeper as well as the difference between the depths of adjacent grooves is made larger as they have a distance longer from the light source.

10. A method of manufacturing a surface light emitting device, characterized by comprising a step of producing a metal mold by flatly machining one surface of a metal mold substrate at a predetermined pitch and by forming a plurality of grooves in a stripe shape to the step portions formed on the surface of the metal mold substrate by the flat machining at the pitch;

a step of producing a light introduction plate by injection molding using the metal mold; and

a step of disposing a light source to the light introduction plate, wherein a groove having a larger distance from the light source of the plurality of grooves is formed deeper as well as the difference between the depths of adjacent grooves is made larger as they have a distance longer from the light source.

11. A method of manufacturing a surface light emitting device according to claim 9 or 10, characterized in that the depth F_n of a n-th groove from the light source of the plurality of grooves is shown by (H_n+d) which is the sum of an effective portion H_n of the depth F_n that contributes to outgoing of light and an ineffective portion other than the effective portion H_n which is the sum of an effective portion H_n of the depth F_n that contributes to outgoing of light and an ineffective portion other than the effective portion H_n and that the grooves are formed such that the depth F_n+1 of a (n+1)-th groove from the light source satisfies a formula F_n+1 =((F_n−

d)×

T/(T−

F_n+d))+d using the depth F_n of the n-th groove, the thickness T of the light introduction plate and the ineffective portion d.

12. A method of manufacturing a surface light emitting device according to claim 10, characterized in that the depths of the plurality of grooves are formed such that the depth H_n (μ

m) of a n-th groove from the light source of the grooves satisfies H_n=an²T +H_n which is shown using the number n of the groove, a coefficient a from 1.0×

10<sup>−

8</sup> or more to 5.0×

10<sup>−

8</sup> or less, the thickness T (μ

m) of the light introduction plate, and the depth H₁ (μ

m) of a first groove.

13. A method of manufacturing a surface light emitting device according to claim 10, characterized in that the depths of the plurality of grooves are formed such that the depth H_n (μ

m) of a n-th groove from the light source of the grooves satisfies a formula H_n=(an²+bn)×

T +H₁ which is shown using the number n of the groove, a coefficient a from 1.0×

10<sup>−

8</sup> or more to 5.0×

10<sup>−

8</sup> or less, a coefficient b from 1.0×

10<sup>−

6</sup> or more to 3.0×

10<sup>−

6</sup> or less, the thickness T (mm) of the light introduction plate, and the depth H₁ (μ

m) of a first groove.

14. A method of manufacturing a surface light emitting device according to claim 10, characterized in that the plurality of grooves are formed such that flat portions are formed between the grooves which are adjacent to each other.

15. A method of manufacturing a surface light emitting device according to claim 14, characterized in that the flat portions are formed such that they have a smaller area as they have a larger distance from a side where the light source is disposed.