Surface light source device and liquid crystal display

• US 5,659,410 A
• Filed: 12/23/1994
• Issued: 08/19/1997
• Est. Priority Date: 12/28/1993
• Status: Expired due to Term

• Current Assignee: Enplas Corporation
• Original Assignee: Enplas Corporation
• Inventors: Arai, Takayuki, Koike, Yasuhiro
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): NGUYEN, TIEP HUU
• Application Number:
  US08/362,955
• Time in Patent Office: 970 Days
• Field of Search: 359/48, 359/49, 359/50, 362/31, 362/32, 362/26, 362/347, 362/349
• US Class Current: 349/62
• CPC Class Codes: G02B 6/0046 Tapered light guide, e.g. wedge-shaped light guide
• CPC Class Codes: G02B 6/0051 Diffusing sheet or layer
• CPC Class Codes: G02B 6/0053 Prismatic sheet or layer; Brightness enhancement element, sheet or layer

Abstract

A wedge shaped parallelized light flux element made of a light scattering guide of an emitting directionality has a specified ranged effective scattering irradiation parameter and correlation distance "a". A light incident into the parallelized light flux element from a fluorescent lamp arranged facing a light incident surface of the parallelized light flux element is emitted from a light output surface as a parallelized light flux G1 by composite factors including forward scattering of the inside, repeated reflection on wedge shaped two sides, critical angular condition and boundary face transmittance for the light output surface. A total amount of parallel light flux G1 emitted from the parallel light flux emitting section F is reflected on a two side prism surface of two prism reflection element PR thereby being converted into sectional area enlarged light fluxes G2 and G3. They are incident on a liquid crystal panel LP through a light diffusion plate DF, and utilized as a backlight. Reflective appearance of a light supply source for supplying a light to the light scattering guide is prevented by forming a reverse slope portion or the like on back surface of the light output surface in adjacent to the light incident surface of the parallelized light flux element.

Claims

1. A surface light source device comprising:

a light supply means; and

a light scattering guide comprising;

a light incident surface region positioned in the vicinity of the light supply means for receiving light from the light supply means;

a light output surface region for emitting light received at the light incident surface region;

a volume region having a uniform scattering power, the volume region having a back side opposite the light output surface region, and first and second portions, the first portion having a thickness extending inward from the light output surface region to the back side, which decreases with increasing distance from the light incident surface region such that in the first portion, the back side has a first slope with respect to the light output surface region; and

reflective appearance prevention means for preventing a reflective appearance from the light supply means, formed in the second portion of the volume region closer to the light incident surface region than the first portion, the second portion having a thickness which increases, decreases or remains the same with increasing distance from the light incident surface region such that in the second portion, the back side has a second slope with respect to the light output surface region which is less than the first slope.

2. A surface light source device as claimed in claim 1, further comprising light reflection means having a regular reflection property, disposed on the back side opposite the light output surface region of the light scattering guide.

3. A surface light source device as claimed in claim 1, further comprising scattering light emitting direction correcting means for correcting an emitting direction, disposed on the light output surface region of the light scattering guide, as a separate structure from the light scattering guide.

4. A surface light source device as claimed in claim 1, further comprising scattering light emitting direction correcting means for correcting an emitting direction, disposed on the light output surface region of the light scattering guide, as a unitary structure with the light scattering guide.

5. A surface light source device as claim 1, further comprising:

scattering light emitting direction correcting means for correcting an emitting direction, disposed on the light output surface region of the light scattering guide as a separate structure from the light scattering guide; and

light reflection means having a regular reflection property, disposed on the back side opposite the light output surface region of the light scattering guide.

6. A surface light source device as claim 1, further comprising:

scattering light emitting direction correcting means for correcting an emitting direction, disposed on the light output surface region of the light scattering guide as a unitary structure with the light scattering guide; and

light reflection means having a regular reflection property, disposed on the back side opposite the light output surface region of the light scattering guide.

7. A liquid crystal display comprising:

a light supply means;

a light scattering guide comprising;

a light incident surface region positioned in the vicinity of the light supply means for receiving light from the light supply means;

a light output surface region for emitting light received at the light incident surface region;

a volume region having a uniform scattering power, the volume region having a back side opposite the light output surface region, and first and second portions, the first portion having a thickness extending inward from the light output surface region to the back side, which decreases with increasing distance from the light incident surface region such that in the first portion, the back side has a first slope with respect to the light output surface region;

reflective appearance prevention means for preventing a reflective appearance from the light supply means, formed in the second portion of the volume region closer to the light incident surface region than the first portion, the second portion having a thickness which increases, decreases or remains the same with increasing distance from the light incident surface region such that in the second portion, the back side has a second slope with respect to the light output surface region which is less than the first slope; and

a liquid crystal device arranged in a position to receive light emitted from the light output surface region.

8. A liquid crystal display as claimed in claim 7, further comprising light reflection means, provided on the back side opposite the light output surface region of the light scattering guide.

9. A liquid crystal display as claimed in claim 7, further comprising scattering light emitting direction correcting means for correcting an emitting direction, disposed on the light output surface region of the light scattering guide, as a separate structure from the light scattering guide.

10. A liquid crystal display as claimed in claim 7, further comprising scattering light emitting direction correcting means for correcting an emitting direction, disposed on the light output surface region of the light scattering guide, as a unitary structure with the light scattering guide.

11. A liquid crystal display as claimed in claim 7, further comprising scattering light emitting direction correcting means for correcting an emitting direction, disposed on the light output surface region of the light scattering guide, as a separate structure from the light scattering guide;

and light reflection means, disposed on the back side opposite the light output surface region of the light scattering guide.

12. A liquid crystal display as claimed in claim 7, further comprising scattering light emitting direction correcting means for correcting an emitting direction, disposed on the light output surface region of the light scattering guide, as a unitary structure with the light scattering guide;

and light reflection means, provided on the back side opposite the light output surface region of the light scattering guide.

13. A surface light source device comprising:

a light supply means;

a parallelized light flux element comprising;

a light incident surface region positioned in the vicinity of the light supply means for receiving light from the light supply means;

a light output surface region for emitting as parallel light, light received at the light incident surface region;

a volume region having a uniform scattering power expressed by a correlation function γ

(r) approximated by exp (-r/a), where r is a distance between two points in said volume region and a is a correlation distance whose value lies in a range of 0.06 μ

m≦

a≦

35 μ

m, the volume region having an effective scattering illumination parameter E whose value lies in a range of 0.5 cm^-1 ≦

E≦

50 cm^-1, the volume region having, at least in a part thereof, a thickness extending inward from the light output surface region to an opposing side, which decreases with increasing distance from the light incident surface region; and

a two sided prism reflection element extending in a reflection plane which is at an angle to the light output surface region of the parallelized light flux element such that the parallelized light flux element does not cross the reflection plane, the reflection element receiving the parallel light from the light output surface region at a first angle to the reflection plane and emitting parallel light at a second angle, different from the first angle, to the reflection plane.

15. A surface light source device as claimed in claim 13, or 14, further comprising light emitting direction correcting means for correcting an emitting direction of the parallel light so that the parallel light is received at the two sided prism element at the first angle, the light emitting direction correcting means being disposed on the light output surface region of the parallelized light flux element.

16. A surface light source device as claimed in claim 13 or 14, further comprising reflecting prevention means for preventing a reflective appearance from the light supply means, formed in the volume region adjacent to the light incident surface region, on the side opposing the light output surface region.

14. A surface light source device comprising:

a light supply means;

a parallelized light flux element comprising;

a light incident region positioned in the vicinity of the light supply means for receiving light from the light supply means;

a light output surface region for emitting as parallel light, light received at the light incident surface region;

a volume region having a uniform scattering power expressed by a correlation function γ

(r) approximated by exp (-r/a), where r is a distance between two points in said volume region and a is a correlation distance whose value lies in a range of 0.06 μ

m≦

a≦

35 μ

m, the volume region having an effective scattering illumination parameter E whose value lies in a range of 0.5 cm^-1 ≦

50 cm^-1, the volume region having, at least in a part thereof, a thickness extending inward from the light output surface region to an opposing side, which decreases with increasing distance from the light incident surface region;

a two sided prism reflection element extending in a reflection plane which is at an angle to the light output surface region of the parallelized light flux element such that the parallelized light flux element does not cross the reflection plane, the reflection element having a reflection surface having surface portions which are angled with respect to one another, in a repeated tilt configuration such that the surface portions define a plurality of sets of parallel planes, the reflection element receiving the parallel light from the light output surface region at a first angle to the reflection plane and emitting parallel light at a second angle, different from the first angle, to the reflection plane; and

a light diffusion plate in an optical path of light emitted from the two sided prism reflection element.

17. A liquid crystal display comprising:

a light supply means;

a parallelized light flux element comprising;

a light incident surface region positioned in the vicinity of the light supply means for receiving light from the light supply means;

a light output surface region for emitting as parallel light, light received at the light incident surface region;

a volume region having a uniform scattering power expressed by a correlation function γ

(r) approximated by exp (-r/a), where r is a distance between two points in said volume region and a is a correlation distance whose value lies in a range of 0.06 μ

m≦

a≦

35 μ

m, the volume region having an effective scattering illumination parameter E whose value lies in a range of 0.5 cm^-1 ≦

E≦

50 cm^-1, the volume region having, at least in a part thereof, a thickness extending inward from the light output surface region to an opposing side, which decreases with increasing distance from the light incident surface region;

a two sided prism reflection element extending in a reflection plane which is at an angle to the light output surface region of the parallelized light flux element such that the parallelized light flux element does not cross the reflection plane, the reflection element receiving the parallel light from the light output surface region at a first angle to the reflection plane and emitting parallel light at a second angle, different from the first angle, to the reflection plane; and

a liquid crystal device arranged in a position to receive light emitted from the light output surface region.

19. A liquid crystal display as claimed in claim 17, or 18, further comprising light emitting direction correcting means for correcting art emitting direction of the parallel light so that the parallel light is received at the two sided prism element at the first angle, the light emitting direction correcting means being disposed on the light output surface region of the parallelized light flux element.

20. A liquid crystal display as claimed in claim 17 or 18, further comprising reflecting prevention means for preventing a reflective appearance from the light supply means, formed in the volume region adjacent to the light incident surface region, on the side opposing the light output surface region.

18. A liquid crystal display comprising:

a light supply means;

a parallelized light flux element comprising;

a light incident region positioned in the vicinity of the light supply means for receiving light from the light supply means;

a light output surface region for emitting as parallel light, light received at the light incident surface region;

a volume region having a uniform scattering power expressed by a correlation function γ

(r) approximated by exp (-r/a), where r is a distance between two points in said volume region and a is a correlation distance whose value lies in a range of 0.06 μ

m≦

a≦

35 μ

m, the volume region having an effective scattering illumination parameter E whose value lies in a range of 0.5 cm^-1 ≦

E≦

50 cm^-1, the volume region having, at least in a part thereof, a thickness extending inward from the light output surface region to an opposing side, which decreases with increasing distance from the light incident surface region;

a two sided prism reflection element extending in a reflection plane which is at an angle to the light output surface region of the parallelized light flux element such that the parallelized light flux element does not cross the reflection plane, the reflection element having a reflection surface having surface portions which are angled with respect to one another, in a repeated tilt configuration such that the surface portions define a plurality of sets of parallel planes, the reflection element receiving the parallel light from the light output surface region at a first angle to the reflection plane and emitting parallel light a second angle, different from the first angle, to the reflection plane;

a light diffusion plate in an optical path of light emitted from the two sided prism reflection element; and

a liquid crystal device arranged in a position to receive light emitted from the two sided prism reflection element after the light passes through the light diffusion plate.