Illuminating device, display device having the same, and light guide plate

• US 20020172031A1
• Filed: 04/24/2002
• Published: 11/21/2002
• Est. Priority Date: 04/24/2001
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Masuda, Takeshi
• Granted Patent: US 6,796,669 B2
• Time in Patent Office: Days
• US Class Current: 362/31
• CPC Class Codes: G02B 6/0026 Wavelength selective element, sheet or layer, e.g. filter or grating
• CPC Class Codes: G02B 6/0035 provided on the surface of the light guide or in the bulk of it
• CPC Class Codes: G02B 6/0046 Tapered light guide, e.g. wedge-shaped light guide
• CPC Class Codes: G02B 6/005 provided by one optical element, or plurality thereof, placed on the light output side of the light guide
• CPC Class Codes: G02B 6/0061 to provide homogeneous light output intensity

Abstract

The illuminating device includes a light source and a light guide plate. The light guide plate has a first side surface receiving light emitted from the light source, a second side surface facing the first side surface, a third side surface, a fourth side surface, an emitting surface and an opposing surface. The third and fourth side surfaces are located between the first and second side surfaces so as to face each other, and the emitting surface and the opposing surface face each other. The light guide plate is formed from a first light guide layer and a second light guide layer. The first light guide layer has a plurality of reflecting films therein for reflecting light entering the light guide plate through the first side surface toward the emitting surface. The second light guide layer has no reflecting film.

Claims

1. An illuminating device, comprising:

a light source; and

a light guide plate having a first side surface receiving light emitted from the light source, a second side surface facing the first side surface, a third side surface, a fourth side surface, an emitting surface and an opposing surface, the third and fourth side surfaces being located between the first and second side surfaces so as to face each other, and the emitting surface and the opposing surface facing each other with the first, second, third and fourth side surfaces interposed therebetween, wherein

the light guide plate is formed from a first light guide layer and a second light guide layer each having a prescribed thickness in a direction normal to the emitting surface,

the first light guide layer has a plurality of reflecting films therein for reflecting light entering the light guide plate through the first side surface toward the emitting surface, and

the second light guide layer has no reflecting film.

2. The illuminating device according to claim 1, wherein an angle α

between a tangent line of the reflecting film and the emitting surface and a critical angle θ

of the light guide plate satisfy the following relation;

45°

−

θ

/2<

α

<

45°

+θ

/2.

3. The illuminating device according to claim 1, wherein an angle α

between a tangent line of the reflecting film and the emitting surface and a critical angle θ

of the light guide plate satisfy the following relation;

θ

<

α

<

45°

+θ

/2.

4. The illuminating device according to claim 1, wherein a light transmittance of the light guide plate is at least 85%.

5. The illuminating device according to claim 1, wherein a sum Σ

Δ

s of respective areas Δ

s of the reflecting films projected on the emitting surface, a reflectance r of the reflecting film, and an area S of the emitting surface of the light guide plate satisfy the following relation;

0<

(Σ

Δ

s/S)·

r≦

0.08.

6. The illuminating device according to claim 1, wherein the reflecting films have a line shape when viewed from the direction normal to the emitting surface.

7. The illuminating device according to claim 1, wherein the reflecting films have an island shape when viewed from the direction normal to the emitting surface.

8. The illuminating device according to claim 1, wherein the reflecting films are transparent dielectric films or dielectric multi-layer films.

9. The illuminating device according to claim 8, wherein provided that a principal ray of the light entering the light guide plate through the first side surface is incident on the dielectric films or the dielectric multi-layer films at an incident angle β

, a refraction angle γ

of the principal ray in the dielectric film or the dielectric multi-layer film, a thickness d of the dielectric film or the dielectric multi-layer film, a refractive index n of the dielectric film or the dielectric multi-layer film, and a refractive index no of the first light guide layer satisfy the following relation;

380 /(4n·

cos γ

)≦

d≦

780/(4n·

cos γ

),and n₀·

sin β

=n·

sin γ

.

10. The illuminating device according to claim 1, wherein

the light guide plate is a lamination of a first light guide element and a second light guide element with an adhesive layer interposed therebetween, the first light guide element, the adhesive layer and the second light guide element being laminated in the direction normal to the emitting surface,

a surface of the first light guide element which faces the adhesive layer has a plurality of tilted regions that are tilted with respect to the emitting surface, and

the reflecting films are formed on the tilted regions of the surface.

11. The illuminating device according to claim 10, wherein the surface of the first light guide element which faces the adhesive layer further has a plurality of vertical regions that extend approximately perpendicularly to the emitting surface, and the tilted regions and the vertical regions are alternately arranged in a prescribed direction.

12. The illuminating device according to claim 11, wherein a width A of the tilted region of the surface in the prescribed direction and a width a of the reflecting film in the prescribed direction satisfy the following relation:

0<

a≦

A.

13. The illuminating device according to claim 11, wherein the reflecting films are formed over a whole surface of the tilted regions of the surface.

14. The illuminating device according to claim 10, wherein the surface of the first light guide element which faces the adhesive layer further has a plurality of vertical regions that extend approximately perpendicularly to the emitting surface and a plurality of parallel regions that extend approximately in parallel with the emitting surface.

15. The illuminating device according to claim 14, wherein the surface of the first light guide element which faces the adhesive layer is located near the emitting surface of the light guide plate, and the parallel regions are located closer to the emitting surface than are the tilted regions.

16. The illuminating device according to claim 14, wherein the surface of the first light guide element which faces the adhesive layer is located near the opposing surface of the light guide plate, and the parallel regions are located closer to the opposing surface than are the tilted regions.

17. The illuminating device according to claim 10, wherein the first light guide element and the adhesive layer have approximately the same refractive index.

18. The illuminating device according to claim 1, wherein

the light guide plate is a lamination of a first light guide element and a second light guide element, the first light guide element and the second light guide element being laminated in the direction normal to the emitting surface,

a surface of the first light guide element which faces the second light guide element has a plurality of tilted regions that are tilted with respect to the emitting surface, and

the reflecting films are formed on the tilted regions of the surface.

19. The illuminating device according to claim 10, wherein the second light guide element is located on a viewer side of the first light guide element and functions also as a transparent input device.

20. A display device, comprising:

an illuminating device including

a light source, and

a light guide plate having a first side surface receiving light emitted from the light source, a second side surface facing the first side surface, a third side surface, a fourth side surface, an emitting surface and an opposing surface, the third and fourth side surfaces being located between the first and second side surfaces so as to face each other, and the emitting surface and the opposing surface facing each other with the first, second, third and fourth side surfaces interposed therebetween, wherein

the light guide plate is formed from a first light guide layer and a second light guide layer each having a prescribed thickness in a direction normal to the emitting surface,

the first light guide layer has a plurality of reflecting films therein for reflecting light entering the light guide plate through the first side surface toward the emitting surface, and

the second light guide layer has no reflecting film,

the display device further comprising;

a reflection-type display panel facing the light guide plate of the illuminating device on a side opposite to a viewer.

21. A light guide plate having a first side surface receiving light emitted from a light source, a second side surface facing the first side surface, a third side surface, a fourth side surface, an emitting surface and an opposing surface, the third and fourth side surfaces being located between the first and second side surfaces so as to face each other, and the emitting surface and the opposing surface facing each other with the first, second, third and fourth side surfaces interposed therebetween, wherein

the light guide plate is formed from a first light guide layer and a second light guide layer each having a prescribed thickness in a direction normal to the emitting surface,

the first light guide layer has a plurality of reflecting films therein for reflecting light entering the light guide plate through the first side surface toward the emitting surface, and

the second light guide layer has no reflecting film.