Liquid crystal display device with edge lit lightguide reflecting light to back reflector by total internal reflection

• US 5,341,231 A
• Filed: 12/03/1992
• Issued: 08/23/1994
• Est. Priority Date: 12/03/1991
• Status: Expired due to Term

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Ishii, Yutaka, Yamamoto, Yoshitaka
• Primary Examiner(s): Gross, Anita P.
• Application Number:
  US07/984,937
• Time in Patent Office: 628 Days
• Field of Search: 359/49, 359/69, 359/50, 362/31, 362/326, 362/328, 362/330
• US Class Current: 349/63
• CPC Class Codes: G02B 6/003 Lens or lenticular sheet or layer
• CPC Class Codes: G02F 1/133615 Edge-illuminating devices, i.e. illuminating from the side
• CPC Class Codes: G02F 1/133616 Front illuminating devices
• CPC Class Codes: G09F 2013/1822 Stair-cased profiled window
• CPC Class Codes: G09F 2013/1827 Prismatic window
• CPC Class Codes: G09F 2013/1831 using more than one light source

Abstract

A reflective type liquid crystal display device excelling in uniformity and capable of making a bright display is presented. At the front side of the liquid crystal display element, that is, at the observer side, a light guide plate is disposed, and a pair of lamps are disposed at the outer side of the confronting side surfaces of the light guide plate. Collimators for limiting the incident angle θ to the upper surface of the light from the lamps are disposed between the light guide plate and lamps. That is, by the collimators, the incident angle θ to the upper surface is defined so that the incident light may be totally reflected, and that the reflected light may not be totally reflected by the lower surface 61b. As a result, the light from the lamps will not reach the observer directly, and a uniform illumination of the liquid crystal display element may be realized. Besides, at the observer side of the liquid crystal display element, a light guide plate forming protrusions is disposed, and a pair of lamps are disposed at the outer side of the confronting side surfaces of the light guide plate. Furthermore, between the light guide plate and lamps, collimators for limiting the incident angle θ of the light from the lamps into the upper surface are disposed. Accordingly, the light from the lamps does not reach the observer directly, and the light entering the protrusions formed on the light guide plate is emitted to the liquid crystal display element side. Thus, a uniform illumination into the liquid crystal display element is realized.

Claims

1. A liquid crystal display device comprising:

a liquid crystal display element composed of a transparent substrate, a counter substrate disposed oppositely to the transparent substrate and possessing reflecting means for reflecting the incident light entering from the transparent substrate side, and a liquid crystal layer interposed therebetween,

a light guide plate disposed at the transparent substrate side of the liquid crystal display element,

a light source disposed at the edge of the light guide plate, and

a collimator disposed between the light guide plate and the light source for controlling the light from the light source,

wherein the condition of

space="preserve" listing-type="equation">n1<

n·

sin θ

<

n2 (1)

is satisfied supposing the refractive index of the light guide plate is n, the refractive index of a substance positioned at the side of the light guide plate opposite the liquid crystal display element is n1, the refractive index of a substance positioned at the liquid crystal display element side of the light guide plate is n2, and the incident angle of the light source light transmitted through the collimator to the side of the light guide plate opposite the liquid crystal display element is θ

.

3. A liquid crystal display device as claimed in claim 1 or 2, wherein the reflecting means has its reflection surface formed in a smooth undulated surface, and is disposed on the surface of the counter substrate opposite the liquid crystal layer.

4. A liquid crystal display device as claimed in claim 1 or 2, wherein the reflecting means has its reflection surface formed in a smooth undulated surface, and is disposed on the surface of the counter substrate on the side of the liquid crystal layer.

5. A liquid crystal display device as claimed in claim 1 or 2, wherein one polarizer is disposed at the viewer side of the light guide plate.

6. A liquid crystal display device as claimed in claim 5, wherein an air layer with a refractive index n1 (satisfying n1<

n·

sin θ

) is interposed between the polarizer and light guide plate.

7. A liquid crystal display device as claimed in claim 5, wherein the surface of the viewer side of the light guide plate is coated with a material with a refractive index n1 (satisfying n1<

n·

sin θ

), and the polarizer is directly disposed on its surface.

8. A liquid crystal display device as claimed in claim 5, wherein the polarizer is made of a material with a refractive index n1 (satisfying n1<

n·

sin θ

) and is directly disposed on the light guide plate.

9. A liquid crystal display device as claimed in claim 1 or 2, wherein two polarizers are disposed, one polarizer at the viewer side of the light guide plate, and the other between the reflecting means located outside the counter substrate and the counter substrate.

10. A liquid crystal display device as claimed in claim 9, wherein an air layer with a refractive index n1 (satisfying n1<

n·

sin θ

) is interposed between the one polarizer and the light guide plate.

11. A liquid crystal display device as claimed in claim 9, wherein the surface of the viewer side of the light guide plate is coated with a material with a refractive index n1 (satisfying n1<

n·

sin θ

), and the one polarizer is directly disposed on its surface.

12. A liquid crystal display device as claimed in claim 9, wherein the one polarizer is made of a material with a refractive index n1 (satisfying n1<

n·

sin θ

) and is directly disposed on the light guide plate.

13. A liquid crystal display device as claimed in claim 1 or 2, wherein a diffusion plate is disposed at the viewer side of the reflecting means.

14. A liquid crystal display device as claimed in claim 1 or 2, wherein a reflector for preventing light leak from the light guide plate is disposed at the edge of the light guide plate not provided with the light source.

15. A liquid crystal display device as claimed in claim 1 or 2, wherein the light source is lit when the surrounding light alone provides an insufficient quantity of light.

29. A liquid crystal display device as claimed in claim 1, wherein the liquid crystal display element side surface of the light guide plate is coated with a film made of a light transmitting material with a refractive index which is lower than that of the light guide plate, and the film thickness of the coating film is decreased, either continuously or in steps, in inverse proportion to the distance from the light source.

2. A liquid crystal display device comprising:

a liquid crystal display element composed of a transparent substrate, a counter substrate disposed oppositely to the transparent substrate and possessing reflecting means for reflecting the incident light entering from the transparent substrate side, and a liquid crystal layer interposed therebetween,

a light guide plate disposed at the transparent substrate side of the liquid crystal display element, and

a light source disposed at the edge of the light guide plate, wherein

plural protrusions are formed on the surface of the light guide plate at the liquid crystal display element side, and the condition of

space="preserve" listing-type="equation">n1<

n·

sin θ

(2)

is satisfied, supposing the refractive index of the light guide plate is n, the refractive index of a substance positioned at the side of the light guide plate opposite the liquid crystal display element is n1, and the incident angle of the light source light to the side of the light guide plate opposite the liquid crystal display element is θ

.

16. A liquid crystal display device as claimed in claim 2, wherein the protrusions are in a conical form.

17. A liquid crystal display device as claimed in claim 2, wherein the protrusions are in a pyramidal form.

18. A liquid crystal display device as claimed in claim 2, wherein the protrusions are in a truncated conical form.

19. A liquid crystal display device as claimed in claim 2, wherein the protrusions are in a truncated pyramidal form.

20. A liquid crystal display device as claimed in claim 2, wherein the sectional shape of the protrusions is nearly semicircular.

21. A liquid crystal display device as claimed in claim 2, wherein the sectional shape of the protrusions is ellipsoidal.

22. A liquid crystal display device as claimed in claim 2, wherein the sectional shape of the protrusions is parabolic.

23. A liquid crystal display device as claimed in claim 2, wherein the sectional shape of the protrusions is arcuate.

24. A liquid crystal display device as claimed in claim 2, wherein the protrusions are identical in shape but differ in size.

25. A liquid crystal display device as claimed in claim 2, wherein the protrusions have plural different shapes.

26. A liquid crystal display device as claimed in claim 2, wherein the array density of the protrusions increases continuously or in steps, in proportion to the distance from the light source.

27. A liquid crystal display device as claimed in claim 2, wherein the size of the protrusions increases, either continuously or in steps, in proportion to the distance from the light source.

28. A liquid crystal display device as claimed in claim 2, wherein the protrusions are disposed in regions other than the pixels of the liquid crystal display element.