Backlight for liquid crystal display device

• US 6,454,452 B1
• Filed: 10/20/2000
• Issued: 09/24/2002
• Est. Priority Date: 04/22/1999
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Yuuki, Akimasa, Oda, Kyoichiro, Iwasaki, Naoko, Matsumoto, Sadayuki, Inoue, Mitsuo, Sasagawa, Tomohiro
• Primary Examiner(s): CARIASO, ALAN B
• Application Number:
  US09/692,200
• Time in Patent Office: 704 Days
• Field of Search: 349/62, 349/64, 349/65, 362/31, 362/330, 362/339, 362/332, 362/561, 362/224, 385/129, 385/132, 385/901
• US Class Current: 362/561
• CPC Class Codes: G02B 6/0031 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0036 2-D arrangement of prisms, protrusions, indentations or roughened surfaces
• CPC Class Codes: G02B 6/0061 to provide homogeneous light output intensity
• CPC Class Codes: G02F 1/133615 Edge-illuminating devices, i.e. illuminating from the side

Abstract

A backlight provides uniform emanating light for a liquid crystal display. In the backlight, light emitted from a light source is incident on a receiving end surface of a light guide plate and emanates through a top surface toward a liquid crystal panel. A bottom surface includes a reflecting hollow wedge extending along the receiving end surface and varying in depth, as measured from the bottom surface, in correspondence with distance from the end surface. A dividing flat portion orthogonal to the reflecting hollow wedge divides the reflecting hollowed portion, and an output surface includes a prism having parallel ridges extending in a direction orthogonal to the receiving end surface.

Claims

1. A backlight for a liquid crystal display device, comprising:

a rod-shaped light source supplying light for displaying information on a liquid crystal panel; and

a light guide plate having a receiving end surface parallel to and adjacent said rod-shaped light source, receiving light from said rod-shaped light source, an output surface located opposite and parallel to a liquid crystal panel, and a bottom surface facing and parallel to said output surface wherein said bottom surface includes a plurality of recesses, each recess having, in a cross-section transverse to said end surface, a triangular shape and including a reflecting surface facing and oblique to said receiving end surface, and a depth extending from said bottom surface into said light guide plate, the recesses being spaced apart and arranged in rows transverse to said receiving end surface, the rows of recesses being separated by planar strip portions of said bottom surface, wherein respective depths of the recesses in each row increase with increasing distance from said receiving end surface and respective widths of said planar strip portions decrease with increasing distance from said receiving end surface.

2. The backlight for a liquid crystal display device, as recited in claim 1, wherein said output surface includes a collecting prism comprising a plurality of aligned simple prisms joined together and having a plurality of parallel alternating valleys and ridges extending in a direction orthogonal to said receiving end surface.

3. The backlight for a liquid crystal display device, as recited in claim 1, wherein said planar strip portions between adjacent recesses have a minimum width of 10 μ

m.

4. The backlight for a liquid crystal display device, as recited in claim 1, wherein said adjacent pairs of the recesses in each row are separated by a part of said bottom surface at least 10 μ

m wide.

5. The backlight for a liquid crystal display device, as recited in claim 4, wherein the portions of said bottom surface separating each adjacent pair of the recesses in each row are not coplanar with said planar strip portions of said bottom surface between the rows of the recesses and are closer to said output surface than are said planar strip portions of said bottom surface.

6. The backlight for a liquid crystal display device, as recited in claim 1, wherein said reflecting surfaces facing and oblique to said receiving end surface form an angle between 40°

and 50°

with respect to said bottom surface.

7. The backlight for a liquid crystal display device, as recited in claim 2, wherein the ridges of each of said simple prisms have an apex angle of at least 100°

.

8. The backlight for a liquid crystal display device, as recited in claim 1, wherein said output surface includes a collecting prism comprising a plurality of simple prisms of different sizes joined together and having a plurality of valleys and ridges at non-uniform distances from said bottom surface and extending in a direction transverse to said receiving end surface.

9. The backlight for a liquid crystal display device, as recited in claim 1, wherein said planar strip portions are sinuous.

10. The backlight for a liquid crystal display device, as recited in claim 1, wherein groups of said reflecting surfaces facing and oblique to said receiving end surface form respective angles with said bottom surface that periodically vary with distance from said receiving end surface.

11. The backlight for a liquid crystal display device, as recited in claim 1, wherein said reflecting surfaces facing and oblique to said receiving end surface are cylindrical surfaces concave with respect to said receiving end surface.

12. The backlight for a liquid crystal display device, as recited in claim 1, further comprising a scattering plate located adjacent to said output surface for scattering a component of light traveling in a direction parallel to said receiving end surface.

13. The backlight for a liquid crystal display device, as recited in claim 1, further comprising a scattering plate located adjacent to said output surface for scattering a component of light traveling in a direction in a direction orthogonal to said receiving end surface.

14. The backlight for a liquid crystal display device, as recited in claim 1, further comprising a collecting prism comprising a plurality of adjacent simple prism joined together side-by-side and located between said light source and said receiving end surface.

15. The backlight for a liquid crystal display device, as recited in claim 1, wherein said light guide plate includes two portions divided along a direction perpendicular to said receiving end surface, said two portions being coupled together.