Back light device of liquid crystal device

• US 5,673,128 A
• Filed: 12/28/1995
• Issued: 09/30/1997
• Est. Priority Date: 01/31/1995
• 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: Ohta, Youko, Terasaki, Hirohide
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): NGO, HUYEN LE
• Application Number:
  US08/580,302
• Time in Patent Office: 642 Days
• Field of Search: 359/48, 359/49, 359/50, 359/70, 362/27, 362/31, 362/32, 385/33, 385/129, 385/901, 385/146, 349/61, 349/62, 349/67, 349/70, 349/65
• US Class Current: 349/62
• CPC Class Codes: G02B 6/0018 Redirecting means on the surface of the light guide
• CPC Class Codes: G02B 6/0041 provided in the bulk of the light guide
• CPC Class Codes: G02B 6/0043 provided on the surface of the light guide
• CPC Class Codes: G02B 6/0046 Tapered light guide, e.g. wedge-shaped light guide
• CPC Class Codes: G02B 6/0061 to provide homogeneous light output intensity

Abstract

A back light device of a liquid crystal display device includes fluorescent tubes on both ends of a light guiding plate. When viewed from a section which is perpendicular to the fluorescent tubes, shapes or internal constitution of the light guiding plate are asymmetrical in order to prevent irregularity of the luminance of a display area of a liquid crystal display panel caused by, e.g., a different in optical characteristics between the fluorescent tubes, a difference between positioning of each fluorescent tubes and the light guiding plate. In other words, a border of the shapes or of the internal constitution of the light guiding plate is set in a position that is nearer to the section where a quantity of incident light is relatively small according to a ratio of the quantities of incident lights on each section obtained by cutting a face that intersect a circumferential end of the display area on the light guiding plate at right angels. As a result, the display area on the liquid crystal display panel is prevented from becoming dark on the section side where a quantity of incident light is smaller.

Claims

1. A back light device of a liquid crystal display device, comprising:

light sources; and

a light guiding body made of a light transmitting material for transmitting light emitted from said light sources so that the light is emitted towards a liquid crystal display panel,

wherein said light guiding body includes a first section where a quantity of incident light is larger and a second section where a quantity of incident light is smaller,

wherein said light guiding body includes a first optical portion for guiding a light from said first section to a central portion of said light guiding body and for emitting a light to the liquid crystal display panel and a second optical section for transmitting a light from the second section to the central portion of said light guiding body and for emitting a light to the liquid crystal display panel,

wherein a border between said first and second optical sections is set nearer to the second section according to a ratio of the quantities of incident light on each section such that a difference in luminance between the first and second optical sections are eliminated.

2. The back light device of liquid crystal display device as defined in claim 1, further comprising reflecting means for reflecting light from said light sources so as to collect the light on each section.

3. The back light device of a liquid crystal display device as defined in claim 1, wherein:

at least one of said light sources is provided behind the back face of said light guiding body,

said light guiding body includes an extended portion for guiding the lights from said at least one of the linear light sources to at least one of the sections, said extended portion is extended to the vicinity of said at least one of the light sources provided behind the back face.

4. The back light device of a liquid crystal display device as defined in claim 3, further comprising reflecting means for covering the back side of the light source of the light guiding body and an outside of the extended portion of the light guiding body.

5. The back light device of a liquid crystal display device as defined in claim 1, wherein said light guiding body is formed such that its thickness becomes smallest on the border between the first and second optical portions.

6. The back light device of a liquid crystal display device as defined in claim 1, wherein said light guiding body includes a reflecting face and a light emitting face, said reflecting face having a plane surface, said light emitting face having an inclination so as to come closest to the reflecting face on the border between the first and second optical portions.

7. The back light device of a liquid crystal display device as defined in claim 1, wherein said light guiding body includes a light emitting face and a reflecting face, said light emitting face having a plane surface, said reflecting face having an inclination so as to come closest to said light emitting face on the border between the first and second optical portions.

8. The back light device of a liquid crystal display device as defined in claim 1, wherein:

said light guiding body includes a reflecting face having scattering/reflecting portions for scattering and reflecting a light,

said scattering/reflecting portions are formed such that their area becomes largest in the vicinity of the border between the first and second optical portions and that their areas become gradually smaller as they get closer to each section from the vicinity of the border.

9. The back light device of a liquid crystal display device as defined in claim 1, wherein:

said light guiding body includes transmitting portions and reflecting portions on a light emitting face, said transmitting portions for transmitting a light and said reflecting portions for reflecting a light toward a reflecting face,

said transmitting portions are formed such that their area becomes largest in the vicinity of the border between the first and second optical portions and that their areas become gradually smaller as the transmitting portions get closer to each section from the vicinity of the border.

10. The back light device of a liquid crystal display device as defined in claim 1, further comprising grains for scattering a light in said light guiding body,

wherein said grains for scattering a light are arranged such that their density becomes highest in the vicinity of the border of the first and second optical portions and that their density becomes gradually smaller as the grains get closer to each section from the vicinity of the border.

11. The back light device of a liquid crystal display device as defined in claim 1, further comprising a reflecting member for returning a emitted light through said light guiding body into said light guiding body on the outside of a reflecting face of said light guiding body.

12. A back light device of a liquid crystal display device, comprising:

light sources; and

a light guiding body made of a light transmitting material for guiding a light emitted from said light source so that the light is emitted towards a liquid crystal display panel,

wherein at least one of said light sources is positioned just under a display area of a liquid crystal panel so as to be laid behind the back face of said light guiding body,

wherein said light guiding body includes sections that intersect a circumferential end of the display area of the liquid crystal panel in the vicinity of the light sources and end faces where light from the light sources enters, either of said section and said face in the vicinity of each light source that is closer to the central portion of the display area being incident end face, one of said incident end face in the vicinity of the light sources where a quantity of incident light is larger being a first incident end face, the other incident end face where a quantity of incident light is smaller being a second incident end face,

wherein said light guiding body includes a first optical portion for guiding an incident light from the first incident end face to the vicinity of the center so as to emit the light to the liquid crystal display panel and a second optical portion for guiding an incident light from the second incident end face to the vicinity of the portion so as to emit the light to the liquid crystal display panel,

wherein a border between said first and second optical portions is set nearer to the second incident end face according to a ratio of the quantities of incident lights on each incident end face such that a difference in luminance between the first and second optical sections are eliminated.

13. The back light device of a liquid crystal display device as defined in claim 12, further comprising a light shielding member for decreasing the luminance intensity from the light source, that is transmitted through said light guiding body substantially parallel to a normal line of the liquid crystal display panel, said light shielding member being positioned between the a face of a light source laying behind the back face of an extended portion of said light guiding body and the liquid crystal display panel.

14. The back light device of a liquid crystal display device as defined in claim 12, further comprising reflecting means for reflecting the lights from said light sources so as to make the lights enter said light guiding body.

15. The back light device of a liquid crystal display device as defined in claim 12, wherein said light guiding body is formed such that its thickness becomes smallest on the border between the first and second optical portions.

16. The back light device of a liquid crystal display device as defined in claim 12, wherein said light guiding body includes a reflecting face and a light emitting face, said reflecting face having a plane surface, said light emitting face having an inclination so as to come closest to the reflecting face on the border between the first and second optical portions.

17. The back light device of a liquid crystal display device as defined in claim 12, wherein said light guiding body includes a light emitting face and a reflecting face, said light emitting face having a plane surface, said reflecting face having an inclination so as to come closest to said light emitting face on the border between the first and second optical sections.

18. The back light device of a liquid crystal display device as defined in claim 12, wherein:

said light guiding body includes a reflecting face having a scattering/reflecting portion for scattering and reflecting a light,

said scattering/reflecting portions are formed such that their area becomes largest in the vicinity of the border between the first and second optical portions and that their areas become gradually smaller as they get closer to each section from the vicinity of the border.

19. The back light device of a liquid crystal display device as defined in claim 12, wherein:

said light guiding body includes transmitting portions and reflecting portions on a light emitting face, said transmitting portions for transmitting a light and said reflecting portions for reflecting a light toward a reflecting face,

said transmitting portions are formed such that their area becomes largest in the vicinity of the border between the first and second optical portions and that their areas becomes gradually smaller as the transmitting portions get closer to each section from the vicinity of the border.

20. The back light device of a liquid crystal display device as defined in claim 12, further comprising grains for scattering a light in said light guiding body,

wherein said grains for scattering a light are arranged such that their density becomes highest in the vicinity of the border of the first and second optical portions and that their density becomes gradually smaller as the grains get closer to each section from the vicinity of the border.

21. The back light device of a liquid crystal display device as defined in claim 12, further comprising a reflecting member for returning a emitted light through said light guiding body into said light guiding body on the outside of a reflecting face of said light guiding body.

22. A method of back lighting a liquid crystal display device, comprising the steps of:

transmitting light emitted from light sources along a light guiding body towards a liquid crystal display panel, the light guiding body including a first section and a second section receiving different quantities of incident light from the light sources;

guiding light, via a first optical section, from the first section to a central portion of said light guiding body and emitting light to the liquid crystal display panel;

guiding light, via a second optical section, from the second section to the central portion of the light guiding body and emitting light to the liquid crystal display panel; and

setting a border between said first and second optical sections according to a ratio of the quantities of incident light on each section such that a difference in luminance between the first and second optical sections are eliminated.