Backlight unit and display apparatus having the same

Abstract

A backlight unit includes a planar light source member that has a light-emitting surface and that emits light having directivity in a perpendicular direction to the light-emitting surface. An optical member has a light-receiving surface opposed to the light-emitting surface of the planar light source member and a light-emitting surface opposite to the light-receiving surface. The light-receiving surface has a multiplicity of prisms. By the prism action, the optical member emits the light having directivity in the perpendicular direction from the planar light source member as light having directivity in at least two directions on opposite sides of the perpendicular direction. The directions of light directivity are changed by varying the apex angle of the prisms.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a display device having a backlight unit according to an embodiment of the present invention.

FIG. 2 a is a sectional view schematically showing an optical member in FIG. 1.

FIG. 2 b is an enlarged view of part 2b in FIG. 2a.

FIG. 3 is a plan view showing the relationship between directions in which light is directed and the orientation of the optical member.

FIG. 4 is a graph showing the results of simulating directional characteristics for various prism apex angles.

FIG. 5 is a perspective view explaining the angle in FIG. 4.

FIG. 6 is a perspective view schematically representing the directional characteristics shown in FIG. 4.

FIG. 7 is a graph showing the results of measuring directional characteristics for various prism apex angles.

FIG. 8 is a perspective view explaining directivity of illuminating light exiting a display device.

FIG. 9 is a plan view of a display apparatus having a backlight unit according to an embodiment of the present invention.

FIG. 10 is a sectional view of an essential part of the display apparatus shown in FIG. 9.

FIG. 11 is an enlarged view of part XI in FIG. 10.

FIG. 12 is a schematic layout showing the positional relationship between a lightguide plate and a light source in FIG. 10.

FIG. 13 is a perspective view schematically showing directional characteristics obtained from trapezoidal prisms of an optical member shown in FIG. 10.

FIG. 14 is a perspective view of an optical member in a modification of the embodiment of the present invention.

FIG. 15 is a fragmentary sectional view schematically showing an essential part of the optical member shown in FIG. 14.

FIG. 16 is a sectional view of an essential part of a display apparatus having a backlight unit according to another embodiment of the present invention.

FIG. 17 is a sectional view of an essential part of a display apparatus having a backlight unit according to a further embodiment of the present invention.

FIG. 18 is a sectional view of an essential part of a conventional liquid crystal display apparatus.

FIG. 19 is a sectional view schematically showing a liquid crystal display apparatus disclosed in Japanese Patent Application Publication No. 2004-172003.

FIG. 20 is an enlarged perspective view of a light-directivity adjusting sheet in FIG. 19.

FIG. 21 is an explanatory view schematically showing how the way in which a display on a liquid crystal display panel is seen changes according to the position from which the display panel is viewed.

Claims

1. A backlight unit comprising: a planar light source member having a light-emitting surface, the planar light source member being adapted to emit light having directivity in a perpendicular direction to said light-emitting surface; andan optical member having a light-receiving surface opposed to said light-emitting surface and a light-emitting surface opposite to said light-receiving surface, said optical member being adapted to emit the light having directivity in said perpendicular direction as light having directivity in at least two directions on opposite sides of said perpendicular direction.

2. A backlight unit according to claim 1, wherein said light-receiving surface and light-emitting surface of said optical member are parallel to said light-emitting surface of said planar light source member, said light-receiving surface having a multiplicity of prisms extending parallel to each other and perpendicular to said perpendicular direction, so that light having directivity in said perpendicular direction that is incident on said light-receiving surface is converted by said prisms into light having directivity in at least said two directions.

3. A backlight unit according to claim 2, wherein said prisms have a triangular sectional configuration projecting toward the light-emitting surface of said planar light source member and extend in a direction perpendicular to said perpendicular direction.

4. A backlight unit according to claim 3, wherein said prisms are spaced from each other with a flat surface between each pair of adjacent ones of said prisms, said flat surface extending parallel to said prisms.

5. A backlight unit according to claim 3, wherein an apex angle of said triangular sectional configuration that faces the light-emitting surface of said planar light source member ranges from 60° to 115°.

6. A backlight unit according to claim 5, wherein said triangular sectional configuration of said prisms is an isosceles triangle.

7. A backlight unit according to claim 2, wherein said prisms have a trapezoidal sectional configuration projecting toward the light-emitting surface of said planar light source member and extend in a direction perpendicular to said perpendicular direction, each of said prisms having a plane surface at a center thereof and inclined surfaces on opposite sides of said plane surface.

8. A backlight unit according to claim 7, wherein an angle made by said inclined surfaces of each of said prisms ranges from 60° to 115°.

9. A backlight unit according to claim 8, wherein said inclined surfaces intersect said plane surface at a same angle.

10. A display apparatus comprising: the backlight unit of claim 1; anda display panel having a light-receiving surface opposed to said light-emitting surface of said optical member of said backlight unit and a light-emitting surface opposite to said light-receiving surface thereof.

11. A display apparatus according to claim 10, wherein said light-receiving surface and light-emitting surface of said optical member are opposed to said light-emitting surface of said planar light source member, said light-receiving surface having a multiplicity of prisms extending parallel to each other and perpendicular to said perpendicular direction, so that light having directivity in said perpendicular direction that is incident on said light-receiving surface is converted by said prisms into light having directivity in at least said two directions.

12. A display apparatus according to claim 11, wherein said prisms have a triangular sectional configuration projecting toward the light-emitting surface of said planar light source member and extend in a direction perpendicular to said perpendicular direction.

13. A display apparatus according to claim 12, wherein said prisms are spaced from each other with a flat surface between each pair of adjacent ones of said prisms, said flat surface extending parallel to said prisms.

14. A display apparatus according to claim 12, wherein an apex angle of said triangular sectional configuration that faces the light-emitting surface of said planar light source member ranges from 60° to 115°.

15. A display apparatus according to claim 13, wherein said triangular sectional configuration of said prisms is an isosceles triangle.

16. A display apparatus according to claim 11, wherein said prisms have a trapezoidal sectional configuration projecting toward the light-emitting surface of said planar light source member and extend in a direction perpendicular to said perpendicular direction, each of said prisms having a plane surface at a center thereof and inclined surfaces on opposite sides of said plane surface.

17. A display apparatus according to claim 16, wherein an angle formed by said inclined surfaces of each of said prisms ranges from 60° to 115°.

18. A display apparatus according to claim 17, wherein said inclined surfaces intersect said plane surface at a same angle.