Backlight device

1. A backlight device comprising:

a light guide having a pair of main surfaces facing each other and a pair of edge surfaces facing each other, guiding the light from a light source arranged on one edge surface to both of main surfaces; and

a control device controlling said light source to illuminate a main lighting region having relatively large size on a side of one main surface through said light guide, and to illuminate a sub-lighting region having relatively small size on a side of another main surface through said light guide, wherein said control device comprises mode selection switch selecting either a mode of illuminating the main lighting region or a mode of illuminating the sub-lighting region; and a power switch switching a power supply to said light source according to the mode selected by said mode selection switch, and wherein said power switch supplies whole light source with electric power in the mode of illuminating the main lighting region, and supplies a part of the light source less than the whole light source with electric power in the mode of lighting the sub-lighting region.

2. The device as claimed in claim 1 , wherein said light source has a plurality of LEDs arranged in parallel along said one edge surface, said power switch supplies only some but not all of the plurality of LEDs having higher contribution to the illumination of the sub-lighting region with the electric power in the mode of illuminating the sub-lighting region.

3. The device as claimed in claim 2 , wherein said LEDs having higher contribution to the illumination are center-located LEDs of the plurality of LEDs arranged in parallel.

4. The device as claimed in claim 1 , wherein said light guide has a diffusion member and an isotropic prism member on both of the main surfaces respectively.

5. The device as claimed in claim 1 , wherein said light guide has a semitransparent reflective member on the main surface of the sub-lighting region side.

6. A liquid crystal display device having a backlight device as claimed in claim 1 .

7. A backlight device, comprising:

a light guide having a first and second light emitting surfaces facing each other and a plurality of edge surfaces between the first and second light emitting surfaces, wherein the first light emitting surface emits light in a first lighting region that illuminates a first display, and the second light emitting surface emits light in a second lighting region that illuminates a second display, and wherein the first lighting region overlaps the second lighting region with respect to the first and second light emitting surfaces of the light guide;

a light source positioned along one of said plurality of edge surfaces, wherein light from said light source is directed to the first lighting region and the second lighting region; and

a controller controlling different amount of light from the light source to be emitted into the light guide, wherein the amount depends on whether light is desired to be emitted through the light guide to illuminate the first display or the second display, wherein the light source comprises a plurality of light emitting devices arranged along said one of the plurality of edge surfaces of the light guide, wherein the controller is configured to switch on a first set of a first number of light emitting devices when light is desired to be emitted through the light guide to illuminate the first display, and a second set of a second number of light emitting devices when light is desired to be emitted through the light guide to illuminate the second display, and wherein the first number and the second number are different.

8. The device as claim 7 , wherein the first lighting region covers a first illumination area and the second lighting region covers a second illumination area, wherein the second illumination area is relatively smaller than the first illumination area.

9. The device as in claim 8 , wherein the second illumination area overlaps entirely within the second illumination area.

10. The device as in claim 9 , further comprising a semi-transparent reflective member on the second light emitting surface of the light guide, wherein the semi-transparent reflective member partially reflect back light emitted from the second light emitting surface and partially transmit light away from the second light emitting surface towards the second display.

11. The device as in claim 7 , wherein the amount of light from the light source is controlled to be relatively less when light is to be emitted through the light guide to illuminate the second display.

12. The device as in claim 7 , wherein the first number of light emitting devices in the first set is larger than the second number in the second set.

13. The device as in claim 7 , wherein the first set of light emitting devices contribute to light to be emitted through the light guide to illuminate the first display, and the second set of light emitting devices contribute to light to be emitted through the light guide to illuminate the second display.

14. The device as in claim 13 , wherein when the second set of light emitting devices are a subset within the first set of light emitting devices.

15. A display device, comprising:

a first display and a second display;

a light guide having a first and second light emitting surfaces facing each other and a plurality of edge surfaces between the first and second light emitting surfaces, wherein the first light emitting surface emits light in a first lighting region that illuminates the first display, and the second light emitting surface emits light in a second lighting region that illuminates the second display, and wherein the first lighting region overlaps the second lighting region with respect to the first and second light emitting surfaces of the light guide; and

a light source positioned along one of said plurality of edge surfaces, wherein light from said light source is directed to the first lighting region and the second lighting region; and

a controller different amount of light from the light source to be emitted into the light guide, wherein the amount depends on whether light is desired to be emitted through the light guide to illuminate the first display or the second display, wherein the light source comprises a plurality of light guide, wherein the controller is configured to switch on a first set of a first number of light emitting devices when light is desired to be emitted through the light guide to illuminate the first display, and a second set of a second number of light emitting devices when is desired to be emitted through the light guide to illuminate the second display, and wherein the first number and the second number are different.

16. The device as in claim 15 , wherein the first lighting region covers a first illumination area and the second lighting region covers a second illumination area, wherein the second illumination area is relatively smaller than the first illumination area.

17. The device as in claim 15 , wherein the amount of light from the light source is controlled to be relatively less when light is to be emitted through the light guide to illuminate the second display.