Backlight unit and liquid-crystal display device using the same

1. A backlight unit comprising:

a light source;

optical members each having a sheet- or plate-like shape; and

a frame-shaped casing for holding the optical members, the optical members being stacked and assembled in the casing;

wherein each of the optical members has a protruding part that protrudes along its plane, the protruding part including at least one protrusion; and

a count of the protrusions of each of the optical members being increased according to a predetermined assembly order in the casing;

and wherein the casing has a depressed part for receiving the protruding parts of the optical members; the depressed part including notches or depressions corresponding to the protrusions of the optical members;

each of the notches or depressions having a depth in a stacking direction that varies according to stacking state of the optical members.

2. The unit according to claim 1 , wherein the optical member to be assembled in a second order or later comprises the protrusion formed at a same position as that of the optical member to be stacked in a preceding order, the protrusion of the member in the second order or later being the same in size and shape as the member to be stacked in the preceding order;

and wherein the depth of each of the notches or depressions is defined according to a total thickness of the stacked optical members having the protrusions at the same position.

3. The unit according to claim 1 , wherein the notches or depressions are formed to penetrate through the casing from inside of the casing to outside thereof.

4. The unit according to claim 3 , wherein the protrusions are formed to stick out of the casing through the corresponding notches when the optical members are assembled in the casing;

and wherein the protrusions are visually recognizable from outside of the casing after assembling operation of the backlight unit is completed.

5. The unit according to claim 1 , wherein the at least one protrusion of each of the optical members is located on at least one edge of the member at a position excluding symmetrical positions on the edge.

6. A backlight unit comprising:

a light source;

optical members each having a sheet- or plate-like shape; and

a frame-shaped casing for holding the optical members, the optical members being stacked and assembled in the casing;

wherein each of the optical members has a protruding part that protrudes along its plane, the protruding part including a protrusion; and

a width or shifted distance of the protrusion of each of the optical members being increased according to a predetermined assembly order in the casing;

and wherein the casing has a depressed part for receiving the protruding parts of the optical members; the depressed part including notches or depressions corresponding to the protrusions of the optical members;

each of the notches or depressions having a depth in a stacking direction that varies according to stacking state of the optical members.

7. The unit according to claim 6 , wherein the optical member to be assembled in a second order or later comprises the protrusion wider than that of the optical member to be stacked in a preceding order;

and wherein the depth of each of the notches or depressions is defined according to a total thickness of the stacked optical members.

8. The unit according to claim 6 , wherein the optical member to be assembled in a second order or later comprises the protrusion shifted at a greater distance than that of the optical member to be stacked in a preceding order;

and wherein the depth of each of the notches or depressions is defined according to a total thickness of the stacked optical members.

9. The unit according to claim 6 , wherein the notches or depressions are formed to penetrate through the casing from inside of the casing to outside thereof.

10. The unit according to claim 9 , wherein the protrusions are formed to stick out of the casing through the corresponding notches when the optical members are assembled in the casing;

and wherein the protrusions are visually recognizable from outside of the casing after assembling operation of the backlight unit is completed.

11. The unit according to claim 6 , wherein the at least one protrusion of each of the optical members is located on at least one edge of the member at a position excluding symmetrical positions on the edge.

12. A backlight unit comprising:

a light source;

optical members each having a sheet- or plate-like shape; and

a frame-shaped casing for holding the optical members, the optical members being stacked and assembled in the casing;

wherein each of the optical members has a depressed part that is depressed along its plane, the depressed part including at least one notch or depression; and

a count of the notches or depressions of each of the optical members being decreased according to a predetermined assembly order in the casing;

and wherein the casing has a protruding part to be fittingly engaged with the depressed parts of the optical members; the protruding part including protrusions corresponding to the notches of the optical members;

each of the protrusions having a height in a stacking direction that varies according to stacking state of the optical members.

13. The unit according to claim 12 , wherein the optical member to be assembled in a second order or later comprises the notch or depression formed at a same position as that of the optical member to be stacked in a preceding order, the notch or depression of the member in the second order or later being the same in size and shape as the member to be stacked in the preceding order;

and wherein the height of each of the protrusions is defined according to a total thickness of the stacked optical members having the protrusions at the same position.

14. The unit according to claim 12 , wherein the at least one notch or depression of each of the optical members is located on at least one edge of the member at a position excluding symmetrical positions on the edge.

15. A backlight unit comprising:

a light source;

optical members each having a sheet- or plate-like shape; and

a frame-shaped casing for holding the optical members, the optical members being stacked and assembled in the casing;

wherein each of the optical members has a depressed part that is depressed along its plane, the depressed part including a notch or depression; and

a width or shifted distance of the notch or depression of each of the optical members being decreased according to a predetermined assembly order in the casing;

and wherein the casing has a protruding part to be fittingly engaged with the depressed parts of the optical members; the protruding part including protrusions corresponding to the notches or depressions of the optical members;

each of the protrusions having a height in a stacking direction that varies according to stacking state of the optical members.

16. The unit according to claim 15 , wherein the optical member to be assembled in a second order or later comprises the notch or depression formed at a same position as that of the optical member to be stacked in a preceding order, the notch or depression of the member in the second order or later being the same in size and shape as the member to be stacked in the preceding order;

and wherein the height of each of the protrusions is defined according to a total thickness of the stacked optical members having the protrusions at the same position.

17. The unit according to claim 15 , wherein the at least one notch or depression of each of the optical members is located on at least one edge of the member at a position excluding symmetrical positions on the edge.

18. A liquid-crystal display device comprising:

a liquid-crystal display panel; and

the backlight unit according to one of the claims 1 , 6 , 12 , and 15 .

19. The device according to claim 18 , wherein the liquid-crystal display panel is held by the casing;

and wherein the optical members are fixed by the panel and the casing.