Plane light source and LCD backlight unit having the same

1. A plane light source having a plurality of light emitting devices arranged in a light emitting device matrix having rows and columns at a substrate, the plane light source comprising:

a first matrix having a plurality of light emitting devices arranged in rows and columns; and

a second matrix having a plurality of light emitting devices arranged in rows and columns, each of the light emitting devices located within a quadrangle formed by four neighboring light emitting devices included in the first matrix,

wherein a pitch S between one light emitting device included in the light emitting device matrix and another light emitting device most adjacent to the one light emitting device satisfies the following equation to obtain uniform luminance distribution at a position on a diffusion sheet, the position distant from a light emitting surface of the light emitting device by an optical length l,

S

⁢

<

_

⁢

l

2

×

tan

⁡

(

θ

2

+

α

)

,

Equation

where −π/18≦α≦π/18 is satisfied, and θ is an orientation angle of the light emitting device.

2. The plane light emitting device of claim 1 , further comprising:

a diffusion sheet arranged along a light emitting path of the light emitting device.

3. The plane light emitting device of claim 2 , wherein the diffusion sheet is separated from the light emission surface of the light emitting device by the optical length l.

4. The plane light emitting device of claim 1 , wherein each of the light emitting devices included in the second matrix is positioned at the center of the quadrangle.

5. The plane light emitting device of claim 1 , wherein the light emitting device emits white light.

6. The plane light emitting device of claim 1 , wherein the pitch S between one light emitting device included in the light emitting device matrix and another light emitting device most adjacent to the one light emitting device satisfies the above-described equation.

7. The plane light emitting device of claim 1 , wherein θ is in the range of 110°≦θ≦130°.

8. The plane light emitting device of claim 1 , wherein α is in the range of −π/90≦α≦π/90.

9. The plane light source of claim 1 , wherein the light emitting device is an LED.

10. An LCD backlight unit attached to a rear surface of an LCD panel, the LCD backlight unit comprising:

the plane light source of claim 1 ,

a diffusion sheet provided toward an LCD panel close to the plane light source and uniformly diffusing light incident thereon from the plane light source, and

at least one light collecting sheet provided toward the LCD panel close to the diffusion sheet and collecting the light diffused by the diffusion sheet in a direction vertical to a plane of the LCD panel.

11. The plane light emitting device of claim 1 , wherein the orientation angle of the light emitting device is a divergence angle of light emitted from the light emitting device with respect to an upper vertical direction of the light emitted from the light emitting device.

12. The plane light emitting device of claim 1 , wherein θ is an angle of a half of a maximum luminous intensity of the light emitted from the surface of the light emitting device.

13. The plane light emitting device of claim 12 , wherein the maximum luminous intensity of the light emitted from the surface of the light emitting device is emitted in an upper vertical direction.