Patent ID: 8054284

Claim:
A back light module, comprising: a plurality of light emitting units, for providing a light source required by a plurality of pixels in a display area; an energy level calculating unit, for calculating an energy level corresponding to the display area; a detecting unit, electrically connected to the energy level calculating unit, for determining a switched-on number of the light emitting units according to the energy level corresponding to the display area; and a driving unit, electrically connected to the light emitting units and the detecting unit, for driving the light emitting units according to the switched-on number of the light emitting units and a dithering scheme wherein a number of the light emitting units is 4 n , the light emitting units are arranged in a 2 n ×2 n matrix, and n is a positive integer; wherein the energy level calculating unit determines the energy level corresponding to the display area from alternative (4 n +1) energy levels; wherein the energy level calculating unit calculates a gray level mean value of the pixels in the display area, and determines the energy level corresponding to the display area from the alternative (4 n +1) energy levels according to the gray level mean value; wherein the energy level calculating unit calculates a gray level peak value of the pixels in the display area, and determines the energy level corresponding to the display area from the alternative (4 n +1) energy levels according to the gray level peak value.