Photodetector of liquid crystal display and luminance control device using the same

A luminance control device for controlling luminance of a backlight for illuminating a liquid crystal module including a liquid crystal panel and a reflector sheet, and a diffusion sheet, a light collective sheet, and a light directing plate located between said liquid crystal panel and said reflector sheet, and a flourescent tube for backlight provided at an edge of said light directing plate, said luminance control device comprising:

• a photodetector for detecting a quantity of light when said backlight is lit at a maximum luminance, and for outputting a signal indicative of said quantity of light, said photodetector provided at the side of said reflector sheet opposite to said liquid crystal panel to detect light transmitted rearwardly through said reflector sheet;
• a cushion member for substantially preventing light other than the light transmitted from said reflector sheet from reaching said photodetector;
• luminance setting means for setting a desired luminance by a user as a function of a desired percentage of the maximum rumination of the backlight;
• and
• control means for controlling luminance of said backlight using said signal as a reference so that the luminance set by said luminance setting means is achieved.

A combination, comprising:

• a liquid crystal module having:
• a liquid crystal panel forming a front surface;
• an opposing back surface;
• and
• a backlight positioned between said front and back surfaces, said backlight transmitting light;
• a light sensor located behind said back surface for detecting light transmitted from said backlight through said back surface;
• and
• a cushion member for substantially preventing light other than the light transmitted through said back surface from reaching said light sensor.