To provide a back projection type video display device capable of appropriately controlling the luminance of a screen in accordance with both the luminance of external light and the luminance of projected light, projecting the light with relatively high luminance when it is bright on the surroundings, thereby showing the screen brightly, and restraining the luminance relatively according as it gets dark on the surroundings, thereby reducing glare concerning a signal having a high APL, while displaying a white video part having small area without lowering brightness, because it is projected with high luminance.
By providing an optical sensor 200 capable of receiving stray light by the video light reflected on the back side of the screen 102 of a liquid crystal projection television 100 and stray light by external light made incident after it is transmitted through the screen 102 and provided at a prescribed position in a housing 101, the intensity of video light projected from a video light projection mechanism 110 is controlled based on the detection output of the optical sensor 200.
Yoshiaki Naito
Cui Shu Tetsu
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