| 摘要 |
A liquid crystal display device 1 of the invention has a liquid crystal display panel in which a liquid crystal layer 14 is provided between a TFT substrate 2 and a CF substrate 25 that has a common electrode 26, a light sensing component LS 1 with a TFT photosensor that senses external light, and an illuminating means controlled according to the output of the light sensing component. The light sensing component is deployed at the periphery of the TFT substrate's display area DA and uses a thin film transistor as photosensor. A capacitor C is connected between source and drain electrodes S<SUB>L</SUB>, D<SUB>L </SUB>for such TFT photosensor. One of the capacitor's terminals is connected to a standard voltage source V<SUB>S </SUB>via a switch element SW, and the other to the common electrode 26. Voltage that is always lower than the voltage applied to the common electrode by an amount corresponding to a reverse bias voltage is applied to the gate electrode G<SUB>L </SUB>for the TFT photosensor. The capacitor's voltage a certain time after the switch element turns off is output. As a result, it will be possible to provide a liquid crystal display device in which the light sensing component incorporated in the liquid crystal display panel is not susceptible to the influence of the drive signals for the display panel, and in which the light sensing component does not induce deterioration of the liquid crystals.
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