LIQUID CRYSTAL DISPLAY DEVICE

1 . A liquid crystal display device, comprising a liquid crystal display panel and a backlight that is positioned so as to face said liquid crystal display panel, characterized in that

said liquid crystal display panel is formed of a number of pixels that are arranged in a matrix in a display region and a number of light sensor circuits that are provided in said display region,

each of said number of light sensor circuits has a light sensor element,

said backlight has a first light intensity and a second light intensity that is different from said first light intensity, and

said first light intensity and said second light intensity are switched between periodically with a predetermined period.

2 . The liquid crystal display device according to claim 1 , characterized in that

said light sensor circuits have a light receiving period during which the amount of light is detected and a readout period during which the amount of light detected during said light receiving period is read out,

said light receiving period is an integer multiple of said predetermined period,

said light sensor elements have a light sensor operating state with a sensitivity to light and a light sensor non-operating state without sensitivity to light during said light receiving period, and

said light sensor operating state and said light sensor non-operating state are switched between periodically with said predetermined period in sync with the switching of the light intensity of said backlight.

3 . The liquid crystal display device according to claim 2 , characterized in that said readout period is said predetermined period.

4 . The liquid crystal display device according to claim 2 , characterized in that

said number of light sensor circuits are arranged in a matrix,

a number of light sensor circuits aligned in the same column from among said number of light sensor circuits take said readout period in sequence, and

the light intensity of said backlight when light sensor elements are in said light sensor operating state is different between light sensor circuits in odd rows and light sensor circuits in even rows from among the number of light sensor circuits aligned in the same column.

5 . The liquid crystal display device according to claim 1 , characterized in that

said liquid crystal display panel has a number of gate signal lines,

said number of gate signal lines have a scanning signal inputted in sequence for each horizontal scanning period, and

said predetermined period is one horizontal scanning period.

6 . The liquid crystal display device according to claim 1 , characterized in that

said liquid crystal display panel has a number of gate signal lines,

said number of gate signal lines have a scanning signal inputted in sequence for each horizontal scanning period, and

said predetermined period is an integer multiple of one horizontal scanning period.

7 . The liquid crystal display device according to claim 1 , characterized in that

said backlight has a light source, and

said first light intensity is a state in which said light source is turned on and said second light intensity is a state in which said light source is turned off.

8 . The liquid crystal display device according to claim 1 , characterized in that

said light sensor circuits have a light sensor element, a capacitor element and a switch, and

said light sensor element and said capacitor element are connected in series with said switch in between.

9 . The liquid crystal display device according to claim 8 , characterized in that said switches are formed of a thin film transistor.

10 . The liquid crystal display device according to claim 1 , characterized in that said light sensor circuits are each formed in one of said number of pixels.

11 . The liquid crystal display device according to claim 1 , characterized in that said light sensor circuits are provided in part of said display region.