| 摘要 |
PROBLEM TO BE SOLVED: To prevent damaging of a light source, etc., for back light by prohibiting malfunction of a heater in the case where there is a trouble in a back light temperature sensor itself. SOLUTION: A peripheral temperature is detected by an external thermister 12, time required after a light source for back light which is almost at a constant temperature in a lighted condition is lighted off and till a light source temperature by a back light thermistor 20 is lowered to an almost similar temperature to the ambient temperature by the external thermister 12 is measured preliminarily, and it is set as a reference time. A heater 26 is driven when time after the light source for back light is actually lighted off is shorter than the reference time, and if the light source temperature is lower than a specified temperature, and the heater 26 is not driven when the time is longer than the reference time, and if difference between the light source temperature and the ambient temperature is larger than a specified value, in which case the back light thermister 20 itself has abnormality. |
