| 摘要 |
PROBLEM TO BE SOLVED: To reduce consumption of a battery by preventing useless lighting of a back light of a portable telephone set. SOLUTION: A photo diode 111 and an operational amplifier 112 convert an incident light made incident from an incident port 12 into an external illuminance signal and it is given to a comparator 113, which compares the external illuminance signal with a reference signal V that is set in advance to the comparator 113 when it is started and only when the comparison result indicates it that the external illuminance signal is smaller than the reference signal, a back light 17 is lighted. |
