Patent ID: 8054457

Claim:
A light intensity detecting device, detecting a light intensity according to pulse duration of a pulse signal output from a light sensor, comprising: a time measuring unit for measuring an elapsed time period of the pulse signal that has been raised; a signal state discriminating unit for obtaining a state of the pulse signal; a sampling unit for directing the signal state discriminating unit to obtain the state of the pulse signal at a sampling interval, wherein the sampling interval corresponds to the elapsed time period of the raised pulse signal measured by the time measuring unit; and a falling detecting unit for detecting the pulse signal that has been fallen when the signal state discriminating unit successively obtains a fallen state of the pulse signal for two times, wherein when the falling detecting unit detects the fallen pulse signal, the sampling unit directs the signal state discriminating unit to obtain the state of the pulse signal at a time point and outputs the time point as the pulse duration of the pulse signal.