Light Sensor

I am designing a circuit that is used to detect light. The sensor is mounted in an eyecup and when the system is turned on the sensor will detect light from the screen display. This is used to track battery life of the system. When the system turns on the sensor will detect light and send a high signal that triggers a clock that tracks the time and when the system runs out of battery life the diplay shuts down and of course emits no light, stopping the clock and activating a buzzer to let the user know the battery life test is complete. I have been looking for a few light sensors and found a few, I just wanted to ask if anyone had suggestions on a sensor that could be used

Sounds like a simple LDR- light dependent resistor would work, and would probably be the easiest to use. Resistance goes up as light decreases.