Light level detection - Sleep as Android

Measures the level of ambient light in your bedroom using the ambient light sensor (lux sensor)

This is a companion discussion topic for the original entry at

How does the light sensor in my phone work? Does it require the phone to be face up all night long? I usually keep my phone face down to prevent notifications from lighting up my room.

Usually, for smartphones, an ambient light sensor is next to a front camera. That means that your phone needs to be facing screen up throughout the night to measure the level ambient light.