Zp3111_multisensor - what does 0.69% luminance mean?

I do have a 4in1

sensor.vision_zp3111_multisensor_4in1

and my

sensor.vision_zp3111_multisensor_4in1_luminance state is always kind of 0.69% or whatever.
what does the current value of 0.69% mean. I mean 0.69% of what? What is 100%.
I am trying to create some triggers. One should tell me if I forgot to switch of the light in the room during night. But I am not positive that I can archive this. Any help??