What is night level?
The night level is a darkness condition that is usually used in some applications. Below is the list describing the night level with the correspondence unit of illuminance:
Night level 1 : full moon condition, 40-1000 mlx
Night level 2 : half-moon condition, 10-40 mlx
Night level 3 : partial moon, 2-10 mlx
Night level 4 : clear starlight, 0.7-2 mlx
Night level 5 : overcast starlight, 0-0.7 mlx