Typical illuminances E and luminances L under daylight and electric lighting.

One of the most remarkable properties of the eye is its ability to adapt to different lighting conditions. We can perceive the world around us by moonlight or sunlight, although there is a difference of a factor of 100,000 in the illuminance. The extent of tasks the eye is capable of performing is extremely wide - a faintly glowing star in the night sky can be perceived, although it only produces an illuminance of 10-12 lux on the eye.