All of us have seen how eyes of nocturnal animals glow in the dark. Cats, cows, deer and other animals who have a habit of roaming or prowling in the dark, must have eyes that are more efficient in gathering the available light so that the animal can see in the dark.
Humans are unable to see clearly in the dark.
Whatever minimum light that is getting reflected or scattered from objects has to be intensified by the mechanism in the eye so that these animals are able to see in the dark. A cat s eye is six times more sensitive to light levels than the human eye. The size of the pupil plays a big role in admitting light into the eye. When there is more light, the pupils contact. When the light is dim, the pupils dilate to admit more light into the eye.