Like other animals, leading nocturnal, cats on the inner surface of the eye is a brilliant layer of tapetum. It is very similar to the mirror and reflects incident light. This reflected light again falls on the photoreceptors. Because of this nocturnal animals can see well at dusk. Therefore, the eyes of cats and other nocturnal predators reflect any, even the weak light source. But in the dark cat eyes glow will not, because they have nothing to reflect.
This function of the eye can occur in other animals and man, if his eyes to direct a strong light source. This explains the effect of "red eye" in photographs made with a bright flash.