Because of this, they are easier to find with a spotlight at night. Light passes through the retina when it enters our eyes. Some of this light is absorbed, and some of it is lost in the background tissues. Many nocturnal animals have what is known as a tapetum, which is a mirror-like membrane situated behind the retina, which reflects the light back through the retina again. The light that we see reflected in our spotlights is the remainder of this light that passes out through the eye again.
Different animals produce a different brightness and colour of eyeshine.
Humans, as seen in flash photographs, have a dull red eyeshine. This is an indication of our poor night vision. In contrast, cats are known to have good night vision as their eyes produce a bright reflection when caught in the headlamps of a car. Possum-spotting experts can often tell which species of possum they are looking at simply by their eyeshine colour. The Herbert River ringtail has a pink or yellow eyeshine, the green ringtail has a dull red, brushtails and striped possums have a pinkish eyeshine, and lemuroid possums have the brightest eyeshine of a white or yellow glare.