Why Do Animal Eyes Glow On Pictures Taken In The Dark?
If you take a photo of your cat in darkness or point a strong torch into the jungle, the result is scary. What is it that makes animal eyes reflect?
The eyes of cats and other animals glow in the dark because of a special layer in the animal eyes called tapetum lucidum. The layer is located at the back of the light-sensitive retina and reflects the light that passes through the retina. This way, the light-sensitive cells in the eye can use the light once more. The reflection increases the light sensitivity of the eyes by up to 50%.
Felines have the reflecting layer in their eyes, but it is found in a number of different species – but not in humans and other primates. "Red eye" in a photo, is due to reflections from the retina itself. Here, the red colour is due to the many blood vessels that supply the eyes with oxygen and nutrients.
Yet, some animals have a red tapetum lucidum, and red eyes are widespread among nocturnal birds. In some species, the eyes even shine with different colours. In fish, the reflection can be so strong the animals use it as a lamp to find their prey or lure it closer.
Only vertebrates have tapetum lucidum, but similar kinds of lightenhancing structures are found in the eyes of moths. Here, however, a nanofilm covers the eyes to make sure that the light is not reflected and reveals the insect to predators.
A beam of light or camera flash pointed into the darkenss of the savannah will show whether a pack of lions is nearby.
A reflecting layer called tapetum lucidum behind the retina makes the animals's eyes glow.