Eyes don't actually glow at night; they reflect available light. This reflection, called eyeshine, can appear in various colors depending on several factors including the animal species, age, and the type of light source.
The Colors of Eyeshine
Eyeshine colors vary widely in the animal kingdom. Examples include:
- Reddish orange: Seen in alligators.
- Yellows and greens: Common in deer and cats.
- Red: Often observed in cats and other animals when photographed with a flash.
- Green: Observed in some animals, like certain types of reindeer in winter.
- Blue: Can appear in reindeer eyes during winter months.
The exact color is determined by pigments in the retina and other substances present in the eye's reflective layer, the tapetum lucidum. This layer enhances night vision by reflecting light back through the retina, improving light sensitivity. The color variation is not fully understood, according to available research.
This phenomenon is different from bioluminescence, where an organism produces its own light. Eyeshine is a purely reflective process. In photographs taken with flash, the red eye effect is a reflection of the blood vessels in the retina. Human eyes, lacking a tapetum lucidum, don't typically exhibit a strong eyeshine.
Factors Influencing Eyeshine Color
Several factors contribute to the apparent color of eyeshine:
- Species: Different species have different tapetum lucidum structures and pigment compositions leading to varying colors.
- Age: The color and intensity of eyeshine might change with age.
- Light Source: The color of the light source significantly affects the perceived color of the reflected light. A weaker light source might produce a different result compared to a bright flash.
It's important to note that while the eyes may appear to "glow," they are only reflecting ambient light. They do not produce their own light.
