Why animal eyes glow green
Animal eyes usually glow green when illuminated at night. This unique phenomenon is attributed to the presence of a layer known as the tapetum lucidum. This thin layer is located behind the retina of animal eyes. However, it is not present in human eyes, and this best explains why human eyes do not glow green, yellow, or blue when illuminated at night. In animals, the tapetum lucidum serves the purpose of reflecting light back through the retina, and thus, animal eyes glow when illuminated at night (Schwab et al 187). However, the color of the glow can be green, blue, or yellow, depending on the type of animal. For instance, cats and dogs often have eyes that glow bright green when illuminated at night, and this is because of the presence of substances such as zinc or riboflavin, which may not be present in the eyes of other animals. As such, the difference in eye glow color among animals is best explained.
Unlike animals, human eyes do not glow green, yellow, or blue when illuminated at night. Instead, human eye is known to have a red glow, a perspective that is commonly known as the “red-eye.” The “red-eye” is common in flash pictures, and it is as a result of a camera’s flash traveling through the pupil and hitting the retina found at the back of the eye. The retina then reflects the light back towards the camera and because of the presence of crisscrossing blood vessels on the retina and it being an icky red mess, the light reflected towards the camera is dyed red (Lukac 433). This explains why human eyes glow red when in flash pictures.
Lukac, Rastislav, ed. Single-sensor imaging: methods and applications for digital cameras. Boca Raton, FL: CRC Press, 2008.
Schwab, Ivan R., et al. “Evolution of the tapetum.” Transactions of the American Ophthalmological Society 100 (2002): 187.