Today's useless fact - Why can't dogs see color?

Popular wisdom has it that dogs are color-blind, but recent research suggests that a dog's world is not all black and white. To understand what dogs can and can't see, it helps to have some basic knowledge of vision in humans and other mammals. Our vision is optimized for seeing in bright light, while dogs, like many other predators, see best in dimmer light.

The retina is a structure at the innermost layer of the eye that senses light and sends visual information to the brain. Two types of photoreceptor cells in the retina -- rods and cones -- respond to light and transmit electric impulses to the optic nerve through a series of chemical reactions. Rods process visual information in dim light and are sensitive motion detectors, while cones handle color and detail. The human retina contains approximately 100 million rods and 7 million cones.

Cone cells contain pigments that perceive specific wavelengths of color. Human vision is trichromatic -- we have three types of cones that recognize different portions of the color spectrum. These cones allow us to see a range of colors that are a mix of red, blue, and green pigments. Dogs have only two types of cones - - their dichromatic color vision is similar to that of a human with red-green color-blindness. In addition, a dog's retina contains a much smaller ratio of cones to rods than ours does.

Before you start feeling sorry for Fido, keep in mind that although he may not have the color range and visual acuity (focus) that you depend on, his night vision is far superior. Thanks to a reflective structure behind their retina called the tapetum lucidum, dogs see objects in the dark as if lit by an eerie glow. Check out the links in our Dog category and Vision category for more.