The inner surfaces of your eyes contain photoreceptors—specialized cells that are sensitive to light and relay messages to your brain. There are two types of photoreceptors: cones (which are sensitive to color) and rods (which are more sensitive to intensity). You are able to “see” an object when light from the object enters your eyes and strikes these photoreceptors.

Some objects are luminous and give off their own light; all other objects can only be seen if they reflect light into your eyes. However, humans can only see visible light, a narrow band of the electromagnetic spectrum (which also includes non-visible radio waves, infrared light, ultraviolet light, X-rays, and gamma rays). In terms of wavelengths, visible light ranges from about 400 nm to 700 nm.

Different wavelengths of light are perceived as different colors. For example, light with a wavelength of about 400 nm is seen as violet, and light with a wavelength of about 700 nm is seen as red. However, it is not typical to see light of a single wavelength. You are able to perceive all colors because there are three sets of cones in your eyes—one set that is most sensitive to red light, another that is most sensitive to green light, and a third that is most sensitive to blue light.

Source: Harvard—Smithsonian Center for Astrophysics

This media asset was adapted from Shedding Light on Science