We also are sensitive to the part of the electromagnetic spectrum called visible light. Wavelength is thus perceived as color or hue. Amplitude of the wave corresponds to the perceived brightness of the colors. Light enters the eye through a hole called the pupil .
Pupil size is regulated by a color muscle called the iris .
Amount of light you re subjected to. In bright light, the pupil contracts. In dim light the pupil dilates. To bring light rays into focus, the eye has a lens directly behind the iris. As an image draws closer, muscles acting on the lens thicken it, which brings the image into focus, a process called accommodation .