When a camera flash is used in a low-light environment, the subject's eyes may appear red in the finished photograph. What is known as "red-eye" is the result of light from the flash reflecting off the pupils of the eyes. The phenomenon of red-eye can be lessened by using the red-eye reduction feature found on many SLR cameras. This feature activates a lamp which shines a small light directly into the subject's eyes. When this happens, the diameter of the pupil is reduced, thus tightening the opening in the iris. Since a smaller pupil means a smaller host for the reflection, the chances of red-eye occurring are greatly reduced.