What Is an Interference Fringe or Pattern?

An interference fringe or pattern results from constructive and destructive interference of light waves. By passing sunlight through two narrow slits, the fringe pattern is viewed on a screen placed behind the slits.

Constructive interference occurs when one wave's peak matches the peak from another, creating a situation in which the waves will add to each other. In destructive interference, a peak from one wave pairs with another wave's trough. These waves will neutralize each other. Constructive interference results in a bright line on the screen, while destructive interference results in a dark line. These patterns of bright and dark lines were first discovered by Thomas Young in 1801.