Interference Theory    [Back]

Light waves are composed of electromagnetic waves that oscillate from positive to negative in a continuous fashion as they travel through space, or any other medium. The number of oscillations per second is known as the frequency.  Light waves travel extremely fast in a vacuum, 299,792,500 meters per second.  The distance that light travels during one cycle is called the wavelength of the light, which represents the color of the light.   The magnitude of each oscillation is known as the amplitude, which corresponds to the intensity or brightness of the light.  When two electromagnetic waves of the same frequency, and thus the same wavelength, come together.  They can add up constructively or destructively depending on the timing, or phase of the two waves.  The illustration below shows how two electromagnetic waves that are in phase, each with an amplitude of one, can add up to a wave with an amplitude of two. This is called constructive interference. However, if the two waves are out of phase by just one half

of the wavelength, they add together such that they cancel each other out, and the result is a zero intensity.  This is called destructive interference, and is shown below.