Color is how our eyes and brains distinguish different wavelengths. Interference refers to what happens when you add two waves together. Constructive interference results when you add the waves together so that their crest match. The amplitude, and therefore the intensity, is doubled and the wave is said to be in phase . A beam in which all the waves are in phase is called coherent .
Coherent waves have the ability to deliver radiation of extremely high intensity.
Laser technology uses coherent light to focus narrow beams of intense radiation of a given energy. Destructive interference results if one of the two waves added together is out of phase. The waves will cancel each other out and the intensity of the light will decrease. Lasers send out very powerful beams of coherent light that can damage bodily tissue and cause blindness. Take extreme care to avoid looking into the laser or moving it from its preset location.