It throws sharp shadows since it travels in a straight line, as particles would. However, if the opening through which light travels is narrow enough, so narrow that it is near the wavelength of the light, the light is diffracted and bent. A diffraction grating has many fine lines that act as narrow slits. When we shine white light through a grating, it is diffracted into the familiar colors of the rainbow. Intensity refers to what we might call the brightness of light.
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.