Visible light is only one type of electromagnetic wave. This theory is very math intensive and we won't discuss it in this course. It is similar to the corpuscular theory of Newton, except that instead of describing light as particles, light is composed of 'packets of energy' or photons. The energy of the photon determines the color. Back to the cloud photograph To explain the iridescent cloud we use of the wave theory of light.
Waves consist of crests and troughs.
Before talking about light, lets consider water waves. Image two water waves having different wavelengths and traveling towards one another. These two waves will interact, and produce a surface with very different characteristics. This interaction of the two waves is called interference . Constructive interference occurs when the crest of one wave is aligned with the crest of the other and the two waves produce large crests and deep troughs.