As light reflects off of my hair I see rainbows. Why?

The simplest possibility is the presence of a film on your hair, with a thickness of at least a quarter wavelength of visible light, and at most a few such wavelengths. read more

This puts it 180° out of phase with light from the same source that reflects directly from the surface of the film, rather than passing through. Consequently, the light is cancelled out. The same will happen for a film that is an odd multiple of a quarter wavelength thick. read more

Diffuse reflection is when light hits an object and reflects in lots of different directions. This happens when the surface is rough. Most of the things we see are because light from a source has reflected off it. For example, if you look at a bird, light has reflected off that bird and travelled in nearly all directions. read more