Thanks Goku, that clears the electric band gaps up. However how does this help overlap with wave phenomena such as light in photonic crystals.
As a stab in the dark (hope no one gets hurt)
Does the interference pattern caused when the wave scatters off an object mean that the light can only be in specific frequerncies (as the others cancel out) and then if you have many waves scattering of a regular arrangement these forbidden levels over lap like in a solid and you get a frequency band gap?
Or am I way off?