How shape of pattern affects the behaviour of light

[nicolauslamsiu]

chameleon can change the colour of its skin by changing the structural arrangement of cell layers. I found someone said that the shape of patterns of particles can determine how the light behaves when striking the object. I wonder how it works?

 

[jerromyjon]

I think the simple explanation is that the space between special lattice atoms is more likely to reflect a photon of light, more so with lower frequency waves. An excited chameleon has a lattice which not only reflects to change color but also to reflect near-infrared light for thermoregulation. When they relax the absorbing atoms are closer together which reflect blue higher frequency photons but absorb most others. They have a yellow pigment to begin with mixed with the relaxed blue makes the typical green.

 

[nicolauslamsiu]

I've also heard that it is possibly due to the formation of photonic crystals and photonic crystals have band gap which can control the propagation of certain wavelength. I want to know how it can control the wavelength that can propagate through the crystals. Is it something related to bragg's law?

 

[jerromyjon]

I'm not sure if interference or just simply absorption is the primary mechanism. It seems to me absorption is necessary for them to use near-infrared for heat, but I really don't know enough specifics to have a reliable answer.