Why do glass and crsytals absorb light?

[Biologik]

What determines of something absorbs light? Is it determined by the orbitals the electrons spin at, and what makes these two things special when other things like wood and metal don't

[cragar]

It defiently has to do with the eletrons in the material. And how all the electrons affect each other ,
We don't have discrete orbitals in a complex material like wood or glass. As the photon comes in an oscillates the electron , The coulomb interaction between the electrons will dictate what light gets re-emitted . This might not be completely accurate but its a start and hopefully someone else can elaborate .

[granpa]

the absorption spectra of gases is determined by their orbitals.
with solids it gets complicated. you get effects like "electronic band structure" that single atoms dont really show
thats why there is a whole branch of physics called 'solid state physics'.

metals are a special case because they are conductors
I really dont know what makes glass (or water) so special.

[Dr Lots-o'watts]

Transparency to visible radiation is simply when there are no electronic transitions possible for the incoming radiation.