English: Left: Photon absorption process in a semiconductor pictures using a simple energy-position diagram. Center: Same process depicted with energy as a function of density of states. Right: representation of how this absorption would be manifest in an absorption spectrum. Red wiggly lines represent low energy optical photons, green wiggly lines represent moderate energy optical photons, and purple wiggly lines represent high energy optical photons. e- denotes an electron and h+ denotes a hole.