The method of natural sunlight or fluorescent tube illumination used in the bleaching of paper is the subject under investigation. The colored components of oxidized cellulose in the presence of water become electronically excited when struck by photons of light. In this higher energy state, the stain molecule absorbs a photon of light. In this higher energy state, the stain molecule absorbs a photon of light and gives up its excess energy as heat. This breaks the molecule up into smaller fragments along with their oxidation to polar (hence water soluble) molecules. The cellulose itself either does not absorb visible or ultraviolet light and so is not directly attacked by it, or if it does absorb, it is more stable in the electronically excited state than are the stain molecules.