The electro-magnetic (light) spectrum is divided in bands from lowest to highest frequency, (radio, microwave, infra-red, visible, ultra-violet, x-ray, gamma and cosmic rays). Higher frequency (shorter wave-length) light photons have greater (and more destructive) energy. Ionizing radiation (the dislodging of electrons from elements and compounds (molecules) by higher energy photons) begins in the upper part of the ultra-violet band of light frequencies and progresses as light frequency (photon energy) increases.