Invisible rays that are part of the energy that comes from the sun. Most ultraviolet C radiation from the sun is blocked from the Earth’s surface by the ozone layer. In medicine, ultraviolet C radiation may also come from special lamps or a laser and is used to kill germs or to help heal wounds. It is also used to treat certain skin conditions such as psoriasis, vitiligo, and skin nodules of cutaneous T-cell lymphoma Also called UVC radiation.