Invisible rays that are part of the energy that comes from the sun. Most UVC radiation from the sun is blocked from the Earth’s surface by the ozone layer. In medicine, UVC 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 ultraviolet C radiation.