ultraviolet radiation

ultraviolet radiation Invisible rays that are part of the energy that comes from the sun. Abbreviated UV. UV radiation is made up of three types of rays: ultraviolet A (UVA), ultraviolet B (UVB), and ultraviolet C (UVC). UVC is the most dangerous type of UV light in its potential to harm life on earth, but it cannot penetrate the earth’s protective ozone layer. UVA and UVB do penetrate the ozone layer and reach earth. UVA is weaker than UVB and less likely to cause sunburn, but it passes farther into the skin. Both UVA and UVB cause melanoma and other types of skin cancer; therefore, it is recommended that people use sunscreens that block both UVA and UVB radiation. The light from tanning lamps is like that from the sun and contains both UVA and UVB. Using tanning lights poses a major long-term risk of skin cancer. Electric arc lamps can also generate UV light to enable motion-picture projectors to show movies. Although UV light can damage health, it can also maintain or improve health. When UV light strikes human skin, it triggers the production of vitamin D, which promotes the growth of bones and teeth. See also basal cell carcinoma; cancer, skin; squamous cell carcinoma; melanoma; sunscreen.