UVA: Ultraviolet (UV) light is an electromagnetic radiation with a wavelength from 400 nm to 100 nm, shorter than that of visible light. Though usually invisible, under some conditions children and young adults can see ultraviolet light.
UV radiation is present in sunlight, and is produced by electric arcs and specialized lights such as mercury-vapor lamps, tanning lamps, and black lights.
Suntan, freckling and sunburn are familiar effects of over-exposure, along with higher risk of skin cancer. Ultraviolet light is also responsible for the formation of bone-strengthening vitamin D in humans. The UV spectrum thus has effects both beneficial and harmful to human health.