Uv rays. Tanning beds give off uv rays at the short end of the visible spectrum. The sun also gives off such rays which causes sunburn. The tanning bed is therefore an artificial sun. The beta, alpha, & gamma rays are from radioactive sources and would be dangerous for a tanning bed and would not cause tanning anyway.
UV radiation. When you tan through the use of sun rays, you are exposing your skin to a combination of uva and uvb rays. Uvb rays only penetrate the top layers of the skin and are responsible for sunburns. Uva rays penetrate deeper in the epidermis and stimulate the melanin to produce a tan. Most tanning beds only expose the individual to uva rays which cause skin cancer.