<prompt> Wavelength of UVB rays is -290 - 320 nm320 - 360 nm360 - 390 nm390 - 420 nm  <response>: Ans. is a i.e., 290 - 320 nm UV rays are used directly to treat skin conditions. It is simply referred to as phototherapy. These may be : ? UVB phototherapy 290-320 nm Narrow band UVB phototherapy 311 nm UVA1 phototherapy 360-380 nm 