<prompt> Wavelength of UVB is :250-280 nm280-320 nm320-400 nm400-700 nm  <response>: Ans. B. 280-320 nmThe wavelength found most effective in treating skin disease with phototherapy is UVB with warden gfh of 311 - 2nm narrow band UVB, NBUVB.The wavelengths between 4N and 7AO nm are visible to the human eye. 