You can get ultraviolet B (UVB) rays from sunlight, especially summer noontime sun. But no matter what the time of day, sunlight also carries UVA rays, which are linked to cancer and rapid aging. The doctor can treat you with UVB rays from a phototherapy unit in his or her office. You can get one to use at home, but these lamps can also give off UVA rays. You'll probably need phototherapy treatments three days a week for two to three months.