Abstract

Background: Ultraviolet (UV) radiation is divided into three regions: UVA, UVB, and UVC. Both the quality and quantity of solar UV radiation vary with various factors including the elevation of the sun above the horizon, as well as absorption and scattering of UV photons by molecules in the atmosphere, notably ozone and clouds. It is clear that whereas a moderate amount of UV exposure is beneficial, too much is detrimental, so there is a need to quantify variations of solar UV on the earth surface, at different time intervals. Materials and Methods: The measurement of solar UV radiation in Yazd city was achieved by two radiometers: 1) a special UVA light meter with maximum sensitivity to 365nm in the range of 320-390nm and 2) a radiometer with a probe for 280-320 nm in UVB radiation: Measurement duration was from 1rst January to the end of December 2008 and from sunrise to sunset; every one hour. Results:Daily integral UVA radiation in December with the lowest (0.38x10(5)Jm(-2)) and July with the highest intensity (5.26x10(5)Jm(-2)) were found. The minimum and maximum monthly UVA radiation on the ground level of Yazd city were 25.8x10(5)Jm(-2) in December and 128.7 x 10(5)Jm(-2) in July, respectively. Conclusion: Based on UVB /UVA ratio the UVB intensity at 12 o'clock is 25 times lower than the UVA. Therefore, the integrated hourly UVB in this time is equal to 3.13 kjm(-2)and almost the effective UVB is 1.56 KJm(-2) so the minimum required exposure time of UVB radiation for one SDD and MED by hands and head are about 22 and 110 minutes respectively. Iran. J. Radiat. Res., 2012; 10(3-4): 187-191