UVA and UVB in sunlight, optimal utilization of UV rays in sunlight for phototherapy.

The disadvantages of sunlight as the source of UVA for phototherapy include variation with time, place, season, and atmospheric conditions. In the present study at Coimbatore, India we measured the UVa and UVB irradiance for one year using PMA 2100 meter. UVB irradiance was maximum between 12.00 noon-1.00 p.m (19.50 microw/cm2 to 40.2 microw/cm2) and UVA between 12 noon-1.15 p.m. (4.70 mw/cm2 tp 6.59 mw/cm2). The ratio of UVA was 1:500 to 1:600 during early hours and late evening and 1:200 during mid-day. At peak time (11.30 a.m. to 1.30 p.m.), the exposure time for 1 June of UVA was 2 min. 32 sec. to 4 min. 31 sec and for 10 mj of UVB it was from 4 min. 55 sec. to 11 min. 22 sec. We recommend the ideal time for UVB phototheraphy between 11.00 a.m. to 2.00 p.m. and for PUVASOL between 9.30 a.m. to 11 a.m. and 2 p.m. to 3.30 p.m. when incidental UVB and infrared rays responsible for heat are less.