ABSTRACT
Sunlight represents a broad range within the electromagnetic spectrum; the two types of radiation we notice are visible light (wavelength 400-760 nm) and infrared ( 760-106nm) in the form of heat. The form of radiation that we are concerned with, however, is ultraviolet B (UVB) (290-320 nm) and ultraviolet A (UVA) (320-400 nm), which are invisible but biologically active components of sunlight. UVB, for example, interacts with 7-dehydrocholesterol in the skin to produce cholecalciferol (vitamin D3).
