ABSTRACT
Directly and indirectly, the sun provides the energy supporting life on earth. All
foods and fuels are ultimately derived from plants using solar energy in the
process of photosynthesis. The sun releases the majority of its energy as visible
light, but infrared (IR) and ultraviolet (UV) rays are also significant parts of
the solar spectrum (1). According to the range of wavelengths, UV light is
divided into UVA (320-400 nm), UVB (280-320 nm), and UVC (100-280 nm).
The spectrum of visible light ranges from 400 to 700 nm. While UVC light is
mainly absorbed by the ozone layer, UVB and UVA rays reach the terrestrial
surface. Exposure to visible and UV light may interfere with essential bio-
chemical functions in living organisms and damage biologically important
structures like DNA, lipids, and proteins (2-4). In DNA, UV radiation leads to
the formation of thymidine dimers, photo-oxidation products, and single-strand
breaks. Animals and plants have developed various strategies of defense against
light-induced damage (5). Photosynthetic organisms make use of carotenoids for
photoprotection of reaction centers and pigment-protein antennae via energy
dissipation (6). Absorption and reflection of light provide other mechanisms of
defense (7). An adaptive response of human skin toward irradiation with
sunlight is pigmentation and thickening of the stratum corneum. The epidermal
pigment melanin provides protection, lowering the radiant energy by the
absorption of UV light.
