Effect of ambient humidity on UV/visible photodegradation of melanin thin films.

Photodegradation of spin-coated thin films of melanin is investigated using UVA and visible light from light-emitting diodes. The gradual increase in transmitted light through the film is measured as melanin photodegrades over the course of several hours. The photodegradation rate is measured for wavelengths in the 365-600 nm range. It is found that the increase in ambient humidity significantly accelerates the photodegradation process. Implications of these observations for evolution of melanism in biological systems are discussed.