Photobiology/photochemistry

Exposure of living organisms to non-ionizing electromagnetic radiation there confined to the visible and part of the ultraviolet, 200-800 nm) can cause a toxic reaction. The details of the exposure, both in intensity and wavelength composition, will determine the degree of effect. If absorbing chromophores, both endogenous and exogenous, are present, additional response can be elicited. Whether the radiation reaches a sensitive target will depend upon the depth of penetration and the opacity of the cell or tissue. The final effect will be determined by the initial photoproducts produced, the subsequent reactions they cause, and the amount of repair of damage by cellular processes. In some cases it is possible to predict the complete response; in others it is variable.