ABSTRACT
Electromagnetic radiation from objects around us covers a wide spectral range from the far ultraviolet into the thermal infrared. The atmospheric transmission cuts the solar spectrum at about 300 nm, whereas the visual window only opens around 400 nm. The shift is due to the yellow pigment that, fills the crystalline lens. When fluorescence occurs, tissue damage may be near by - and that brings us to the second possible benefit of the lens pigment: protection. The far UV that produces corneal or conjunctival inflammation is already stopped by the water content of the ocular media. But the near UV, in the domain between 300 and 400 nm would be able to pass those media if it were not for the yellow pigment of the lens. The absorption spectrum of melanin increases steadily towards short end of the visible spectrum. Below 500 nm the absorption of the lens rises sufficiently rapidly to compensate for any further increases from melanin absorption.
