Color naming and the phototoxic effects of sunlight on the eye.

Many languages have no basic color term for "blue." Instead, they call short-wavelength stimuli "green" or "dark". We show that this cultural, linguistic phenomenon could result from accelerated aging of the eye because of high, chronic exposure to ultraviolet-B (UV-B) in sunlight (e.g., phototoxic lens brunescence). Reviewing 203 world languages, we found a significant relationship between UV dosage and color naming: In low-UV localities, languages generally have the word "blue"; in high-UV areas, languages without "blue" prevail. Furthermore, speakers of these non-"blue" languages often show blue-yellow color vision deficiency. We tested our phototoxicity hypothesis in a color-naming experiment, using computerized, colorimetric simulations of Munsell colors as viewed through clear and brunescent lenses. As predicted, our young subjects used "blue" as in English when the simulated lens was clear, but named colors as in tropical languages when the lens was dense. Our within-subjects design precludes a cultural explanation for this result.