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Sunburn effect (as measured by the UV index) is the product of the sunlight power spectrum (radiation intensity) and the erythemal action spectrum (skin sensitivity) across the range of UV wavelengths. [9] [10] The UV index is a number linearly related to the intensity of sunburn-producing UV radiation at a given point on the Earth's surface.
Highest ultraviolet index measured: On 29 December 2003, a UV index of 43.3 was detected at Chile/Bolivia's Licancabur volcano, at 19,423 feet (5,920 m) altitude. A light-skinned individual in such conditions may experience moderate sunburn in as little as 4 minutes.
The WHO-standard ultraviolet index is a widely publicized measurement of total strength of UV wavelengths that cause sunburn on human skin, by weighting UV exposure for action spectrum effects at a given time and location. This standard shows that most sunburn happens due to UV at wavelengths near the boundary of the UVA and UVB bands.
Consider the sunburn, a deterministic effect: [4] when exposed to bright sunlight for only ten minutes [5] at a high UV Index, that is to say a high average dose rate, [6] the skin can turn red and painful. The same total amount of energy from indirect sunlight spread out over several years - a low average dose rate - would not cause a sunburn ...
In the second process, triggered primarily by UVB, there is an increase in production of melanin (melanogenesis), [10] which is the body's reaction to direct DNA photodamage (formation of pyrimidine dimers) from UV radiation. [11] Melanogenesis leads to delayed tanning, and typically becomes visible two or three days after exposure. [10]
A photochromic eyeglass lens, part of the lens darkened after exposure to sunlight while the other part remained covered. A photochromic lens is an optical lens that darkens on exposure to light of sufficiently high frequency, most commonly ultraviolet (UV) radiation.
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The second paragraph of the introduction says “The UV index is designed as an open-ended linear scale…” The article, then refers to the (American) Fitzpatrick scale devised in 1975. Only in the third paragraph, the reader learns that the UV index was developed by Canadian scientists in 1992. The juxtaposition of these references is confusing.