Uv index

Synonym(s)

UVI

Definition
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The UV index (UVI) is a measure of the strength of the sunburning UV radiation. The UVI value is usually highest around midday ("noon sun").

General information
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The UV index is defined as the erythema efficacy (Eer = 0.2541 W/m2 or 25 mW/m2 ) of the reference sun multiplied by 40 and rounding the whole year value to whole numbers. Accordingly, a UV index of 2 corresponds to a radiation of about 25 mW/m2. A maximum UV index of 12 can be achieved, which corresponds to extremely strong UV radiation (approx. 300 mW/m2). A UVI of 12 is only found near the equator and/or in areas with a reduced ozone layer (danger of UVC radiation). The daily updated UV indices are offered nationwide and internationally by weather services.
The UV-Index is internationally uniformly fixed, so that the numerical values of different countries can be compared with each other without the introduction of correction coefficients. UVI describes the expected daily peak value of sunburning UV radiation on the ground. On uncloudy days this value is reached at noon ("midday sun"). Significantly lower values can be achieved on overcast days. The higher the UVI, the higher the risk of sunburn. The time it takes to achieve sunburn is then low and different for different skin types. By definition, protective instructions and times to reach the sunburn threshold for skin type II for untanned skin are given.
The UVI depends mainly on the position of the sun; therefore it changes with the season and latitude. The ozone situation in the atmosphere, cloud cover and the altitude of a place also play a role. Reflections from sand and snow also influence the altitude of the UVI.
Not included in the UV index are subjective factors, e.g. the use of light-sensitizing medication.

Literature
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Ezzedine K et al (2007) Travellers to high UV-index countries: sun-exposure behaviour in 7822 French adults. Travel Med Infect Dis 5: 176-182
Pettazzi A (2007) Evaluation of promotional gadgets integrating UV patches for public awareness on ultraviolet radiation. Photodermatol Photoimmunol Photomed 23: 203-208
Thieden E et al (2005) Sunburn related to UV radiation exposure, age, sex, occupation, and sun bed use based on time-stamped personal dosimetry and sun behavior diaries. Arch Dermatol 141: 482-488

Tables
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UV index*	UV exposure	solar dermatitis	Light protection measures**
1	low UV-intensity	unlikely	not required
2
3	average UV-intensity	after approx. 30 minutes	highly recommended (depending on skin type; protection by clothing and light protection)
4
5
6	high UV-intensity	after approx. 20 minutes	required (protection by clothing and light protection agents)
7
8	very high UV intensity	after about 15 minutes	obligatory (protection by clothing and light protection means; avoid the midday sun from 11-15 o'clock)
9
10
11	extremely high UV intensity	after approx. 10 minutes	obligatory (protection by clothing and light protection means; avoid the midday sun from 11-15 o'clock)
12