UV index
The UV index is a measure of the strength of UV radiation in sunlight at a specific moment. The scale starts at UV index 0 (no UV radiation) and is open towards the top. The table below gives you an idea of what the different UV index strengths are.
| UV index 0 | UV index 1 | UV index 3 | UV index 7 | UV index 10 | |
|---|---|---|---|---|---|
| interpretation | No UV radiation | Very weak UV radiation | Weak UV radiation | high UV radiation | extremely high UV radiation |
| example | Inside or at night | Early in the morning or when it rains | Cloudy morning | Midday in early summer | Noon in midsummer |
definition
The UV index (UVI) takes into account both UVA and UVB radiation in sunlight. The UV components are weighted as they cause damage to the skin. That means UVB, which causes more damage than UVB, is weighted more heavily than UVA. It is also important to know that the UV index has a linear scale. This means that a UV index twice as high causes twice the damage to the skin. The UV index is therefore a suitable measure to indicate the potential harmfulness of UV radiation. If you want to know the more precise mathematical definition of the UV index, we recommend the English Wikipedia article on the subject.
UV index forecasts
In many places you can see UV index forecasts for one day. Be it in weather apps or on the websites of health authorities. But what does this single UV index number mean?
In the forecasts for the day, the maximum UV index is specified, which is reached on this day for at least half an hour. This means that if the prognosis predicts a UV index of 7, the UV radiation should be above UV index 7 for half an hour around noon on this day. The World Health Organization recommends the following protective measures with regard to UV index prognoses:
| UV index 1 - 2 | UV index 3 - 7 | UV index 8 – 11 | |
|---|---|---|---|
| Need protection? | No protection needed | Protection needed | Extra protection needed |
| Recommended protective measures | – | Shade looking over lunchtime, t-shirt, suntan lotion, hat | Stay inside over lunchtime, look for shade, T-shirt, sunscreen, hat |
The difficulty with these forecasts, however, is that they only relate to lunchtime and say nothing about how dangerous UV radiation is in the morning or when it is cloudy in the meantime, for example. They also say little about the expected UV dose you can get that day.
sun-a-wear can give you more precise UV index forecasts that relate not only to noon, but to the whole day. The sensor also allows you to better estimate the UV dose and thus better adapt the protective measures to your personal situation.
Further reading:
Sources:
- Wikipedia article on the UV index: https://de.wikipedia.org/wiki/UV-Index
- English Wikipedia article on the UV index: https://en.wikipedia.org/wiki/Ultraviolet_index
