UV index
Radiation & sun UVI
The UV index describes the strength of sunburn-producing ultraviolet radiation at ground level. Higher values mean unprotected skin can be damaged more quickly.
Radiation you cannot feel
A fresh breeze can make a day pleasant without reducing UV radiation. UV light is invisible, and neither air temperature nor the sensation of warmth reliably indicates its strength. The index is a comparison value without a unit.
UV-index categories
On small screens, scroll sideways to see all columns.
| UV index | Category |
|---|---|
| 0–2 | Low |
| 3–5 | Moderate |
| 6–7 | High |
| 8–10 | Very high |
| 11 or more | Extreme |
The scale has no fixed upper limit. A daily value often means the expected maximum around the highest sun position; an hourly display refers to a different period.
What changes the radiation?
Solar elevation, ozone, altitude, cloud and reflective surfaces such as snow affect the value. Thin cloud does not reliably block UV, and cloud edges can temporarily enhance it.
When is protection needed?
From UV index 3, WHO recommends protection: shade, covering clothing, a hat and suitable sunglasses, plus sunscreen on uncovered skin. Take particular care to avoid midday sunshine at very high values. Appropriate exposure also depends on skin type and circumstances; the index cannot supply a universal number of “safe minutes”.