See today's UV index for your location – hour by hour. When is UV at its highest and when should you apply sunscreen?
The UV index is an international scale describing the strength of the sun's ultraviolet radiation at ground level. It starts at 0 and is effectively open-ended. At mid-latitudes it rarely exceeds 8, while in the tropics and high in the mountains it can pass 11. The higher the number, the less time it takes to get sunburnt.
The UV index depends mainly on how high the sun is in the sky. That is why it peaks around solar noon and is greatest in summer near the longest day of the year. Clouds, the ozone layer, altitude and reflection from snow or water also affect the value. Note that UV does not follow the temperature — you can get sunburnt on a cool, clear spring day.
The WHO recommends sun protection whenever the UV index is 3 or higher: use sunscreen of at least SPF 30, seek shade around midday, and wear sunglasses and a hat. About two-thirds of the day's total UV falls between 10:00 and 16:00. The radiation is weakest around sunrise and sunset, as the chart above shows.
See today's UV index hour by hour for a city such as London, New York, Los Angeles, Sydney or Singapore.