An ultraviolet sensor (UV sensor) is a device that measures UV light from the Sun.

The UV index is an international standard measurement of how strong the ultraviolet (UV) radiation from the sun is at a particular place on a particular day. It is a scale primarily used in daily forecasts aimed at the general public.

Its purpose is to help people to effectively protect themselves from UV light, of which excessive exposure causes sunburns, eye damage such as cataracts, skin aging, and skin cancer (see the section health effects of ultraviolet light).

A UV Index reading of 0 to 2 means low danger from the sun’s UV rays for the average person.
  • Wear sunglasses on bright days.
  • If you burn easily, cover up and use broad spectrum SPF 30+ sunscreen.
  • Watch out for bright surfaces, like sand, water and snow, which reflect UV and increase exposure.

A UV Index reading of 3 to 5 means moderate risk of harm from unprotected sun exposure.

  • Stay in shade near midday when the sun is strongest.
  • If outdoors, wear protective clothing, a wide-brimmed hat, and UV-blocking sunglasses.
  • Generously apply broad spectrum SPF 30+ sunscreen every 2 hours, even on cloudy days, and after swimming or sweating.
  • Watch out for bright surfaces, like sand, water and snow, which reflect UV and increase exposure.

A UV Index reading of 6 to 7 means high risk of harm from unprotected sun exposure. Protection against skin and eye damage is needed.

  • Reduce time in the sun between 10 a.m. and 4 p.m.
  • If outdoors, seek shade and wear protective clothing, a wide-brimmed hat, and UV-blocking sunglasses.
  • Generously apply broad spectrum SPF 30+ sunscreen every 2 hours, even on cloudy days, and after swimming or sweating.
  • Watch out for bright surfaces, like sand, water and snow, which reflect UV and increase exposure.

A UV Index reading of 8 to 10 means very high risk of harm from unprotected sun exposure. Take extra precautions because unprotected skin and eyes will be damaged and can burn quickly.

  • Minimize sun exposure between 10 a.m. and 4 p.m.
  • If outdoors, seek shade and wear protective clothing, a wide-brimmed hat, and UV-blocking sunglasses.
  • Generously apply broad spectrum SPF 30+ sunscreen every 2 hours, even on cloudy days, and after swimming or sweating.
  • Watch out for bright surfaces, like sand, water and snow, which reflect UV and increase exposure.

A UV Index reading of 11 or more means extreme risk of harm from unprotected sun exposure. Take all precautions because unprotected skin and eyes can burn in minutes.

  • Try to avoid sun exposure between 10 a.m. and 4 p.m.
  • If outdoors, seek shade and wear protective clothing, a wide-brimmed hat, and UV-blocking sunglasses.
  • Generously apply broad spectrum SPF 30+ sunscreen every 2 hours, even on cloudy days, and after swimming or sweating.
  • Watch out for bright surfaces, like sand, water and snow, which reflect UV and increase exposure.

Return to Help Center >>