“A day without sunshine is like, you know, night.” — Steve Martin
1) High noon (for your skin): UVB is most intense during the summer months and when the sun is highest in the sky, with levels peaking at noon, and remaining high between 10 am and 2 pm. In temperate regions, the daily summer peak of UVB radiation can be one thousand times higher than in winter.
2) Clear skies: Clouds really do have a silver lining since cloud cover scatters UV radiation from the sun back into space. The more opaque the cloud, the less UVB will penetrate it. Scattered clouds allow around 89% of UV to pass through, broken clouds transmit 73% and overcast skies reduce UV levels to 31%.
3) Exotic locations: The closer your location to the equator, the higher the levels of UV radiation reaching the earth. It’s no accident that you find populations at tropical latitudes have darker skin; melanin acts as a protective shield against ultraviolet radiation. The lighter your skin tone, the higher the risk of damage in the tropical sun.
4) High times: The earth’s atmosphere is thinner at high altitudes and consequently filters less UVB radiation. With every 1000 meters increase in altitude above sea level, UV levels increase by 10% to 12%.
5) Snow, sand and sea: Snow, water and sand are highly reflective surfaces that bounce UV rays back upwards. Snow can reflect as much as 80% of UV radiation, beach sand about 15% and sea foam roughly 25%, increasing your chances of sun damage.
6) No-go zone: The ozone layer is a layer in the Earth’s atmosphere containing relatively high concentrations of ozone gas, which absorbs UVB. The intensity of UVB radiation at the top of the atmosphere can be up to 350 million times stronger than at the Earth’s surface. The thickness of the ozone layer varies based on latitude and season, with higher levels in areas further from the equator. Ozone levels have also been depleted by chlorofluorocarbons (CFCs).
The UV Index is a standard measurement of the strength of the UV radiation at a particular place on a particular day. It takes sun altitude, elevation, reflection, cloud cover, and ozone concentration into consideration. SkinVision’s UV forecast feature tracks your local UV index and provides advice on how to protect your skin appropriately.