Factors that affect UV radiation levels

UV levels are affected by several different factors, this means that UV levels are higher in some parts of NSW than in others – even on the same day.

Geographic location

In regions closer to the equator the sun is higher in the sky. The sun’s rays have a more direct pathway to earth (straight down, not angled) and pass through less atmosphere which acts to absorb UV radiation. For example, all areas north of Sydney need to use sun protection all year round to protect their skin.

An image showing sun protection recommendations across the state of NSW. North of Sydney, the recommendation is all year round. South of Wollongong, it is recommended year round except for June and July.

Altitude

In higher altitudes (i.e. in the mountains) the air is cleaner and the thinner, and atmosphere absorbs less UV radiation. UV levels increase by 10%-12% with every 1000 metres increase in altitude.

Time of year or season

The angle of the sun varies depending on the time of year. UV radiation is greatest in summer as the sun is high in the sky and its rays pass through less atmosphere before reaching the earth’s surface. In winter, the sun is lower in the sky and its rays have a longer course through the atmosphere; more UV radiation is absorbed, and UV levels are lower.

A chart showing sun protection recommendations by season. In winter the advice is to check UV levels daily. All other seasons, sun protection is recommended every day.

Time of day

UV radiation levels are lower in the morning, peaking in the middle part of the day (when the sun is overhead) and gradually dropping again throughout the afternoon as the sun moves lower in the sky.

Cloud cover

Thick cloud provides a good filter for UV radiation. Thin and scattered cloud does little to reduce UV levels. Always check your daily local UV levels, as UV can be 3 or above on cool or cloudy days

Reflection

Surfaces such as snow, water and sand reflect UV radiation. Snow reflects between 50 and 88% of UV radiation, sea surf (white foam) reflects 25 to 30% and dry beach sand reflects 15 to 18%. This means that UV radiation reaches you directly and indirectly (when it is scattered and reflected by the snow). Read more about sun protection at the snow.

Artificial UV radiation

UV radiation is available from artificial sources such as solaria (solariums, sun lamps, tanning booths). Research has shown that people who use solariums before the age of 35 increase their risk of developing melanoma by 59%. Commercial solariums were banned in NSW in 2014.

There are many different factors that affect UV levels – even on the same day, UV levels can be higher in some parts of NSW than in others. Remember to check the SunSmart App daily for your local sun protection times – when UV is 3 or above sun protection is needed.

Remember, always use more than one form of sun protection. Never rely on just one.

Read more about when sun protection is required in your local area or check your local sun protection times.