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Temperature does not determine risk: infrared versus ultraviolet radiation

The sun provides us with light and heat.  However it is also a source of radiation which can have a negative impact on our health when we get too are over exposed to it.

The spectrum of radiation received on earth from the sun includes infrared, visible and ultraviolet radiation.  The light spectrum ranges from the colour violet to red, just as you would see on a rainbow.  Next to the violet colour is ultraviolet (UV).  This is the radiation to which overexposure can cause harm in humans.  At the other end of the visible light spectrum, next to red is infrared.  This is the type of radiation that creates warmth.

This is an important point to understand because many people think of heat and UV radiation as the same thing. Actually they appear are opposite ends of the spectrum and are delivered from the sun in different proportions.

Visible light region

When the sun is not visible we receive no UV radiation.  As the sun rises, the level of UV increases until it reaches its peak at solar noon, when the sun is directly above us.

It’s often the cooler days that result in the worst sunburns because the UV level is high while the temperature is not.  It can be hard to mentally disconnect heat and UV because when it is hot our skin does feel like it is burning, but in reality the heat we are feeling is the Infra Red radiation which does not cause sunburn.  Damaging UV is invisible and cannot be felt.  This also explains why it can still be 35 degrees on a summer in later afternoon yet there is no chance of getting sunburnt.  In fact even in the middle of summer in Perth the UV level after 4.30pm each day is generally low enough to not require any sun protection.

Conversely, when the weather is cool in Perth in the middle of winter there can still be the need to apply sun protection as the UV level can rise to 3 or above.

Understanding the difference between UV and heat, as well as understanding the UV index and the times you are at risk, plus taking sun protective measures can dramatically reduce your risk of skin cancer in the future.

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AUS
Trigg Max Recorded UV 7.8
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AUS
South Lake Max Recorded UV 6.8
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AUS
Churchlands Max Recorded UV 7.8

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Forecast - Perth

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UV level
's Forecast UV Index -
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UV observation courtesy of ARPANSA

UV readings from around AUS
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