Physicists classify ultraviolet
light into three types, by its wavelengths: UVA, UVB and UVC. The dimensions of
their wavelengths are roughly 400 to 320 nanometers (nm) for UVA, 320 to 290 nm
for UVB, and 290 to 200 nm for UVC. Although it may seem backwards, the shorter
the wavelength and the lower the number, the greater the energy level of the light
and the more damage it can do. For example, direct exposure to UVC for a length
of time would destroy the skin. Fortunately, UVC is completely absorbed by gases
in the atmosphere before it reaches the ground.
The longer wavelengths
of UVB and UVA pass right through the atmosphere, even on a cloudy day. That's
why you can still get sunburned on a cloudy or hazy day. The molecules in sunscreens
absorb most UVB and prevent it from reaching the skin just as the molecules of
the atmosphere absorb UVC and prevent it from reaching the ground. But UVA is
another story. Most sunscreens do not protect the skin from the longer UVA
wavelengths. And that may be critical to the creation of skin cancer. Approximately
65% of melanomas and 90% of basal and squamous cell skin cancers are attributed
to UV exposure.
UV Level 2 or Less
Low UV Level
An UV Index reading of 2 or less means
low danger from the sun's UV rays for the average person
Wear
sunglasses on bright days. In
winter, reflection off snow can nearly double UV strength. If
you burn easily, cover up and use sunscreen
UV Level 3 to 5 Moderate
UV Level
An UV Index reading of 3 to 5 means
moderate risk of harm from unprotected sun exposure. Take precautions,
such as covering up, if you will be outside. Stay
in shade near midday when the sun is strongest.
UV Level 6 to 7 High
UV level
An UV Index reading of 6 to
7 means high risk of harm from unprotected sun exposure.
Apply
a sunscreen with a SPF of at least 15. Wear
a wide-brim hat and sunglasses to protect your eyes.
UV Level 8 or Higher Dangerous
UV Level
A UV Index reading of 8 to 10 means very high risk
of harm from unprotected sun exposure.
Minimize
sun exposure during midday hours, from 10 a.m. to 4 p.m. Protect
yourself by liberally applying a sunscreen with an SPF above 15. Wear
protective clothing and sunglasses to protect the eyes.
