I recently bought an Oregon Scientific UV888 Personal UV Monitor (~$30).
Among other things, it measures the UV flux and computes the UV Index
(UVI), then determines a "safe exposure time" based on your input of
skin type and the SPF of the sunscreen you are using.

Naturally, I made a measurement in the sun (UVI = 8), then another one
inside the cockpit (UVI = 0), indicating the canopy provides quite a bit
of protection. Testing other kinds of plastic, like baggies, plastic
wrap, Lexan, etc., gave readings from 0 to 7, so not every kind of
plastic is protective.

These measurements made me curious about what the UVI index is, so I did
some searching and learned a few things:

* The UVA band (315 nm to 400 nm) is the primary tanning and
wrinkling band
* The UVB band (280 nm to 315 nm) is the primary skin damage band
* The UVC band is almost entirely blocked by the atmosphere, so has
essentially no effect
* The UVI is a weighted value that accounts for the skin's response
to different irradiation frequencies (almost none to UVA, quite a
bit to UVB)

The most interesting discovery for me is that tanning can occur without
harmful skin damage (I know, we hate wrinkles, but they don't kill!), so
getting a tan, such as the tan described by a letter writer to a recent
Soaring magazine, does not mean you are also damaging your skin.

Looking at an "erythemal dose rate" chart, you can see almost all (99%)
of the dosage in the direct sun occurs below about 330 nm. Since our
canopies block UV below about 360-370 nm, they provide essentially
complete protection from damaging rays. The fraction of the UVA that
comes through will still give you some tanning, and some fabrics will
fade slowly, but your skin is protected from the UVB. This is very good
news, that the canopy affords even more protection than I first thought.

So, cover yourself as much as possible (hat, long sleeves, etc), put the
sunscreen on when you get to the gliderport, do your rigging and outside
preparation early in the morning, and take shelter under a wing, under
an umbrella, or inside a building or vehicle (glass protects, too) while
waiting to take your tow. Breathe easy while you are flying the glider,
and apply more sunscreen when you land, unless the sun is low.

This is the main reference I used for my education and conclusions:

* http://www.aero.jussieu.fr/~sparc/News21/21_Long.html

Other interesting references a

* A simpler version of the main reference (National Weather Service):
http://tinyurl.com/evfc7

* UV meter:
http://tinyurl.com/f3uuy

--
Eric Greenwell - Washington State, USA
Change "netto" to "net" to email me directly

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org