How much harmful uv radiation does a standard untinted car windscreen
block?
I have heard some say that it blocks all harmful radiation, but then
there is the tinting companies claiming that the tinting blocks 99.9%
radiation
which implies that it doesn't.  My mum also claims that she gets
sunburned in the car.

Hi there,

I found an authorative answer at the website of the Australian
Radiation Protection and Nuclear Safety Agency:

Tinted car windscreen: PF 75
Regular glass: PF 10
http://www.arpansa.gov.au/is_upf.htm

A PF of 75 means 75 times more effective than nothing at all.

They describe regular glass as offering "moderate protection", and
tinted windshields as having "maximum protection".

So, in theory, from behind a regular glass windscreen, it would
typically take ten times longer to get sunburnt. That's quite a lot of
protection.

Four people offer their opinions in this discussion, and all say that
windscreens help a lot, but do not offer 100% protection:
http://www2.abc.net.au/science/k2/stn-archive1/posts/topic1075.shtm

This promotional page for Ming Tinting states a PF of 9-16 for regular
windscreens, and 99-100% (PF 110) for their product:
http://members.ais.net.au/ming/tint.htm

Most people I know who get sunburned when driving - the burnt skin is
on the arm which hangs out the open window...


Search strategy
---------------

"uv radiation" windscreen
absorption windscreen


I trust this answers your question. If any portion of my answer is
unclear, please ask for clarification.

Best wishes,
robertskelton-ga

This cleared it up for me, thank you.  Hmmm...I did a google search
myself but I did not quite try the combinations that you did. Cheers!