UVA destroys Vitamin D in the body (many previous hints of this).
Window glass block most of UVA, but ALL of UVB – thus getting UV thru glass appears to decrease your levels of vitamin D.
This may be one of the reasons that truckers live much shorter lives:

UVA without UVB : lowering of vitamin D levels.
UVA + UVB: net increase in blood levels of vitamin D.

UVB only: larger net increase (a single hint that it might be 6x this has not been confirmed).
Some bulbs have just UVB.
There is a way to block all but UVB:i.e. block UVA and visible and IR (Heat) – see below:

http://www.vitamindwiki.com/UVA+decreased+serum+levels+of+vitamin+D+-+RCT+Oct+2012

http://www.vitamindwiki.com/Vitamin+D+from+low-cost+UVB+lamps

http://www.uvguide.co.uk/phototherapyphosphor-tests.htm

http://www.who.int/uv/health/solaruvradfull_180706.pdf

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