I have not tested. Plans are to either to set up a lab in Colorado to do some testing or work with someone in Co (or other legal state) that will do the testing for me if I provide the equipment.
From what I read, the THC increase can be from 5% to those playing around...
http://medicalmarijuanagrowing.blogspot.com/
to 28% for those getting serious...
http://www.hightimes.com/read/grow-hack-how-use-uv-lamp-increase-thc
I suspect those percentages can even push higher by targeting the buds with a strong UVB dose everyday, because you got remember... the whole purpose of THC is that it is part of the plant's process to protect itself from high UVB.
And it has to be UVB, not UVA. A big part of the UV that your lamp produces is UVA... the UVA is mostly just wasted photons.
It is UVB that causes our body to tan as a response (or sun burn if you over do it.)
Fortunately, there is already a standardized method of measuring and rating the effects of UV.... it is call the UV Index...
http://www2.epa.gov/sunwise/calculating-uv-index
http://www2.epa.gov/sunwise/uv-index-scale
So next question is to ask is... what UV index rating do I need to grow high THC weed?
The answer is likely that you want to mimic the UV index in mountainous regions of the world where the highest THC weed is grown.
See
http://www.uvawareness.com/
I think your target UV index "at the bud" should be about 11 to 14.
Next question is... how to measure it? There are some relatively cheap meters to do this...
http://www.amazon.com/Portable-Checker-Atmospheric-Light-Meter/dp/B00481APE8
http://www.amazon.com/gp/product/B001Q3KW4O
To get 11 to 14 UV index "at the bud", it is going to be "side lighting".