The theory is to simulate mid day sun no? I've heard of some growers pulling the glass sheet out of the reflectors to increase UVB light, and because they're tired of cleaning it so often.
Not the reflector, but the glass that comes with some reflectors. Most glass filters out UVB light, varies depending on the kind of glass.
To CultivateSelf: this damn message board will not let me upload my data sheets, but I ran a side by side 2-3 years ago... Real Lemon Tree strain without 'shocking the monkey' = 19.00% Max THC Real Lemon Tree strain with UVB augmentation* = 22.92% Max THC Max THC is the summation of measured stable delta-9 THC and the measured THC acid multiplied by 0.877. (decarboxylation of acid form to stable form causes a 12.3% weight loss) *this experiment tried to provide 1200 watt-hours of 8-10% UVB for last two weeks of flowering under a single 1000w HPS light (per Ed Rosenthal's site), however, I did this by using my 600w tanning bed run for 2 hours each night.(night being our 'on' phase of flowering lights) Ha! It Did post one of the sheets!
See my post replying to Cultivate self, but per Ed Rosenthal, you would want approximately 60w of tanning light on during your 12 hr 'on' phase of HPS for last 2 weeks of flower. However, I just found a tanning bulb supplier who is sending me some bulbs to experiment with, and he told me that some growers are advocating less wattage but longer time, ie the majority of flowering time, not just the last 2 weeks. I'll let u know!
In nature the sun has the highest uvb ratios at polar noon so at lunch time. I herd that at sun rise and sun set there's almost no uvb light at all so to minc nature I would turn the uvb light on for no more than 5 hours a day during flowering