Not sure, but not bad.
I can't really come up with anything bad to say about this. It's hard to say if it's actually clearing the air or not, but I'll give it the benefit of the doubt; my apartment might be slightly less smelly. I would recommend buying a couple replacement bulbs at the same time. First one lasted maybe a month. Second one about 4 months, on my third one now. A lot of people seem to complain about the noise, but I really don't see much of a problem with the quiet whirring.
Rating: 4 stars