Well true that a Blacklight can produce UVB along with near UV visible and UVA (wikipedia), I highly doubt this light is the one you want to use. It sounds like most of your light will go to waste. I use UVB lights from a reptile store as supplemental which would be a much better choice.

If you happen to have a ballast with florescent type blacklight or something, then check the size (like T5 or T12 etc...) and replace the bulb with a normal 6500k white which can grow.

I hope it helps.