It is not a blacklight
It is a PUR light - called purple because it is strong in both red and blue parts of the spectrum, blue and red makes purple.
Apparently ordinary fluros emit 100% PAR (Photosynthetically Active Radiation) but PUR lights concentrate on Photosynthetically Useful Radiation (PUR). According to the source 'PURple is generally accepted by the experienced as the best" fluorescent plant light'. (source:
PURple for the highest quality)
This web site is well worth a look at, it gives some good description on this subject with links to various articles. There is an article there on new lighting technology photoponics, based on this PUR technology - sulphur plasma lamps (the only true full-spectrum lamp) which I must say sound absolutely amazing, although not hugely available or affordable. They go on to explain the sulphur microwave lamp currently only supplied to research centres and nasa this lamps efficiency is so good that a 1000w is equal to a 2500w HID in terms of photoponic output and apparently you can change your plants to a 20 hour day cycle and flower in 20% less time with the same or greater yield with less energy - to top all of this the bulb is said to only need changing every seven years.