EDIT: Ok, I just googled "purple lighting growing" and got results saying that purple lighting is somehow good for plant growth?! GUWHA??!?!?!??!?!?!
Well, what I can't really comment on is your light - I'd need to see a spectograph of its output to say whether it is a plant useful PURple light.
The PURple lights designed for plant growth do output an enhanced blue and red spectrum and a reduced yellow/green spectrum - that's why to human eyes these lights look Purple - it's the mix of the high outputs of red and blue. The human eye is most sensitive to the 500-600 nm light spectrum range, with the peak at about 550. This is the nm range that contains the most yellow and green light, and the light spectrum range that plants simply do not use for either photosynthesis or chlorophyll synthesis which takes place entirely in the 400-500 blue nm range and 600-700 red/orange nm range. This is also why plants leaves look green to us, because all colours the human eye sees is reflected light and as plants do not absorb any green spectrum light - but reflect it - that's why it appears green to us. I have seen some research done that suggests plants are sensitive to yellow light, but there's no evidence that they actually use it for any plant important functions.
Because PURple lights output enhanced blue and red spectrum light, which is the light spectrum plants mostly use, and reduced green/yellow, their PAR rating (Photosynthetic Active Radiation) which is the light plants actually use (ie mostly the blue and red spectrums) is high - somewhere around 80% PAR output, not a 100% because it still contains some yellow/green light.
This also explains why HID lights, which output HUGE amounts of that yellow/green light that plants simply do not use, have such HUGE lumen ratings. Lumens is a light measurement, that measures light the human eye sees (not the light that plants see) - which is light in that yellow/green spectrum.
This is the reason that HID lights (MH or HPS) are extremely expensive to run in terms of their lumen per PAR watts as opposed to their lumen per watts ratings. A HPS or MH will output something like 20-40% PAR, so whilst it may have very high lumen outputs, the actual plant useable light is only between 20-40% of that total lumen rating. So for a 250w HPS outputting say 25,000 lumens, only about 5,000 - 10,000 of those lumens are in the plant useable light spectrum. Compare that to a 200w PURple CFL, which outputs 13,700 lumens of which 80% will be in the plant useable light spectrum. So 13,700 x 80% = 10,950, roughtly the same as the higher level of the 250w HPS.
The major difference of course is the cost to operate. A 200w PURple CFL draws 161w, a 250w Magnetic HPS will draw 300 watts and a digital one about 260-70.
Not hard to see then that you're paying upwards of double the running cost of the 250w HPS compared to the PURple CFL for the same plant useable light.
Don't take my word for this. See for yourself at
nlite - Flourescent CFL and take a look particularly at the spectographs of the PURple light and the 6,400k Daylight and see the differences in red, blue and yellow/green outputs.
what a disapointment!
