You want to light up your plants to grow killer weed most efficiently (that is with min. power consumption, min heat generation, and max use of grow space)?
Use 48 inch double vho t5's and ZooMed 10.0 uvb t8 "lizard lights".
Trust me: I have tried almost everything! I have $1000 worth of 600w and 400w HID's sitting idle - I only really need them as heat sources during the cold months.
For the lizard lights Get a $35 48" t8 double light with POLISHED ALUMINUM reflector at Home Depot. Get two 48" vho t5s from any high bay contractor lignt source (about $40 each last time I checked). Put the uvb fixture in the middle and run the t5's parallel on each side. Hang the t5's slightly lower that the uvbs. Inclduing bulbs, this all costs about $225
Now you will have a full 4 square feet (less than 300 watts too) of (pefectly uniform) 6000+ lux with uvb supplementation. You won't believe how great this works!!!
After some experimantation, you will discover what strains respond best to this lighting. Fertilyzer choice makes a big difference too (I'll be dammed if after all the fancy shit I have tried for nutes, rabbit manure supplemented by kelp works fantastic)