I've seen this mentioned in more than one place so I'll pass it along here. The newest 1000 watt lighting recommendation that I heard about goes like this:
VEG with a 6000K to 7000K MH bulb - Apollo Horticultural sells 6500K's on Ebay for under $40
BLOOM use a 2000K to 2500K HPS bulb - The Eye Hortilux HPS bulb is 2100K and can't be beat - $75 on Ebay
THE FINAL 3 WEEKS use a 10000K MH bulb - UltraSun is available on Ebay for around $50. There's other brands that seem more expensive. SolarMax (around $90) comes to mind....
From the UltraSun website: The Ultra Sun™ Metal Halide (MH) Blue Enhanced Performance lamps offer extra emphasis in the blue and violet spectrums with Kelvin temperatures of 7,500°K and 10,000°K. This line of Ultra Sun™ lamps is exceptional for vegetative growth and for the final fruiting and flowering stages of a plants development. These lamps have been specifically engineered for horticulture applications. Ultra Sun™ lamps are high quality, feature robust construction and have excellent reliability at an economical price.
It's day 45 of the bloom at my house and the 10k bulbs go into production tomorrow. IF you have the means and you're NOT doing this....let's just say you're missing out on an easy - no EASY 10+% gain PLUS those buds really FROST UP under that 10K light!!!!
Don't question my premise. Do your own test and see if you get the same results. For the $50 or $60 bucks each bulb costs, it's a CHEAP gain.