I'd suspect the greenhouse industry would prefer the longer life.
They watch their $$$ closely.
Our 'industry' requirements are different.
Well a few hours.. In Scandinavia they are on all winter. Of course during the summer they don't use them. But in greenhouses lamps are also replaced based on light degradation, we measure those lamps (in the sphere of course) to recommend change or not.
Wow the science was way over my head there boys but thanks for the discussion none the less. Now lets see somebody buy a Pro1000 or even better a Pro600 and do a test grow with a regular 600 and see what we have. Oh, and fast, I'm in the market for a new 600-1000W setup.