I took the white and warm white spectral distributions here: http://www.luxeon.com/pdfs/DS23.pdf
Question: Is it correct that the warm-white Luxeon has 20 lumens per watt, and the white Luxeon has 45 lumens per watt?
If so, the warm white Luxeon has a very lousy PUR-efficiency of 0.13 microEinsteins per Joule (comparable to an ordinary Halogen), and the white Luxeon has 0.38 microEinsteins per Joule.
The PUR-efficiency was calculated with an action spectrum for green plants (B): http://www.cartage.org.lb/en/themes/...rition/706.GIF
This means you would need apx 7-8 times as much watts when using Luxeon Stars compared to an efficient T8-bulb like Philips Aquarelle (0.8 microEinsteins per Joule) to achieve the same growth-rate.