I'm now using LED lighting with a 60x60x80 grow tent. Despite the upgrade from the 50W CFL lamp to the LED light, growth is still relatively slow.
Lighting intensity is adjusted to ~400 PPFD (the maximum with the LED lamp)
No nutrients are being used (the soil is surprisingly rich in minerals - see week 3)
Daytime temperature is 22°C (according to Captain Hindsight; it might be beneficial to increase it a bit)