I currently am using a 400w in a pretty open area. I keep it between 24 and 19 inches above my plants canopy. My plants have been veg'in for less then a week so they are still quite small. I can keep the temp anywhere between 75-89 degrees, I was wondering what whould be ideal for 6 growing White Widows. I figure upper 80's wouldn't hurt, but I hear horror stories of plants overheating and whilting quickly.
From what I've read, 75-78 is ideal if you are not adding co2. My temps tend to stay in the low 80's, and in my opinion my growth is kinda sluggish. It would benefit your plants if you could find a way to lower your temps a bit.
Anywhere in the 70s is great. Can be a little cooler during dark period. Above 85F and the plants can have difficulty uptaking CO2.