I have a 400w mh light now, how far away from the plants should I put them and would that be enough for 4-6 plants?
would love to help,just need a little more info. 1- How old are the plants? 2- how are you growing, vertically, scrog, combo? 3- what type of ventilation do you have going on? A 400 watt MH light with a wing fixture will cover a 4ft by 4ft area with a little more in the indirect light column just past that. With good air flow you should be able to get them to around 12 inches no problem. If you ever wonder, use the back of your hand over the top of the canopy, if your hand gets hot after a minute or two so will your plants tips thus stunting growth.
the plants are about 3 weeks old(will be putting 2 new ones in as well) gonna 4 way lst most likely(they're still young so haven't decided. I have a fan constantly moving air around and the room the setup is in stays at 70 degrees(the whole house does for that matter lol)
The HPS light will produce some heat so you'll see 70 dip into the 80's. I would use the hand rule or go buy a cheap thermometer and get it at canopy level
Put your hand on the tops of your plant. Lower your light until it starts to feel hot on your hand. Keep raising it as it grows, repeating the process above.