400w mh for veg?

Hey guys, had a few questions on lighting. how many plants can I fit under a 400w mh bulb, how tall would the plants be till I need to switch to flower, and how far away from the tops of the plants? Thank you!

A 400 watt HID bulb can cover a 3' x 3' and a good hanging height is about 14" - 16" above the top of the canopy.

One way to check - "the back of your hand" test. If your hand doesn't feel warm at 14" below the light, that's a good height. If it does, lower your hand until it's not warm and that is your hanging height.

I am getting the sense that plant height might be a concern ... what is the total height of the grow space?

Itswoody said:

Hey guys, had a few questions on lighting. how many plants can I fit under a 400w mh bulb, how tall would the plants be till I need to switch to flower, and how far away from the tops of the plants? Thank you!

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Agreed 3x3. Check the manufacturer's specs though, it should be 3x3 veg and 2x2 or 2x3 flower.
How many plants? There are a few factors. For instance, are you growing autos or photoperiod? I wouldn't put more than two autos in that space, but photos you could probably go more since you are in control of when you drop the light to 12/12. Strain matters too. Sativas could prolly fit more since they tend to be skinnier. But if you train them, that goes out the window. How tall, again depends on auto/photo. Autos are interesting. I'm growing my first autos now. 5 x 5 tent, 1000w HPS, 5 gal smart pots with soil. My tent is 80" (6'8") tall and I've trained the plants twice. Defoliated three times. I have six plants in a 5 x 5 tent which should have given me enough room to dance around in there. Instead its like a magic trick every two days getting them in/out so I can water them. This is week two of flower. I've got a big reflector for the HID so that's 18 inches. 6'8" tent height so the light is at 5 feet. 1000w HPS distance to the canopy for flower is around 18 inches which means my plants should be around 3.5 feet. HA! I've trained them twice and they're easily over 4 feet. If you learn anything from that example it's don't assume as I did for some reason auto flower means small. In general (and this isn't a hard-fast rule) when growing with "standard' ceiling heights or tent heights, you can expect to throw your girls into flowering somewhere around week 3-5. Of course, you could keep a photoperiod in veg indefinitely and create a 10-foot monster, but definitely not in a 3x3 rent.