Enough light

Can use 2 13.5 gallons bins under a 400 watt hps/mh,4 plants per bin,tent big enough for the two bins,havent bought yet,will be ordering tomorrow.All input is welcome.

I wouldn't try to do anymore than 9sq ft with a single 400 watt light... look into the inverse square law. Once you get a basic understanding of it, you can do a rough calculation on how many lumens u are getting say 3 ft from the bulb... You will shit yourself when you see how every ft you move away from the light source, you lose 3/4 of your light intensity...

How large of an area do the two bins together cover, like side by side. (example 24 X 32 inches)

You can stretch your wattage per plant with a light-mover, but I personally would go with 600w and a mover.