to my knowlege all hps requires a ballast but some of the smaller ones may use a smaller socket.
as per using 6 50's instead of one 400 thats really not a good idea as you would need about 12 50's to come close to equal the lumen output of the 400
so the 400 would be the obvious choice for a 2 by 3 area.
or maybe a 250 for a 2.5 sq area.
bejay Reviewed by bejay on . Lumens and number of lights For a fairly small grow cab situation (no bigger floor area than 2' x 3', or possibly 2.5' x 2.5'), I was debating which would be the best use of light, considering... - I don't want a lot of noise - I want to use as little power as possible - I have no immediate plans for C02 enrichment. As such, I'd like the lights to give adequate light per square foot, but not generate unnecessary heat (necessitating further climate control measures, hence more noise and more power consumption.) Rating: 5