lighting/ yield.... first grow

i have two plants flowering right now with two 100W Metal Halide lights over them, they are in the end and are about done and am noticing my yield is rather low. they are in a 2x4 box but i notice many people have much much more lighting.. i have my second round coming soon with four plants and would like to know how much light i should be using and what kind?

For a 2x4, look into a 400watt HPS. 100W is ok for vegging on your scale but you wont yield much during flowering.

The more lighting the better. And for four plants I would also recommend the 400 hps. I have a friend that does amazing things with his

should i have one or two 400 hps?

one is good, unless the future holds bigger things in store...