for a 5x5 space you want a 1000watt HID light.

More light = more yield (given that everything else is in order).

With that said; if you are set on a 5x6 grow area then use a 1000 watt light for maximum yield. Also, grow more than 4 plants. That is a huge waste of space and so much light that would hit the floor that should be covered with canopy instead to make as much usage of your electricity as possible.

Otherwise I would suggest a 3x3 grow space and use a 600 watt HID. That should be perfect for 4-6 plants in 5 gallon containers.

Good luck :thumbsup: