Welcome japkon. What kind of LEDs are you using? bc I highly doubt that they are equivlent to a 400w hps. That might be what the manufacturer said, or the guy that sold it to you, but that's not what they really are. I have 3 x 7 watt LEDs that ran me about $150 for all three. They are batwings (the good kind). Sweet little things, but they say they are equivilent to a 250w hps, but not likely. More like a 50w hps if that.
The downside that you arn't reading about hydrogrower, is that the 'pannels' and the led 'spot lights' that everyone is trying to sell you for $20 or so are crap. Pure crap. The only ones that will net you anything more than a few leaves off a plant are the batwing ones. I don't know too much about them, a buddy got them for me (at least hooked me up with a source, I still had to pay). The UFO led light I've heard is sweet, and the 100w protocron (or whatever the hell it is called) is suposed to be good, both by led standards and both cost $400-$600. THOSE lights are close to a 400w hps, but not quite there. You would need about 12 of those 'panels' and about 12 more of those 'spot light' leds to do a grow in a 3'x4' space. Even at $20 a pop, that isn't cheap. Those LEDs have a small angle of light released, mainly straight down. So if you don't have enough of them you are F'ed. And as the plant grows if you don't have them positioned at just the right spot, you are F'ed. Plus, those shitty leds don't have the penetration power of actual lighting, meaning that they can barely penetrate into the leaf of the plant to provide enough energy for photosynthesis, let alone peircing through the canopy to get to the rest of the plant.
Shed a little bit of light on the situation for you?