I have more light when should i use them!

I have my plants under a 400 watt MH right now and there about three weeks old from seed.

I have another 400 watt HPS and am wondering when i should crank her on.....

If /when they out grow the space. Then divide the plants up and some for each light.

how many plants do you have ?

10 now but will be 7 just growing some for a friend.

So i should run them now???

Depends on the size of them. How old again? You will know if they fit under the 1 light or not

Three weeks old.

Yea they will all fit i see what you mean now.

I just want to make sure that its not to much light for that small of a plant.

They will grow great under that 400