Lighting wattage - how much is too much?

[howdy20012002]

i just bought a 90 gallon setup that came with 2 400 W MH lights and 2 110 watt atinic-i am not sure what the k rating is. Is this too much lighting for this tank?
as well i have another tank that has a 150 w - 20 K MH....what effect does the 20 k part affect? is this a good one to have or should it be lower like a 10 k?
any help would be appreciated
thanks
Neal