Originally Posted by Psycho4Bud
Ballasts are based on a wattage rating. If you have a 1000 watt ballast there is no reason why you can't use a smaller lamp. BUT if you have a 400 watt ballast DO NOT use a higher wattage lamp! Why? Amp. draw.
When you use a lower wattage lamp, basically your not using the ballast to it's full potential or amperage rating. If you put in a LARGER lamp your now increasing the amperage pull from that ballast past its "safe" rating which means you WILL create heat and have the possibility of burning out the ballast prematurely. GOOD LUCK!!!
Imagine using about 4 1000 watt lamps on a single 110v household outlet. You would be pulling 36 amps though an outlet more than likely rated for 15 amps. BAD KARMA!!!