I have a 250 hps sun system II with a 250 new hortilux bulb running on a 20 amp circuit with a gfic breaker. I bought the light used and has been in operation for three weeks with no problems. Now the gfic "trips" when the light goes on. What could wrong with the light to cause the gfic to trip?

i'd try replacing the GFI. maybe check and make sure the polarity and grounding of your circuit are correct as well. Breaker could be going out as well

Problem solved! I took the light apart to check the capacitor and it was fine. Looking around inside the light I noticed a black carbon deposit on the metal housing. It appears when the light was assembly the wire became "pinched" between the metal plates and over time created a "dead short" causing the gfic to trip because current was leaking to the ground. A gfic trips off at 4 to 6 milliamps. Ever one should have gfic in there grow rooms. Safety is proactive not reactive! So be safe!!!