I would run a 30 amp 240v circuit- which is able to run four 1000 watt lights (around 5 amps each)- leaves room for growth. However, if you are limited, a 1000 watts at 120v (10 amps) on a 15 amp breaker will do- and nothing else on that circuit, or you risk running hot ( no bueno)
"Each circuit breaker is rated for a specific current flow. If the current exceeds a circuit breaker’s rating, it will warm up to a point where it will “break” the circuit, cutting power to the device/devices to prevent an electrical fire. In addition to excessive current flow, circuit breaker overheating can be the result of poor quality electrical connections. Poor electrical connections increase the resistance to the flow of electrical current, resulting in the generation of heat. Potential problem areas include where the wires connect to the circuit breaker, where the circuit breaker connects to the main panel or possible electrical connections within the circuit breaker itself. Generally, the temperature of a circuit breaker should not exceed 140oF. If it does, this means the circuit breaker is in danger of tripping. A good "rule of thumb" is that if you can't hold your finger on the plastic part of the circuit breaker without getting burned, it is too hot."
I think a general rule of thumb, is run up to 80% of the amps the circuit is rated for.
A x V = W
W / V = A
W / A = V