Why does my circuit breaker keep tripping for a lighting circuit?
A tripping breaker is either faulty, undersized for the load, or trying to save your life.


If it's faulty, then you can replace it with a new one and the problem will go away. If you're unfamiliar working inside of a breaker panel, then I recommend getting a professional for this.
If it's undersized, you need to move some load onto a different (possibly new) circuit. The breaker is sized the the wires in the wall, so you can't upgrade the breaker without replacing the wiring. With only 4 70 watt bulbs, that's under 3 amps, well within capacity of a 20 amp breaker, so unlikely to be your problem.
And if it's trying to save your life, there's a fault in the circuit and you should stop resetting the breaker. The fix is to correct the fault. From the sounds of it, you could have a short in the circuit, perhaps water getting into the lines or a bad junction. Either way, electricity in that situation is dangerous and needs to be corrected.