I understand that you would use 480V light fixtures as opposed to 277V because the 480V have a lower current draw, resulting in a more efficient system. What I don't understand is how this circuit works. In the following paragraphs, I'm using the term "supply" as current flowing to the load and "return" as current flowing back to the breaker panel.
In a simple single-phase lighting circuit, you would have two wires: say, 120V hot wire and a neutral wire. Current flows from the hot to the light fixture and back through the neutral, assuming conventional direction of current flow. This completes the circuit and you can calculate the wattage by measuring the current pulled and the voltage supplied.
However, I don't see a 3 phase lighting circuit with 480V light fixtures work like that. Consider a 3 ph system A, B and C. If the A and B phase are connected to the fixture in a "480V single phase" manner, which phase supplies and which one returns current? If A supplies and B returns, then what about a load that's connected across B and C? That would mean C supplies and B is the one carrying the return current at all times, or else you will have a conductor with two currents flowing in opposite directions.
OR is the fixture drawing current from both phases? If so, then that's not single phase. Also, wouldn't you use 3 single-pole breakers as opposed to 1 3-pole breaker to supply the 3 phases. Please advise.