I suggest a "worst case followed by refinements" approach. To start off, assume you have the 60 LEDs all located at a distance corresponding to the farthest distance any single LED is from the panel. Put all the load at that distance, and calculate it as a balanced three-phase load. For example. if the farthest LED is 600 feet from the panel, a #8 wire will get you to a 3% VD. That might be a bigger wire than you would want to use.
You can refine this by dividing the run into smaller chunks. For example, place 30 LEDs at a distance of 300 feet and the rest at 600 feet. The first section will include the load from all LEDs, but the second section will only have half the LEDs. With #10 wire, the VD from the panel to the first point (with 8 amps of load) is 2%, and the VD from the first point to the second (with only 4 amps of load) is 1%. Calculated this way, you can use #10 wire for the entire run.
You can further refine this by putting a third of the load spaced out at distances 200 feet. I will leave that math to you.