A higher voltage drop may be more acceptable if the voltage drop is at least uniform. The catch is, the lights closer to the source will have a higher voltage than the lights at the far end of the run. It's a lot easier to see that the system has a problem if the lights are not equal in brightness.

I do not know if this kind of wiring meets code, but so far I've not run across anything in NEC that would prohibit it:

Run a 3-wire cable (white, black, red) along all the post lights. Run a 2-wire cable (white, black) from the house to the first post light. Connect like color wires at each junction, including the red wires in the 8 middle post lights. Wire each light to white and RED (not black). At the very last light connect red and black together.

This won't eliminate voltage drop. But what it will do is make it uniform and more tolerable. The hot side of the circuit runs down the black wire all the way to the end. Then it runs backwards along the red wire to each light. Each light is thus involving an equivalent length of wire and equivalent voltage drop. So you will get the same voltage at each light, however low that happens to be.

To calculate what the drop will be, figure it as if all lights are at the very end of the run.

You might then correct the voltage drop with a buck-boost transformer if you're sure of the exact wattage that will always be used. Or maybe just order some 100 volt bulbs from Japan [Linked Image]