I don't know which HD lighting system you are talking about, they make several, from MH to Mercury Vapor to High Pressure Sodium to Incadecent and so on, but...
MH bulbs need a MH ballast, same wattage for both....a 250W bulb will not burn on a 150W ballast. Also, MHs come in 70, 150 250, 400, and 1,000 watt choices... I don't know of a 500W choice.