im new to growing myself and am using some cheap lights i found around the house too. a 160 watt outdoor floodlight and a 60 watt outdoor light and i have a 1 and a half foot almost 2 foot tall plant. i expect to get maybe an eighth in the end. but fuck it ill invest into better lights later. its still working just fine. think about it yours is 500 watts you might get SOME sort of results. i suggest just going to htgsupply.com they have full kits starting from 69.95 for a 150 watt light, ballast, reflector and your choice of bulbs metal halide or high pressure sodium, then they have 400 watt light starting at like 117.00 you can spend a little more and it will come with timer and some other goodies which is worth it seeing and you must have a constant light stability/timer or its not worth even trying to work your schedule around turning on and off your plant lighting EVERY FUCKING day. so i say try it just keep the lights FAR away from your plant. like 18-20 inches. ideal heating for a plant is 75-80 degrees. although u might be able to go closer