William, Is 3500W the peak or continuous rating?I'm gonna guess that it's peak and your continuous is 3000 watts. Take 80% of the continuous rating (3000 X .8 = 2400). You should try to limit the load to that number. This means that 5 - 500 wattbulbs would be pushing your genny pretty hard.
G.E. makes a bulb that fits in a standard T3 fixture that draw less current. One is 350 watts the other is 225 watts. I run the 225's on the CIRFCU and really like them. Only problem is they're not cheap. either bulb is gonna cost you in the neighborhood of 8 to 10 bucks. I even seen folks sellin' them online for more.