I measured several sets of "icicle lights" with 150 bulbs per set and got between 56 and 60 watts for the full set. they were all drawing around .5 A at 120v
I needed to know because they have 3A fuses and I was trying to figure out how many I could string together without blowing the fuses. I find that I can get away with 5 strands and have a little safety factor left.
If you have a local Radio Shack, they have a neat little device called a "kill a watt". it plugs into your outlet and lets you plug a device into it, and gives you voltage, wattage, power factor, amperage ect. I paid right at $20 for mine. you could check at each point where you have lights plugged into an outlet and get a total power. To totally go around my house I have around 1500 watts of lights.
Most power inverters that I have seen are rated to handle double their nominal rated power output for short term peaks (on the order of a few seconds to just a minute or two).
By my figures 300 lights should be around 120 watts. even with the 100% overload that most inverters can handle short term it should shut down.
200 would be around 75-80 watts (give or take, 72 is just as good a number) or so and the 50 watt inverter could run it short term (minutes) before getting overheated and maybe shutting down via a thermal safety switch.
If it is a cheaper inverter the voltage will drop, say to 100vac on the output side, that will inturn drop the overall wattage and the little lamps don't care about voltage. So I would hazzard a guess it is about 50w in reality.
So far, the front of my house, the tree in the yard, the front door and the tree and bannister indoors are drawing 25W from my many strings of Foreverbrites. It probably costs me more to open the door and let the heat out, than it does to run my lights each night.
LOL, I have 6 strings of foreverbrights outside and found they pull about 8w. The mechanical timer pulls 4w. So in the long run it is cheaper to leave them plugged in a running rather then use the timer [img]/ubbthreads/images/graemlins/smile.gif[/img]