Or if you are in a hurry remember this simple saying:
West VirginiA …… or watts divided by volts = Amps
keep it at 100 volts and you always will be safe
for example:
1000 watt lamp divided by 100 volts = 10 amps
In the real world the voltage would be 110 in a house so the amps would be 9.09, safe for a 15 amp breaker
but you can see you could not plug two 1ooo watt lamps into a 15 amp circut
good luck
Tom