The formula for figuring watts, the unit the electric company measures, is A x V = W. Another permutation of this formula is A = W/V (A = amperes, think of it as the amount of electricity; W = watts, think of it as the pressure; V = volts).
A 1000-watt lamp uses 1000 watts, or 1 kilowatt plus the electricity to run the ballast, say 250 watts. That is a total of 1250 watts. Dividing by the voltage (110) shows that the lamp uses about 11.36 amperes of electricity. Running at 220 volts, with the pressure doubled, only half as much electricity is needed to do the same work so the system uses about 5.68 amperes.
Either way, each hour, it uses 1250 watts, or 1.25 kilowatt hours.
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