I did some back of the envelope calculations and if everyone on the planet runs 1.4 20W lightbulbs (100W equivalent CFL) half the time, that comes to the amount of energy expended on smelting Aluminium.

Aluminium per year: 720000GWh

20W (100W equivalent CFL) Lightbulb on half the year: 87.6KWh

Aluminium = 8.21917808 × 10e9 lightbulbs

Probably wrong in many ways, but I'll post it here anyway.