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Furthermore, can I use a 120v bulb in a 250v socket?
It only serves to pass the current from the wall to the light bulb. In your case, the fixture can handle any voltage up to 250V. You can use a 120V or a 240V bulb. The maximum voltage is simply the highest voltage that the fixture is rated to withstand, without arcing or breaking down in some fashion.
Keeping this in consideration, what does 660 watts mean?
If the OUTLET says 660 W, then it means that the maximum current that the outlet would tolerate is 660/120 = 5.5 Amps. Then, a 60 W light bulb would require a current of 0.24 A to run. This means that the outlet can tolerate (660/250 = 2.64 A) and you can connect (2.64 / 0.24 = 11 such bulbs in parallel.
Just to clarify a 120v light bulb from NA put into a 220v european lamp in europe. Would that work? No, unless you want to have one quick flash. However, you can use a 220/240 watt bulb in North America.