Can a 240V light fixture be used in the US with a 120V light bulb?
Hard to say without details. If it is an incandescent lamp with a replaceable screw-in bulb, and the socket fits a bulb made for here and 120V, then yes, it shouldn't matter.
But again, the devil is in the details. If we are discussing screw-in base bulbs, Europeans mainly use E14 and E27 bases. E14 is equivalent to what we in North America call a &quot;medium&quot; base, which is not very common (specialty lamps like aquarium bulbs). We use &quot;candelabra&quot; bases for small bulbs, which is equivalent to an E11, but that is uncommon in Europe. Larger bulbs in Europe are E27 bases. The E number has to do with the width of the base; E27 is 27mm wide. Here in NA we use what's called an &quot;Edison base&quot; and it is 26mm wide, what the EU would call an E26. So it's possible, because of tolerances, for an E27 bulb to screw into an Edison (E26) socket, meaning you can use an EU light bulb in NA fixtures (however the voltage is usually wrong). But going the other way; an Edison (E26) bulb screwed into an EU E27 socket, results in the bulb being loose in the threads and possibly getting jammed, then difficult to remove.
If the lamp has a CFL or LED, then it would depend on whether the &quot;ballast&quot; for the CFL or the &quot;driver&quot; for the LED is able to accept the different voltage. A whole different kettle of fish.