Two or more.
only one to screw it in (though the 1/4" brushed aluminum base is much heavier than it needs to be), but at least one more to argue that you need to replace the tungsten filament with something more neutral.
only one to screw it in (though the 1/4" brushed aluminum base is much heavier than it needs to be), but at least one more to argue that you need to replace the tungsten filament with something more neutral.