I have quite good experience with what you call “shooting into empty space”. So the background has to be very fare away and should not get any light. The room has to be dark and perhaps you have to construct some kind of tube around your lamp to avoid scattering light into the room.
A flash is of cause a very convenient way to darken the room. A short shutter time will remove all other light sources in the room (Your leaf shutter has no limit for the synchronizing time)