What about using a spot light with a very wide angle(attunation?) instead?
Unfortunetly florescent lights are going to need multiple lights to simulate them as there are no light shapes other then round.
You could also try using a emissive material to light up the ceiling, But you have to enable a option in the Lightmass settings for it to compute lighting from emissive materials.
You could then place a plane just below the ceiling and hide it in the game, Or just make the ceiling material emissive(But that would require some tweaking to get it to look right)
HTH