In addition to the timer switch or motion detector, I'd strongly
recommend a couple of low wattage CFL bulbs to avoid tenants
suddendly being dropped in darkness. With two twenty watt
CFLs on continually, you're looking about a dime per day
for electricity. Far cheaper than a lawsuit resulting from
personal injury? Perhaps with this 'background' light, you'd
need only a single timer?

A former employer installed a motion detector switch for the
employee restrooms. The restrooms were in an interior
hallway with no light from outside. It was disconcerting to
be sitting in a stall on the 'throne' and have a normally bright
room plunge into darkness. And waving a hand around inside
the stall wouldn't trigger the motion switch. Had to open the
stall door and close it to restore the light.