Who is that man? What is he really doing? What's in the darkness?

So my last post generated these questions from a gentle reader. :) I'll elaborate. The man is short - almost troll-like in appearance, with long scraggly grey hair and constant grey stubble no matter how recently he shaved. He has been doing this job for as long as he can remember, learning at the knees of his dad who did the job before him and his grandfather before that. But he is lonely - there being no son to follow in his footsteps, so he walks around in his room, feet making tap-tap-tap noises as he walks, turning the lights on at dusk and off at dawn. He goes outside as little as possible during the day as too much light makes him uncomfortable as does too much sky. In the corner of his room there is a cot where he sleeps.

The darkness has monsters. His job is to keep them at bay by turning the lights on when they start to stir, and turn them off again when sun's early light begins to chase them back to their hidey-holes for another day.