How can a light-bulb possibly disinfect water?

That's what they say in this video: a href="http://www.youtube.com/watch?v=KUnZikcA0Co" rel="nofollow"http://www.youtube.com/watch?v=KUnZikcA0…/a they pump dirty water up out of a beaker, through a fabric filter, and then into a wool-covered light-bulb. It seems to me like the fabric filter does more to clean up the water than light-bulb.