Why are bugs attracted in the direction of light?

Moths & other insects naturally get attracted to the light. Some get a pull from sunlight while the majority of the others get attracted to moonlight. Since the light fixtures we use everywhere also emit light, the bugs get to them in hordes as if a magnet is pulling iron in its direction. Another reason is that traditional bulbs emit heat, yet another factor for bugs to stay connected to the source of light. But technology is advancing every minute implying that gone are the days of bugs bugging you constantly.