Why are many insects attracted to sources of light?

This is an excellent question! Actually, there has been some debate on this topic. One theory is that they are attracted to the light because they use it as a navigational aid. Instinctively, they head towards the light because they associate it with a less dangerous situation than their current one. In other words, they see moving towards the light as 'moving up'. Another theory is that the insects' eyes cannot easily switch between light and dark, so they stay near the light where there is continual brightness. If they flew away from the light, then there would be some time where seeing much of anything would be difficult.