Moon light on front of boat

I have decided to start trolling for walleye and I know nothing about it, rather then let the plug out behind the boat and just a few more things for a starter. But the other night I was on the lake and trolling and I could see way off a white light on another boat that was headed in my direction. After a while we met and that light didn`t glow bright, not even enough that I could see them or what kind of boat it was. I say we were about 100 feet (more or less) from each other when we passed. What I would like to know is there a purpose for that light when trolling?