I just started cycling recently, and I had experienced something very weird. I rode twice for the past couple of weeks, each time a little over an hour. When I went home, got down from the bike and enter the relatively dark apartment, a bright yellow/greenish horse shoe shaped image appeared in front of my eyes. Upon closer inspection I found actually it's two crescent/boomerang shaped images, one for each eye. They overlapped and formed the horse shoe. They are like the odd shaped images I used to see when I closed my eyes and pressed my eyeballs with my fingers for a period of time (they will linger for a while even after you open your eyes). I used to do that to see those ever changing images when I was a child.
Anyone had similar experience? I suppose it must be something your see only (if at all) when you are a beginner, and will wear off with more experience.