Not sure if this is a glitch or intended, but for me the light crystal always floats back to the gate straight down from the shop. I move it but as soon as I let go, it goes back to the portal (or rather a little in front of it). Anyway, I'm loving the game. It's so simple but also so fun at the same time. Keep up the good work.
Edit: I also noticed that the crystals make noises that get louder and softer, kinda like a metal detector. I wonder if this has anything to do with the purpose of them. For now, they just add some really cool lighting to my shop. Maybe that's the point of them.