I've played Skyrim for a long time now and I basically know the game like the back of my hand, but something has always confused me. Sometimes when I'm out in the wild randomly, there will be these big flashes of light that either appear in the sky or in other places. They are not just like a screen flash, but something more akin to a spell. Like vampires bane but 8 times bigger and it appears and then disappears in like 2 seconds. I see it most frequently in the Plains around Whiterun. I've seen people see something similar but they played on a pc and assumed it was a glitch but I use my 360 and this definitely seems more solid than a glitch. There is no sound involved with it either. I brought it up because I was playing just a while ago and it appeared nearer to me than it ever has before and I was able to run t9 the spot where it originated and upon investigation there was nothing there.

The only thing I can think of are mages of some kind. That's typically the only light sources that will fit your description.

I considered that, and yet I've never seen a spell casted by a person of that magnitude. It's BIG. Like when you shoot a sun hallowed arrow up into the sky and you see that first big burst of light with the spell webbing. It appeared one time on the side of a cliff and it really gave a good sense of scale. It was far larger than any spell I can recall.

The only thing I can think of that might fit the bill is some kind of magic effect permanently attached to the player

That's a good thought. I do have alot of active effects. But I can't immediately think of anyone of them that would produce such a thing. I'll look into the next time I play.