Seeing lights and spots

What is the difference between seeing lights and colors due to problems directly from the eye, or due to problems in the brain (like hallucinations)? I've been seeing these for years and have no idea why. They aren't affecting my vision permanently, but usually happen every day. I've looked up conditions and they seem to fit symptoms of many things, most of which I can't find much information on. I'm mainly curious how you could - if at all - tell the difference between the two.

[Ray T Oyakawa, MD]

Flashes related to the eye last seconds.  The ones related to the brain last minutes--usually 20 minutes or more.

Dr. O.

[Zeppelyn]

Thanks, mine would be due to the eye then. What could cause it? I'm only 17.