There are flashes from a retinal origin and also from the brain. You should see an ophthalmologist.
Dr. O.
The retina knows no pain, but if there is some pulling on it, it may give the sensation of flashing lights. It warrants a checkup sooner rather than later. If it is accompanied by a "curtain" across your vision, it warrants an IMMEDIATE emergency check up. Lookup retinal detachment and PVD (posterious vitreous detachment).