Does your friend get migraines? I know that some people experience flashing lights before getting a migraine. The site below mentions that it is more common in older people. I thin it's worth getting checked out. From http://www.mdsupport.org/library/floaters.html
Flashers
When the vitreous gel rubs against or pulls on the retina, it can produce the illusion of flashing lights. Flashers can be perceived as a sparkle, disco light, fireflies, lightning, fire works, or sparks. The same experience can happen after being hit in the eye, giving the illusion of seeing stars. All of these flashers are generated by any abnormal stimulus to the retina.
Light flashes can happen on and off for many weeks, or even some months. This is a common occurrence during the aging process, and it is generally not cause for concern. At times, however, a significant number of new floaters will appear, accompanied by light flashes, and partial sight loss of peripheral vision could occur. If this happens, it is important to see an ophthalmologist quickly in order to evaluate whether the cause is a torn retina or retina detachment.
Migraine flashers appear as zigzag, shimmering, or even colorful, lines that may move within the visual field. They usually last from five to thirty minutes and can occur in both eyes at once. They are most likely caused by a sudden spasm of blood vessels in the brain. These flashers are often associated with headache, nausea, or dizziness, but more often occur without such symptoms. In this case, they are commonly called an ophthalmic migraine, or a migraine without the other accompanying symptoms.
As in the case with floaters, an eye specialist should attend to any abrupt onset of an abundance of light flashes. The exam would involve close observation of the retina and vitreous fluid.
Floaters and Flashers are common visual symptoms that can be representative of normal aging changes in the eye or the onset of an eye disease that could lead to vision loss if left unattended. It is always prudent to consult an eye specialist when such vision changes occur.
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Does your friend get migraines? I know that some people experience flashing lights before getting a migraine. The site below mentions that it is more common in older people. I thin it's worth getting checked out. 
