Is there scientific evidence to prove that bright lights prevent dementia?

No. Light therapy has been shown to help with more restful sleep and possibly with mood or anxiety but there is no evidence it has any preventative benefits.
Symptoms. See http://www. Solg. Nl/data/userfiles/file/ambient%20light%20in%20dementia. Pdf dementia causes many mood, circadian (cyclic) and behavioral effects, even though it is primarily a deterioration of cognition. Light therapy may help with the former and so improve the quality of life. It won't [revent dementia, however.
Not a shred. There is no evidence that sunshine or bright light has any influence on the presentation or continuation of any kind of dementia. We use soft light at night to assist orientation of confused pts, but no light therapy otherwise has a substantial impact on course of the disease.
Not that I know of. Many things have been tested as possible prevention methods for dementing illnesses. There are different types of dementia, alzheimer's being the most common and multi infarct, or vascular dementia, the next most prevalent. We all tend to have gradual deterioration of our memory and cognitive skills as we age. Using and stimulating your brain may be one thing that does help, so turn off your tv.