A lot of it has been studied and while there's some blue-light nonsense (not so much nonsense as heavily misinterpreted by the health blogosphere), there is evi

A lot of it has been studied and while there's some blue-light nonsense (not so much nonsense as heavily misinterpreted by the health blogosphere), there is evidence that a vast proportion of the human population is suffering from circadian rhythm disruption of some sort. This is especially prevalent in populations living with heavy noise and light pollution, AKA urban residents. There are studies somewhere that if you ship people out to camp in remote areas with only fire as a light source, their circadian rhythms almost always realign within a few nights. Furthermore, the genetics that determine how light-sensitive one's circadian rhythms were never selected against because it really didn't affect survivability except at the very far ends. Event then, Delayed Sleep Phase Syndrome might have been allowed to remain around because it produced night-watchers that contributed to the survival of the pack. The result is there is a very large spectrum of light-sensitivity fairly well distributed amongst the human population. All this adds up to: Very few people are not light sensitive, and a majority of it display varying degrees. So much so, difficulty maintaining a natural sleep pattern is considered the norm and not many people question it anymore.