Reply #8: here's a fun fact

[orleans]

"Soon after Berson's finding, Figueiro and others began testing how well blue light can reset people's circadian clocks. Over the past 3 years, for instance, Figueiro has worked with eight Alzheimer's patients who tended to fall asleep around 7 p.m. Their body clocks were running amok—probably, she says, because these shut-ins didn't encounter blue skies or other light that was bright enough to prevent circadian drift.

"Exposure to red light around suppertime for 2 hours each day for 10 successive days had no effect on the patients' disordered sleep. However, Figueiro found, a similar exposure to blue-LED light prompted the study participants to fall asleep later and then sleep longer and better than they had before the treatment.

http://www.sciencenews.org/articles/20060527/bob9.asp