For years, Dr. Charles Czeisler has studied sleep. The chief of the division of sleep medicine at Brigham and Women’s Hospital knew that the invention of the light bulb had profoundly altered human life and biology. His work had shown that shifting sleep schedules could have dramatic effects on health.
But it was his study of the circadian rhythms of a blind college student that convinced him that artificial light was even more potent than he had believed. Czeisler was interested in the role that a subset of cells in the eye played in sleep. Even among people who have no rods and cones, the cells that translate light into vision, have a subset of light-sensitive cells in the eye. Those cells don’t allow them to see, but, he discovered, mean that even without the ability to discern whether a room is light or dark, a person’s sleep schedule can be shifted.