I am concerned about how poorly people sleep in our culture. The use of medications is at an all-time high, and these drugs do not reproduce natural sleep. Most of them suppress dreaming. One detrimental influence on our sleep is our ability to light up the night, which is a significant change in our environment over the past hundred years. There’s a body of literature suggesting that exposure to light at night, even briefly, greatly increases cancer risk, especially risk of breast cancer in women. Women who are blind from birth have very low rates of breast cancer. Women who work night shifts have high rates of breast cancer. I tell people it is best to sleep in complete darkness, and if you have to get up in the middle of the night, don’t turn on the light, or else use a red Christmas-tree bulb, because it appears that light at the red end of the spectrum is safest.
– Dr. Andrew Weil, interviewed in The Sun