A reader asks:

 If a SAD person sleeps with the bedroom window covered to block night street lights, will their ability to wake in the morning be affected?


Yes, indeed. The brain needs to receive an early-morning light signal to keep sleep behavior synchronized with the external day-night cycle. That is at the heart of the light therapy effect. People with street light invading their bedrooms therefore are faced with a Catch 22. You are smart to keep your bedroom dark during the night, but you are doing this at the expense of missing the natural dawn signal. The best technological work-around is artificial dawn simulation, as described at CET fact sheets. An additional benefit of dawn simulation is that you can “force the sun to rise in a springtime pattern” while it is still dark outside in winter, which is a proven therapeutic maneuver.