A reader asks:

In answer to another person’s question, you said, “Waking up to bright morning light, whether from outdoors or timed artificial light sources, is far healthier than waking in a dark bedroom.” Can you explain why this is true? I usually go to bed between 11:00 pm and midnight. I set my alarm for 9:00 am and get up sometime before 10:00 am. I put blackout shades in the bedroom because during the summer the sun was waking me up at about 6:00 am, which meant I was getting only 6-7 hours of sleep. (I think I need about 8-9 hours). However, with the blackout shades, I find it hard to wake up, and when I do I feel sleepy rather than refreshed. I suspect that my sleep habits may be negatively affecting my mild depression and mild winter blues. Do you have any suggestions? If I want to change my sleep schedule so that I am waking up earlier, what increments of change would you recommend?


This is a meaty, intelligent question! Our body clock, which modulates sleep and wakefulness, relies on daily early-morning light exposure to stay in sync with the external world. Without appropriately timed exposure, the clock is vulnerable to drifting later and later — and telling our brain to wake up later than we might desire. Grogginess and depressed mood commonly accompany this “delay shift.” You complain about the very early sunrise in summer, which causes you to wake earlier than you want. On the other hand, your blackout shades are triggering a bothersome delay shift. Short of moving southward, where the sun rises later in summer, the only obvious solution is technical: timed artificial dawn simulation in your bedroom, with the shades drawn. See cet.org’s section on dawn simulation, and the description of apparatus at the CET Store. Simply forcing yourself to wake up earlier in a dark bedroom is no solution, because your sleep will then get out of sync with your clock, and you will lose the refreshing benefit of an optimum night in bed.