A reader asks:

I get the impression from everything I have read that exposure to light at the time of waking is important for fighting Seasonal Affective Disorder (SAD). However, in the winter, when I am suffering, I tend to wake up after sunrise to get exposure early in the day.  On the other hand, in the summer I often wake up well before sunrise by a couple of hours and sit in a room that is dark except for the light coming from my computer screen. In summer I feel much better. Why is that?


Nice question! As summer sunrise moves earlier, it can cause the internal circadian clock to shift earlier by varying amounts in different people. If you’re getting a big clock shift, it can cause you to awaken substantially earlier than sunrise itself. Such a shift is not necessary for “feeling much better.” However, we think the very process of shifting earlier, even by smaller amounts, has a therapeutic effect. Even with artificial light therapy in winter, some people find themselves waking up in the dark — well before the light therapy session has been scheduled. Although they may feel better while this is happening, it is unnecessary. By reducing the dose of the light setting (for a shorter period, at lower intensity, or with a slightly later wake-up time), they can find a combination that allows them to sleep longer, getting up for the light.