A reader asks:

The morningness-eveningness questionnaire (AutoMEQ) indicated my melatonin onset as 9:45 p.m. and my ideal light therapy session time as 6:30 a.m. I usually sleep until 8:00 to 9:30 a.m. (I usually go to bed around 11:00 to 11:45 p.m.) Can I do light therapy in the late morning, like around 10:00 a.m.? Or will I need to change my whole morning routine in order to do light therapy?


Sleep Long, Wake Early

Everyone who is a “long sleeper” — in your case, around 10 hours — will have the same reaction to the MEQ’s recommendation that you wake up earlier for the most successful treatment. (This is not a problem for shorter sleepers — say, 7 hours.) There are two considerations here. First, do you sleep that long in the summer, when you are not fighting depression? If your long sleep is restricted to the fall and winter, you should associate shorter sleep with higher mood and energy. Second, we have learned that the response to light therapy is strongest when the treatment resets the internal biological clock to a significantly earlier hour.n

Experiment with Times/Duration of Sleep

In general, such shifts occur around 9 hours after melatonin onset — which, in your case, lies in the range of 6-7 a.m. You can try using the lights at 10 a.m., but you may not achieve an optimum response. However, you could start a bit later than 6:30 a.m. — say, 7 a.m. — and still get full benefit. After trying this for a few days, you may find that you are quite comfortable with the reduced sleep duration. On the other hand, you may find that you want to adjust your bedtime somewhat earlier — say, 10:30 p.m. — to partially compensate for the morning sleep loss. Play around with it, to find out what works best for you, but maintain each test schedule for at least 3-4 days before switching.