A reader asks:

 I’ve been using light therapy for SAD for about a month and have found it tremendously helpful for my mood. I suffered with SAD for about 6 months out of the year during winter for the past six years and just recently read Winter Blues by Rosenthal and realized that the 30 min I had stuck to for light therapy probably hadn’t been enough. I now do about an hour right when I wake up, and about an hour later sometime before 2 or 3 PM. Lately my body has been waking up between 4:30 (yikes!) and 5:45, which has not been great for me. I have shifted my bedtime earlier and I fall right asleep, but am tired of waking up so early and not being able to fall back asleep- and, I am okay with bed at 9:30 or 10, but don’t want to sleep earlier because then I miss so much of my evening, but since my body wakes me up so early, I am seriously exhausted by 8 PM. I’m 28 years old, active, and by 8 PM I feel like I’m 90 years old!!! Is there any way to alter my light therapy so that I can sleep in later? Try less or at a different time? Thanks for your help!


You are making a big mistake with self-treatment.  See Dr. Terman’s book, Reset Your Inner Clock, for a detailed explanation of setting light therapy parameters: duration of the session, timing of the session relative to your circadian (“inner”) clock, intensity of the light, sitting distance from the light box screen, and spectral quality (amount of blue in the white color mixture).  In a nutshell, you almost certainly have given yourself a light overdose by doubling the duration of exposure upon wake-up.  If 30 minute sessions were inadequate – which implies persistent, residual symptoms of depression – you might increase exposure duration in a series of small steps (such as 5 minutes), testing each step for three or four days before increasing it further.  A 60 minute exposure at 10,000 lux is virtually the maximum used in clinical practice, most often for patients who have not responded at all to shorter durations.  A major effect of such overdose is a large shift in the circadian clock to an earlier hour, resulting in premature awakening and evening sleepiness – just as you describe.  Adding another hour of light exposure later in the day is almost surely also excessive.  If you are slumping in the afternoon, a relatively short supplementary session – such as 10 or 15 minutes – is sufficient for most people to truncate the slump.