A reader asks:

 I’m using a light box (10,000 lux) for 30 minutes at 7:30 each morning for depression and to help me get up at a reasonable hour. Initially, 30 minutes of light worked very well but now it doesn’t seem to help as much––I don’t get that same sense of energy and well-being. I live in the mid-western USA and it’s early summer here. Should I extend the duration of my light exposure in the morning? Do people develop a tolerance to light therapy in the same way they do to some drugs? Thanks.


Tolerance, in the same sense as for drugs, is not a problem with light therapy. However, dose adjustments (intensity, exposure duration, and timing) are sometimes needed. Think about outdoor lighting conditions in the summer. (We’re answering this question on June 21, the summer solstice, when the length of daylight is the longest of the year!) There is much more evening light preceding your bedtime, which can have the effect of delaying your internal circadian clock and making it harder to wake up in the morning. There is also much more morning light, which begins well before your wake-up time at 7:30 a.m.

If 7:30 a.m. remains your target, make sure you restrict evening light exposure as much as possible, by using dark sunglasses outdoors and keeping indoor light as low as possible while remaining comfortable for reading, etc. If that doesn’t do the trick, also use a 45 minute light exposure at 7:15 a.m. And if that combination doesn’t work, add a very low dose of melatonin (0.1 mg) 12 hours before you use the lights (for example, 7:15 p.m.). It would also be wise to complete our Automated Morningness-Eveningness Questionnaire at for a summertime assessment, since the recommended time for light therapy can change with the seasons.