A reader asks:

Does the effect of light therapy drop off after a while? I got great results (using all the wrong equipment and angles, not knowing any better) the first few days, and have had lesser results (with better equipment and correct angle) since.


In general, there is no build-up of tolerance with light therapy. Once you find your best dose, it should serve well in the long run. Many users do, however, titrate their light dose during the season — for example, more in January and February, less in March. An experienced user does this almost instinctively — you get a “feel” on a day-to-day basis for how much light you need. When you changed apparatus, you may have inadvertently dropped to a significantly lower lux level, in which case you may need to sit at the lights somewhat longer or use them earlier in the morning. In making such adjustments, it is smartest to stay with a particular combination of distance, duration and time of day for 3-4 days before switching, so you do not “miss” a positive result before it has time to develop.