A reader asks:

I am so grateful for the study that came out in 1998 showing that light therapy works on the backs of the knees as well as through the eyes because I can use a regular low-cost fluorescent light instead of the expensive ones. I use my light between 3-5 PM for controlling evening food cravings. So far I have lost 15 pounds just by not eating junk food at night. Why is this effect not more well-known? People can have food cravings even though they do not have depression, right?


We’ll answer your question in two parts (and hope we do not quell your enthusiasm too much!)

  1. Sad to say, the “light behind the knees method” has not been replicated, despite many attempts since the original, highly publicized publication appeared. The main effect reported was for circadian rhythm phase shifts, i.e., moving the internal clock earlier or later with timed lighting. That has not been replicated. Second, investigators thought that if the phase-shifting effect were real, light behind the knees should also suppress the production of melatonin by the pineal gland, just as retinal light does. However, despite several attempts, no one has been able to suppress melatonin with light behind the knees. Finally — and most importantly for this discussion — despite several attempts, no one has been able to demonstrate a specific antidepressant effect of light behind the knees. Even with these clinical failures, however, light behind the knees could exert a strong placebo effect, which is probably why some people who have tried it believe it “works.”

Stick with Light Therapy for Eyes

Our strong advice is to stick with bright light therapy to the eyes, using a carefully designed light box. (Important design factors are outlined at www.cet.org.) Yes, this may cost more than placebo light to the knees, but we know it works better than placebo!

  1. You are correct, indeed, that food craving (and eating, even bingeing) can occur without depressed mood. Furthermore, these problems can occur seasonally, peaking in winter, even in patients who do not have SAD. There is every indication that light therapy helps to reduce such winter cravings, even with dramatic reductions in binge eating. In your case, however, it sounds like self-control of your nighttime food intake has been the major factor helping you to reduce weight. Great!