Dr. Rosenthal, as the “father” of light therapy, how did you got interested in doing research on seasonal affective disorder?
Well, I came to this country from South Africa in 1976. I started my psychiatry residency at Columbia, and I had always been interested in the mood disorders. In New York City, which is at 40 degrees north latitude, as opposed to Johannesburg, which is 23 degrees south, I personally encountered cycles of changes in mood and energy with the seasons that I had never encountered in South Africa. I noticed that in the long days of summer I would take on all these projects, and then I would slow down in the winter, and I would think, “What had got into my head to take on all these projects?” I felt tired and slowed down, and I would just hunker down and keep plodding through the winter. And then came the spring, and I would feel like myself and everything became right. I watched this cycle happen for three years in a row, and it was really a curious experience.

And when did you start researching this problem?
After residency, I went to do research at NIMH and I got into Fred Goodwin’s group. They were doing work with biological rhythms, and Al Lewy had just done his original work showing that melatonin could be suppressed in humans by bright light. This was the first suggestion that light had nonvisual effects in humans, and they even had mapped out the pathway by which this occurred – through the retina to the hypothalamus. Given the symptoms of seasonal depression – changes in eating, sleeping, energy, and rhythms – a hypothalamic pathway made sense.

And when did you make the leap to using bright lights as a treatment?
One of our patients at NIMH was an engineer who had seasonal mood changes and who had already mapped out his own seasonal rhythms. Based on the ways his moods paralleled the changes in daylight and changes in duration of the day, he suggested that we devise a way of giving an increased period of light everyday. We gave him this treatment, and it brought him out of his depression.

So he was the first light therapy patient?
Yes. And at that point I decided to look for similar patients in order to do a study. This was in 1981 or so, and we persuaded a journalist to run an article in The Washington Post, expecting to get a handful of patients. But in fact we got in excess of 3,000 responses from all over the country. I sent the responders questionnaires about their symptoms; and as I read through them, I got excited because there was a uniformity to their answers, and the syndrome just kind of fell out of these responses. That became the basis for the syndrome of seasonal affective disorder.

Did you actually name the syndrome?
I did. At that point, the current iteration of the DSM referred frequently to “affective disorders” rather than mood disorders, and it was clearly seasonal affective disorder, and the acronym of “SAD” seemed appealing and apt.

And then you began to study it in earnest.
Yes, and we did the early studies, which were so remarkable. It was like seeing the sunrise for the first time. These people, about half a dozen of them initially, just emerged from their depression. You don’t see those kinds of transformations very often; as a researcher, it felt like such a privilege.

That must have been very gratifying. Moving on to diagnosis, what do you ask your patients about?
I begin, quite simply, by asking, “Have you noticed any change in your mood or energy or behavior with the changing seasons?” I also often ask, “Do you notice a real difference in your mood when Thanksgiving comes and when Christmas comes?” People often peg their memories to the holiday season. I also use a very simple questionnaire, called the Seasonal Pattern Assessment Questionnaire. It is in the public domain, so it is free. [Readers can download a copy of the questionnaire from our website, www.TheCarlatReport.com].

I have often recommended light boxes to patients but a high percentage of them never follow through. Maybe I’m not convincing enough! What do you tell patients to convince them?
I say things like, “Why don’t you get yourself a light box? According to regulations, the companies have to take the box back within 30 days if you are not satisfied, no questions asked. And since the light therapy usually works in two weeks, why don’t you try it?” Or sometimes I frame it this way: “Why don’t you be scientific about this? Don’t take my opinion. Don’t take anybody’s opinion – check it out for yourself. But you have got to do it right – you need to track some symptoms before and during the treatment. If you don’t find any change, you can send the box back within a month and they have to refund your money.”

When a patient asks, “What are the chances that I am going to get better, doc?” what do you say?
I say, “If you do have seasonal affective disorder, there is a 60% to 80% chance that you will feel significantly better. You may not feel as good as you do in the summertime, but you are very likely to feel well enough that you will want to keep the light box.”

In terms of the actual equipment, what type of box do you recommend?
Patients often will prefer the small light boxes because they are cheaper, handy, and inconspicuous. People are concerned about being stigmatized, so they don’t want a large funny-looking appliance in their homes. There hasn’t been a rigorous study comparing small and large light boxes, but I can tell you from 25 years of clinical experience, bigger is better, because it bathes a larger area of your retina. And if you have to sit right up close to a small box, the glare will dazzle you.

So the light has to shine into your eyes to work?
Yes, and we did various studies to prove that. We shined it on the eyes and covered the skin, and conversely we tried shining it on the skin and giving patients dark glasses. Shining it on the eyes worked better. As you move your head, there is a great fall-off in the amount of light entering the eye, so the smaller the box, the more your eyes are going to move outside of the illuminated area.

So spending a little bit of extra money for a larger light box may well be worth the investment. And when should patients sit in front of the light?
The morning is the best time for light therapy. Michael Terman at Columbia has done some interesting work looking at whether being a morning or an evening person predicts the optimal time for light therapy. He learned that morning people benefit from the light earlier than night owls. His website, www.cet.org, is worth checking out because patients can answer a series of questions and then receive suggestions including the best time for their light therapy.

Can you tell me a bit about the dawn simulators?
A dawn simulator is a bedroom light that gradually increases to full strength and simulates a summer dawn. It is not a light box, and it does not go up to 10,000 lux, but it is still effective, probably because the eyes are extremely sensitive early in the morning.

What about the light visor?
The light visor is a visor with small lights attached to it that shine into your eyes. I consider it to be a specialty item. It allows people to have some sort of light therapy away from home, but the data are not as strong as for the light box.

Do you have any specific product recommendations for clinicians and patients?
On my website (www.normanrosenthal.com), I have a list of links to reputable companies that have been in business for more than a decade.