TCPR: You published the first clinical report on light therapy in seasonal affective disorder (SAD) back in 1984. What have we learned since then?
Dr. Rosenthal: One thing is confirmation. Light therapy now has over 30 randomized trials in depression and is recognized in practice guidelines from the American Psychiatric Association and the Veterans Administration. We’ve also learned that it works in nonseasonal depression and bipolar depression (Menegaz de Almeida A et al, JAMA Psychiatry 2025;82(1):38–46). The biggest problem with light therapy is that many clinicians overlook it or do not realize the diverse situations where it can be helpful. It augments antidepressants and works in various populations—adolescents, elderly, and perinatal depression.

TCPR: Is it mainly for mild depression?
Dr. Rosenthal: It works for mild depression—but also for moderate and severe depression. It can work as monotherapy or augmentation, and severity is not a disqualifying criterion. Even in severe cases of SAD, light therapy is first line. Medications are also effective in SAD, and bupropion is FDA approved there, but light therapy works faster, with noticeable benefits within a week.

TCPR: How potent are these benefits?
Dr. Rosenthal: The effect size is large for SAD (0.84). In nonseasonal depression it’s moderate (0.53) but still compares well to antidepressants (Golden RN et al, Am J Psychiatry 2005;162(4):656–662). Raymond Lam ran a landmark trial in nonseasonal depression that illustrates this. They had four groups: light therapy alone, light therapy plus fluoxetine, fluoxetine alone, and placebo. Light therapy was more effective than fluoxetine, which didn’t actually separate from placebo, and the combination was somewhat better than light therapy alone (Lam RW et al, JAMA Psychiatry 2016;73(1):56–63). When you’re treating refractory depression, adding medications can get complicated with side effects and pharmacokinetic interactions. But adding light therapy doesn’t carry those risks—it’s a clean add-on.

“Depression, in some ways, can be seen as an aberration of the quiescence of night—low energy, slowed activity, the physiology of sleep intruding into waking hours.” - Norman Rosenthal, MD

TCPR: What about in children?
Dr. Rosenthal: For children and adolescents, there are around seven randomized trials in depression, both seasonal and nonseasonal (Ballard R et al, Curr Psychiatry Rep 2023;25(9):373–386). I conducted a pediatric study with Susan Swedo at the NIMH that combined light therapy with dawn simulation. They awoke to a gradual increase in light over two hours, then started an hour of light therapy, while the placebo group received dim light (Swedo SE et al, J Am Acad Child Adolesc Psychiatry 1997;36(6):816–821). We used a lower-intensity light box (2,500 lux) for children under 9 and an adult dose (10,000 lux) for teens. It was effective. For preteens who struggle with waking up early for school due to their circadian rhythms, a dawn simulator is a practical, nonpharmacologic approach.

TCPR: Do dawn simulators treat SAD on their own?
Dr. Rosenthal: Yes. They did so in nine small trials, and some people prefer them for the ease of use (Danilenko KV and Ivanova IA, J Affect Disord 2015;180:87–89). Patients can try them and see what works. One symptom of SAD that gets in the way of treatment is sleep inertia. People feel groggy and unmotivated when they wake up, and that can last for hours. A dawn simulator reduces sleep inertia, so it can help people get out of bed and start the light box, especially if they are not a morning person (Thompson A et al, Eur J Appl Physiol 2014;114(5):1049–1056).

TCPR: Light therapy makes sense in the winter, but how do you explain how it works in other seasons?
Dr. Rosenthal: Light is fundamentally an activating principle. We’ve evolved to be active during the day and quiescent at night. Depression, in some ways, can be seen as an aberration of that quiescence—low energy, slowed activity, the physiology of sleep intruding into waking hours. Some people may be particularly vulnerable to that tendency, and most of us live indoors so we may not get enough of the activating signal even in the summer. Light wakes you up and gets you moving. On a bright day you’re out walking, and on a gloomy day you’re inside. Light isn’t just about mood—it affects activity, energy, and circadian rhythms. All those systems are disrupted in mood disorders. It’s fundamental. “Let there be light” is the first spoken line in Genesis.

TCPR: Walk us through how you typically prescribe light therapy.
Dr. Rosenthal: The standard is a 10,000-lux light box in the morning, starting with 20–30 minutes of treatment. If no benefit arises after 2 weeks, use judgment to decide how much to increase treatment by (perhaps up to 60 minutes) or whether to add evening light therapy as well (but not after 8:00 pm). For ocular safety, the box should have a UV filter, and the screen should be approximately 12 x 17 inches. Position it a foot or two in front of the face. To prevent eye strain, don’t get too close to the screen (say, less than 12 inches), and don’t stare into the light for prolonged periods. Be sure that the light is in front of you and ideally directed toward you. Light works through the eyes. In order to make light therapy as convenient as possible, combine it with something you’re going to do anyway—for example, checking email, eating breakfast, coffee, tea, or meditation. My light box is right above my monitor. Make the process easy and you’ll be more likely to do it.

TCPR: When should patients who get depressed in, say, mid-November start treatment?
Dr. Rosenthal: Before they need it. They won’t wake up one day and say, “Oh, here’s the depression.” They’ll notice subtle signals: less energy, less enthusiasm at work, decreased libido, increased appetite, or a few pounds gained. They should start when they first notice those prodromal signs. After a while, it becomes instinctive.

TCPR: How quickly should patients expect to see a response?
Dr. Rosenthal: Often within a couple of days, sometimes even within hours. One-hour response in SAD patients predicts response at one week. With nonseasonal depression, it builds more gradually over a couple of weeks—more like the time frame for an antidepressant. The protocol is similar for both populations.

TCPR: What about timing? Is morning always best?
Dr. Rosenthal: Morning is generally more potent. But some people have a mood drop in the late afternoon or early evening, and for them, light at that time—say, 4–6 pm—can be beneficial. I’d advise against using it after 8 pm, as it can disrupt sleep. Be empirical: Try it, listen to what your patient reports, and adjust. I don’t recommend Morningness-Eveningness Questionnaire (MEQ) testing to determine timing—just start early in the morning and go from there. Good clinicians are always experimentalists.

From the Q&A with the Expert
“Light Therapy: Beyond Seasonal Depression”
by Norman Rosenthal, MD
The Carlat Psychiatry Report, Volume 24, Issue 9
September 2026
www.thecarlatreport.com

These products were used in clinical trials or endorsed by the Center for Environmental Therapeutics or the National Sleep Foundation.

From the Q&A with the Expert
“Light Therapy: Beyond Seasonal Depression”
by Norman Rosenthal, MD
The Carlat Psychiatry Report, Volume 24, Issue 9
September 2026
www.thecarlatreport.com

TCPR: What are the common problems patients encounter?
Dr. Rosenthal: First: positioning. Make sure it’s in front of the face, at eye level or slightly above, not too far away. Second: the size of the box. A small device may be labeled 10,000 lux, but you’ll only get that dose if you put it inches from your face—no one actually does that. Use an adequately sized box. Third: timing. If someone is using it at 8 pm, try shifting to morning. Fourth: dosage. In patients with severe winter depression, I’ll sometimes have them sit in front of multiple light boxes to increase the effective dose. The 10,000 lux at a standard distance is what’s needed for research standardization—but clinically, you can push it, using longer durations or multiple boxes.

TCPR: What if a patient says they’d rather sit in a sunroom or walk outside in the morning?
Dr. Rosenthal: I say, “Try it. Come back in a week or two and tell me how it’s going.” And then they may come back and tell me they couldn’t get up, they couldn’t get outside, or the sunroom needs work. If it doesn’t help, I’ll say, “Why not try a light box?” With most products, they can buy the light box, keep the packing materials, use it for two weeks, and return it if it doesn’t work. Light box manufacturers tell me over 90% of people don’t return their purchase. In winter, on a cold morning, a light box is much more user-friendly than bundling up for an outdoor walk.

TCPR: Can patients get enough light by walking outdoors for an hour?
Dr. Rosenthal: Possibly in the summertime, when the morning light is around 10,000–20,000 lux, depending on latitude. Around the winter solstice, probably not. And you’re entirely dependent on weather and cloud cover. Light therapy frees patients from that variability. That said, outdoor exercise has its own benefits—the light, the physical activity, the cold air. Kelly Rohan at the University of Vermont has done excellent NIH-funded work on cognitive behavioral therapy for SAD that specifically incorporates outdoor walking and socialization. So walking outdoors can be therapeutic in multiple ways, not only as a light source.

TCPR: Patients often ask about alternatives, like light visors to wear on their head.
Dr. Rosenthal: I don’t recommend light visors. We studied those extensively at the NIH and even held a patent on the design. However, we could never demonstrate a dose-dependent relationship—more light was not better and less light was not worse. We eventually couldn’t claim it did anything meaningful. There are also practical problems: The light leaches pigment from the eye, making it harder to see where you’re walking. You certainly shouldn’t drive wearing one.

TCPR: The typical light box uses white light, but what about other colors?
Dr. Rosenthal: There are a lot of claims about red light. When I look at the data behind those claims, I’m struck by how thin they are compared to the rigor of the standard light therapy trials. Maybe red light has value for tissue penetration, joint pain, other applications—I genuinely don’t know. But for mood? I haven’t seen convincing data.

TCPR: I noticed the boxes now come with LED or fluorescent lights.
Dr. Rosenthal: Modern LED boxes have diffusing screens that prevent you from seeing the individual diodes, so the light looks clean and even. They appear to be as effective as fluorescent lights. Importantly, fluorescents degrade over time, so their efficacy can go down after a few years. LEDs don’t have this problem. In that sense, LEDs may be the more durable long-term investment.

TCPR: Does SAD tend to get worse in the months of December and January, when the light is at its nadir, or around the fall equinox, when the light is declining more rapidly?
Dr. Rosenthal: You’ll see both of those patterns. We’re all different. I had a patient who reliably got depressed in August—6 weeks after the summer solstice—when he’d lost about 30 minutes of light at a crucial point in his circadian rhythm. Shifting his light exposure to that exact period resolved his symptoms. He never had another complaint. I think about azaleas blooming at different times in my garden—each plant has its own clock. People are the same. Try different approaches until you find what works. Patients can learn about their own brain and their own responses.

TCPR: Any final thoughts for our readers?
Dr. Rosenthal: Be curious—I’ve never regretted it, even when seasonal depression was a laughingstock and people ridiculed the concept. At my core, I knew there was something there because I felt it myself every autumn. That’s what guided me to this work and has kept me fascinated for 40 years. Practically, light therapy is safe, well tolerated, fast acting, and effective across a much broader range of patients than most clinicians realize. If you’re not offering it, your patients are missing out.

TCPR: Thank you for your time, Dr. Rosenthal.