Seasonal Depression: Photobiomodulation or Traditional Light Therapy?

Every fall, the same scenario plays out for millions of people: the days grow shorter, energy levels drop, and moods become more fragile. This winter blues, known as seasonal affective disorder (SAD) or simply seasonal depression, affects 1 to 3 percent of the population. To combat it, two light-based approaches are increasingly being discussed: traditional light therapy and photobiomodulation. They are often confused, even though they work in completely different ways.

Seasonal Depression: When the Body’s Internal Clock Loses Its Bearings

Seasonal affective disorder is not simply a passing bout of melancholy. Its symptoms are well defined: persistent low mood, intense fatigue, excessive sleepiness, increased cravings for carbohydrates, and difficulty concentrating. These symptoms recur in the fall and winter and disappear in the spring. To be considered seasonal depression in the strict sense, seasonal depressive episodes must be significantly more numerous than non-seasonal episodes over the course of a person’s life.

The mechanism at work is fairly well understood. In winter, the decrease in natural light disrupts our internal clock—the biological system that regulates the sleep-wake cycle. This clock, controlled by a brain structure called the suprachiasmatic nucleus, normally receives its synchronization signals from the retina. When daylight becomes too scarce, the signal weakens: melatonin (the sleep hormone) is secreted in excess, serotonin (which affects mood) drops, and circadian rhythms become disrupted. People who are most sensitive to these changes in light are the first to suffer the consequences.

Light Therapy: Targeted Light Exposure to Regulate the Body Clock

Light therapy is based on a simple principle: exposing the eyes to high-intensity white artificial light to compensate for the lack of natural light. A typical session involves sitting about 30 centimeters from a lamp calibrated to 10,000 lux for 20 to 30 minutes within two hours of waking up. The lamp’s intensity and the duration of exposure are directly related.

It is this effect on the retina that makes all the difference. The light perceived by the eye sends a signal to the suprachiasmatic nucleus, thereby resetting the internal clock. Melatonin production is suppressed, serotonin production is stimulated, and biological rhythms gradually resynchronize. The effectiveness of light therapy for depressive episodes associated with seasonal affective disorder is now well documented: according to studies, between 40 and 90 percent of individuals report an improvement in their seasonal depressive symptoms. The response often becomes apparent as early as the first or second week of treatment.

Its side effects are rare and generally mild (headaches, mild irritability in the first few days), making it a well-tolerated treatment. Light therapy is not addictive and can be done independently at home, provided you choose a certified light therapy lamp.

Photobiomodulation: Light That Works Deep Within the Skin

Photobiomodulation (PBM) works through a radically different mechanism. It does not act through the eyes, but rather through the skin and tissues. It uses specific wavelengths in the red and near-infrared spectrum—typically between 630 and 850 nm—emitted by LEDs or low-power lasers. These wavelengths penetrate the cells and interact with the mitochondria—the powerhouses of our cells—to stimulate the production of ATP (cellular energy).

Unlike bright light therapy, photobiomodulation does not act directly on melatonin or circadian resynchronization. Its effect on mood occurs through other mechanisms: reduction of brain inflammation, modulation of certain neurotransmitters, and improvement of microcirculation. A pilot study conducted by Schiffer et al. (2009) had already observed an improvement in symptoms of anxiety and depression after two weeks of transcranial exposure to near-infrared light. More recently, a meta-analysis published in 2024 in *Frontiers in Psychiatry* confirmed that PBM helps improve depressive symptoms, particularly by affecting sleep.

What Comparative Studies Show

When comparing the effectiveness of the two methods for treating seasonal depression, the data are not equally well-established.

For light therapy, the evidence is robust and has been accumulating for forty years. A landmark meta-analysis (Golden et al., 2005, *American Journal of Psychiatry*) showed that light therapy is as effective as antidepressants in helping to manage seasonal affective disorder. Three other meta-analyses of randomized trials concluded that bright light therapy significantly outperforms placebo lights (low-intensity red, green, or blue lights) in alleviating seasonal depressive episodes. More recently, a meta-analysis published in JAMA Psychiatry (de Almeida et al., 2025), involving 11 randomized trials and 858 participants, confirmed its effectiveness even in cases of non-seasonal depression, with a symptom remission rate of 40.7% compared to 23.5% in groups without light therapy.

Scientific evidence on photobiomodulation is accumulating at a rapid pace. A meta-analysis published in early 2024 in *Frontiers in Psychiatry*, which pooled data from several randomized controlled trials, confirmed that PBM helps improve depressive symptoms and sleep quality. Experimental studies also show that red light reduces inflammation in brain regions involved in mood and stimulates the production of GABA, a neurotransmitter essential for stress regulation. This body of evidence, focused on depression in the broadest sense, is rapidly expanding. Studies specifically dedicated to seasonal affective disorder are even fewer in number than those on white light therapy, simply because PBM is a more recent approach in this field. This gap is not due to a lack of efficacy but rather to a lag in the scientific timeline.

How do you choose between the two approaches?

The two methods are not quite suited to the same needs, and their key differences are essential for making an informed choice:

• Light therapy is the standard treatment for seasonal affective disorder. It acts directly on the body’s internal clock and melatonin regulation. It is particularly recommended in the morning, at the start of the fall and winter seasons, and can help prevent symptoms from developing in individuals who are regularly prone to them.
• Photobiomodulation focuses on cellular balance and inflammation management, with a broader impact on overall well-being. It can be considered as a complementary treatment, particularly at the end of the day when exposure to white light would be contraindicated.
• Both approaches are noninvasive, well-tolerated, and do not require the use of any substances. Depending on the individual’s profile, they can be used in a complementary rather than an exclusive manner.

It is important to note that neither of these is a substitute for appropriate treatment for clinical depression. If symptoms are persistent or severe, professional advice remains essential.

The complementary approach: a serious avenue to explore

White light in the morning to reset the body’s internal clock, red light during the day to support cellular energy: this combination is attracting more and more users and is beginning to draw the interest of researchers. Red light photobiomodulation does not replace traditional light therapy in the management of seasonal depressive symptoms. However, it can enhance its effects on overall well-being, particularly regarding sleep quality, fatigue, and inflammation.

One thing is certain: the science of light is advancing rapidly. The coming years will likely yield more precise comparative data, making it possible to better define the respective indications for each approach and the conditions under which combining them is most appropriate.

Frequently Asked Questions (FAQ)

What is the difference between light therapy and photobiomodulation for seasonal depression? Light therapy uses intense white light (10,000 lux) perceived by the eyes to resynchronize the body’s internal clock and regulate melatonin. Photobiomodulation uses red and near-infrared wavelengths (630–850 nm) that act directly on cells, bypassing the retina. The former has long been established as effective for seasonal affective disorder; the latter shows promising results for mood and sleep, but studies specifically focused on seasonal depression are still limited.

Can photobiomodulation be used instead of a light therapy lamp in the winter? No, the two devices do not work in the same way. A photobiomodulation device does not affect melatonin or the circadian rhythm in the same way as a light therapy lamp calibrated to 10,000 lux. PBM can be considered as a complementary treatment.

When is the best time of day to use light therapy or photobiomodulation? Light therapy is recommended in the morning, within two hours of waking up, because of its effect on the body’s internal clock. Photobiomodulation is more flexible: it can be used at any time of day, including in the evening, without the risk of disrupting sleep.

How many sessions are needed to feel the effects of light therapy? Most people report an improvement in seasonal depressive symptoms after one to two weeks of daily sessions. Regular exposure is key: intermittent use reduces the effectiveness of light therapy.

Does light therapy have any side effects? They are rare and usually temporary: mild headaches, irritability, or sleep disturbances if exposure occurs too late in the day. These effects generally go away by adjusting the duration or timing of exposure.

See also:

• What Is Photobiomodulation? Mechanisms, Applications, and Challenges
• FAQ: The Benefits of Photobiomodulation
• Photobiomodulation: dangers, contraindications and misconceptions
• Portable LED Devices: At-Home Photobiomodulation