Three short hours in Dijon, four in Rennes, nine in Strasbourg, barely ten in Paris… Between November 1 and 13, sunlight became rare, very rare, in certain cities, indicates Weather France. This year, autumn is particularly trying in France, particularly in the regions of the northern half of the country, which are going through an unusually gray period. This lack of brightness is not without consequences. It can particularly have an impact on mental health, ranging from a drop in morale to seasonal depression.
To counter these harmful effects, manufacturers have developed light therapy lamps, which produce white, blue or cyan light intended to reproduce, in part, the light of the Sun. However, the positive effects of these devices remain little known and their commercial success is quite relative. These lamps are often considered placebos, or even scams. But when we delve into scientific studies, we discover that not only has their effectiveness against seasonal depression been proven for a long time, but that recent work also demonstrates their usefulness for treating classic depressions and depressive phases in bipolar people. Synchronization of sleep cycles, increase in energy and concentration… The benefits seem multiple and push researchers to explore their interest in other applications, such as sleep apnea or even… Weaning cocaine addicts .
Strong scientific evidence
“The physiological effect of light has been known since Antiquity, but there has been renewed interest in recent years thanks to neuroscience, which taught us a lot”, explains Professor Pierre Alexis Geoffroy, professor of psychiatry at the Paris University Hospital Group and at Bichat Hospital (AP-HP) and a leading specialist in light therapy. research started in the 1960s, we now know that the reduction in the amount of sunshine in autumn and winter causes a decline in serotonin, the happiness hormone, and conversely an increase in melatonin, the hormone of night which promotes sleep. A harmful cocktail, which can lead to a drop in mood and energy. It has also been shown that light can have a direct effect on certain centers of the brain, notably those of emotion and vigilance, and on processes linked to mood disorders.
The first clinical study suggesting the effectiveness of light therapy for seasonal depression was published in 1984 by American psychiatrist Norman E. Rosenthal. This work showed that it was possible to correct sleep cycles through exposure to light which synchronizes the internal clock by inhibiting the production of melatonin. In 2006, after the publication of new studies On the subject, the American Psychiatric Association has recognized light therapy as an effective treatment for seasonal depression and certain sleep disorders. In subsequent years, other work suggested effectiveness on non-seasonal depression.
In 2019, a meta-analysis – a compilation of the results of numerous scientific studies – published by Prof. Geoffroy and his team confirms this new lead. This work focuses on the effect of light therapy in depression in all its forms, seasonal or not, bipolar (a pathology which combines depressive and manic phases) or unipolar. They demonstrate not only that light therapy works as well as antidepressants, but also that the combination of the two provides better results than antidepressants alone, for both seasonal and non-seasonal depression.
Doubts nevertheless appear in 2021, after the publication of a meta-analysis concluding that light therapy is ultimately not effective in the treatment of depression. “But this work has several biases: it includes trials that use blue light and not white light, and the total duration of exposure to light therapy was probably too short to obtain significant results on depression,” analyzes Sébastien Catoire , psychiatrist and addictologist at Vinatier hospital (Lyon).
The effectiveness of light therapy in depression has finally been confirmed by another meta-analysis. These works, published in October 2024 in the journal JAMA, were interested in its effects on non-seasonal depression. Conclusion ? “Light therapy is an effective adjunctive treatment for depressive disorders. Additionally, it may improve response time to initial treatment [NDLR : par antidépresseurs]”, indicate the researchers.
When, where and how to do light therapy?
Under what conditions is light therapy beneficial? Can it be performed at any time and with any device? In the case of seasonal depression, it should ideally be done after waking up. “With the lack of light in winter, people can feel sleepy in the morning because their body continues to produce melatonin, which can lead to lethargic states which promote low morale. However, light is an inhibitor of production melatonin”, underlines Professor Geoffroy. For non-seasonal depression, morning exposure is less important, but specialists point out that it should be avoided after 3 p.m. due to the stimulating properties of light and the risk of disrupting sleep cycles.
The lamp should be placed about forty centimeters away for thirty to forty minutes at maximum power, generally 10,000 lux. If the power is 5,000 lux, you have to expose yourself for an hour, etc. The light should ideally be white, which has a more effective wavelength, and not blue or cyan. “There is no real reason to believe that the devices on the market have gross errors, but I most often recommend those that have a CE mark,” adds Dr. Catoire. However, if the lamp is too far away or not facing the face, the effects are reduced and the exposure must be prolonged.
People prone to seasonal depression but who benefit from teleworking can therefore easily spend their day with a lamp close to them, without it necessarily being at full power or right in front of them. For those who do not have the luxury of time, it is possible to use light therapy glasses – a bit like regular glasses, but equipped with rows of small LEDs on the frame. Their positioning close to the retina allows lower brightness and also allows them to move around and perform other activities. Psychiatrists also favor this device in very depressed patients. “We especially recommend glasses for our patients because sitting for a long time in front of a fixed lamp can promote inactivity and therefore indirectly ruminations and depression,” indicates Dr. Catoire.
Light therapy can provide rapid benefits such as increased energy and improved concentration. “A session can be as refreshing as a nap,” assures Dr. Catoire. On the other hand, for depressive symptoms, doctors point out that treatment must be followed for at least a month to benefit from positive effects. For people suffering from seasonal depression, it may be necessary to follow it throughout the fall-winter season.
However, there are some rare contraindications. It is of course impossible to drive while wearing light therapy glasses. Treatment should be avoided in individuals with unstabilized epilepsy and those with ophthalmologic problems, particularly retinopathy. “And in bipolar patients, light therapy must always be carried out under the cover of a mood stabilizer which protects against a manic turn, because like any antidepressant, there is a risk of inducing a pathological increase in mood and energy”, underlines Professor Geoffroy.
“Patients who understand that it works for them no longer need us”
Can we also practice light therapy for prevention, for example from October, to prevent seasonal depression? On this point the Cochrane reviewa reference on the subject, indicates that the scientific evidence is insufficient. “There are more studies on the curative aspect – that is to say during depression, but there is a lack of data on the preventive level, before the onset of depression, recognizes Sébastien Catoire. But we must remain pragmatic: it would be logical for light therapy to work in prevention.” And since there are almost no side effects, people prone to seasonal depression would be wrong to deprive themselves of it.
Professor Geoffroy confirms: “The sale of lamps is not very profitable and the manufacturers who manufacture them do not have the financial power of the pharmaceutical industry to conduct randomized controlled studies with hundreds of participants – very expensive – in order to demonstrate the benefits in prevention.” The specialist also points out that most studies on light therapy are university studies. “For seasonal depression, patients who have understood that it works for them no longer need us, they do it preventively when the first symptoms appear,” he adds.
Ways to combat cocaine and sleep apnea
The light even seems so promising that researchers are exploring its benefits in other applications. The CokeLux project, launched by the Vinatier hospitalthus aims to explore the use of light therapy during hospital withdrawal from cocaine. More than 250 participants will be included in this trial, which has obtained funding of 692,000 euros. “The problem with cocaine is that there is no replacement treatment or indication for withdrawal, unlike alcohol, tobacco or opiates,” explains Dr. Catoire. But cocaine disrupts sleep rhythms. And during withdrawal, cocaine addicts experience the opposite effects of cocaine: they are lethargic, have difficulty getting up in the morning and concentrating, etc. “As light therapy reduces drowsiness and fatigue and increases concentration, it is hoped that it will reduce the urge to resort to stimulants during withdrawal,” he adds.
Another project, also launched by Vinatier, aims to explore the effect of light therapy in patients with sleep apnea syndrome. This time, the idea is to introduce a prescription for light therapy at the same time as the classic treatment for sleep apnea, machines that can be difficult for some people to tolerate. Researchers hope that light therapy can help reduce the symptoms of sleep apnea, and therefore indirectly help increase the patient’s motivation to continue with traditional treatment. If these benefits are confirmed, it is a safe bet that researchers will try to explore other avenues.
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