The mother of today’s Bright Light Therapy (BLT), Heliotherapy, has been the longest used form of phototherapy and the only one until the mid-nineteenth century. Sun therapies were applied in ancient Chinese, Hindu and Egyptian medicine over 15 centuries BC. Since the invention of the electric light bulb and the progress of medicine, heliotherapy shifted to: ultra-violet (UV) phototherapy, which is still used today in dermatology, immunology or neonatology; and to light therapy (UV filtered light) in the treatment of neurological, endocrinological and psychiatric affections. BLT is today the gold standard treatment of the Seasonal Affective Disorder, and is recommended in various others affective disorders. Recent findings as the Zeitgeber Theory involving the Central Biological Clock, and the implication of photo transductor melanopsin in the regulation of the circadian clock are guiding chrono-biologists to understand the physiological insights underlying BLT’s action on affective disorders. Those researches combined with ongoing clinical trials could guide us toward an optimal use in mood disorders of this millennial therapeutic resource.
The relationship between mood and light changes has been described since Antiquity, and has shown growing interest since the publication of a series of cases of patients successfully treated for winter depression by Rosenthal and his colleagues [
We conducted a critical and narrative review of the scientific literature, searching for relevant national and international articles that had an interest in light treatment for mood disorders. The publications were obtained from the Medline, Google Scholar and SUDOC electronic database. The literature search was performed using the keywords: (“bipolar disorder” OR “mood” OR “depression” OR “Depressive disorder”) AND (“light” OR “bright light therapy” OR “phototherapy” OR “heliotherapy”). The search was updated until September 1st, 2018. Only articles written in English or French were considered as eligible. We included books, comments, original studies, reviews, case series and studies, that assessed light as a treatment for mood disorders.
Humans from all latitudes, ever since Antiquity, have always worshiped the Sun which has been repeatedly considered as a god all around the world: Ra in Egypt, Helios in Greece, Inti for the Incas. The relationship between mood disorders and the light changes between seasons is described for the first time by Wong Tai over 4700 BC [
Not far from there, Aretaeus of Cappadocia (II–I century BC) will be the first to consider melancholy and mania as part of the same nosological entity. He is therefore the first to conceptualize what is now called bipolar disorder [
The first application of light therapy in modern psychiatry can be identified in the
He guided the construction of many French hospitals such as in Marseille, Le Mans, Rouen, Montpellier, Nantes and his major work: The Royal House of Charenton. He led the architect ÉmileJacques Gilbert in the design of what was then called “The Asylum of Charenton,” as he states in
During the same period, exposure to the sun was indicated as a treatment for tuberculosis or for skin conditions such as lupus and eczema. The therapeutic virtues of the sun were recognized on the psychiatric, cutaneous and immunological fields. Sanatoria were built to benefit from natural sunlight during the late 19th century to fight the tuberculosis epidemic. Sanatoria were founded to provide patients with good food, fresh air and sunlight exposure. Arnold Rikli, Oskar Bernhard and August Rollier were the firsts to seriously use sunlight (helio) therapy in the treatment of tuberculosis [
In 1890 the Danish physicist Niels Ryberg Finsen developed the first carbon arc lamp (
Since then, ancient heliotherapy was thus separated into two distinct medical branches: 1) phototherapy, which uses natural or artificial UV rays A and B (then associated with exogenous photosensitive molecules in dynamic phototherapy), and 2) light therapy, which uses natural—then artificial—light spectrum, without UV rays (UV filter) to treat depressive syndromes (amongst other syndromes) by a direct effect on the central nervous and hormonal systems and indirect effects on the biological clock [
As far as the field of psychiatry is concerned, it was not until the beginning of the 1980s that Norman Rosenthal, a South African doctor practicing in Washington, got interested in light therapy, observing at his own expense that he was feeling depressed at the arrival of autumn and then feeling a mood improvement in early spring. In 1984, with the help of his group of researchers at the National Institute of Mental Health in the United States, he published the first scientific description of the Seasonal Affective Disorder, or SAD [
Following Rosenthal’s publications, the scientific community’s interest in light therapy became increasingly important. The devices used in Bright Light Therapy (BLT) are now a part of the personal care industry and are being miniaturized or portabilized; they should provide a light intensity going from 2000 to 10,000 lux [
The 2000s witnessed the emergence of personal light lamps, getting more and more manageable, and new devices such as dawn simulators or portable light therapy glasses.
A large number of studies have since been carried out, initially about SAD, then about non-seasonal major depressive disorder (MDD) [
In order to be defined as BLT devices, the luminous intensity delivered must be higher or equal to 2,500 lux [
The BLT is now recognized as the first-line treatment of depressive episodes in SAD. Its use is recommended as soon as the photoperiod decreases. The use of the Morningness-Eveningness Questionnaire has made it possible to create an algorithm for the use of BLT in this condition [
The use of BLT in MDD is now recommended as an adjunctive therapy to conventional antidepressants (for example fluoxetine, sertraline and imipramine) [
The use of BLT during depressive episodes in patients with bipolar disorder should consider the risk of manic shift and should be done in the presence of an effective mood stabilizing treatment [
There is currently no consensus regarding BLT in bipolar depression, but we recommend using this treatment under close medical supervision, so that the duration of exposure can be adjusted rapidly if the patients were to show hypomanic symptoms such as irritability, psychomotor agitation, or sleep disorders. In case of poor tolerance, the duration of exposure should be reduced and the time of exposure may be shifted to midday, as suggested by the study from Sit et al. [
The light coming to the eye sends to the brain two different types of information: the so-called “visual” information, relayed by photoreceptors known as rods and cones; whereas “non-visual” information results from the detection by the eye of variation in light intensity and is then transmitted to the brain through melanopsin. This photosensitive protein discovered in the early 2000s and its major role in mediating the effects of light has been the subject of numerous research [
In the SAD, it is the action of light on the indirect circadian process that seems to be at the origin of the therapeutic efficacy of BLT on mood disorders, this mechanism would be influenced by external light information, thus influencing the production of melatonin by the pineal gland in the brain [
Even more recent studies observe that light may exert a direct action (non-circadian action) on monoaminergic systems [
The anti-depressive action of the BLT would therefore be the sum of two interconnected processes—direct and indirect—mediated by the RGCs and the ipRGCs.
BLT has a rapid action on depressive symptoms with observable results from the first days of treatment, although some studies have periods of exposure of up to 6 weeks [
Regarding the tolerance of BLT in BD, the data in the literature are more contradictory [
Heliotherapy has been the longest used form of phototherapy and the only one until the mid-nineteenth century. Since the invention of the electric light bulb and the progress of medicine, heliotherapy shifted to UV phototherapy and to light therapy (UV filtered light). BLT is today the gold standard treatment of the SAD, and is recommended in various others affective disorders with non-seasonal patterns. Recent findings helped to better understand the physiological insights underlying BLT’s action on affective disorders and may pave the way toward an optimal use in mood disorders.
The authors have no potential conflicts of interest to disclose.
Conceptualization: Jérémy Choukroun, Pierre Alexis Geoffroy. Data curation: Jérémy Choukroun, Pierre Alexis Geoffroy. Formal analysis: Jérémy Choukroun, Pierre Alexis Geoffroy. Funding acquisition: Jérémy Choukroun, Pierre Alexis Geoffroy. Investigation: Jérémy Choukroun, Pierre Alexis Geoffroy. Methodology: Pierre Alexis Geoffroy. Project administration: Pierre Alexis Geoffroy. Resources: Pierre Alexis Geoffroy. Software: Jérémy Choukroun, Pierre Alexis Geoffroy. Supervision: Pierre Alexis Geoffroy. Validation: Jérémy Choukroun, Pierre Alexis Geoffroy. Visualization: Jérémy Choukroun, Pierre Alexis Geoffroy. Writing—original draft: Jérémy Choukroun, Pierre Alexis Geoffroy. Writing—review & editing: Jérémy Choukroun, Pierre Alexis Geoffroy