Light Therapy

Seasonal affective disorder and bright light

A 1984 paper by Rosenthal and colleagues described seasonal affective disorder as a syndrome of recurrent depressions that begin at the same time each year. The authors reported 29 patients, most with bipolar II disorder, whose depressions were marked by sleeping more, overeating and carbohydrate craving. In 11 patients, preliminary studies suggested that extending the photoperiod with bright artificial light had an antidepressant effect.

The sources reviewed for this page do not trace earlier uses of light for health, so no earlier history is given here. The 1984 report is the earliest source opened, and it described a small preliminary observation, not a confirmed treatment effect. Photobiomodulation and chromotherapy have their own pages and are not covered in this history.

From a case description to guideline listings

Later work tested bright white light in randomized trials, and by 2016 a Canadian guideline listed light therapy as a first-line single treatment for seasonal depression and as a second-line option for mild to moderate depression without a seasonal pattern. The American Academy of Sleep Medicine added recommendations for some circadian rhythm sleep-wake disorders in 2015. These listings are summarized in later sections.

Names used in the literature

The sources reviewed use several overlapping terms: light therapy, bright light therapy, bright white light, and visible light therapy. The NHS describes a bright light, sometimes called a SAD lamp or light box, used to simulate daylight in winter. Rosenthal and colleagues wrote of extending the photoperiod, meaning the length of daily light exposure, with bright artificial light.

Light color and related pages

Trials of seasonal affective disorder have compared white light with blue, green and red light, and a 2022 review looked at blue or blue-enhanced devices alone. In that research, color is a variable inside a single clinical question and not a separate practice. Photobiomodulation, which concerns low-level red and near-infrared light, and chromotherapy, which concerns color for emotional or energetic purposes, are separate pages and should not be inferred from the trials described here.

What a session involves

The NHS describes light therapy as using a bright light box, or SAD lamp, to simulate daylight in winter. It advises choosing a device that is UV-free and carries a UKCA or CE mark, and it says the therapy is not usually provided by the NHS. This page does not describe exposure schedules, device settings or distances. Those details belong with a clinician who knows the person.

How studies deliver light

Trial reports describe timed daily exposure to a lamp, often in the morning, and compare it with dim light, inactive devices, negative ion generators, medicines or usual care. The sleep medicine guideline refers to light with or without behavioral interventions, and its recommendations for some groups specify evening or post-awakening timing. The reviews cited here differ in lamps, timing and length of treatment, which limits direct comparison between them.

Seasonal affective disorder

The NHS describes seasonal affective disorder as a type of depression that usually appears in winter and lifts in summer, with a diagnosis usually considered when symptoms recur at the same time of year for at least two years. It lists light therapy alongside antidepressants and talking therapies. The CANMAT guideline lists light therapy as a first-line single treatment for seasonal depression, based on level 1 evidence.

Depression without a seasonal pattern

The same Canadian guideline lists light therapy as a second-line single or added treatment for mild to moderate depression without a seasonal pattern, based on level 2 evidence. Reviews have also examined light added to antidepressants and light in bipolar depression, and these are described under research and evidence. They concern adults with a diagnosed mood episode and should not be read as covering low mood in general.

Circadian rhythm sleep-wake disorders and dementia

The American Academy of Sleep Medicine guideline suggests light therapy for adults with advanced sleep-wake phase disorder, for children and adolescents with delayed sleep-wake phase disorder when combined with behavioral treatment, and for elderly people with dementia who have irregular sleep-wake rhythm disorder. It labels these recommendations as weak. For adults with delayed phase disorder and for non-24-hour disorder it found too little evidence to recommend light.

Reviews of light in dementia have examined sleep, mood, behavior and cognition. The sources reviewed do not cover other claimed uses of light therapy, such as shift work, jet lag or conditions outside mood and sleep, so none are described here.

Seasonal affective disorder trials

A 2025 network meta-analysis of 17 randomized trials with 773 patients ranked white light as most effective for seasonal affective disorder, followed by green, blue and red light, and found usual care more effective than green light. It called for larger studies. A 2015 critical review of eight seasonal trials of bright white light of adequate quality found a pooled advantage over control conditions at endpoint (standardized mean difference -0.54, 95% confidence interval -0.95 to -0.13).

That 2015 review also found a week-by-week advantage only at weeks two and three, and its authors concluded that most trials had considerable methodological problems and that the evidence was not unequivocal. Blue light was not clearly better than inactive or active light conditions in a review of nine trials with 347 participants. These results cover short-term changes in rating scale scores.

Depression without a seasonal pattern

A 2024 meta-analysis of 15 randomized trials with 883 patients with non-seasonal major depression reported a pooled standardized mean difference of 0.48 (95% confidence interval 0.22 to 0.74) in favor of bright light, with a higher response rate. A 2019 review of seven populations with 397 participants found no clear difference between light alone and antidepressants alone, and found light added to an antidepressant superior to the antidepressant plus placebo (standardized mean difference 0.56).

The 2015 critical review performed no pooled analysis for non-seasonal depression because the studies differed too much, and the CANMAT guideline notes methodological limitations and few long-term data for complementary treatments in general. Trials have used varied comparators, so effect sizes differ between reviews.

Bipolar depression, circadian disorders and dementia

A 2019 review of seven double-blind trials with 259 people with bipolar depression found a significant improvement on the Hamilton depression scale (standardized mean difference 0.43, 95% confidence interval 0.04 to 0.82) and a higher clinical response rate, but no difference in remission. The authors described the evidence as positive but not conclusive, citing small samples, short treatment and varied light parameters.

For dementia, a 2024 meta-analysis of 24 studies with 1,074 participants reported small-to-medium effects on several sleep measures, depression and behavior. A separate 2023 meta-analysis of 11 trials found a significant reduction only in night awakenings, with no significant effect on agitation or depression. The two reviews therefore differ, and long-term effects remain unclear.

Gaps in the trial evidence

The NHS states that light therapy is not usually available on the NHS because there is not enough evidence to tell whether it is effective, while noting that many people find it helps. This differs from the Canadian guideline, which grades the evidence higher for seasonal depression. The 2015 critical review explains part of the gap, since pooled results depended heavily on which trials were selected.

A person cannot be unaware of sitting before a bright lamp, so blinding is difficult, and trials used a range of comparators from dim light to negative ion generators. The sources reviewed for this page do not provide independent audits of conflicts of interest, and none were searched for industry funding.

What remains unknown

The reviews describe small samples, short treatment periods and differing light parameters, and the Canadian guideline notes few long-term data. For bipolar depression the authors called the evidence positive but not conclusive, and for dementia two reviews reached different pooled results. The sources reviewed do not establish which people are most likely to benefit.

Common effects and eye and skin cautions

The CANMAT guideline states that light therapy is generally well tolerated and lists eye strain, headache, agitation, nausea and sedation as common side effects. The NHS advises speaking to a doctor first, because light therapy may not suit people with certain eye conditions or those taking medicines that increase sensitivity to light. It advises devices that are UV-free and carry a UKCA or CE mark.

A 1996 analysis by an ophthalmology-led group reported that ultraviolet and visible light can cause distinct lesions of ocular tissue under certain experimental and naturalistic conditions, and that the emission spectra of treatment lamps were mostly unknown to users. It proposed lamps without damaging emissions and eye monitoring for people with eye disease. The source is old and gives no frequency of eye injury with current devices. The sources reviewed do not describe skin effects beyond the medicine caution above.

Mania and hypomania in bipolar disorder

Light can be activating. A meta-analysis of seven trials in bipolar depression reported mild activating symptoms such as agitation, anxiety and arousal in several studies, and switch rates into mania or hypomania of 3.0% with active light and 1.6% with control, a difference that was not significant (odds ratio 1.30, 95% confidence interval 0.38 to 4.44). Six of the seven studies recorded no switches, and the authors advised that people with bipolar disorder be actively monitored for hypomanic symptoms.

In a 2025 trial of 38 people with bipolar depression who were taking mood stabilizers, two (6%) had a hypomanic switch and five had subsyndromic hypomanic symptoms. The authors reported that these improved within three days after exposure was reduced. The trial was designed to test tolerance and had no comparison group, so it cannot show how often switches occur without light.

Suitability, care boundaries and training

Light therapy is described in the sources as a treatment for diagnosed mood or sleep conditions, and the sources reviewed do not describe it as a substitute for assessment. Depression, thoughts of self-harm, new eye symptoms or an unusual rise in energy need assessment by a health professional, and light therapy should not delay or replace necessary care. People with bipolar disorder, eye disease or light-sensitizing medicines are named as groups needing medical advice first.

No professional register, training standard or protected title for light therapy was found in the sources reviewed, and no statutory regulation or training standard was identified. Devices are bought by the public, and the NHS advises checking that a lamp is UV-free and carries a UKCA or CE mark.