Current research suggests that depression is caused by a combination of genetic, biological, environmental, and psychological factors.

  • Depression can happen at any age, but often begins in adulthood. Depression (major depressive disorder or clinical depression) is a common but serious mood disorder. It causes severe symptoms that affect how you feel, think, and handle daily activities, such as sleeping, eating, or working.
  • Seasonal affective disorder (SAD) is characterized by the onset of depression during the winter months, when there is less natural sunlight. This depression generally lifts during spring and summer. Winter depression, typically accompanied by social withdrawal, increased sleep, and weight gain, predictably returns every year in seasonal affective disorder.


Light therapy can treat SAD.

CAUTION: Light therapy devices can contribute to retinal damage, especially LED devices, if they  do not emit near infrared light (NIR).


Lack of sunlight causes or contributes to SAD, thus getting more full-spectrum light usually reverses it. The most common treatment for SAD is light therapy, which consists of daily exposure to light that mimics natural, outdoor light. Full-spectrum light exposure leads to increases in serotonin levels in the brain that will help lift moods and relieve other symptoms.
Light therapy works by stimulating photoreceptors in the retina that connect to the hypothalamus, a part of the brain that helps control circadian rhythms. Activating the hypothalamus at a certain time every day can restore a normal circadian rhythm and thus banish seasonal symptoms.

Light therapy is most effective when you have the proper combination of light intensity, duration and timing.

  • Intensity: The intensity of the light is recorded in lux, which is a measure of the amount of light you receive. For SAD, the typical recommendation is to use a 2500 – 10,000 lux light at a distance of about 18 to 24 inches from your face.
  • Duration: Light therapy typically involves daily sessions of about 20 to 30 minutes. But a low-intensity light, such as 2,500 lux, may require longer sessions.
  • Timing: For most people, light therapy is most effective when it’s done early in the morning, after you first wake up.

Can light therapy treat non-seasonal depression too?

Light therapy can treat more than just winter depression. A 2014 study found that light therapy in combination with sleep deprivation helped reduce depressive symptoms in people with bipolar disorder. Other studies have suggested that light therapy may improve sleep among people with dementia and may ease lower back pain.
Additionally, a carefully designed randomized controlled trial — of the kind considered the gold standard in medicine — suggests bright light therapy deserves a closer look. The study was small, involving only 89 patients ages 60 and older, but the results were remarkable.
Compared with a placebo, light therapy improved mood just as well as conventional antidepressant medications, said Dr. Ritsaert Lieverse, the paper’s lead author and a psychiatrist at the VU University Medical Center in Amsterdam.

The effect sizes we found in this study are comparable to those reported for antidepressants, so I think efficacy is of comparable magnitude.

—Dr. Ritsaert Lieverse


How much light are you getting?

The amount of light reaching your eyeball from interior lighting is far less than the amount from outdoor sunlight. So unless you are outside much of the day you are relying on electric light for your photons. Here’s how much less light you receive indoors versus outdoors (Lux is a standard unit of light flow).
  • Bright Moonlight: 1 lux
  • Average Living Room Light: 1-200 lux
  • Average Office Fluorescent Light: 3-500 lux
  • Bright Sunlight: 20-100,000 lux

I think this opens up another treatment option for people with non-seasonal depression and we need more treatment options because not everybody gets better with the standard treatment options.

Dr. Raymond W. Lam, professor of psychiatry, University of British Columbia.

Dr. Lam is the lead author of a study, which was published in the journal JAMA Psychiatry..