In the early 1980’s, scientists researching depression noted a consistent pattern of symptoms becoming more severe in many patients during the long winter months, particularly in the northern hemisphere. Significantly these symptoms eased ordisappeared completely as the longer summer days returned.

In 1982 The National Institute of Health (NIH) identified winter depression and coined the term, ‘SAD’ for Seasonal Affective Disorder.

The scientists found that 'SAD' was related to an imbalance in the body's natural circadian rhythms. The Circadian rhythm, or the body’s inner clock governs the timing of sleep, hormone production, body temperature, and other biological functions.

In 1984 these pioneering scientists discovered that exposure to bright white light is very effective at treating seasonal affective disorder.

For many years doctors had relegated light therapy to the periphery of credible science. It wasn’t until 2001 that researchers from NIH, Thomas Jefferson Medical University and Apollo Health fully understood how exposure to specialised bright light, stimulates the production of brain chemicals to relieve the symptoms associated with seasonal depression Dr. George Brainard’s team at Thomas Jefferson Medical University, identified a photo receptor in the human eye, responsible for reacting to light and controlling the production of melatonin.

They found specifically that light in the range of 447-484 nm (nanometers) is responsible for suppressing melatonin production and shifting circadian rhythms. Indeed, this particular bandwidth of light is up to ten times more effective than other wavelengths. Light in this range appears blue to the human eye and is often referred to as Blue Light.

Seasonal affective disorder
While full sunlight is preferred for seasonal affective disorder (SAD), light boxes may be effective for the treatment of the condition. The United States Food and Drug Administration has not approved the use of light boxes to treat SAD due to unclear results in clinical trials,[1] but light therapy is still seen as the main form of treatment for SAD.[2] Direct sunlight, reflected into the windows of a home or office by a computer-controlled mirror device called a heliostat, has also been used as a type of light therapy for the treatment of SAD.[3][4]
It is possible that response to light therapy for SAD could be season dependent.[5]

Non-seasonal depression
Light therapy has also been suggested in the treatment of non-seasonal depression and other psychiatric disturbances, including major depressive disorder, bipolar disorder[6] and postpartum depression.[7][8]

Circadian rhythm sleep disorders (CRSD)
Chronic CRSD
In the management of circadian rhythm disorders such as delayed sleep phase syndrome, the timing of light exposure is critical. For DSPS, the light must be provided as soon after spontaneous awakening as possible to achieve the desired effect, as shown by the phase response curve for light in humans. Some users have reported success with lights that turn on shortly before awakening (dawn simulation). Morning use may also be effective for non-24-hour sleep-wake syndrome, while evening use is recommended for advanced sleep phase syndrome.
Situational CRSD
Light therapy has been tested for individuals on shift work,[9] and for jet lag.[10]

 

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