Light therapy or phototherapy also referred to as heliotherapy, consists of exposure to (full-spectrum) daylight or to specific wavelengths of light. The light is administered for a prescribed amount of time and, in some cases, at a specific time of day.
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Many ancient cultures practiced various forms of heliotherapy, including people of ancient Greece, Egypt, and Rome.
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Until the early 1930s, light therapy was considered an effective and mainstream medical therapy.

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A common use of light therapy which strikes the retina of the eyes is used to treat circadian rhythm disorders and can also be used to treat seasonal affective disorder (SAD), as well as some non-seasonal psychiatric disorders including major depressive disorder, bipolar disorder and postpartum depression. Additionally, the term is associated with the treatment of skin disorders and beauty procedures.
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Light therapy is preferred over antidepressants because it is a relatively safe and easy therapy.

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The effectiveness of light therapy for treating SAD is linked to the fact that light therapy makes up for lost sunlight exposure and resets the body’s internal clock. Studies show that light therapy helps reduce the debilitating and depressive behaviors of SAD, such as excessive sleepiness and fatigue.
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Sleep disorder in Parkinson’s disease

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Light therapy has been trialed in treating sleep disorders experienced by patients with Parkinson’s disease.
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Sleep Disorder in Alzheimer’s Disease

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Studies have shown that daytime and evening light therapy for nursing home patients with Alzheimer’s disease, who often struggle with agitation and fragmented wake/rest cycles effectively led to more consolidated sleep and an increase in circadian rhythm stability.
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Photobiomodulation.

Photobiomodulation (cellular modulation by light) is also known as LED Phototherapy or LED Therapy. NASA originally developed it for plant growth experiments on shuttle missions and later found it to have promise for wound treatment and helped regenerate the skin from aging.
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WARNING

In order to reduce the risk of retinal damage caused by LEDs, invisible near infrared light (NIR) wavelengths should be emitted from a light therapy device in conjunction with the visible spectrum.

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LED light exposure that is not balanced with full (spectrum) sunlight loaded with the red parts of the spectrum is always damaging to your biology.

Dr. Alexander Wunsch, MD, PhD
world class expert on photobiology.