Light therapy, or phototherapy, classically referred to as heliotherapy

Light therapy includes exposure to outdoor daylight or specific indoor artificial light sources.

Care for unipolar depression recommends light therapy especially for depression that follows a seasonal pattern: seasonal affective disorder.

The second kind of light therapy, called ultraviolet light therapy, is meant to treat neurodermatitis, psoriasis, acne vulgaris, eczema and neonatal jaundice.

A blue-light (420–470 nm) phototherapy lamp can treat newborn jaundice.

Exposure to light at specific wavelengths of narrowband UVB enables the body to produce vitamin D to treat vitamin D deficiency.

Light therapy treatments for the skin usually involve exposure to ultraviolet light.

Light exposures therapy can be to a small area of the skin or over the whole body surface, as in a tanning bed. 

The most common light treatment is with narrowband UVB, with a wavelength of approximately 311–313 nanometers. 

Full body phototherapy can be delivered using a large high-power UVB booth.

Tanning beds, however, generate mostly UVA light, and only 4% to 10% of tanning-bed light is in the UVB spectrum.

The evidence for light therapy and lasers in the treatment of acne vulgaris is not sufficient to recommend them.

While light therapy appears to provide short-term benefit, there is a lack of long-term outcome data or data in those with severe acne.

Light therapy is considered one of the best monotherapy treatments for atopic dermatitis (AD) when applied to patients who have not responded to traditional topical treatments. 

For psoriasis, UVB phototherapy has been shown to be effective.

Ultraviolet radiation is known to suppress the immune system and reduce inflammatory responses. 

Light therapy for skin conditions like psoriasis usually use 313 nanometer UVB though it may use UVA (315–400 nm wavelength) or a broader spectrum UVB (280–315 nm wavelength). 

UVA combined with psoralen, a drug taken orally, is known as PUVA treatment. 

About 1% of the population has vitiligo which causes painless distinct light-colored patches of the skin on the face, hands, and legs. 

Phototherapy forces skin cells to manufacture melanin to protect the body from UV damage. 

Narrowband UVB is more suitable to the face and neck and PUVA is more effective at the hands and legs.[20]

Laser therapy is a potential treatment for chronic wounds, but scientific literature have not supported its widespread application. 

Some types of phototherapy may be effective in the treatment of polymorphous light eruption, cutaneous T-cell lymphoma and lichen planus. 

Preliminary evidence suggests light therapy is an effective treatment for diabetic retinopathy and diabetic macular oedema.

The effectiveness of light therapy for treating seasonal affective disorder (SAD) as it resets the body’s internal clock.

Light therapy helps reduce the debilitating and depressive behaviors of SAD, such as excessive sleepiness and fatigue, with results lasting for at least 1 month. 

Light therapy is preferred over antidepressants in the treatment of SAD.

 Bright light and dawn simulation, have similar success rates in the treatment of SAD.

A Cochrane Collaboration study concluded that for patients suffering from non-seasonal depression, light therapy offers modest though promising antidepressive efficacy.

Bright light therapy is available for the treatment of nonseasonal depression, as adjuvant therapy to antidepressant medication, or eventually as stand-alone treatment for specific subgroups of depressed patients.

Light exposure to the eyes before or after core body temperature rhythm can affect the phase response curve.

Use of light upon awakening may also be effective for non-24-hour sleep–wake disorder.

Some, but not all, totally blind people whose retinae are intact, may benefit from light therapy.

Daytime and evening light therapy for nursing home patients with Alzheimer’s disease, who often struggle with agitation and fragmented wake/rest cycles have more consolidated sleep and an increase in circadian rhythm stability.

Light therapy is used to treat cases of neonatal jaundice:

Phototherapy uses the energy from light to isomerize the bilirubin and consequently transform it into compounds that the newborn can excrete via urine and stools. 

Bilirubin is most successful absorbing light in the blue region of the visible light spectrum, which falls between 460 and 490 nm.

Photodynamic therapy is a form of phototherapy using light-sensitive compounds that are exposed selectively to light, whereupon they become toxic to targeted malignant and other diseased cells.

One of the treatments is using blue light with aminolevulinic acid for the treatment of actinic keratosis.

For  the purpose of manipulating melatonin levels or timing, light boxes provide specific types of artificial illumination to the retina of the eye.

Light therapy uses either a light box which emits up to 10,000 lux of light at a specified distance, much brighter than a customary lamp, or a lower intensity of specific wavelengths of light from the blue (460 nm) to the green (525 nm) areas of the visible spectrum.

Green light therapy at doses of 350 lux produces melatonin suppression and phase shifts equivalent to 10,000 lux white light therapy.

Ultraviolet light causes progressive erythematous damage to 

 skin at even small doses.

Ultraviolet light causes genetic, and collagen damage, as well as destruction of vitamin A and vitamin C in the skin and generates free radicals.

Ultraviolet light is also known to be a factor in formation of cataracts, and is strongly linked to incidence of skin cancer.

Bright light therapy may activate the production of reproductive hormones, such as testosterone, luteinizing hormone, follicle-stimulating hormone, and estradiol.

Modern phototherapy lamps are considered safe and effective for the intended purpose: as long as photosensitizing drugs are not being taken at the same time and in the absence of any existing eye conditions.

Light therapy is a mood altering treatment.

Light therapy can possibly trigger a manic state from a depressive state, causing anxiety and other side effects. 

Contraindications to light therapy: conditions that might render the eyes more vulnerable to phototoxicity, tendency toward mania, photosensitive skin conditions, or use of a photosensitizing herb or medication, and porphyria.

Side effects of light therapy for sleep phase disorders:  include jitteriness, headache, eye irritation and nausea.

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