Light therapy is a common treatment for a variety of conditions, from auto-immune disorders including psoriasis and eczema, to wound healing, to depression and seasonal affective disorder, to circadian rhythm sleep disorders
Light therapy or phototherapy (classically referred to as heliotherapy) consists of exposure to daylight or to specific wavelengths of light using lasers, light-emitting diodes, fluorescent lamps, dichroic lamps or very bright, full-spectrum light, usually controlled with various devices. The light is administered for a prescribed amount of time and, in some cases, at a specific time of day.
Common use of the term is associated with the treatment of skin disorders (chiefly psoriasis), sleep disorder and some psychiatric disorders. Light therapy directed at the skin is also used to treat acne vulgaris, eczema and neonatal jaundice. Light therapy which strikes the retina of the eyes is used to treat circadian rhythm disorders such as delayed sleep phase syndrome and can also be used to treat seasonal affective disorder, with some support for its use also with non-seasonal psychiatric disorders.
Other medical applications of light therapy also include accelerated wound healing, hair growth, improvement in blood properties and blood circulation, and sinus-related diseases and disorders. Many of these use low level laser therapy and red light therapy in the 620–660 nm range.
Medical uses 
Skin conditions 
Two forms of phototherapy exist, non-targeted phototherapy (from sunlight, a tanning booth or a light box), and targeted-phototherapy, in which light is administered to a specific, localized area of the skin. Current targeted phototherapy is administered via excimer laser, elemental gas lamp, or via LED light. Current FDA cleared devices on the market include XTRAC excimer laser, BClear, Theralight, and Psoria-Light LED phototherapy. Targeted phototherapy is only administered to the affected skin, not the entire body, thus sparing healthy skin from UV rays which may lead to other health issues including skin cancer. With targeted phototherapy only being administered to the affected area of skin, more intense dosages of light can be administered, allowing skin conditions to be repaired in less time. As of early 2012, the only FDA-cleared device to offer both UVA and NB-UVB treatment within one device is the Psoria-Light.
In psoriasis, UVB phototherapy has been shown to be effective. A feature of psoriasis is localized inflammation mediated by the immune system. Ultraviolet radiation is known to suppress the immune system and reduce inflammatory responses. Light therapy for skin conditions like psoriasis use UV-A (315–400 nm wavelength) or UV-B (280–315 nm wavelength) light waves. UV-A, combined with psoralen, a drug taken orally, is known as PUVA treatment. In UVB Phototherapy the exposure time is very short (1–2 minutes with Broadband UVB lamps and 5–15 minutes with Narrowband UVB lamps). The time must be controlled with a timer that turns off the lamps after the treatment time ends. Too-long exposure results in burning of the skin; this is analogous to over exposure to sunlight.
One percent of the population suffer from vitiligo, and Narrowband UVB Phototherapy is an effective treatment. "NB-UVB phototherapy results in satisfactory repigmentation in our vitiligo patients and should be offered as a treatment option."
Acne vulgaris 
Evidence for light therapy and lasers in acne vulgaris as of 2012 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.
Cutaneous T-cell lymphoma 
Other skin conditions 
Wound healing 
Some case studies have found low-level laser light to be possibly helpful as an adjunctive treatment in wound healing, although a review of the overall scientific literature does not support the use of low-level laser therapy for this purpose.
Seasonal affective disorder 
While full sunlight is preferred for seasonal affective disorder (SAD), light boxes may be effective for the treatment of the condition. Light boxes for seasonal affective disorder are designed to filter out most UV light, which can cause eye and skin damage. Mayo Clinic states that light therapy is of proven effectiveness for treating seasonal affective disorder and light therapy is seen as its main form of treatment. Controlled-trial comparisons with antidepressants show equal effectiveness, with less expense and more rapid onset of therapeutic benefit, though a minority of patients may not respond to it. 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.
The effectiveness of light therapy for treating SAD may be linked to the fact that light therapy makes up for lost sunlight exposure and resets the body's internal clock.
It is possible that response to light therapy for SAD could be season dependent.
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 and postpartum depression. A meta-analysis by the Cochrane Collaboration concluded that "for patients suffering from non-seasonal depression, light therapy offers modest though promising antidepressive efficacy." A more recent meta-analysis from Journal of Affective Disorders confirms this and is even more hopeful: "Overall, bright light therapy is an excellent candidate for inclusion into the therapeutic inventory available for the treatment of nonseasonal depression today, as adjuvant therapy to antidepressant medication, or eventually as stand-alone treatment for specific subgroups of depressed patients."
Circadian rhythm sleep disorder 
- Chronic CRSD
In the management of circadian rhythm disorders such as delayed sleep phase syndrome (DSPS), the timing of light exposure is critical. For DSPS, the light must be provided to the retina 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
Neonatal jaundice 
Light therapy is used to treat cases of neonatal jaundice through the isomerization of the bilirubin and consequently transformation into compounds that the newborn can excrete via urine and stools. A common treatment of neonatal jaundice is the bili light.
Photodynamic therapy 
Photodynamic therapy is a form of phototherapy using nontoxic light-sensitive compounds that are exposed selectively to light, whereupon they become toxic to targeted malignant and other diseased cells
Light boxes 
The production of the hormone melatonin, a sleep regulator, is inhibited by light and permitted by darkness as registered by photosensitive ganglion cells in the retina. To some degree, the reverse is true for serotonin, which has been linked to mood disorders. Hence, for the purpose of manipulating melatonin levels or timing, light boxes providing very specific types of artificial illumination to the retina of the eye are effective.
Light therapy either uses a lightbox which emits up to 10,000 lux of light, much brighter than a customary incandescent lamp, or a lower intensity of specific wavelengths of light from the blue (470 nm) to the green (525 nm) areas of the visible spectrum. Newer light therapy devices use LED technology, making them much smaller and more convenient for users. A 1995 study showed that green light therapy at doses of 350 lux produces melatonin suppression and phase shifts equivalent to 10,000 lux white light therapy, but another study published in May 2010 suggests that the blue light often used for SAD treatment should perhaps be replaced by green or white illumination, because of a possible involvement of the cones in melatonin suppression.
In treatment, the patient's eyes are to be at a prescribed distance from the light source with the light striking the retina. This does not require looking directly into the light.
Considering three major factors – clinical efficacy, ocular and dermatologic safety, and visual comfort – CET recommends the following criteria for light box selection:
- Light boxes should have been tested successfully in peer-reviewed clinical trials.
- The box should provide 10,000 LUX of illumination at a comfortable sitting distance. Product specifications are often missing or unverified.
- Fluorescent lamps should have a smooth diffusing screen that filters out ultraviolet (UV) rays. UV rays are harmful to the eyes and skin.
- The lamps should give off white light rather than colored light. "Full spectrum" lamps and blue (or bluish) lamps provide no known therapeutic advantage.
- The light should be projected downward toward the eyes at an angle to minimize aversive visual glare.
- Smaller is not better; when using a compact light box, even small head movements will take the eyes out of the therapeutic range of the light.
Risks and complications 
Ultraviolet light causes progressive damage to human skin. This is mediated by genetic damage, collagen damage, as well as destruction of vitamin A and vitamin C in the skin and free radical generation. Ultraviolet light is also known to be a factor in formation of cataracts. Researchers have questioned whether limiting blue light exposure could reduce the risk of age-related macular degeneration.
Modern phototherapy lamps used in the treatment of seasonal affective disorder and sleep disorders either filter out or do not emit ultraviolet light and 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, and just as with drug treatments, there is a possibility of triggering a manic state from a depressive state, causing anxiety and other side effects. While these side effects are usually controllable, it is recommended that patients undertake light therapy under the supervision of an experienced clinician, rather than attempting to self-medicate.
There are few absolute contraindications to light therapy, although there are some circumstances in which caution is required. These include when a patient has a condition that might render his or her eyes more vulnerable to phototoxicity, has a tendency toward mania, has a photosensitive skin condition, or is taking a photosensitizing herb (such as St. John's wort) or medication. Patients with porphyria should avoid most forms of light therapy. Patients on certain drugs such as methotrexate or chloroquine should use caution with light therapy as there is a chance that these drugs could cause porphyria.
Side effects 
Side effects of light therapy for sleep phase disorders include jumpiness or jitteriness, headache, and nausea. Some nondepressive physical complaints (such as poor vision and skin rash or irritation) may improve with light therapy.
Many ancient cultures practiced various forms of heliotherapy, including people of the Ancient Greece, Ancient Egypt, and Ancient Rome. The Inca, Assyrian and early German settlers also worshipped the sun as a health bringing deity. Indian medical literature dating to 1500 BC describes a treatment combining herbs with natural sunlight to treat non-pigmented skin areas. Buddhist literature from about 200 AD and 10th-century Chinese documents made similar references.
Faroese physician Niels Finsen is believed to be the father of modern phototherapy. He developed the first artificial light source for this purpose, and used his invention to treat lupus vulgaris. He received the Nobel Prize in Physiology or Medicine in 1903.
Since then a large array of treatments have been developed from the use of controlled light. Though the popular consumer understanding of "light therapy" is associated with treating seasonal affective disorder and skin conditions like psoriasis, other applications include the application of low level laser, red light, near-infrared and ultraviolet lights for pain management, hair growth, skin treatments, and accelerated wound healing.
See also 
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