Light therapy

# Overview
Light therapy or phototherapy consists of exposure to specific wavelengths of light using lasers, LEDs, fluorescent lamps, dichroic lamps or very bright, full-spectrum light, for a prescribed amount of time. It has proven effective in treating Acne vulgaris, seasonal affective disorder, and for some people it has ameliorated delayed sleep phase syndrome. It has recently been shown effective in non-seasonal depression. Proponents claim demonstrable benefits for skin conditions such as psoriasis and, more controversially, a degree of "skin rejuvenation."

# Skin related

## Acne Vulgaris

### Blue/Red Light Treatment
Sunlight has long been known to improve acne, and this effect was thought to be due to antibacterial and other properties of the ultraviolet spectrum, which cannot be used as a treatment due to the associated long-term skin damage. However, artificial UV was not as effective as natural sunlight.
It was found that some of the visible violet light, present in sunlight, in the range 405-420 nm activates a porphyrin (Coproporphyrin III) in Propionibacterium acnes which damages and ultimately kills the bacteria by releasing singlet oxygen. A total of 320 J/cm2 of light within this range renders the bacteria nonviable. This part of the spectrum is just outside the ultraviolet and produces little if any tanning or sunburn.
Application of the light for 3 consecutive days has been shown to reduce the bacteria in the pores by 99.9%. Since there are few porphyrins naturally found in the skin, the treatment is believed safe except in patients with porphyria; although eye protection is necessary due to light sensitive chemicals in the retina. The light is usually created by fluorescent lamps, bright LEDs or dichroic filament bulbs.
Treatment is often accompanied with application of red light which has been shown to activate ATP in human skin cells (essentially a photobiomodulation effect), and seems to improve response rates.
Overall improvements of on average 76% for 80% of patients occurs over 3 months; most studies show that it performs better than Benzoyl peroxide but treatment is far better tolerated. However, approximately 10% of users see no improvement.
Home use light boxes usually work well, are effective for people with long-term acne, are likely to be cheaper than dermatologist office light treatments, and can be repeated over several years for negligible cost, as opposed to once weekly or fortnightly. However, the strength of light at a dermatologist clinic is likely to be of a much higher strength, possibly negating the disadvantage of not being used so often, the most prominent model of which is Omnilux. As of 2007 even though they are not cheap, the cost is on a par with the total cost of benzoyl peroxide, moisturiser and facial washes over the total life of the light box, and the light boxes may yet get cheaper due to economies of scale.

### Photodynamic therapy
Application in a dermatologist's office is usually much more costly, and not necessarily any more effective, but the visible blue light is sometimes used with off-label use of aminolevulinic acid; this causes the bacteria to generate more than normal quantities of porphyrins and this greatly improves response. Whilst temporary redness and edema is experienced, this can give over a year of clearance with just a few applications.
There is some skepticism and lack of data over some of the treatments of acne vulgaris through visible light, mainly for the newer and relatively experimental photodynamic treatments. For more information.

## Psoriasis and eczema
A feature of psoriasis is localized inflammation mediated by the immune system. UV radiation is known to suppress the immune system and reduce inflammatory responses. Light therapy for skin conditions like psoriasis or eczema use UVA (315-400nm waveband) or UVB (280-315nm waveband) light waves. UVA normally combined with an orally taken drug is known as PUVA treatment. Narrow Band UVB is the 310nm wave length and is given as a light therapy treatment rather than full spectrum UVB.

## Tanning
Tanning is caused by the effects of two different types of ultraviolet radiation: UVA and UVB.

## 'Antiaging'
Visible red light at 660nm activates ATP in skin cells and increase the rate of production of collagen for a few days, giving a lifting effect. No permanent improvement of skin aging has been demonstrated, but completion of the healing of skin damage does seem to proceed faster.

## Wound healing and neuropathy
Monochromatic infrared light emitted at a wavelength of 890nm has been shown effective through limited clinical studies, to help restore sensation and reduce pain in patients with Neuropathy, and to improve circulation, thus increasing the healing rate of non-healing ulcers. It is thought that the infrared light helps to release nitric oxide into the bloodstream, which aids in increasing local circulation and improving blood flow. People with diabetes have poor circulation due to their naturally low levels of nitric oxide and, oftentimes, sedentary lifestyles.

# Mood and sleep related

## Seasonal affective disorder
Full sunlight is preferred for seasonal affective disorder. Other treatments are based upon infrared light exposure. There are a number of products (such as light boxes) using very intense artificial illumination that are effective for seasonal affective disorder. These products must provide 10,000 lux or more directed angularly at the user's eyes, without harmful ultraviolet radiation.
New research indicates that using only certain wavelengths of light (i.e., the "blue" wavelengths) is at least as efficacious as using 10,000 lux, at least until one approaches old age, when blue light is no longer more effective than red or green. The most effective wavelengths of blue light are given as ranging between 460 nm and 480 nm by most sources, with some sources specifying peak photopigment sensitivity at 479 nm (in mice).

## Non-seasonal depression
Only recently have clinical studies been conducted which specifically excluded all patients with any degree of seasonality. Before these studies, there was suspicion that any depressed patients who benefitted from light treatment were really only having the SAD component of their depression treated. However, light therapy is now an established treatment for depression, regardless of seasonality, and has an advantage over drugs in that it might take less time to see a benefit. Typically, antidepressant drugs take several weeks to achieve full effectiveness.

## Delayed sleep phase syndrome
When treating delayed sleep phase syndrome, the timing of the exposure is critical. The light must be provided as soon after arising as possible to achieve any effect. Some users have reported success with lights that turn on shortly before waking (dawn simulation).
See Also: Phase response curve

# Neonatal jaundice
Light energy creates isomerization of the bilirubin and consequently transformation into compounds that the newborn can excrete via urine and stools.

# Jet lag
Light therapy is also considered as a viable treatment for jet lag. Exposure to bright light during the appropriate time periods before, during and after air travel can reduce the symptoms of jet lag and accelerate the recalibration of the body clock. NASA has used timed doses of bright light to prepare astronauts for late night launches since 1991.

# Heliotherapy
Within the tanning and spa industry the term "heliotherapy" has become popular to describe medical therapy by exposure to light, usually in the UVA/UVB range. This could include direct sunlight but more often refers to the use of tanning beds and booths, which have both ultraviolet and infrared.  The treatment of psoriasis, eczema, vitamin D deficiency and seasonal affective disorder are included in this list. As with any exposure to UV, there are some risk associated, but these are usually outweighed by the benefits provided by the treatments. Often, UV treatments are given at a doctors office, but it is becoming more common for a doctor to prescribe regular visits in a tanning bed for persons who have moderate problems, as this is lower in UV than medical devices, and is more convenient and less expensive for the patient.  In very rare and extreme cases, the purchase of home tanning beds are prescribed by a doctor and covered by insurance.
There is also evidence that exposure to some frequencies of light (UV in particular) causes the body to release small amounts of endorphins, which would explain the benefit for some disorders such as SAD, as endorphines are often called "the body's own morphine," as well as the concerns for potential tanning addiction, not to be confused with what is commonly called tanorexia, a psychological syndrome whereby an individual sees themselves as pale even if they have a substantial tan.

# Disadvantages

## Safety of phototherapy
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.
Visible blue light has been suggested to cause DNA breaks, but carcinogenesis has not been demonstrated, and enzymes within the cells are believed to repair the breaks reasonably well. However, cancer has been induced in cells with deliberately damaged repair mechanisms. Also, researchers have questioned whether limiting blue light exposure could reduce the risk of age-related macular degeneration (ARMD).
Modern phototherapy lamps used in the treatment of seasonal affective disorder 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, as 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.

## Contraindications
There are few absolute contraindications to light therapy, although there are some circumstances in which caution is required. These include when the patient 1) has a condition that might render his or her eyes more vulnerable to phototoxicity, 2) has a tendency toward mania, 3) has a photosensitive skin condition, or 4) is taking a photosensitizing medication or herb. Patients with porphyria should avoid most forms of light therapy. Patients on certain drugs (e.g., methotrexate or chloroquine) should exercise caution in deciding whether to undergo 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, feeling "wired," headache, and nausea. Some nondepressive physical complaints (such as poor vision and skin rash or irritation) may improve with light therapy (M. Terman and Terman 1999).