From yee Wiki:
Light therapy or phototherapy (classically referred to as heliotherapy) consists of exposure to daylight or to specific wavelengths of light using polychromatic polarised light, 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 disorder and can also be used to treat seasonal affective disorder, with some support for its use also with non-seasonal psychiatric disorders.
Mood and sleep related
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.
The 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.
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
In the management of circadian rhythm disorders such as delayed sleep phase disorder (DSPD), the timing of light exposure is critical. For DSPD, 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 disorder, while evening use is recommended for advanced sleep phase disorder.
Light therapy has been tested for individuals on shift work, and for jet lag.