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."

Seasonal affective disorder, or SAD, also known as winter depression is an affective, or mood, disorder. Most SAD sufferers experience normal mental health throughout most of the year, but experience depressive symptoms in the winter or summer.