Light Therapy:
Light therapy refers to two different categories of treatment, one used in mainstream medical practice and the other in alternative/complementary medicine. Mainstream light therapy (also called phototherapy) includes the use of ultraviolet light to treat psoriasis and other skin disorders, and the use of full-spectrum or bright light to treat Seasonal Affective Disorder (SAD). Light therapy for SAD was first introduced in the 1980s and is now a widely approved form of treatment for the disorder.
Photo Therapy:
In phototherapy, UV irradiations are used for the treatment of skin disorders. In Dermatology UVB (290-320nm) or UVA (320-400nm) irradiation is used. UVA rays are used after administration of psoralens (PUVA).
Psoralens:
Photo-chemotherapy depends on treatment with drugs that reacts to ultraviolet radiation or sunlight. PUVA is a photo-chemotherapy treatment used to treat severe skin conditions as psoriases and other dermatoses. PUVA is a combination of Psoralens (P) and Ultraviolet A (UVA) radiation. Psoralens are photosensitizing agents (light activated drugs) found in medicinal plants. The drug delivered by psoralens is taken 2 or 3 hours before ultraviolet a treatment session. When absorbed by the body it has the opposite effect of sunscreen. It makes the skin cells more susceptible to UVA light.
Dosimetry:
Dosimetry is essentially how much radiation exposure you get from substances or machines that produce radiation. The dose refers to the amount of energy in joules delivered.