light therapy
Meaning of light therapy: Different wavelengths do entirely different jobs, so the color of the light is as much a part of the prescription as the timing.
Definition of light therapy
Light therapy is the use of controlled doses of light to treat a condition. The wavelength is chosen for the effect wanted: bright white light in the morning for seasonal depression, ultraviolet light for psoriasis and eczema, and blue light for jaundice in newborns. Sessions are timed, since intensity and duration together determine the dose delivered.
How can light treat anything?
Light is absorbed by particular molecules in the body, and each absorbing molecule leads somewhere different. Bright light entering the eye reaches cells in the retina that report the time of day to the brain's clock, shifting the timing of sleep and of melatonin release. Ultraviolet light entering the skin damages the DNA of overactive immune cells there and slows the rapid turnover of skin cells. Blue light absorbed by bilirubin in a newborn's skin changes that molecule into a form the body can excrete without processing it through the liver. Nothing is heated, and treatment works only where the light actually reaches.
What is used for what?
| Condition | Type of light | How it is delivered |
|---|---|---|
| Seasonal affective disorder | Bright white light with ultraviolet filtered out | A light box used at a set time each morning |
| Psoriasis and eczema | Narrowband ultraviolet B | A cabinet or handheld unit, over repeated sessions |
| Newborn jaundice | Blue light | An overhead lamp or a fiber optic blanket |
| Some skin cancers and precancers | Red or blue light after a sensitizing cream | Photodynamic therapy |
Is it the same as radiation therapy?
No, and the distinction is worth being clear about. Radiation therapy uses ionizing radiation, which carries enough energy to break chemical bonds throughout tissue and is aimed at destroying cells. Light therapy uses non ionizing light, absorbed at the surface or by specific molecules, which does not reach deeply. Ultraviolet sits at the boundary, since it does damage skin DNA, and that is why repeated courses raise the long term risk of skin cancer and why cumulative exposure is recorded. Phototherapy is the same treatment under another name.
What are the practical limits?
Effects depend on regular repetition, so a course is a commitment rather than a single visit. Eye protection is used with ultraviolet sources. Some medicines and some conditions make skin far more sensitive to light, which changes what can safely be given. Devices sold for home use vary widely in output, and a lamp that fails to deliver the intended intensity at the intended distance does not deliver the treatment. Light emitting diode therapy is a newer variation using narrower bands of wavelength.
Also known as
Used in a sentence
Narrowband ultraviolet B light therapy was arranged for widespread plaque psoriasis.
Good to know
Light therapy uses non ionizing light and is not a form of radiation therapy, although repeated ultraviolet courses do raise the long term risk of skin cancer, so cumulative exposure is recorded.