What is phototherapy?

It is about the therapeutic use of light.

As we know the sun is the main source of energy and its solar radiation has three components:

  • Thermal
  • Visible
  • Photochemical

Natural phototherapy is the exclusive use of sunlight for therapeutic purposes and is known as heliotherapy, and its benefits include:

  • Strengthening of the immune system
  • Rickets
  • Anemia
  • Postsurgical episodes
  • Processes related to calcium intake
  • Maintenance of good condition in general.

Heliotherapy is not recommended in:

  • Albino people
  • Pellagra
  • Systemic lupus erythematosus
  • Critical stage multiple sclerosis
  • Conjunctivitis
  • Porphyria

Light theories

– 18th Century Corpuscular Theory:

He says that the light is made up of numerous particles emitted by incandescent bodies that propagate linearly through transparent media.

– Ripple Theory:

In 1870 Maxwell indicates that electromagnetic waves propagate in the form of wave movements and indicate that light is a form of electromagnetic energy.

– Quantum theory:

Planck in the twentieth century says that energy is propagated by quanta or energy packages and not by continuous waves.

– Photonic theory:

Einstein in 1905. Applies quantum theory in the field of electricity and light.

Photon: Elementary radiation corpuscle that contains an amount of energy.

Phenomena of electromagnetic wave propagation

The propagation of electromagnetic waves can suffer from the following phenomena:

  • Refraction: Change of direction that the light experiences when passing from one medium to another
  • Dispersion: Decomposition of a ruinous beam of light in its different radiations
  • Reflection: Angle of incidence with the normal at the incident point.
  • Transmission: Transmitted light that emerges from a medium or proportion of radiant flow through a medium.
  • Absorption: The ability of molecules to retain energy.
  • Penetration depth: Distance that energy runs within matter.

Laws applicable to phototherapy:

– Law of the inverse of the square of the distance:

The intensity is inversely proportional to the square of the distance.

– Lambert Cosine Law:

The maximum intensity is obtained when the beam affects perpendicularly.

– Bunsen Roscoe Law:

The product of intensity for the time raised to a power.

– Grotthus Draper’s Law:

Only absorbed energy is effective.

Visible light

It is the spectrum of light that is perceptible by the human retina. This corresponds to 40% of the total solar emission.

The rest of the solar emission is in:

  • Infrared radiation: 59%
  • Ultraviolet radiation: 1%

Visible light comprises wavelengths of 400 to 180 nm, between IR and UV.

White light is a mixture of different colors (red, orange, yellow, green, blue, indigo and violet).

Thanks to this visible light, we have the regulation of circadian rhythms and the regulation of sleep (thanks to the inhibition of melatonin).

Visible light can be used in cases of:

  • Hyperbilirubinemia: Exposure to intense white light causes the production of bilirubin and luminorubin isomers.
  • Diagnostic scope

The other applications of phototherapy in Physical Therapy correspond to

  • Infrared
  • Ultraviolet

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