Light Basics

Light travels fast, penetrates deep, heats, burns and eliminates, brightens and heals

Light therapy or phototherapy 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. The light is administered for a prescribed amount of time and, in some cases, at a specific time of day.

Visible light is usually defined as having a wavelength in the range of 400 nanometres (nm) to 700 nanometres – between the infrared, with longer wavelengths and the ultraviolet, with shorter wavelengths.

Primary properties of light are intensity, propagation direction, frequency or wavelength spectrum, and polarisation.
  • Light intensity :
    the quantity of visible light that is emitted in unit time per unit solid angle. The unit for the quantity of light flowing from a source in any one second (the luminous power, or luminous flux) is called the lumen.

  • Light propagation :
    light travels in waves while its propagation is defined by its wavelength, reflection and refraction. light wave transports its energy through a vacuum at a speed of 3.00 x 108 m/s, its propagation through a material medium occurs at a net speed which is less than 3.00 x 108 m/s.

  • Light frequency and wavelength spectrum :
    The wavelength and frequency of light are closely related. The higher the frequency, the shorter the wavelength. Because all light waves move through a vacuum at the same speed, the number of wave crests passing by a given point in one second depends on the wavelength. That number, also known as the frequency, will be larger for a short-wavelength wave than for a long-wavelength wave.

  • Light polarisation :
    a light wave that is vibrating in more than one plane is referred to as unpolarized light. Light emitted by the sun, by a lamp in the classroom, or by a candle flame is unpolarized light.It is possible to transform unpolarized light into polarized light. Polarized light waves are light waves in which the vibrations occur in a single plane. transforming unpolarized light into polarized light is known as polarization. There are a variety of methods of polarizing light. The four methods discussed on this page are: Polarization by Transmission, Polarization by Reflection, Polarization by Refraction, Polarization by Scattering.

Phototherapy and treatment chromophores

A chromophore is the part of a molecule responsible for its color. The color arises when a molecule absorbs certain wavelengths of visible light and transmits or reflects others. The chromophore is a region in the molecule where the energy difference between two different molecular orbitals falls within the range of the visible spectrum.

Light based systems in the aesthetic industry are designed to target specific skin chromophores.
  • Melanin :
    There are three basic types of melanin: eumelanin, pheomelanin, and neuromelanin. The most common type is eumelanin, and is produced in 'black' and 'brown' subtypes. This kind of melanin absorbs light in the visible light spectrum ranges 400-800nm. Pheomelanin is a cysteine-containing red-brown polymer of benzothiazine units largely responsible for red hair and freckles, absorbs light only in the UV range. Neuromelanin is found in the brain, though its function remains obscure.

  • Oxyhemoglobin :
    Oxyhemoglobin is formed during physiological respiration when oxygen binds to the heme component of the protein hemoglobin in red blood cells. Oxyhemoglobin absorbs light in the visible & IR range. systems treating vascular lesions are based on targeting this chromophore.

  • Water :
    sub-epidermal water are the most targeted chromophore targeted in wrinkle reduction treatments. heating the water in between the epidermal and dermal layers can cause a micro-thermal trauma stimulating a corrective regeneration of the dermal layer and production of newer collagen fibers.

Selective Photothermolysis

"The matching of a specific wavelength and pulse duration to obtain optimal effect on a targeted tissue with minimal effect to surrounding tissues"

Enderson & Parrish, Science 1983

  • The longer the wavelength, the deeper the penetration
  • Pulse duration is usually set according to the heat capacity of the relevant tissues. the thermal capacity of a skin tissue is defined by the term - thermal relaxation time (TRT). Thermal relaxation time is the time required for a tissue to cool to 50% of the heated temperature, for example: Epidermal TRT: 3-7ms, Follicle TRT: 40-100ms (Depending on follicle diameter).
  • Pulse wavelengths and duration are set so the targeted tissue be destroyed while the surrounding tissue is kept protected.
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