Photobiomodulation: lasers vs. light emitting diodes?

Abstract

Photobiomodulation (PBM) is a treatment method based on research findings showing that irradiation with certain wavelengths of red or near-infrared light has been shown to produce a range of physiological effects in cells, tissues, animals and humans. Scientific research into PBM was initially started in the late 1960s by utilizing the newly invented (1960) lasers, and the therapy rapidly became known as "low-level laser therapy". It was mainly used for wound healing and reduction of pain and inflammation. Despite other light sources being available during the first 40 years of PBM research, lasers remained by far the most commonly employed device, and in fact, some authors insisted that lasers were essential to the therapeutic benefit. Collimated, coherent, highly monochromatic beams with the possibility of high power densities were considered preferable. However in recent years, non-coherent light sources such as light-emitting diodes (LEDs) and broad-band lamps have become common. Advantages of LEDs include no laser safety considerations, ease of home use, ability to irradiate a large area of tissue at once, possibility of wearable devices, and much lower cost per mW. LED photobiomodulation is here to stay.

Figure 1.. Basic mechanism of operation of a laser.

(A): Principle of population inversion and stimulated emission; when a majority of the atoms in a laser material are pumped to a higher electronic state, an incoming photon can cause release of the excess energy as coherent photons of the same wavelength. (B) Principle of a laser cavity confined by two mirrors, one of which is partially transmissive.

Figure 2.. Basic structure of an LED.

In a PIN-type semiconductor, positive holes occur in the P-region, negative electrons in the N-region, and these recombine in the I (intrinsic)-region to give non-coherent light whose wavelength is determined by the semiconductor composition

Figure 3.. Proposed mechanism of mitochondrial stimulation by laser speckles.

The size of the laser speckles approximately matches the size of mitochondria inside the cell.

Figure 4.. Incandescent light bath by physician John Harvey Kellogg.

In the early 20th century, incandescent bulbs were used as a source of therapeutic light in an “electric light bath”. Kellogg was one of the notable inventors and authors of this era. [Fuzheado / Wikimedia Commons / CC-SA-3.0]. No permission needed.