What exactly is Low-Level-Light Therapy? Or should we be calling it Low-Level-Laser Therapy? Or Low-Level-Laser-(light) Therapy? Or Cold Laser Therapy? Or Photobiomodulation Therapy? What the heck is Low-Level-LED-Therapy? Who is in charge of naming these things anyways? What is the point of all these syllables?
Tongue-twisters aside, these questions are important. How are we able to have a discussion about this topic if we are not sure what exactly we are discussing? The semantics can be surprisingly difficult to sort through, in no short measure due to misinformation (perhaps purposefully) perpetuated by medical device marketers, and unqualified keyboard warriors (with hopeful exception of the present blogger). Even the scientific literature can be misleading, due to non-standard and constantly changing terminology.
So let’s start with a few clarifications:
- Low-Level-Light Therapy, and Photobiomodulation Therapy, can be considered synonymous, and are used interchangeably. Photobiomodulation is arguably a more scientifically valid term, and has more acceptance within the scientific community.
- Low-Level-Laser Therapy, and Cold Laser Therapy, are also used interchangeably with the terms in #1. However these terms do not accurately describe comparable therapies, which do not utilize lasers, but have the same physiological mechanism of action. For this reason Low-Level-Laser-(light) Therapy, or Low-Level-LED Therapy (if LEDs are the light source) might be used in certain cases.
- Low-Level-Light Therapy, Low-Level-Laser Therapy, Low-Level-Laser-(light) Therapy, and Low-Level-LED Therapy are all commonly abbreviated LLLT. Photobiomodulation Therapy is abbreviated PBMT, but is most commonly seen as Photobiomodulation, or PBM.
- In this blog we will be using Low-Level-Light Therapy (which we will abbreviate LLLT). This is partially because LLLT is easy for me to type, but mostly because LLLT is well recognized, and is either synonymous with, or inclusive of all other alternative terminologies.
So what is LLLT?
LLLT can be defined by exposure of cells or tissues to “low-levels” of light, within a specific range of wavelengths. These wavelengths typically correspond to red or near-infrared (NIR) light, but may be expanded to include all non-ionizing light in the visible and infrared (IR) spectrum. “Low-level” refers to the amount of energy delivered per unit time and area, which is too low to cause excessive heating and/or damage to tissues. LLLT instead has anti-inflammatory, immunomodulatory, and regenerative effects, which allow it to stimulate healing and restoration of damaged and/or dysfunctional tissues.
The physiological response of LLLT arises from absorption of light by intracellular photoacceptors. These molecules are specialized for light absorption as they contain small pigment-containing functional groups called chromophores. When chromophores absorb light of appropriate wavelength, they induce functional changes in the photoacceptor, which cascade into larger-scale effects within the cell and local tissue. Since different photoacceptors are sensitive to different wavelengths of light, the mechanism of LLLT on the cellular level varies depending on type of light used.
The primary mechanism for red and NIR light is relatively well established. In mammals, red/NIR, light is absorbed by the enzyme cytochrome c oxidase (CCO), embedded in the inner mitochondrial membrane. As part of the electron transport chain, CCO plays an integral role in oxidative metabolism. Light absorption increases the activity of CCO, which in turn improves efficiency of cellular respiration, and increases production of ATP. A primary effect of this is the cell is able to function more efficiently in a given environment, essentially allowing it to work harder, with less metabolic input. Additionally this results in production of various secondary mediators, such as reactive oxygen species and nitric oxide, which can dramatically influence cell behavior by modulating cell signaling and transcriptional pathways.
Light/heat gated ion channels, which play important roles in cell signaling and maintenance of cellular homeostasis, are proposed as another photoacceptor for red/NIR light. However their precise role has not been elucidated as clearly as CCO. Like red/NIR light, IR is also thought to activate CCO, however may also induce a unique response due to specific interactions with intracellular water. Higher energy wavelengths within the visible spectrum (e.g. green and blue light), likely interact with distinct photoreceptors other than CCO. This would explain distinct physiological effects these light sources can induce, such as the antimicrobial effect of blue light. In general the physiological mechanisms of LLLT using wavelengths other than red/NIR are not well understood.
For those interested in digging more deeply into the molecular and cellular mechanisms of LLLT, this review by our chief science advisor Dr. Hamblin is a good place to start: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5844808/