Low Level Light / Laser Therapy (LLLT) utilises the photonic energy of light to stimulate cell and tissue responses (photobiomodulation - PBM) to promote healing, reduce inflammation and induce analgesia. Research in this area has led to several thousand publications and has significant interest from specialist groups such as NASA, the US Navy and UK military, in its therapeutic application. Notably LLLT/PBM is efficacious in a range of injuries and diseases at multiple sites in the body including the joints, connective tissues, neuronal tissues, bone, teeth, skin, muscle and the vasculature. It has been shown to promote wound healing processes including vasodilation, angiogenesis, cell proliferation, cytoprotection, adhesion, migration, differentiation and tissue formation.

Commonly LLLT utilises low power lasers or light emitting diodes (LEDs) of less than 500mW, emitting in the red to near infrared (NIR) spectrum (400-1100nm) and levels of irradiance are neither ablative nor provide a heat-based therapy (- 5-50mWcm-2 ) . Recently cold diffuse lasers for photo-activated disinfection (PAD) or photodynamic therapy (PDT) have been developed. These local approaches utilise light indirectly to trigger photosensitive chemicals to release antibacterial or anti-cancer agents such as reactive oxygen species (ROS).

PBM is proposed to exploit natural and evolutionary preserved pathways. Cells respond to light by increasing synthesis of growth factors, nitric oxide (NO), ROS, ATP, RNA and DNA. Although exact cellular and molecular mechanisms are not yet fully understood, the current photodissociation theory' suggests specific wavelength ranges of IR and NIR light is absorbed by the mitochondrial enzyme cytochrome c oxidase (COX) resulting in release of bound NO, which competitively displaces oxygen. NO release allows oxygen to re-bind COX enabling increases in cellular respiration and energy generation (ATP). Notably, inflammation and tissue damage can increase NO binding to COX and impede respiratory activity. The extracellular release of NO, ATP or growth factors can result in local and distant activation of tissue repair processes.

Many clinical LLLT devices utilise specific wavelengths in the 400-1000 nm spectrum (with ~660 nm and 810 – 830 nm wavelengths frequently used). Successful treatment is critically dependent on the parameters of applied irradiation including, "intensity" (properly termed, irradiance or flux, Wm-2) , treatment/irradiation time (s), "dose" (fluence, or radiant exposure, measured in Jm-2; the product of irradiance and exposure time), treatment frequency, treatment intervals, total number of treatments, number of treatment target points and coverage. The depth of penetration needed to irradiate target cells also needs consideration as light is reflected, absorbed, refracted and scattered to different degrees within different tissues. Light transport is significantly affected by pigments within tissues and its absorption properties. LLLT applied at the wavelengths and doses described are not harmful, however, lack of standardisation of treatment parameters can result in reduced or non-therapeutic effects, which contribute to false-negative data and the controversy that surrounds the field.