The dark art of light measurement: accurate radiometry for low-level light therapy

Abstract

Lasers and light-emitting diodes are used for a range of biomedical applications with many studies reporting their beneficial effects. However, three main concerns exist regarding much of the low-level light therapy (LLLT) or photobiomodulation literature; (1) incomplete, inaccurate and unverified irradiation parameters, (2) miscalculation of ‘dose,’ and (3) the misuse of appropriate light property terminology. The aim of this systematic review was to assess where, and to what extent, these inadequacies exist and to provide an overview of ‘best practice’ in light measurement methods and importance of correct light measurement. A review of recent relevant literature was performed in PubMed using the terms LLLT and photobiomodulation (March 2014–March 2015) to investigate the contemporary information available in LLLT and photobiomodulation literature in terms of reporting light properties and irradiation parameters. A total of 74 articles formed the basis of this systematic review. Although most articles reported beneficial effects following LLLT, the majority contained no information in terms of how light was measured (73 %) and relied on manufacturer-stated values. For all papers reviewed, missing information for specific light parameters included wavelength (3 %), light source type (8 %), power (41 %), pulse frequency (52 %), beam area (40 %), irradiance (43 %), exposure time (16 %), radiant energy (74 %) and fluence (16 %). Frequent use of incorrect terminology was also observed within the reviewed literature. A poor understanding of photophysics is evident as a significant number of papers neglected to report or misreported important radiometric data. These errors affect repeatability and reliability of studies shared between scientists, manufacturers and clinicians and could degrade efficacy of patient treatments. Researchers need a physicist or appropriately skilled engineer on the team, and manuscript reviewers should reject papers that do not report beam measurement methods and all ten key parameters: wavelength, power, irradiation time, beam area (at the skin or culture surface; this is not necessarily the same size as the aperture), radiant energy, radiant exposure, pulse parameters, number of treatments, interval between treatments and anatomical location. Inclusion of these parameters will improve the information available to compare and contrast study outcomes and improve repeatability, reliability of studies.

Development and application of LED arrays for use in phototherapy research

“…Whilst the beneficial effects of PDT are realised through an intermediatory photosensitizing step, PBM involves the application of low powered (<500 mW), non‐thermal, non‐ablative light sources, predominantly lasers and light emitting diodes (LEDs), within the red to near infrared wavelength range ˜600–1000 nm to directly stimulate or inhibit cellular and biological processes. In either case, the therapeutic effects of light are attributed to the photophysical characteristics of the applied light, which include specific irradiation parameters such as wavelength, irradiance, exposure time and pulse frequency .…”

“…Although beneficial clinical effects of PBM are commonly reported, the associated photophysics of light delivery remains poorly understood and mis‐reported in a significant proportion of PBM publications. Undoubtly, this raises many questions about the reliability and reproducibility of such studies ; both of which are concerns in many areas of science . These problems are further exacerbated by the frequent reporting of incomplete, inaccurate, and unverified irradiation parameters with ambiguous or incorrect terminology despite several articles already emphasising their importance .…”

“…Undoubtly, this raises many questions about the reliability and reproducibility of such studies ; both of which are concerns in many areas of science . These problems are further exacerbated by the frequent reporting of incomplete, inaccurate, and unverified irradiation parameters with ambiguous or incorrect terminology despite several articles already emphasising their importance . There also currently exists no common consensus for the most effective irradiation parameters for any given PBM application.…”

Flexible nine-channel photodetector probe facilitated intraspinal multisite transcutaneous photobiomodulation therapy dosimetry in cadaver dogs

“…10,11 To our knowledge, no study has reported the skin-to-spinal-cord light transmission of a photobiomodulatory dose that is translatable to humans. Previously, a single photodiode sensor was used to sequentially measure transcutaneous light transmission of 980-nm irradiation to five vertebral locations including T12-13, T13-L1, L1-2, L2-3, and L3-4 in a cadaver dog.…”

Effects of the led therapy on the global DNA methylation and the expression of Dnmt1 and Dnmt3a genes in a rat model of skin wound healing

“…Despite the undoubted recent increase in the knowledge of the effectiveness and applicability of light-based therapies for healthcare, very little is still known about the molecular impacts of the photostimulations [2,3].…”