The source provides a comprehensive discussion on the comparison between laser and LED photobiomodulation (PBM) regarding efficacy and underlying biological mechanisms across various medical conditions [1]
Historically, PBM research, initially known as 'low-level laser therapy' (LLLT), heavily relied on lasers due to their invention in 1960 [2] In fact, almost all PBM research before the 21st century utilized lasers, leading to assumptions that the therapeutic benefits of red and near-infrared light were dependent on laser-specific properties like monochromaticity, coherence, and collimation [20]. However, the source argues that this assumption is debatable [20].
In recent years, non-coherent light sources such as light-emitting diodes (LEDs) have become common in PBM3. LEDs offer several advantages over lasers, including no laser safety considerations, ease of home use, ability to irradiate large tissue areas, suitability for wearable devices, and significantly lower cost per mW [3] LED photobiomodulation is now considered a well-established phenomenon with demonstrated efficacy in many reports [3].
Regarding the underlying biological mechanisms, the source indicates that the primary cellular photoacceptor for both visible red light and near-infrared radiation in PBM is believed to be the copper centers of cytochrome c oxidase (CCO) in the mitochondrial electron transport chain [9]. Irradiation with specific wavelength ranges can promote electron transport, leading to increased mitochondrial membrane potential, oxygen consumption, and ATP levels [10]. This fundamental mechanism of light absorption by photoacceptors is not exclusive to laser light, suggesting that non-coherent light can also initiate these beneficial effects [40].
The debate about the necessity of laser-specific properties, particularly coherence, for PBM efficacy has been ongoing for over 30 years [33] Some proponents argue for the superiority of coherent laser light, especially for bulk tissue penetration [39] They suggest that laser speckles, formed by the interference of coherent light in tissue, might better stimulate mitochondria due to their size matching subcellular organelles [34] However, other editorials and studies suggest that PBM is primarily a photobiological phenomenon, and coherence is not necessarily required for therapeutic effects31.... The term "photobiomodulation therapy" (PBM) was adopted partly to reflect that a laser is not essential for therapeutic benefits [7].
The source presents a review of approximately 40 newer papers comparing laser and LED photobiomodulation in animals, cell cultures, and humans [45, Tables 4, 5, 6]. It is important to note that most of these comparisons have a high risk of bias due to differing key parameters (wavelengths, power outputs, spot sizes) between the LED and laser groups, making reliable comparisons difficult [46].
Despite these limitations, the source summarizes the findings of these comparative studies:
•Animal research [58]: Many studies in animal models of conditions like oral mucositis, paw edema, wound healing, nerve regeneration, bone repair, burn wounds, and arthritis showed that both LED and laser photobiomodulation could be effective [68]. Some studies indicated similar beneficial effects between lasers and LEDs68..., while a few suggested potential superiority of lasers in specific contexts like nerve regeneration or arthritis87.... One study found LEDs more effective in reducing wound diameter in diabetic animals [88], and another showed more pronounced effects with LEDs on mandibular growth in rats [77].
•In vitro research [94]: Comparisons in cell cultures (keratinocytes, pre-osteoblasts, adenocarcinoma, epithelial, osteosarcoma, and fibroblasts) yielded mixed results. One study suggested lasers might have some effects on mucosal colonies where LEDs were ineffective, but statistical significance wasn't calculated [94]. Another indicated that lasers were more effective than LEDs on pre-osteoblast growth [95]. However, other studies found comparable effects of lasers and LEDs on cell migration and wound closure in vitro [96], and both showed significant effects on fibroblast proliferation [97].
Clinical trials [99]: Clinical studies on conditions like temporomandibular disorder, oral mucositis, knee osteoarthritis, and orthodontic pain also presented varied outcomes. Some trials found no significant differences between laser and LED treatments [104], while others reported similar effectiveness in alleviating oral mucositis [106]. One study even suggested more pronounced effects with LEDs for oral mucositis [106]. In orthodontic pain, LEDs were found effective after surgery [107]. A study on coronary bypass surgery patients showed both laser and LED to be effective in reducing hyperemia and incision bleeding or dehiscence [103].
The source concludes that the current total evidence supports the idea that photobiomodulation is not dependent on lasers or coherence, and quasimonochromatic LED devices can also yield physiological effects [54]. The comparisons between lasers and LEDs generally support this idea, although the low quality of many comparison studies due to parameter mismatches limits definitive conclusions [54] The debate about the equivalence of laser and LED remains controversial in the PBM field [55] The authors emphasize the need for more high-quality head-to-head comparison studies to determine if there are significant differences in dose response or physiological effects between LED and laser PBM and whether treatment parameters from laser studies can be directly applied to LED-based treatments [56]
Source: NIH - Photobiomodulation: Lasers vs Light Emitting Diodes?