Photobiomodulation (PBM) or low-level laser therapy uses red to near-infrared (NIR) light to stimulate healing, relieve pain, and reduce inflammation. A central point of discussion in research is whether pulsed PBM (with periodic light pulses) offers clinical advantages over continuous wave (CW) light application. This comprehensive review summarizes current scientific findings on the underlying biological mechanisms, comparative clinical outcomes, and safety aspects of both therapy forms.
Mechanisms: Pulsed vs. Continuous Light
Shared Mechanisms of Action
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Absorption by mitochondrial cytochrome c oxidase (CCO)
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Increased electron transport chain and ATP production
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Production of transient reactive oxygen species (ROS)
Differences Due to Pulsing
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Avoidance of chromophore saturation: Pulsed PBM can promote the re-activation of CCO through repeated release of nitric oxide (NO).
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Enhanced mitochondrial stimulation: Pulsed light has often shown a stronger increase in mitochondrial ATP production than CW in studies.
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Deeper tissue penetration: Higher peak power with low thermal load allows for deeper tissue penetration.
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Frequency-dependent biological effects: Specific frequencies (10 Hz, 40 Hz) activate biological rhythms and neural oscillations (gamma waves) that are not activated by CW.
Clinical Evidence
Dermatological Applications and Wound Healing
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Pulsed light (especially 10 Hz) accelerates healing, increases collagen production, and reduces inflammatory processes more effectively than CW.
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However, very high pulse frequencies (>100 Hz) may be less effective than CW.
| Study | Wavelength & Mode | Outcome |
|---|---|---|
| Kymplova 2003 (human episiotomy) | 670 nm (10–50 Hz vs. CW) | Pulsed faster than CW |
| Keshri 2016 (animal model) | 810 nm (10 Hz vs. CW, 100 Hz) | 10 Hz pulsed significantly superior |
| Al-Watban 2011 (animal model) | 635 nm (CW vs. 100–500 Hz pulsed) | CW slightly superior to high pulse frequencies |
Neurological Applications (Brain Injuries, Cognitive Functions)
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Pulsed PBM shows better results in neurological recovery and cognitive performance, especially at specific frequencies (10 Hz and 40 Hz).
| Study | Wavelength & Mode | Outcome |
| Ando 2011 (animal TBI model) | 810 nm (CW vs. 10 Hz, 100 Hz pulsed) | 10 Hz pulsed significantly superior |
| Lapchak 2007 (animal stroke model) | 808 nm (CW vs. 100, 1000 Hz pulsed) | Pulsed improves neurological recovery more |
| Tang 2023 (humans, cognition) | 660/810 nm (CW vs. 40 Hz, 100 Hz) | 40 Hz pulsed significantly optimizes cognitive function |
Pain Therapy and Anti-Inflammatory Effects
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Both CW and pulsed light are effective against pain, but pulsed light often shows a stronger and more energy-efficient effect.
| Study | Wavelength & Mode | Outcome |
| Sushko 2015 (animal model acute pain) | 670/830 nm (CW vs. 10, 600, 8000 Hz pulsed) | 10 Hz pulsed most effective pain relief |
| Bjordal 2006 (clinical meta-analysis joint pain) | 810/830 nm CW vs. 904 nm pulsed | Equal efficacy with pulsed therapy at half the energy dose |
Metabolic and Systemic Effects
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Studies on systemic effects (e.g., diabetes, thyroid, exercise recovery) predominantly use CW; a direct comparison between CW and pulsed is still lacking.
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The potential of pulsed light is suspected but not yet confirmed.
Safety and Seizure Risk
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Both CW and pulsed PBM are considered safe with minimal to no side effects.
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Pulsed light (especially NIR 10–40 Hz) does not carry an increased seizure risk and could even be neuroprotective.
Summary and Clinical Recommendations
Pulsed PBM offers comparable or better therapeutic effects than CW in most clinical applications (especially in wound healing, neurological disorders, and pain relief). Clinical and preclinical studies support the superiority of specific pulse frequencies (10 Hz, 40 Hz). While CW remains effective, pulsing allows for improved therapy control and could achieve better clinical results with lower energy input. Future studies should further investigate optimized pulse parameters and their indications to enable individualized and targeted light therapy.
