Photobiomodulation (PBM), or low-level laser therapy, uses red to near-infrared (NIR) light to stimulate healing, alleviate pain, and reduce inflammation. A key 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 therapies.
Mechanisms: Pulsed vs. continuous light
Common mechanisms of action
-
Absorption by mitochondrial cytochrome c oxidase (CCO)
-
Increased electron transport chain and ATP production
-
Production of transient reactive oxygen species (ROS)
Differences due to pulsation
-
Avoidance of chromophore saturation: Pulsed PBM can promote the reactivation of CCO through repeated release of nitric oxide (NO).
-
Enhanced mitochondrial stimulation: Pulsed light has often shown a greater increase in mitochondrial ATP production than CW in studies.
-
Deeper tissue penetration: Higher peak power at low thermal stress enables deeper penetration into the tissue.
-
Frequency-dependent biological effects: Specific frequencies (10 Hz, 40 Hz) activate biological rhythms and neuronal oscillations (gamma waves) that are not activated by CW.
Clinical evidence
Skin applications and wound healing
-
Pulsed light (especially 10 Hz) accelerates healing, increases collagen production and reduces inflammatory processes more effectively than CW.
-
Very high pulse frequencies (>100 Hz) may be less effective than CW.
| study | Wavelength & Mode | Result |
|---|---|---|
| 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 is clearly superior |
| Al-Watban 2011 (Animal Model) | 635 nm (CW vs. 100-500 Hz pulsed) | CW is slightly superior to high pulse rates. |
Neurological applications (brain injuries, cognitive functions)
-
Pulsed PBM shows better results in neurological recovery and cognitive performance, especially at specific frequencies (10 Hz and 40 Hz).
| study | Wavelength & Mode | Result |
| Ando 2011 (Animal Model TBI) | 810 nm (CW vs. 10 Hz, 100 Hz pulsed) | Pulsed at 10 Hz, significantly superior |
| Lapchak 2007 (Animal model of stroke) | 808 nm (CW vs. 100, 1000 Hz pulsed) | Pulsed therapy improves neurological recovery more effectively. |
| Tang 2023 (Humans, Cognition) | 660/810 nm (CW vs. 40 Hz, 100 Hz) | Pulsed at 40 Hz significantly optimizes cognitive function |
Pain therapy and anti-inflammatory treatment
-
Both CW and pulsed light are effective against pain, however pulsed light often shows a stronger and more energy-efficient effect.
| study | Wavelength & Mode | Result |
| Sushko 2015 (Animal model of acute pain) | 670/830 nm (CW vs. 10, 600, 8000 Hz pulsed) | 10 Hz pulsed most effective pain relief |
| Bjordal 2006 (clinical meta-analysis of joint pain) | 810/830 nm CW vs. 904 nm pulsed | Equal efficacy with pulsed therapy using half the energy dose |
Metabolic and systemic effects
-
Studies on systemic effects (e.g., diabetes, thyroid, training recovery) predominantly use CW; a direct comparison between CW and pulsed is still lacking.
-
The potential of pulsed light is suspected, but not yet confirmed.
Safety and seizure risk
-
Both CW and pulsed PBM are considered safe with minimal to no side effects.
-
Pulsed light (especially NIR 10–40 Hz) does not pose an increased risk of seizures and may even have a neuroprotective effect.
Summary and clinical recommendations
Pulsed photobleaching (PBM) offers comparable or better therapeutic effects than continuous wave (CW) in most clinical applications (especially wound healing, neurological disorders, and pain relief). Clinical and preclinical studies support the superiority of specific pulse frequencies (10 Hz, 40 Hz). Although CW remains effective, pulsing allows for improved therapy control and could achieve better clinical outcomes with lower energy input. Future studies should further explore optimized pulse parameters and their indications to enable individualized and targeted use of light therapy.
