In recent years, light-based treatments like near infrared light therapy and infra red light therapy have become increasingly popular in both clinical and home settings. These therapies, known collectively as phototherapy, use specific wavelengths of light to stimulate biological processes and promote healing. One key aspect of phototherapy that often sparks debate is whether to use a continuous wave (CW) or pulsed wave (PW) mode of light delivery. This article explores the differences between these two modes, their respective advantages, and guidance on how to choose the right one for your specific therapeutic needs.
Understanding the Basics
What Is Continuous Wave (CW)?
In continuous wave mode, the light source emits a steady, unbroken stream of energy. This is the simplest form of light delivery and has been used since the earliest days of laser and light-based medical treatments. The light remains on throughout the entire exposure time, providing a consistent energy flow to the target tissue.
What Is Pulsed Wave (PW)?
In pulsed wave mode, the light is emitted in periodic bursts, with defined intervals of "on" and "off" time. This allows tissues to absorb energy in smaller doses over time, potentially reducing heat buildup and offering different physiological effects compared to CW. The key parameters in PW are the pulse duration, frequency (how many pulses per second), and duty cycle (the percentage of time the light is on during one cycle).
Scientific Basis and Biological Effects
A number of peer-reviewed studies have investigated how CW and PW differ in their biological effects.
Cellular Response
A 2023 study by Khalaj et al., published in Photochemistry and Photobiology, explored the effects of 980 nm infra red light therapy on human gingival fibroblasts. The researchers found that CW light significantly promoted cell proliferation and migration compared to PW light at a frequency of 50 kHz. This suggests that CW may be more effective for applications involving tissue regeneration and wound healing where cell motility is crucial.
Wound Healing
In a study involving immunosuppressed rats, Ando et al. (as cited in a 2017 review) found that 810 nm PW light at 10 Hz led to superior wound healing outcomes compared to CW or higher-frequency PW light. The authors hypothesized that the intermittent nature of pulsed light allowed better mitochondrial activation without overwhelming the cells with continuous energy, which can sometimes be counterproductive.
Thermal Effects
A 2025 modeling study by Kaib and Schmitz, published in the Journal of Biophotonics, showed that PW light at 1064 nm allowed deeper tissue penetration with less surface heating than CW light. This is particularly important in near infrared light therapy, where the goal is often to reach deeper structures like muscles or joints without causing discomfort or burns.
Oxygen Consumption and Photodynamic Therapy
In the context of photodynamic therapy, a 2004 study in Lasers in Medical Science compared CW and PW modes in Renca tumor cells. It found that CW light caused higher oxygen consumption and greater photobleaching, leading to more pronounced cytotoxic effects. For applications that rely on oxygen-dependent mechanisms, such as cancer therapy, CW might offer advantages due to its continuous energy delivery.
Advantages and Disadvantages
Continuous Wave (CW)
Advantages:
Simpler hardware requirements
More predictable and uniform energy delivery
Effective in applications requiring strong and steady stimulation, such as cell proliferation
Potentially more effective in oxygen-dependent treatments like photodynamic therapy
Disadvantages:
Higher risk of thermal buildup
May cause tissue fatigue with prolonged exposure
Pulsed Wave (PW)
Advantages:
Reduces thermal load on tissues
May enhance specific biological responses at certain frequencies (e.g., 10 Hz for wound healing)
Offers more parameter customization (pulse duration, frequency, duty cycle)
Disadvantages:
More complex devices and settings
Not universally superior—results vary by condition and application
How to Choose Between CW and PW
Choosing between continuous wave and pulsed wave depends on several factors:
1. Therapeutic Goal
For wound healing, especially in compromised conditions (like diabetes or immune suppression), PW at low frequencies (e.g., 10 Hz) might be more effective.
For nerve regeneration or fibroblast proliferation, CW light has shown better outcomes in some studies.
2. Target Tissue Depth
PW is generally better for deep tissue applications due to reduced surface heating and greater penetration efficiency.
CW might be suitable for surface-level treatments where consistent energy delivery is crucial.
3. Device Availability
Most consumer-grade near infrared light therapy devices offer CW operation.
High-end clinical devices often provide both CW and PW options, allowing for more tailored treatments.
4. Safety Considerations
If overheating is a concern (e.g., in sensitive skin or areas with poor circulation), PW may be safer.
For short-duration treatments with adequate cooling, CW can be both effective and safe.
Practical Applications
Near Infrared Light Therapy
Near infrared light therapy (typically 800–1100 nm) is widely used for muscle recovery, joint pain, and inflammation. PW mode may be preferable here due to its ability to penetrate deeper tissues with less heat. Athletes and physiotherapists often choose PW settings for post-exercise recovery and pain management.
Infra Red Light Therapy
In the broader category of infra red light therapy (including wavelengths around 700–1400 nm), the choice of CW or PW should be guided by the intended use. CW may be beneficial for stimulating superficial skin tissues, promoting collagen production, or treating acne. In contrast, PW might be better for systemic applications or treating inflammation deep within the body.
Final Thoughts
There is no one-size-fits-all answer when it comes to choosing between continuous wave and pulsed wave in phototherapy. The right choice depends on the specific medical condition, target tissue, and desired outcomes. Both modes offer unique advantages backed by scientific literature. The trend in research suggests that while CW remains effective for many regenerative purposes, PW is gaining traction due to its flexibility and potential to minimize unwanted thermal effects.
As light therapy continues to evolve, understanding these foundational concepts can empower consumers and practitioners to make more informed decisions. Whether you're a healthcare professional or an individual exploring at-home solutions, knowing the differences between CW and PW modes can help you maximize the benefits of near infrared and infra red light therapy.
References
Khalaj et al. (2023), Photochemistry and Photobiology--- Photobiomodulation effects of pulsed and continuous wave near-infrared laser on the proliferation and migration of human gingival fibroblasts: An in vitro study - PubMed
Ando et al. (2017), rat wound healing study
Review: Hamblin et al., 2010, effect of pulsing in low-level light therapy
Review of photobiomodulation parameters, 2025, PubMed Central
