What is the difference between red light and near-infrared light?

What is the difference between red light and near-infrared light?

Light is a fascinating phenomenon. It allows us to see the world around us, but it also carries a vast spectrum of unseen colors, each with unique properties.

Today, we will be focusing on two specific regions of this spectrum: red light and near-infrared light. While they might seem similar at first glance, these colors/wavelength bands have distinct characteristics and applications.



Exploring the spectrum of light

Light is a form of electromagnetic radiation. Imagine a wave – the distance between the peaks of the wave is called the wavelength. The vast spectrum of light encompasses a range of wavelengths, undetectable by our eyes. 

Visible light, the portion we can perceive, occupies a very narrow band within this spectrum. Within the visible spectrum, different wavelengths correspond to different colors we see – red at the longest end, transitioning through orange, yellow, green, blue, and indigo, to violet with the shortest wavelength.

 

What is red light?

Red light, on the other hand, falls within the visible spectrum. It has the longest wavelength of all visible colors, appearing closest to orange on the color wheel (620-750 nm).

When it comes to the brain, due to its shorter wavelength, red light has a limited ability to penetrate the skull. Most red light gets absorbed by scalp tissue, but doesn't reach the brain directly, for instance. However, some studies suggest red light therapy might still influence brain function indirectly, potentially through stimulating nitric oxide production or other mechanisms, such as arteries, for instance.

Research suggests red light may offer a variety of other potential benefits, including:

  • Wound healing: Studies indicate red light therapy might promote faster healing of wounds and improve tissue regeneration [1,2];
  • Skin conditions: Red light therapy is being explored for its potential role in managing certain skin conditions like eczema and psoriasis [3];
  • Pain management: Some research suggests red light therapy might help alleviate pain associated with arthritis and other musculoskeletal conditions, such as knee pain, osteoarthritis, total hip arthroplasty, fibromyalgia, temporomandibular disorders, neck pain, low back pain, and others [4,5].


What is near-infrared light?

Near-infrared (NIR) light resides just beyond the red end of the visible spectrum (751–1,400 nm). This means NIR light has longer wavelengths than red light and is therefore invisible to the human eye. However, we can feel its warmth on our skin when exposed to sources like sunlight or a fireplace. Actually, 50% of the sun’s wavelength is infrared light, while about 32% is near-infrared light [6].

The NIR spectrum itself is further divided into subcategories based on wavelength, each with its own applications – from night vision technology to medical imaging.

Near-infrared light (NIR) offers better penetration through the skull compared to red light. This allows NIR light to potentially reach deeper brain regions and directly interact with brain cells.

Beyond the familiar warmth it brings us in sunlight, near-infrared light is finding exciting new applications, particularly in the field of brain health. Here are some examples:

  • Working memory enhancement: Research from 2022 investigated whether shining near-infrared light at 1064nm on the brain could improve visual working memory. People performed better on visual working memory tasks that involved remembering the direction or color of things they saw. This improvement happened when they received the 1064nm tPBM treatment. In another experiment, they used red light at 852 nm and saw no improvement in working memory [7];
  • Depression: A systematic search of ten databases, including over 3,200 studies and randomized controlled trials (RCTs) for depression, specifically focused on photobiomodulation fro depression treatments. The overall results suggested that photobiomodulation using near-infrared light therapy might help ease symptoms [8];
  • Alzheimer’s disease: A study investigated the potential of near-infrared light therapy to improve memory function in individuals with dementia or Alzheimer's disease. The study involved five participants with mild to moderate memory problems who received light therapy using a device once a week. After 12 weeks of light therapy, the participants' memory scores on standardized tests showed significant improvement, also reporting experiencing overall well-being benefits, including better sleep, reduced anger outbursts, and decreased anxiety. Notably, when the light therapy was discontinued for four weeks, the participants' memory scores reverted to pre-treatment levels [9];
  • Traumatic Brain Injury (TBI): Some early studies suggest that light therapy might improve cognitive function, such as thinking and memory skills, concentration, anxiety, sleep, and PTSD symptoms. More research is needed to determine optimal treatment protocols for different types of TBI [10,11].


Similarities and differences: A side-by-side comparison

While both red and near-infrared light offer potential benefits, a key difference lies in their ability to penetrate the skull and reach the brain. Beyond penetration depth, different wavelengths within the red and NIR spectrum might target specific cellular mechanisms in the brain. 

For example, red light might be beneficial for stimulating cytochrome c oxidase, an enzyme within the mitochondria (cell's energy powerhouse) that plays a role in energy production, whereas NIR light might have a broader impact, potentially influencing nitric oxide production, blood flow regulation, and neuronal activity.

Here's a table summarizing the key differences between red light and near-infrared light:


Red light

Near-infrared light

Visibility

Visible to the human eye

Invisible to the human eye

Wavelength

Longest in the visible spectrum (620-750 nm)

Longer than red light, outside the visible spectrum (751–1,400 nm)

Feeling

No warmth sensation

Can feel warm on the skin

Applications

Wound healing, skin conditions, pain management

Cognitive function enhancement, mood regulation, sleep quality, Alzheimer's disease, dementia, traumatic brain injury (TBI)

Brain Penetration

Limited penetration depth

Offers better penetration depth through the skull


 

It's important to remember that light therapy or photobiomodulation (PBM) isn't simply about the color of light. Other factors influence the results, such as:

  • Light dose (power x time): The amount of light delivered is crucial. Too little might have minimal effects, while too much could be detrimental;
  • Delivery mode: The way light is delivered (continuous, or pulsed) can influence outcomes;
  • Protocols: The specific wavelengths, dose, and duration of application will vary depending on the targeted outcome (e.g., cognitive enhancement, mood regulation).


Brain Light Therapy Research

Studies have shown that brain light therapy, also called as transcranial photobiomodulation, holds immense potential for enhancing brain function and potentially treating various neurological conditions. 

Understanding the differences between red and near-infrared light, along with other key factors, is crucial for optimizing photobiomodulation (PBM) applications. 

As research progresses, we can expect further advancements in this exciting field, paving the way for a future where light-based therapies play a significant role in brain health.



References
  1. Giannakopoulos, E., Katopodi, A., Rallis, M., Politopoulos, K., & Alexandratou, E. (2022). The effects of low power laser light at 661 nm on wound healing in a scratch assay fibroblast model. Lasers in medical science, 38(1), 27. https://doi.org/10.1007/s10103-022-03670-5
  2. Chaves, M. E., Araújo, A. R., Piancastelli, A. C., & Pinotti, M. (2014). Effects of low-power light therapy on wound healing: LASER x LED. Anais brasileiros de dermatologia, 89(4), 616–623. https://doi.org/10.1590/abd1806-4841.20142519
  3. Kennedy R. (2023). Phototherapy as a Treatment for Dermatological Diseases, Cancer, Aesthetic Dermatologic Conditions and Allergenic Rhinitis in Adult and Paediatric Medicine. Life (Basel, Switzerland), 13(1), 196. https://doi.org/10.3390/life13010196
  4. DE Oliveira, M. F., Johnson, D. S., Demchak, T., Tomazoni, S. S., & Leal-Junior, E. C. (2022). Low-intensity LASER and LED (photobiomodulation therapy) for pain control of the most common musculoskeletal conditions. European journal of physical and rehabilitation medicine, 58(2), 282–289. https://doi.org/10.23736/S1973-9087.21.07236-1
  5. Gale, George & Rothbart, Peter & Li, Ye. (2006). Infrared Therapy for Chronic Low Back Pain: A Randomized, Controlled Trial. Pain research & management : the journal of the Canadian Pain Society = journal de la société canadienne pour le traitement de la douleur. 11. 193-6. 10.1155/2006/876920. 
  6. I. Kochevar, M. Pathak and J. Parrish, “Photophysics, photochemistry, and photobiology,” Fitzpatrick’s Dermatology in General Medicine, 220 –229 McGraw-Hill, New York (1999)
  7. Zhao, C., Li, D., Kong, Y., Liu, H., Hu, Y., Niu, H., Jensen, O., Li, X., Liu, H., & Song, Y. (2022). Transcranial photobiomodulation enhances visual working memory capacity in humans. Science advances, 8(48), eabq3211. https://doi.org/10.1126/sciadv.abq3211
  8. Ji, Q., Yan, S., Ding, J., Zeng, X., Liu, Z., Zhou, T., Wu, Z., Wei, W., Li, H., Liu, S., & Ai, S. (2024). Photobiomodulation improves depression symptoms: a systematic review and meta-analysis of randomized controlled trials. Frontiers in psychiatry, 14, 1267415. https://doi.org/10.3389/fpsyt.2023.1267415
  9. Saltmarche, A. E., Naeser, M. A., Ho, K. F., Hamblin, M. R., & Lim, L. (2017). Significant Improvement in Cognition in Mild to Moderately Severe Dementia Cases Treated with Transcranial Plus Intranasal Photobiomodulation: Case Series Report. Photomedicine and laser surgery, 35(8), 432–441. https://doi.org/10.1089/pho.2016.4227
  10. Naeser, M. A., Zafonte, R., Krengel, M. H., Martin, P. I., Frazier, J., Hamblin, M. R., Knight, J. A., Meehan, W. P., 3rd, & Baker, E. H. (2014). Significant improvements in cognitive performance post-transcranial, red/near-infrared light-emitting diode treatments in chronic, mild traumatic brain injury: open-protocol study. Journal of neurotrauma, 31(11), 1008–1017. https://doi.org/10.1089/neu.2013.3244
  11. Chao, L. L., Barlow, C., Karimpoor, M., & Lim, L. (2020). Changes in Brain Function and Structure After Self-Administered Home Photobiomodulation Treatment in a Concussion Case. Frontiers in neurology, 11, 952. https://doi.org/10.3389/fneur.2020.00952



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