The research

The science of red light.

For decades, universities and hospitals have studied what happens when specific wavelengths of red and near-infrared light reach the body's cells. This page gathers that research, with a link to every study.

SOURCE 630 nm VISIBLE RED 660 nm DEEP RED 830 nm Near-infrared SHORTER WAVELENGTH DEEPER · LONGER WAVELENGTH
Thousandsof peer-reviewed
studies on PBM
1903first Nobel Prize
for light therapy
~8 cmhow deep near-infrared
light reaches in tissue
01 · How it works

How light talks to your cells.

The field rests on one finding. Certain wavelengths of light are absorbed inside your cells and change how those cells make and manage energy. Here is the mechanism in four parts.

01

Light fuels the mitochondria

Red and near-infrared photons are absorbed mainly by cytochrome c oxidase, the cell's energy enzyme inside the mitochondria. Absorbing that light is associated with smoother electron transport and more ATP, the fuel every cell runs on.

02

It shifts the cell's redox balance

The same light triggers a brief, controlled shift in the cell's redox signalling. It has also been linked to more melatonin made inside the cell, where it acts as a local antioxidant against oxidative stress and does not make you sleepy (Zimmerman & Reiter, 2019).

03

More is not better

The dose-response is biphasic. A moderate amount stimulates the cell, and too much loses the benefit. In practice that favours short sessions, commonly ten to twenty minutes, over longer or more intense exposure.

04

Wavelength sets the depth

How deep the light reaches depends on its wavelength. Visible red (about 630 to 660 nm) works nearer the surface. Near-infrared (about 830 nm) passes deeper into the tissue beneath. Pairing them covers both.

02 · Wavelength & depth

How deep each wavelength reaches.

Longer wavelengths reach deeper into tissue, the same physics that lets bass travel further than treble. Visible red works nearer the surface and near-infrared reaches deepest. The wavelengths below are among the most-studied in their bands.

630 nmVisible red

Acts nearer the surface, on skin and the tissue just beneath it.

660 nmDeep red

Sits near a key absorption peak of the cell's energy machinery.

830 nmNear-infrared

Invisible and the deepest-reaching. The most-studied near-infrared wavelength in PBM research.

03 · What researchers are exploring

The research, by theme.

Photobiomodulation works at the level of the cell, so researchers study it across many tissues. Below are the areas they explore most, grouped by the part of everyday wellbeing they touch. Tap any study to read the original.

Recovery & inflammation

Some of the strongest light research sits in exercise science. Trials and meta-analyses ask whether red and near-infrared light used around training is linked to less soreness and faster recovery, and reviews map the inflammation pathways involved.

Sleep quality

Researchers have asked whether red and near-infrared light is associated with how well people sleep, including one trial using a near-infrared collar worn on the neck. The findings rely on how people rated their own sleep and are still early.

Mood & emotional balance

A group led from Harvard and others have run trials shining near-infrared light at the forehead and tracking mood. The results are mixed. Some trials and a pooled analysis report an effect; a larger sham-controlled trial found none.

Stress & relaxation

Small studies have explored whether near-infrared light directed at the forehead is associated with people rating themselves calmer and less anxious. The samples are small, and no large trial has yet confirmed the effect.

Mental clarity & focus

This is among the most-replicated findings in the field. In healthy adults, single sessions of near-infrared light on the forehead were associated with faster reaction times, better attention and better working memory. Reviewers note the trials are small and not all randomized.

Cellular energy & vitality

Reviews describe how light absorbed in the mitochondria is associated with more available cellular energy (ATP). Exercise trials then test whether that shows up as less fatigue.

Skin & collagen

The best-controlled red-light trials are in skin. Split-face and placebo-controlled studies have reported higher collagen density and smoother skin with fewer lines in treated areas.

Thyroid-area research

Light applied over the neck has been tested in published clinical trials from 2010 to 2018: a pilot study, two randomized placebo-controlled trials using 830 nm light, and a follow-up that tracked participants for six years. This body of research is smaller than for skin or recovery and still growing.

04 · A short history

Light therapy isn't new.

It is older than most people assume, and the cellular understanding behind it has been building for half a century.

  1. 1903

    Phototherapy wins a Nobel Prize

    Danish physician Niels Ryberg Finsen received the Nobel Prize in Physiology or Medicine for treating skin conditions with concentrated light, which established light as a medical therapy.

  2. 1967

    Mester discovers laser "biostimulation"

    Hungarian surgeon Endre Mester noticed that low-power laser light sped hair regrowth and wound healing in mice. It was the first demonstration of photobiostimulation and the start of low-level laser therapy.

  3. 1990s

    NASA brings LEDs into the field

    With SBIR research funding, NASA and Dr. Harry Whelan adapted LEDs built for growing plants to human tissue and showed that LED light could speed cell growth. That moved the field from lasers to practical LED devices.

  4. 2001

    Clinical evidence for LED light

    Whelan's team published research linking LED light developed with NASA to faster wound healing, with treated cells growing markedly faster than controls. Interest in light sources other than lasers grew.

  5. 2015

    The field is formally renamed

    "Photobiomodulation" became an official MeSH term of the U.S. National Library of Medicine. It replaced the vaguer "low-level laser therapy" and reflects that LEDs and other light sources are now widely used.

  6. Today

    A maturing evidence base

    Thousands of peer-reviewed studies now cover photobiomodulation, and clinical trials on its mechanisms and uses continue worldwide.

Full reference list
  1. de Freitas LF, Hamblin MR. Proposed Mechanisms of Photobiomodulation or Low-level Light Therapy. IEEE J Sel Top Quantum Electron. 2016. PMID 28070154.
  2. Karu TI. Multiple roles of cytochrome c oxidase in mammalian cells under action of red and IR-A radiation. IUBMB Life. 2010. PMID 20681024.
  3. Huang YY, Chen ACH, Carroll JD, Hamblin MR. Biphasic Dose-response in Low-level Light Therapy. Dose-response. 2009. PMID 20011653.
  4. Zimmerman S, Reiter RJ. Melatonin and the Optics of the Human Body. Melatonin Research. 2019. doi:10.32794/mr11250016.
  5. Vanin AA, Verhagen E, Barboza SD, Costa LOP, Leal-Junior ECP. Photobiomodulation therapy for the improvement of muscular performance and reduction of muscular fatigue associated with exercise in healthy people: a systematic review and meta-analysis. Lasers Med Sci. 2018. PMID 29090398.
  6. Luo WT, Lee CJ, Tam KW, Huang TW. Effects of Low-level Laser Therapy on Muscular Performance and Soreness Recovery in Athletes: A Meta-analysis of Randomized Controlled Trials. Sports Health. 2022. PMID 34428975.
  7. Nampo FK, Cavalheri V, Ramos SP, Camargo EA. Effect of low-level phototherapy on delayed onset muscle soreness: a systematic review and meta-analysis. Lasers Med Sci. 2016. PMID 26563953.
  8. Hamblin MR. Mechanisms and applications of the anti-inflammatory effects of photobiomodulation. AIMS Biophysics. 2017. PMID 28748217.
  9. Zhao J, Tian Y, Nie J, Xu J, Liu D. Red Light and the Sleep Quality and Endurance Performance of Chinese Female Basketball Players. J Athl Train. 2012. PMID 23182016.
  10. Kennedy KER, Wills CCA, Holt C, Grandner MA. A randomized, sham-controlled trial of a novel near-infrared phototherapy device on sleep and daytime function. J Clin Sleep Med. 2023. PMID 37141002.
  11. Gaggi NL, Parincu Z, Peterson A, et al. Enhancing sleep, wakefulness, and cognition with transcranial photobiomodulation: a systematic review. Front Behav Neurosci. 2025. PMID 40822571.
  12. Cassano P, Petrie SR, Mischoulon D, et al. Transcranial Photobiomodulation for the Treatment of Major Depressive Disorder: The ELATED-2 Pilot Trial. Photomed Laser Surg. 2018. PMID 30346890.
  13. Ji Q, Yan S, Ding J, et al. Photobiomodulation improves depression symptoms: a systematic review and meta-analysis of randomized controlled trials. Front Psychiatry. 2024. PMID 38356614.
  14. Iosifescu DV, Norton RJ, Tural U, et al. Very Low-level Transcranial Photobiomodulation for Major Depressive Disorder: The ELATED-3 Multicenter, Randomized, Sham-Controlled Trial. J Clin Psychiatry. 2022. PMID 35950904.
  15. Salehpour F, Mahmoudi J, Kamari F, Sadigh-Eteghad S, Rasta SH, Hamblin MR. Brain Photobiomodulation Therapy: a Narrative Review. Mol Neurobiol. 2018. PMID 29327206.
  16. Maiello M, Losiewicz OM, Bui E, et al. Transcranial Photobiomodulation with Near-infrared Light for Generalized Anxiety Disorder: A Pilot Study. Photobiomodul Photomed Laser Surg. 2019. PMID 31647775.
  17. Helali H, Samani N, Tabeie F, Eiliaei S, Kheradmand A. The effectiveness of transcranial photobiomodulation therapy (tPBM) on reducing anxiety, depression, and opioid craving in patients undergoing methadone maintenance treatment: a double-blind, randomized, controlled trial. BMC Psychiatry. 2025. PMID 39901090.
  18. Caldieraro MA, Cassano P. Transcranial and systemic photobiomodulation for major depressive disorder: A systematic review of efficacy, tolerability and biological mechanisms. J Affect Disord. 2019. PMID 30248638.
  19. Barrett DW, Gonzalez-Lima F. Transcranial infrared laser stimulation produces beneficial cognitive and emotional effects in humans. Neuroscience. 2013. PMID 23200785.
  20. Blanco NJ, Maddox WT, Gonzalez-Lima F. Improving executive function using transcranial infrared laser stimulation. J Neuropsychol. 2017. PMID 26017772.
  21. Salehpour F, Majdi A, Pazhuhi M, et al. Transcranial Photobiomodulation Improves Cognitive Performance in Young Healthy Adults: A Systematic Review and Meta-analysis. Photobiomodul Photomed Laser Surg. 2019. PMID 31549906.
  22. Lee TL, Ding Z, Chan AS. Can transcranial photobiomodulation improve cognitive function? A systematic review of human studies. Ageing Res Rev. 2023. PMID 36371017.
  23. Hamblin MR. Mechanisms and Mitochondrial Redox Signaling in Photobiomodulation. Photochem Photobiol. 2018. PMID 29164625.
  24. Leal-Junior ECP, Vanin AA, Miranda EF, de Carvalho PdT, Dal Corso S, Bjordal JM. Effect of phototherapy (low-level laser therapy and light-emitting diode therapy) on exercise performance and markers of exercise recovery: a systematic review with meta-analysis. Lasers Med Sci. 2015. PMID 24249354.
  25. Bezerra LO, de Macedo LES, da Silva MLA, et al. Effects of photobiomodulation therapy on the functional performance of healthy individuals: a systematic review with meta-analysis. Lasers Med Sci. 2023. PMID 38150056.
  26. Rossato M, Dellagrana RA, Sakugawa RL, Baroni BM, Diefenthaeler F. Dose-response Effect of Photobiomodulation Therapy on Muscle Performance and Fatigue During a Multiple-Set Knee Extension Exercise: A Randomized, Crossover, Double-blind Placebo-controlled Trial. Photobiomodul Photomed Laser Surg. 2020. PMID 33232629.
  27. Wunsch A, Matuschka K. A controlled trial to determine the efficacy of red and near-infrared light treatment in patient satisfaction, reduction of fine lines, wrinkles, skin roughness, and intradermal collagen density increase. Photomed Laser Surg. 2014. PMID 24286286.
  28. Lee SY, Park KH, Choi JW, et al. A prospective, randomized, placebo-controlled, double-blinded, and split-face clinical study on LED phototherapy for skin rejuvenation. J Photochem Photobiol B. 2007. PMID 17566756.
  29. Barolet D, Roberge CJ, Auger FA, Boucher A, Germain L. Regulation of skin collagen metabolism in vitro using a pulsed 660 nm LED light source: clinical correlation with a single-blinded study. J Invest Dermatol. 2009. PMID 19587693.
  30. Le Thi Nhu Ngoc, Moon JY, Lee YC. Utilization of light-emitting diodes for skin therapy: Systematic review and meta-analysis. Photodermatol Photoimmunol Photomed. 2023. PMID 36310510.
  31. Höfling DB, Chavantes MC, Juliano AG, et al. Low-level laser therapy in chronic autoimmune thyroiditis: a pilot study. Lasers Surg Med. 2010. PMID 20662037.
  32. Höfling DB, Chavantes MC, Juliano AG, et al. Assessment of the Effects of Low-level Laser Therapy on the Thyroid Vascularization of Patients with Autoimmune Hypothyroidism by Color Doppler Ultrasound. ISRN Endocrinol. 2012. PMID 23316383.
  33. Höfling DB, Chavantes MC, Juliano AG, et al. Low-level laser in the treatment of patients with hypothyroidism induced by chronic autoimmune thyroiditis: a randomized, placebo-controlled clinical trial. Lasers Med Sci. 2013. PMID 22718472.
  34. Höfling DB, Chavantes MC, Buchpiguel CA, et al. Safety and Efficacy of Low-level Laser Therapy in Autoimmune Thyroiditis: Long-term Follow-up Study. Int J Endocrinol. 2018. PMID 30532779.

Every reference links to its PubMed record or DOI.

This page summarises independent, peer-reviewed research on photobiomodulation and red and near-infrared light, for educational purposes only. It describes studies of light in general, not any specific product, and is not medical advice. These statements have not been evaluated by the Food and Drug Administration. Always consult a qualified healthcare professional before making changes to your health routine.