LED Lighting, Screens and Health

Insights from photobiomodulation therapy research

Beyond the visual system, much of this research has been in the field of photobiomodulation therapy. Researchers apply originally low-energy laser light, but now LED light to the surface of the body, and have observed a wide range of beneficial biological effects, including faster wound-healing and improved recovery from brain injury. Much of this work has used red and near-infrared (near-IR) light, but work with other wavelengths has begun as well. The apparent health benefits of red and near-IR light have been suggested as a possible explanation for the health benefits of more sunlight that can't be explained by vitamin D production. Scientists are still working to understand which biological molecules can absorb light, what the downstream effects of light absorption might be, and which wavelengths, doses, and patterns of light pulsing result in what kinds of biological effects. While such specific patterns are still emerging, general conclusions that can be drawn include:

• Many biological molecules besides eye photopigments can absorb visible light and initiate significant complex cellular/tissue processes. Molecules in tissues throughout the body can absorb light.

• Different wavelengths of visible light are absorbed by different molecules and produce different effects.

• Pulsed light (flickering light) can have different effects than continuous, non-flickering light and the frequency of pulsing matters. The literature calls these treatments "pulsed wave" and "continuous wave."

• The dose of light treatment matters. Too high of a dose is not optimal. Relatively brief, several minute, treatments can result in long-lasting effects, in some cases at least weeks.

Hamblin MR. Shining light on the head: Photobiomodulation for brain disorders. BBA Clin. 2016 Oct 1;6:113-124. https://doi.org/10.1016/j.bbacli.2016.09.002 

Hashmi JT, Huang YY, Sharma SK, Kurup DB, De Taboada L, Carroll JD, Hamblin MR. Effect of pulsing in low-level light therapy. Lasers Surg Med. 2010 Aug;42(6):450-66. https://doi.org/10.1002/lsm.20950 

Salehpour F, Mahmoudi J, Kamari F, Sadigh-Eteghad S, Rasta SH, Hamblin MR. Brain Photobiomodulation Therapy: a Narrative Review. Mol Neurobiol. 2018 Aug;55(8):6601-6636. https://doi.org/10.1007/s12035-017-0852-4 

Zein R, Selting W, Hamblin MR. Review of light parameters and photobiomodulation efficacy: dive into complexity. J Biomed Opt. 2018 Dec;23(12):1-17. https://doi.org/10.1117/1.jbo.23.12.120901 

What kinds of molecules absorb visible light in humans?

Light is a form of energy. Energy cannot be created or destroyed, but it can be transformed from one form into another. When light encounters biological tissues, the light passes through some molecules and light is absorbed by other molecules. In some cases, the light energy is transformed into heat energy, but in other cases, the absorption of light energy may cause a physical change in the shape in the absorbing molecule or may initiate a chemical change. Many biological light-absorbing molecules are pigments - they are colored molecules because they reflect certain wavelengths of visible light.

The previous section describes the eye photopigment opsin proteins responsible for vision and for regulating circadian rhythms. Other light-absorbing molecules include:

• Hemoglobin,myoglobin, and melanin all absorb light, and some think that they probably do not create biological effects relevant to photobiomodulation therapy other than preventing light from reaching deeper tissues.However, others have proposed that dissociation of oxygen from hemoglobin or dissociation of nitric oxide from myoglobin might occur during treatments.

• Flavins

• Various cytochromes (cellular pigments) that are a class of "heme" proteins that participate in chemical processes involving the transfer of electrons. These include multiple cytochromes with key roles in the electron transport chain, the mitochondrial system that produces ATP, the cellular energy currency. Cytochrome c oxidase in the electron transport chain is a proposed target of red light in photobiomodulation therapy. Its absorption of light is thought to lead to dissociation of inhibitory nitric oxide and greater ATP production.

• Surface-associated water molecules.While free water molecules do not absorb visible light well, water molecules associated with membranes or membrane protein channel surfaces can absorb visible light. Examples of possible effects include potential disruption of the shape of membrane transport channels and changes to the viscosity of water surrounding the ATP synthase in the electron transport chain that allow faster rotation of the ATP synthase and more ATP production.

• Light-sensitive ion channel membrane proteins, such as those in the TRP family that absorb blue or green light.This large family of proteins has been include proteins involved in light perception in insects as well as other proteins that sense a wide variety of stimuli, including heat, pain, pressure, or spices.

• Bilirubin - As has long been understood for the treatment of jaundice in infants, absorption of blue (430-490 nm) or green (510 nm) light causes the chemical breakdown of bilirubin into lumirubin, which is more easily excreted from the body than bilirubin.

de Freitas LF, Hamblin MR. Proposed Mechanisms of Photobiomodulation or Low-Level Light Therapy. IEEE J Sel Top Quantum Electron. 2016 May-Jun;22(3):7000417. https://doi.org/10.1109/jstqe.2016.2561201 

Karu T. Primary and secondary mechanisms of action of visible to near-IR radiation on cells. J Photochem Photobiol B. 1999 Mar;49(1):1-17. https://doi.org/10.1016/s1011-1344(98)00219-x 

Salehpour F, Mahmoudi J, Kamari F, Sadigh-Eteghad S, Rasta SH, Hamblin MR. Brain Photobiomodulation Therapy: a Narrative Review. Mol Neurobiol. 2018 Aug;55(8):6601-6636. https://doi.org/10.1007/s12035-017-0852-4 

Sommer AP. Mitochondrial cytochrome c oxidase is not the primary acceptor for near infrared light-it is mitochondrial bound water: the principles of low-level light therapy. Ann Transl Med. 2019 Mar;7(Suppl 1):S13. https://doi.org/10.21037/atm.2019.01.43 

Wang Y, Huang YY, Wang Y, Lyu P, Hamblin MR. Photobiomodulation (blue and green light) encourages osteoblastic-differentiation of human adipose-derived stem cells: role of intracellular calcium and light-gated ion channels. Sci Rep. 2016 Sep 21;6:33719. https://doi.org/10.1038/srep33719 

Wang Y, Huang YY, Wang Y, Lyu P, Hamblin MR. Red (660 nm) or near-infrared (810 nm) photobiomodulation stimulates, while blue (415 nm), green (540 nm) light inhibits proliferation in human adipose-derived stem cells. Sci Rep. 2017 Aug 10;7(1):7781. https://doi.org/10.1038/s41598-017-07525-w