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Red light and microcirculation in the feet: What does scientific research show?
Red light and microcirculation in the feet: What does scientific research show?
From the colour of light to measurable parameters
With light applied to the feet, it is natural to wonder where it reaches and what it might trigger there. The answer starts with physics: what light the source emits, how much reaches the skin and what happens to it in tissue. This article explains optical stimulation. Warmth and traditional points have separate articles in the series.
Simply put
Red is the colour we see. Assessing a light stimulus also requires measurements. The sensation of warmth, the device setting and the light dose are different pieces of information.
How does red light differ from near-infrared light?
Red light belongs to the visible spectrum. Near-infrared radiation, abbreviated NIR, has longer wavelengths beyond the red edge and is normally invisible to the human eye. [1]
A visible red component therefore does not confirm the presence of NIR. An NIR source may not appear to glow. The source specification matters, rather than a photograph or a mode name.
↑ Back to questionsWhat happens when light reaches the skin?
Some light is reflected and some enters the tissue. There it may scatter in different directions and be absorbed. Absorption transfers light energy to matter. [2]
Scattering changes the direction of propagation; absorption removes energy from the light field. These processes do not automatically mean improved cell function. They first describe the movement and transfer of energy.
↑ Back to questionsCan we say how deeply light penetrates?
There is no single universal figure. It depends on wavelength, tissue thickness and optical properties. Human measurements also show differences between individuals. [3]
Light has no sharp boundary beyond which it suddenly disappears. A claim that it penetrates several centimetres needs to explain what was measured and how much energy remained at that depth. Visible light on the surface cannot replace this measurement.
↑ Back to questionsWhat are chromophores, and why are mitochondria mentioned?
A chromophore is part of a molecule, or a molecular system, capable of absorbing light of a particular wavelength. Photobiomodulation research investigates possible cellular targets, including the mitochondrial enzyme cytochrome c oxidase, CCO.
This mechanism cannot be described as a consistently confirmed increase in ATP. Quirk and Whelan found no increase in oxygen consumption by isolated CCO under the tested conditions at 670 and 830 nm. [4] An isolated-enzyme result is also not an assessment of the whole human body.
↑ Back to questionsIs photobiomodulation the same as heating?
No. Photobiomodulation research examines biological responses to absorbed light that are not explained solely by a rise in temperature. A thermal stimulus describes a change in thermal conditions.
Both processes can occur in a real device. Feeling warm does not by itself establish photobiomodulation, and the absence of warmth does not tell us how much light reaches the skin. Research therefore needs to distinguish optical parameters from temperature. [4, 5]
↑ Back to questionsIs an LED automatically weaker than a laser?
The label LED or laser alone does not justify that conclusion. Sources can differ in spectrum, beam distribution and power. A source with greater total power may spread its light over a larger area.
At a particular point on the skin, the relevant quantity is therefore the power arriving per unit area. An experiment with one laser or LED cannot be attributed to another source merely because of its name. [5]
↑ Back to questionsWhat do nm, W, mW/cm² and J/cm² mean?
These units answer different questions: nm describes wavelength; W describes optical power when it refers to light output; mW/cm² describes power arriving per unit area; J/cm² describes energy received per unit area over a period of time.
The measurement location must also be clear when comparing specifications. A value at the source may differ from the value at the skin. The electrical input power of the whole device is not the optical power of its light.
↑ Back to questionsHow is light dose related to time?
For constant irradiance: energy per area = power per area × time. A purely mathematical example: 20 mW/cm² = 0.020 W/cm²; 0.020 × 300 seconds = 6 J/cm².
This explains the units; it is not a recommendation for use. The calculation assumes a constant value at the point concerned. It does not tell us how much energy a deeper layer absorbs, and equal J/cm² alone do not confirm equal biological results.
↑ Back to questionsDoes warmer skin prove better microcirculation?
Microcirculation means blood flow through small vessels. Skin temperature and blood flow can be related, but they are different quantities. A warm contact surface can also change skin temperature through direct heat transfer.
Neither feeling warm nor a photograph of a redder foot is sufficient to assess blood flow. Research needs an appropriate measurement method and a comparison of conditions. Whether someone feels comfortable is a separate question.
↑ Back to questionsWhat does research into red light and blood vessels show?
In 2022, Keszler and colleagues measured increased perfusion in mice after 670 nm illumination and investigated the role of compounds related to nitric oxide. [6]
This is mechanistic research in a particular animal model. It was not a test of KINGRAY BioWave or confirmation of an effect on human feet. The parameters of such an experiment are not instructions for home use.
↑ Back to questionsWhat does the brochure tell us about BioWave light?
The KB-136C brochure specifies an electrical input power of 300 W and a coloured ring indicating setting ranges: 01–10 white, 11–20 blue and 21–30 red. This indicator's colour provides information about the setting. [7]
The available brochure does not specify the exact wavelength of the light output or irradiance at the skin in mW/cm². Neither 300 W nor the ring colour lets us calculate an optical dose or confirm equivalence with the source used in a study.
↑ Back to questionsHow can this information guide everyday use?
Choose the controls, duration and restrictions according to the current instructions for your model. Do not extend the time based on the formula in this article or in order to feel more heat.
When reading research, separate three things: the source used, what the scientists actually measured and who or what the experiment involved. This makes it possible to explain light clearly without automatically turning a research finding into a promise about a device.
↑ Back to questionsFrequently asked questions – short answers
How does red light differ from NIR?
Red light is visible; NIR lies beyond the red edge of the visible spectrum. Its presence must be confirmed by the specification.
Does feeling warm establish photobiomodulation?
No. Feeling warm does not measure an optical dose or confirm photobiomodulation.
Is knowing the time enough to determine the dose?
Time alone is insufficient. We also need the power arriving per unit area and how it changes over time.
Was the cited study carried out on BioWave?
No. The cited study investigated an animal model and a different light source.
Can a light dose be calculated from 300 W electrical input power?
No. In the brochure, 300 W is the device's electrical input power, and the coloured ring indicates a setting, not a measured light dose.
Sources and supporting material
These sources explain physics, methods and specific experiments. They do not demonstrate the effectiveness of KINGRAY BioWave.
- NASA: Visible Light Visible spectrum. Open sourceRelevant NASA text read.
- NASA: Wave Behaviors Reflection, scattering and absorption. Open sourceRelevant NASA text read.
- Piazena H, Meffert H, Uebelhack R (2017). DOI: 10.1111/php.12785. Measuring optical properties of human skin. Open sourceAbstract checked; the full text was not assessed.
- Quirk B, Whelan HT (2021). DOI: 10.1089/photob.2020.4978. Laboratory experiment with an isolated enzyme. Open sourceAbstract checked; the full text was not assessed.
- Jenkins PA, Carroll JD (2011). DOI: 10.1089/pho.2011.9895. Reporting light stimulus parameters. Open sourceAbstract checked; the full text was not assessed.
- Keszler A et al. (2022). DOI: 10.3389/fphys.2022.880158. Vascular response in a mouse model. Open sourceRelevant full-text sections read: methods and results.
- KINGRAY BioWave KB-136C Technical specifications and the colour indicator. Internal brochure supplied by the site operator, page 11. A public link is not yet available.
