Study: Longer Wavelengths in Sunlight Improve Vision

A study by G. Jeffery et al titled “Longer wavelengths in sunlight pass through the human body and have a systemic impact which improves vision” posted on 8 July 2025 has found that longer wavelengths “improves mitochondrial function and ATP production”.

The paper is 11 pages long and therefore relatively short. It is not the first study on the positive effects of light on the human body, and indeed relies on and corroborates these studies.

Mitochondria is light sensitive and produce ATP, “often referred to as the cellular currency of cells in terms of energy production”.

It should be noted that the sunlight spectrum at ground level ranges from approximately 300 nm to >3000 nm. The visible spectrum for humans is approximately 380 nm to 700 nm.

Longer wavelengths, approximately from 660 nm to 1000 nm, “increase mitochondrial membrane potential and ATP production particularly when they have declined with age or disease and can improve performance”. In contrast, shorter wavelengths from 400 nm to 450 nm “have the opposite effect”.

The study included 40 Caucasian individuals of both sexes aged 25 to 63 years, measuring how light can penetrate the chest (and hands). Not all participated in every experiment.

Light in the 850 nm range that is found in sunlight shows a clear ability to penetrate deeply through the body and it is likely that such wavelengths improve mitochondrial function that likely impacts on physiological ability.

Clothing can obviously change what the body is exposed to, depending on fabric type and thickness. Although this was not quantitatively studied, the researchers showed that 850 nm light penetrates a polyester/polyamide T-shirt and shirt and a woollen jumper.

Hence, clothing is unlikely to be a barrier to long wavelength penetration of the body and any subsequent functional improvements that may occur because of it.

Figure 2: Body transmission of sunlight in a representative individual.

For the visual function test, the participants did the color contrast test and were then exposed to the 850 nm light or a sham exposure (control) for 15 minutes. After 24 hours, another color contrast test was conducted. A sub-group even had their heads wrapped in foil to act as a potential barrier.

Figure 7 shows colour contrast threshold measurements made for protan and tritan. Thresholds for protan contrast sensitivity were reduced by a significant 9% (p = 0.0053) following 850 nm exposure to the back. Although they were also reduced when the head was shielded from the light, this was not significant (p = 0.1856). Thresholds for tritan are more sensitive than protan to long wavelength exposure, with relatively larger improvements following exposures as shown in previous studies using 670 nm. Thresholds for tritan following 850 nm exposure were reduced by a significant 16% (p = 0.0003) with exposure to the back and by a significant 7% (p = 0.0351) when the head was shielded. These data confirm that light exposure to the body can improve visual function independent of ocular input, but to different degrees. With the head shielded the consequences of exposure must have been mediated by light transmitted through other regions of the body.

So, “conspiracy theorists” who wear tin-foil hats can still benefit from sunlight exposure.

Figure 7: Colour contrast measurements made for protan (red) and tritan (blue) contrast sensitivities.

In short, longer wavelength sunlight can pass through clothing and have a therapeutic effect, although one should never look directly at the sun. According to this study, one does not need to anyway.

The researchers also highlighted the potential dangers of LED light.

Both fire light and light from older incandescent lighting have significant longer wavelength components and hence similarities to solar light. This is not the case for standard LED lighting used in buildings that has come to dominate over the last 20 years. In white LED lighting whether warm or cool there are few if any wavelengths over 650 nm and the dominant wavelength is blue at approximately 450 nm: 420–450 nm is known to undermine mitochondrial function, particularly in the absence of IR. Such wavelengths are intense in lighting units with colour temperature of 4000–5000 K. These wavelengths not only undermine mitochondrial performance, but also have an immediate effect significantly increasing human heart rate and significantly reducing blood pressure. This is most likely mediated by surface skin absorbance.

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