The Artificial Light We Live In Deprives Us of Violet Light
We have failed to provide the deep violet that is essential for eye and brain health
We spend over 90% of our time indoors1 illuminated by artificial light that differs greatly from natural light. Conventional LED lights emit primarily blue, green, and yellow wavelengths, with no ultraviolet, no visible violet, and no deep red or infrared.
Even when we are near a window and do not need electric lights because daylight is bright enough to read and work, we may still not be illuminated by natural light.
Window glass in modern buildings filters out much of the ultraviolet, deep violet, and infrared parts of the natural light spectrum2. The windscreens of our cars also block ultraviolet and deep violet light.
Even when we are outside in natural daylight, most sunglasses, and prescription eyewear block the ultraviolet and deep violet light from entering our eyes3.
What is the impact of depriving us of the deep violet part of the natural light spectrum? Among other outcomes, it has led to a global epidemic of myopia ( i.e., short-sightedness), which is projected to rise from 23% to 50% of the world’s population by 20504.
UVB includes deep violet visible light
The justification for filtering natural light is to reduce the potential harm from ultraviolet rays and the heating effects from sunlight. But the problem is that the definition of UV-A 315 - 400 nm ultraviolet light includes a critical part of the healthy light spectrum. i.e. 360 - 400 nm deep visible violet light.
Does this matter?
John Ott, a pioneer in time-lapse photography, wrote a book in 1973 called Health and Light which sold over three million copies5. He was not a professional scientist and was largely ignored by the academic community, but he was a keen observer of nature. When using window glass that blocked ultraviolet light including deep violet light, he found apples didn’t ripen, plants were more susceptible to viruses, rabbits produced fewer offspring, and mink were more aggressive. He also reported many anecdotes about people with various ailments becoming healthier when exposed to the full spectrum of natural light.
50 years later, we now know that people who spend more time outdoors in full spectrum natural daylight live significantly longer - an effect that can be as large as smoking versus non-smoking. As I discuss in my book THE LIGHT DOCTOR, the people exposed to the most sun are at a lower risk of all-cause mortality, cardiovascular disease mortality, and cancer mortality than people who stayed indoors most of the time.
The Eyes Have It
Ott reported that people, when outdoors, who were wearing a contact lens in one eye that transmitted ultraviolet and deep violet light had a much smaller pupil than the other eye fitted with an ultraviolet/deep violet-blocking contact lens. Because UV light with wavelengths less than 360 nm does not penetrate the eye’s cornea, this suggests that our eyes sense and adapt to the deep violet visible wavelengths in natural light.
Now 50 years later, we know that violet light (360 - 400 nm) is critical in preventing myopia in children. A photopigment called Neuropsin (Opsin 5m) with a peak sensitivity at 380 nm has been identified in retinal ganglion cells in the eye. Activating these receptors with deep violet light maintains the thickness of the choroid tissue filled with blood vessels, which supply nutrients and oxygen to the eye’s retina6.
When children are not sufficiently exposed to the deep violet light in natural daylight, eyes are damaged and they are at much greater risk of developing myopia or short-sightedness. If these children are given corrective eyewear that blocks all UVA light, including visible violet, their myopia gets much worse. However, if children are given eyewear that transmits deep violet light, this stops the myopia from progressing7.
This is also true for adults fitted with intraocular lenses to correct their short-sightedness. The myopia progresses when the lenses block all deep violet light, but is prevented if the lenses allow violet light to reach the eyes.
We are learning other benefits from being bathed in visible violet light. It is an effective disinfectant killing viruses and bacteria. Also, violet light has shown to be effective at promoting alertness and cognitive performance, and improving memory8.
Redefining UV-A light
The problem is that when seeking to prevent damage from UV light, we tend to remove the deep violet essential for eye health. This suggests that UV-A should be redefined to a 315-360 nm range. While short wavelength UVA can cause cataracts there is little evidence that deep violet 360-400 mm creates such lens damage9.
No cut-off filter is perfect, and a lot of violet is currently excluded by UV-blocking filters. So we need to rethink UV-A filtering and preserve our access to deep violet 360 - 400 nm light
We also need to revise LED lighting to provide a fuller spectrum that encompasses the healthy wavelengths in natural light, modulated by the needs for daytime and night illumination.
Sources
For further details, please consult my new book, THE LIGHT DOCTOR: Using Light to Boost Health, Improve Sleep, and Live Longer.
Klepeis, NE et al. (2001). The national human activity pattern survey (nhaps): A resource for assessing exposure to environmental pollutants. J. Expo. Anal. Environ. Epidemiol. 11 (3), 231–252. doi:10.1038/sj.jea.7500165
Investigating Low-E Coating Technology for Glass. https://kierantimberlake.com/updates/investigating-low-e-coating-technology
Giannos SA et al. (2019) Spectral Evaluation of Eyeglass Blocking Efficiency of Ultraviolet/High-energy Visible Blue Light for Ocular Protection. Optometry and Vision Science 96:513-522, . | DOI: 10.1097/OPX.0000000000001393
Holden BA et al. (2016) Global Prevalence of Myopia and High Myopia and Temporal Trends from 2000 through 2050. Ophthalmology123:1036-1042
Ott JN (1973) Health and Light. The Devin-Adair Company. Greenwich CT
Torii H et al (2016) Violet Light Exposure Can Be a Preventive Strategy Against Myopia Progression. http://dx.doi.org/10.1016/j.ebiom.2016.12.007
Tsubota K (2023) Whitney G. Sampson Lecture: Violet Light Hypothesis for the Control of Myopia Progression. https://www.aao.org/eyenet/academy-live/detail/violet-light-hypothesis
Hayano M et al (2023) Violet light modulates the central nervous system to regulate memory and mood. ARVO Annaul Meeting Abstract https://iovs.arvojournals.org/article.aspx?articleid=2790376
Oriowo OM et al (2001) Action Spectrum and Recovery for In Vitro UV-Induced Cataract Using Whole Lenses. Invest Ophthalmol Vis Sci. 42:2596–2602)
Great post doctor. My rudimentary understanding is that ultra important POMC biology is also driven by naked eye exposure to UV light . So even the non violet portion of UVA is still massively important for human health.
Absolutely fantastic post !