We are faced with a global epidemic of myopia (short-sightedness) because we are deprived of deep violet light (360-400 nm). Myopia is projected to rise from 23 to 50 percent of the world’s population by 2050 as the world moves indoors under conventional blue-pump LED lights and UV-A filtering window glass that blocks deep violet light.
Previous generations spent much more time outdoors bathed by a natural light spectrum that includes ultraviolet, deep violet, the other colors of the visible light spectrum, and infrared wavelengths. But nowadays, we spend over 90 percent of our time indoors 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 have no need for electric lights because the 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 spectrum. The windscreens of our cars also block ultraviolet and deep violet light.
Even when we are outside in natural daylight, sunglasses, and prescription eyewear block most of the ultraviolet and deep violet light from entering our eyes.
UV-A 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 current definition of UV-A 315-400 nm ultraviolet light includes a critical part of the healthy light spectrum: 360-400 nm deep visible violet light. And those deep violet light rays do not harm our eyes
John Ott, a pioneer in time-lapse photography, wrote a book in 1973 called Health and Light which sold over three million copies. 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.
Fifty years later, we now know that people who spend more time outdoors in full spectrum natural daylight tend to live significantly longer—an effect that can be as large as smoking versus non-smoking. As I discussed in a previous post, people exposed to the most sun are at a lower risk of all-cause mortality, cardiovascular disease mortality, and cancer mortality than people who stay 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.
We also know that violet light (360-400 nm) is critical in preventing myopia in children. A newly discovered 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 retina.
When children are not sufficiently exposed to the deep violet light in natural daylight, they are at much greater risk of developing myopia or short-sightedness. If these children are given eyewear that blocks all UV-A 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 progressing.
Environment Essential Reads
This is also true for adults given intraocular lenses to correct their short-sightedness. The myopia progresses when the lenses block all deep violet light, but is prevented if the lenses do not block violet light.
Redefining UV-A Light
The problem is that when seeking to prevent damage from UV light, we tend to remove the deep violet that is essential for eye health. This suggests that UV-A should be redefined to a 315-360 nm range. No cut-off filter is perfect, and a lot of violet is currently excluded by UV-blocking filters
In summary, the fear of eye damage from long-wavelength UV-A is misguided. Deep violet light does not cause cataracts or eye disease. Yet our LED lighting technology and energy-efficient windows remove it from our eyes.
