Dr Martin Moore-Ede is a former Harvard Medical School professor, leading circadian clock researcher, and Chief Health Advisor at LightHealth. He discovered the suprachiasmatic nucleus, the biological clock in the human brain, and has spent over 40 years studying how light governs human health.
Myopia, or short-sightedness, has become one of the fastest-growing health epidemics of the 21st century. In East Asia, rates among young adults have risen to over 80% in some populations. In the UK and Europe, rates have roughly doubled in the past 50 years. By 2050, researchers estimate that half the world's population will be myopic.
The conventional explanation is screen time and near-work. But the evidence increasingly points to a different culprit: the disappearance of a specific wavelength from our daily light exposure.
What violet light does to the eye
Violet light, the wavelengths in the 360 to 400nm range at the very edge of visible light, plays a specific role in eye development and in regulating axial length, the distance from the front to the back of the eye. When the eye grows too long, distant objects fall out of focus. That elongation is the physical basis of myopia.
Research has shown that violet light suppresses the expression of genes that regulate eye growth. In the absence of violet light stimulation, the eye continues to elongate beyond its optimal length. The myopia epidemic, on this account, is not simply about what we look at. It is about what we look in.
Where violet light has gone
Natural outdoor light is rich in violet wavelengths. But our indoor light sources are almost entirely devoid of them. Standard LED bulbs emit virtually no violet light. The 360 to 400nm band is absent from their spectral output. Fluorescent tubes are similarly violet-poor. For a guide to what to look for when choosing bulbs, including which spectral questions to ask, see our piece on what to ask before you switch on the lights.
Making matters worse, standard window glass absorbs violet wavelengths. Even sitting next to a window in a building, you are receiving a spectrum stripped of the violet component that outdoor exposure would provide. And most corrective lenses, including spectacles and contact lenses, have UV and violet-blocking coatings applied as standard, which means that the very people already experiencing myopia are also most efficiently blocked from the wavelength that might slow its progression.
The outdoor light connection
This explains a puzzle that the screen-time hypothesis cannot fully account for: why outdoor time is consistently more protective against myopia than indoor time, even when controlling for near-work activity. Children who spend more time outdoors develop myopia at significantly lower rates than those who spend equivalent time indoors, regardless of how much reading or screen use they do. The protective factor is the outdoor light spectrum, and particularly its violet component. For a picture of what abundant natural light actually delivers biologically, see our piece on why the summer solstice is the healthiest day of the year.
What to do about it
For children in particular, maximising genuine outdoor time remains the most practical intervention. Thirty to sixty minutes of outdoor light exposure daily has been shown in clinical studies to meaningfully slow myopia progression.
For indoor environments, sourcing lighting that includes the violet spectral band is an emerging consideration, particularly for schools, offices, and children's bedrooms. Full-spectrum lighting that extends into the 380 to 400nm range begins to address what standard LEDs omit. For the broader evidence on how the light we live under shapes long-term health, see our piece on could more sunlight help you live longer.
We have spent decades asking what people are looking at. It is time to ask what light they are looking in.
