In a massive study of more than 80,000 adults, scientists have found a link between bright artificial light in the evenings and age-related eye disease. At the extreme, light exposure was associated with a 31% higher risk of age-related macular degeneration (AMD), as well as an 18% and 47% increased risk of cataracts and glaucoma, respectively.
"Modern urbanization has fundamentally altered human light exposure through pervasive artificial light at night (ALAN), which disrupts circadian rhythms," the researchers write in the study. "While nocturnal light exposure has been linked to systemic disorders such as type 2 diabetes and cardiovascular dysfunction, its impact on the eye – the primary organ for both visual processing and non-image-forming circadian entrainment –remains insufficiently explored."
The researchers, from China's Shanghai General Hospital and Shanghai Jiao Tong University School of Medicine, analyzed accelerometer data from 82,826 participants in the UK Biobank who had worn AX3 devices equipped with light sensors for seven days. The wrist-worn device contained a built-in APDS9007 sensor to record real-time light exposure intensity.
The participants were aged between 40 and 69 years at the time of recruitment for the study, which took place from 2006 to 2010.
From this data, the researchers placed participants into one of four groups, based on their average light exposure between 8 pm and 11.30 pm: The lowest 50%, 50–70%, 70–90%, and the highest 10%. Some 8,283 people were assigned the extreme-light-exposure top 10% group.
The researchers then tracked the population for a median of 7.85 years to see who developed age-related eye diseases such as cataracts, age-related macular degeneration (AMD), and glaucoma, and adjusted their results to account for age, sex, smoking, BMI and other variables.
They found that 6,058 people developed age-related eye diseases within this almost-eight-year period. Those exposed to the brightest artificial light had a 31% higher risk of age-related macular degeneration, an 18% higher risk of cataracts and a 47% higher risk of primary open-angle glaucoma compared with the people in the lowest 50% group.
"High-intensity evening illumination was identified as a potent, modifiable driver of ocular aging trajectories," the scientists write in their paper. "While daytime light exposure primarily elevates cataract risk – likely reflecting cumulative photochemical damage – excessive illumination during the evening transition window (20.00-23.30) significantly increases the hazards."
So what does "high-intensity evening illumination" mean? The scientists deemed this to be at around 1,000 lux or above. Lux is a measure of illuminance, or how much light reaches a surface. Household lighting is around 100–500 lux, while supermarkets clock in around 500-750 lux.
ALAN breaching 1,000 lx – where the highest eye-disease risk lands – is most commonly found in specialist workplaces, like operating theaters, laboratories, and offices that involve detailed work and color analysis tasks.
"While standard residential lighting typically ranges from 100 to 500 lux, intensities exceeding 1000 lux are common in high-precision occupational fields and are permissible under international standards for domestic luminaire," the researchers write.
That's not to say those who experienced lower light intensity during this evening window were immune to elevated damage.
"All levels of light exposure we determined showed significant time-response relationship with overall age-related eye diseases and cataract," the researchers note in their results.
The good news is that there's little evidence linking lights at home to an increased risk of premature eye degeneration. But the 1,000-lux threshold is worth keeping in mind if you happen to find yourself exposed to high-intensity artificial light in the evenings.
As to why this light exposure might impact the eyes long-term, the researchers link it to earlier circadian rhythm disturbances caused by ALAN. The 1,000-lux threshold is around the intensity needed to produce a meaningful – and potentially detrimental – shift in the body's internal clock. Lower light levels can affect melatonin and other light-sensitive pathways, but 1,000 lux seems to be the point at which evening light can delay circadian timing.
This is perhaps the most interesting aspect of the observational study and warrants further investigation. The results aren't directly related to how our eyes cope with bright lights, but rather to the long-term impact ALAN has on other biological pathways. From what we know, age-related eye diseases are complex conditions influenced, on a molecular level, by inflammation, oxidative stress, and mitochondrial dysfunction.
The researchers argue that, despite the study's clear limitations, excessive artificial light at night may disrupt circadian rhythms during a period when the body's biological clock is particularly sensitive to such brightness. Chronic circadian disruption could then contribute to the cellular processes that drive ocular aging.
"The identification of 1000 lx as a data-derived 'vulnerability threshold' provides a reference point for clinical advice and industrial design," the team documents. "Currently, typical indoor lighting for reading or office work is set between 300 and 500 lx, which appears relatively safe according to this data. However, modern high-brightness displays and specialized task lighting can easily exceed 1000 lx. Encouraging high-precision workers (e.g., surgeons, lab technicians) to utilize 'circadian-safe' recovery periods after exposure to high-intensity occupational lighting."
The study was published in the journal GeroScience.
Source: Springer Nature
Fact-checked by Mike McRae
