LED lighting (350-650nm) undermines human visual performance unless supplemented by wider spectra (400-1500nm+) like daylight

We demonstrate that the visual performance of those working under standard LEDs is significantly improved by exposure to incandescent light, which has a spectrum similar to daylight with a broad infrared component. These data are consistent with the hypothesis that LED lighting impairs human visual performance. This result is consistent with laboratory experiments where the specific red/infrared wavelength range generated by LEDs has been used to improve visual function in animals and humans in a conserved manner.^13,16,17. But there are three important differences from these earlier studies. First, we have transformed environmental lighting into a free-flowing work environment. Second, we have achieved significant balanced improvements in both the Proton and Triton ranges. Previously, exposure to restricted experimental 670 nm had resulted in only a strongly improved favoring of Triton function.¹³. Therefore, exposure to full spectrum light leads to a balanced pattern of improvement in visual performance. Third, we have shown that improvements in visual function after exposure to incandescent light persist for up to 6 weeks and possibly longer, whereas benefits from single LED restricted-range red light were limited to about 5 days.¹³. These three characteristics change the way in which long wavelength light can be applied to improve human physiology by delivery into the general environment with lasting balancing effects. These results are new and may have implications for public health.

Our study used 22 subjects, but was statistically significant using both before and after metrics and against an independent control group. They are also similar in group size in aspects to Shinhamar et al.¹³ (Figures 2, 3, 4 and 5). However, future studies would clearly benefit from including a larger number of subjects.

The evolution of life on Earth spans 4 billion years, and the evolution of humans from the last common primate ancestor spans approximately 4–5 million years. All this occurred under sunlight whose spectral range is approximately 300–2500 nm+, within which there has been an invariant balance between short and long wavelengths. Humans who adopted fire 1–2 million years ago supplemented sunlight as they moved out of Africa because its spectrum is similar to that with a large infrared component. Similarly, the development of the Edison filament luminaire, which was common until about the year 2000, had a spectrum similar to that of sunlight. However, around 2010 LED lighting became common with a highly restricted spectrum (350–650 nm) and energy saving characteristics, resulting in the loss of infrared light in the built environment.¹.

The physiology of life forms in all species adapts to natural environmental light in highly conserved patterns. Light impacts mitochondrial function, a key regulator of metabolism and aging in animals. When the balance of short and long wavelengths changes there are consequences for mitochondria. When short wavelength exposure is predominant, such as in LED lighting, mitochondrial function declines. Mitochondrial complex proteins are reduced and ATP production is reduced.^2,3. Decreased mitochondrial demand for glucose leads to increased body weight and disruption of serum cytokines⁴. As a result, the cell/organism’s susceptibility to aging and death increases, consistent with the mitochondrial theory of aging¹⁸. It has been suggested that this is partly due to 420–450 nm light, which is predominant in LEDs, being absorbed by the porphyrin and subsequent production of oxygen singlets causing inflammation.³.

In contrast, exposure to longer wavelengths is associated with an increase in mitochondrial membrane potential and an increased concentration of mitochondrial complex proteins that is decreased with aging and disease. This in turn is linked to elevated ATP, reduced inflammation and extended average lifespan.^7,9,10,19. The experimental use of longer wavelengths in such situations is commonly known as photobiomodulation.

The retina has the highest metabolic rate and highest mitochondrial concentration in the body²⁰. Retinal metabolism decreases with age, but this can be partially recovered with long wavelength light in all species^16,21. In humans a 3-minute exposure to 670 nm improves color vision within 3 hours, which persists for about a week.¹³. But the authors of this study did not appreciate that it was within a population that worked and lived primarily under LED lighting that may have weakened their baseline measurements. Here, we made no attempt to control light exposure or subject movements as is the case in laboratory-based experiments. Rather, our aim was to introduce broad spectrum long wavelengths into the work environment to improve human performance through mitochondrial manipulation at the translational stage.

There is ample evidence that the introduction of longer wavelengths has systemic effects. Durieux et al.²² Regarding experiments in C. elegans it is stated that “We have found that mitochondrial perturbations in one tissue are perceived and implemented by the mitochondrial stress response pathway in the distal tissue”. Exposure to both short and long wavelength light causes significant specific changes in serum cytokine expression in mice.^4,23. Similarly, long wavelength exposure to human body surface except eyes significantly reduces blood sugar levels and increases oxygen consumption in humans. This is likely because mitochondrial upregulation will increase carbohydrate demand to support increased ATP production.¹². Other systemic effects can be found and are evident in experimentally induced Parkinson’s in primates. Light targeted by the implant, which is focused on the substantia nigra, is effective in reducing symptoms.²⁴But there are also those that are directed to remote places²⁵.

A single 3 minute 670 nm exposure remains effective for approximately 5 days¹³. But we show that with broad spectrum they remain effective for up to 6 weeks, although we did not find an end-to-end effect. Here it is worth considering possible mechanisms of action that remain a subject of debate. Historically, red light enhancement was thought to be due to light absorption by cytochrome c in the respiratory chain.²⁶. However, in its absence positive effects are found in vitro. As a result, it has been suggested that longer wavelengths reduce the viscosity of water around rotary ATP pumps thereby increasing rotor speed.²⁷. This cannot explain the continued effects of light exposure as this effect must be relatively transitory as viscosity will increase rapidly after light withdrawal. However, a key feature of long wavelength light absorption is an increase in respiratory chain protein synthesis. These proteins are in flux throughout the day²⁸ And complex IV is upregulated after exposure to red light¹⁹. Therefore, while red light may initially increase rotor pump speed, there is a rapid increase in protein synthesis that may establish greater respiratory chain capacity. The lifetime of these proteins can then determine the duration of the effect.

Only thirteen polypeptides are formed in mitochondrial protein synthesis. This probably slows with age and possibly contributes to aged mitochondrial decline.¹⁸. But critically, we do not know the speed of mitochondrial protein synthesis, the lifetime of such proteins, or the speed of their degradation. We suggest that these may be key events in the duration of the effects of light exposure.

LED lighting clearly has the potential to impair visual performance through reduced mitochondrial function. Systemic effects of light-induced changes in mitochondrial potential have been shown to occur as^{4,15,22,23,25}The effects of LEDs revealed here may be more widespread than initially estimated. Given the prevalence of LEDs, this may be a significant issue in public health and clinical environments where changing lighting patterns in appreciation of this point may have significant positive consequences²⁹.

Given our results, it is important to ask what solutions can be found to improve health in the context of lighting in the built environment. Incandescent lighting, which has a significant positive impact on standard LEDs, is being universally phased out for reasons of energy efficiency, where the focus is solely on the visible light produced.

A solution may be found in creating lighting units with multiple long wavelength LEDs to cover a wider span of near infrared. However, our efforts here have met with limited success. Multiple closely connected spectral peaks do not produce smooth spectral output as found in incandescent light and sunlight, which is problematic in improving function and has not yet been delivered. This could possibly be overcome by using a greater number of spectral peaks with shorter distances. But this leads to a different series of problems with respect to cost and increased energy consumption, making this solution no better than maintaining incandescent sources in terms of environmental sustainability.

Key to this issue is the question of how much infrared is needed to maintain optimal function? There are relatively few absorbers in the built environment in the infrared and current studies require relatively few absorbers to be added to the environment to have an effect. However, a viable alternative is to run an incandescent light at a lower temperature resulting in energy savings and increased unit life and by shifting the peak spectral output toward longer wavelengths.

If this is done with a halogen bulb, which is a type of incandescent tungsten bulb, the filament lasts longer because the evaporated tungsten is redeposited on the filament instead of blackening the bulb glass. Therefore, the use of halogen bulbs at low voltage is a realistic option in terms of health and energy consumption.