Modern energy-saving lighting and glazing may have unintentionally altered the biological quality of indoor light, according to a New Scientist feature article examining emerging research on red and infrared (IR) wavelengths. The article argues that the widespread move to LEDs and IR-filtering window glass has substantially reduced people’s exposure to long-wavelength light—a change that some researchers believe could affect cellular energy production and, ultimately, health.
A changed indoor spectrum
For most of human history, daylight, firelight, candles, gas lamps and incandescent lamps supplied substantial visible red and infrared radiation. Red light spans roughly 650–750 nanometres, while IR extends beyond the visible spectrum. These longer wavelengths can penetrate clothing and tissue more effectively than short wavelengths such as ultraviolet light.
By contrast, standard LEDs emit little or no radiation beyond approximately 750 nm, while high-performance glazing is commonly designed to reduce IR transmission for thermal control. The article quotes University College London neuroscientist Glen Jeffery as estimating that modern indoor environments may have lost about 95% of the spectrum previously available through traditional sources and unfiltered daylight. Since people can spend up to 90% of their time indoors, that shift could be significant for lighting designers and building operators.
The proposed mitochondrial mechanism
The central hypothesis is that red and near-infrared light can modestly enhance mitochondrial activity. Mitochondria generate ATP, the molecule that powers cellular work, through the electron transport chain. Researcher Tiina Karu’s earlier work associated red and near-IR exposure with faster ATP production, laying foundations for what is now called photobiomodulation or red-light therapy.
The exact mechanism remains unsettled. One proposal is that long-wavelength photons affect components of the electron transport chain or water molecules within mitochondria, helping electrons move through the system. Researchers cited in the article contend that blue-rich light from LEDs and screens may have the opposite effect, slowing this process. The evidence for clinical red-light therapy is described as “patchy, but growing,” and questions remain over dose, wavelength and long-term effects.
Health claims need caution
The article links the long-wavelength-light hypothesis to metabolic dysfunction, diabetes, cognitive decline and other age-associated diseases. It highlights a UCL experiment in which 15 minutes of red-light exposure reportedly reduced the post-glucose blood-sugar rise. It also cites an office experiment in which adding dim incandescent lighting was associated with lower average blood sugar than LED-only conditions.
A Maastricht University study involving 13 people with type 2 diabetes reportedly found better blood-sugar control during 4.5 working days under natural light than during a comparable LED-lit period. Observational evidence is also cited for associations between greater daylight exposure and lower dementia risk. These findings are intriguing, but they do not establish that LED lighting alone causes the health outcomes discussed; daylight brings many correlated exposures and behavioral changes.
Implications for lighting practice
For the lighting industry, the article’s most practical message is not an immediate return to incandescent general lighting. Rather, it raises a design question: should energy-efficient buildings preserve more biologically relevant spectral content and access to daylight?
Potential responses include:
- Prioritizing daylight access and outdoor breaks in workplaces, healthcare settings and schools.
- Evaluating spectral power distribution, not only lumens, efficacy and color rendering.
- Considering carefully designed red/near-IR supplementation where research and regulations support it.
- Avoiding unvalidated, overly powerful consumer “red-light” products, which the article notes may provoke inflammation if overdosed.
- Treating clinical and wellness claims cautiously until larger, independent studies clarify benefits, exposures and safety.
The article notes that King’s College Hospital in London opened a six-bed outdoor rooftop ward after a survey found little long-wavelength light in its critical-care environment. This example illustrates a broader opportunity: building lighting and daylight strategies may increasingly be judged not only by energy and visual performance, but also by their potential effects on human physiology.
The full New Scientist article can be found here.
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