Near‑infrared in LEDs

Near-infrared light is the band just beyond red that people cannot see, and sunlight carries a lot of it while most indoor light-emitting diode lamps do not. A 2024 study found that adding some of that missing light back into indoor lighting changed people’s heart-rate variability and mood in a lab test. (pnnl.gov) The study, published in the *Journal of Environmental Psychology*, used a within-subjects, double-blind design, meaning the same people experienced both lighting setups and did not know which one they were getting. Both rooms used 3500-kelvin white light, but one condition added near-infrared peaks at 875 and 960 nanometers and far-red at 735 nanometers. (sciencedirect.com) Researchers reported that the near-infrared and far-red condition improved resting high-frequency heart-rate variability and heart-rate variability responses during cognitive demand, and it increased feelings of pleasure. The same paper also found worse performance on a visual-search task, so the effects were not uniformly positive. (sciencedirect.com) Heart-rate variability measures the tiny changes in time between heartbeats, and the high-frequency portion is commonly used as a marker of vagal, or parasympathetic, activity. A 2025 systematic review of 36 studies and 5,501 participants found that higher positive affect was most often linked with higher vagally mediated heart-rate variability, although results varied by setting and method. (pubmed.ncbi.nlm.nih.gov) The lighting result lands in a broader argument about modern buildings: people now spend most waking hours indoors, under efficient lamps and behind windows that do not reproduce the full spectrum of daylight. The Pacific Northwest National Laboratory summary of the study says near-infrared was stripped from most modern electric lighting as an energy-saving measure even though sunlight contains roughly equal visible and near-infrared energy. (pnnl.gov) Scientists often discuss near-infrared in the context of photobiomodulation, a field that studies how red and near-infrared light can alter cell activity. Reviews in PubMed describe one leading hypothesis as photon absorption by cytochrome c oxidase, an enzyme in mitochondria that helps cells use oxygen to make energy, though the mechanism is still debated. (pubmed.ncbi.nlm.nih.gov, pubmed.ncbi.nlm.nih.gov) That debate matters because the new paper tested ordinary ambient room light, not a medical treatment device aimed at one body part. The authors said it was the first study to examine whether near-infrared in ambient illumination can influence people at cognitive, emotional, or physiological levels during everyday-style indoor exposure. (pnnl.gov) Earlier human work has pointed in a similar direction, but under different conditions. A 2022 double-blind, randomized, placebo-controlled study of 56 adults with mild sleep complaints found that morning exposure to 850-nanometer near-infrared light for four weeks improved several well-being and health measures, with benefits showing up in winter but not in sleep or circadian outcomes. (pmc.ncbi.nlm.nih.gov) The new study does not settle whether offices, schools, or homes should change lighting standards, and it does not show long-term health effects. It does show that the “invisible” part of light that engineers removed to save energy can still register in the body when people spend hours under it. (sciencedirect.com, pnnl.gov)