Effects of near-infrared radiation in ambient lighting on cognitive performance, emotion, and heart rate variability

Although sunlight contains approximately equal amounts of near-infrared radiation (NIR) and visible light, NIR is absent from most present-day electric lighting systems and is filtered by energy-efficient windows. However, NIR is biologically active and is commonly applied in targeted photobiomodulation treatments for a range of cognitive, emotional, and physical conditions. Given the removal of NIR from indoor illumination, it is critical to understand how ambient NIR may influence psychological and physical health, and whether reduced exposure to NIR in indoor environments could because for concern. In a preregistered within-subjects double-blind experiment, acute effects of NIR and far-red wavelengths in ambient illumination on cognition, emotional state and cardiovascular health were examined in a sample of 151 university students (117 females, 34 males). During a 2-h laboratory session, participants were monitored at rest and while engaged in cognitively demanding tasks across two counterbalanced lighting conditions. Both included 3500 K white light generated by a light-emitting diode (LED) system, while one additionally included LEDs with peak wavelengths in the NIR (875 nm, 960 nm) and far-red (735 nm) spectrum. The addition of NIR and far-red to the ambient lighting showed beneficial effects on resting high-frequency heart rate variability (HF-HRV), HF-HRV responses to cognitive demand, and feelings of pleasure, but reduced performance on a visual search task. These findings reveal that the absence of NIR from architectural lighting influences humans at a psychological and physiological level, with implications for health and well-being that need to be balanced with energy-saving considerations.