The Hidden Part of Sunlight: Why Near-Infrared Light Matters

A blog post by Dr. Aida Farshadi

For millions of years, humans lived under the full spectrum of sunlight. Our physiology evolved not just with visible light, but also with near-infrared light (NIR), an invisible wavelength that makes up nearly half of the sun's energy reaching Earth.

Photo by Todd Rhines on Unsplash

What is near-infrared light and why we're missing it?

Near-infrared sits just beyond the red end of the visible spectrum, in the 700–1100 nm wavelength range. Unlike shorter wavelengths that stop at the skin surface, NIR penetrates centimeters into the body, reaching muscles, blood vessels, and the mitochondria within those deeper tissues. Think of mitochondria as tiny batteries inside our cells. Research shows that NIR light helps recharge these batteries, boosting cellular energy while also improving blood flow.

These aren't exotic laboratory effects; they appear to be part of how our bodies evolved to interact with sunlight.

Here's the challenge: modern life has effectively removed NIR from our daily light exposure. Outdoors, sunlight delivers substantial NIR irradiance to our skin, in the range of tens to hundreds of milliwatts per square centimeter. But indoors? Architectural glass blocks most solar NIR. And while incandescent bulbs and candles do emit some infrared, their intensity is one to two orders of magnitude lower than natural sunlight. This matters because NIR effects are dose-dependent. Below a certain threshold, there is no meaningful biological response; just negligible background exposure. Simply having "some" infrared in a light source is not enough; the irradiance must approach levels comparable to what the sun provides. Most indoor environments fall far short of this.

This lack of NIR may contribute to common complaints of modern indoor life: fatigue, poor sleep, reduced alertness, and slower recovery. While definitive causal links are still under investigation, the emerging picture suggests that NIR is not a luxury; it's closer to an environmental nutrient we've unknowingly removed from our daily lives.

What can we do?

The simplest solution remains: spend more time outdoors. Even on a cloudy day, natural daylight delivers far more NIR than any indoor environment.

For those of us who spend most of our time inside, the future may include purpose-built NIR lighting: calibrated sources designed to restore this missing part of the solar spectrum. Not to replace sunlight, but to bring back what modern architecture has filtered out.

And there's more to explore. We know that blue light entrains our circadian system, but in nature we never receive blue light in isolation; it always arrives alongside the full spectrum, including NIR. Understanding how these wavelengths might work together could open new directions in light and health research.

Good light isn't just about brightness or colour. It's about the full spectrum, including the part we cannot see.

References:

1. Hamblin MR. Mechanisms and applications of the anti-inflammatory effects of photobiomodulation. AIMS Biophysics. 2017;4:337–361.

2. Avci P, Gupta A, Sadasivam M, et al. Low-level laser (light) therapy (LLLT) in skin: stimulating, healing, restoring. Seminars in Cutaneous Medicine and Surgery. 2013;32:41–52.

3. Jeffrey G, et al. LED lighting undermines human visual performance unless supplemented by wider spectra like daylight. Nature Scientific Reports. 2026; 16:3061.