Light & Environment

Morning light, evening darkness, and the growing research on light as a biological signal.

Guides

Evidence: Supported

A Better Sleep Environment: Light, Sound, Temperature, and Air

Your bedroom is a set of physiological signals. Here's how to tune each one, ranked by evidence and cost.

Published Jul 12, 2026

Evidence: Established

Environmental Noise, Sleep, and Health: What the Evidence Actually Says

Noise is one of the best-documented environmental health exposures — and one of the most fixable.

Published Jul 12, 2026

Evidence: Emerging

Red-Light Therapy Devices: Questions to Ask Before Buying

Photobiomodulation research is real but young — and device marketing runs far ahead of it. Here's how to shop without being fooled.

Published Jul 12, 2026

Related research

Evidence: Supported

Light exposure during sleep associated with cardiometabolic effects and impaired sleep physiology

Randomized trial · 2022 · Healthy young adults in a laboratory sleep setting

One night of sleeping in moderate room light (100 lux) versus dim light (<3 lux) increased nighttime heart rate, decreased heart-rate variability, and increased next-morning insulin resistance.

What remains uncertain Every topic on this site has open questions — that's how science works. Individual guides call out specific uncertainties, and our methodology explains how we grade what we publish.