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Sleep Environment & Optimization

Human Performance & Health › Sleep & Recovery › Sleep Environment & Optimization

This page covers three parts of the sleep environment that the sources measure: light, temperature and bedroom air.

Light

NIGMS: “Light and dark have the biggest influence on circadian rhythms” (NIGMS).

Nighttime Light Exposure

Artificial light after sunset suppresses melatonin, the hormone the brain “produces in response to darkness” (NCCIH), and pushes the internal clock later: ordinary room light (under 200 lux) in the hours before bed shortened the nightly melatonin signal by about 90 minutes compared with dim light (Gooley et al., 2011), and light falling before the temperature minimum delayed the clock (Khalsa et al., 2003).

Morning Light Exposure

In the human phase-response study, light falling after the nightly core body temperature minimum, which is the early morning for most people, shifted the clock earlier (Khalsa et al., 2003).

Temperature

Sleep onset is accompanied by a drop in core body temperature (Harding, Franks & Wisden, 2019). The Sleep Foundation’s physician-reviewed guidance puts the best room temperature for sleep at “approximately 65 degrees Fahrenheit (18.3 degrees Celsius)” (Sleep Foundation, reviewed July 2025).

Bedroom Air

In a two-week study of students in identical dormitory rooms, a fan that brought in outdoor air whenever carbon dioxide rose above 900 ppm kept bedroom carbon dioxide near 835 ppm on average, against about 2,395 ppm with the windows closed and the fan off. With the fresher air the students spent more of their time in bed asleep and tended to score better on next-day concentration tests; they also reported the air as fresher and themselves as more rested, with drier mouth and skin as the trade-off (Strøm-Tejsen et al., 2016). The study varied ventilation and tracked carbon dioxide as the marker of stale air; it did not measure oxygen.

What Comes Next

→ Continue to Sleep Timing & Behavioral Alignment for light timing, wake time and caffeine timing.

GoldBlock Workshop is educational. We explain how the body works and what the research says. We do not diagnose, treat, or give personal medical advice. Talk to a qualified professional about persistent sleep problems.

Sources and further reading

  • Light as the master signal for the circadian clock, and morning light advancing it: National Institute of General Medical Sciences, “Circadian Rhythms” (read 2026-10-18). NIGMS · Khalsa et al., human phase-response curve to light, Journal of Physiology (2003). PubMed
  • Evening light suppressing melatonin: National Center for Complementary and Integrative Health, “Melatonin: What You Need To Know.” NCCIH · Gooley et al., Journal of Clinical Endocrinology & Metabolism (2011). PubMed
  • Core body-temperature drop and sleep onset: Harding, Franks & Wisden, Frontiers in Neuroscience (2019). PubMed
  • Bedroom temperature guidance: Sleep Foundation, “Best Temperature for Sleep,” medically reviewed, updated July 11, 2025 (read 2026-10-18). Sleep Foundation
  • Bedroom carbon dioxide, ventilation, and sleep quality: Strøm-Tejsen et al., “The effects of bedroom air quality on sleep and next-day performance,” Indoor Air (2016). Journal