Last updated on

Sleep Timing & Behavioral Alignment

Human Performance & Health › Sleep & Recovery › Sleep Timing & Behavioral Alignment

This page covers the daytime and evening factors the sources tie to sleep timing: light, wake time, time awake, and caffeine.

The Two Systems

The two-process model describes sleep as the product of a homeostatic pressure that builds with time awake and a circadian clock (Borbély et al., 2016). NINDS describes the first as a drive that “gets stronger every hour you are awake” (NINDS). For the second, NIGMS: “Light and dark have the biggest influence on circadian rhythms” (NIGMS).

Light Timing Across the Day

Morning

In the human phase-response study, light falling after the nightly core body temperature minimum (the early morning for most people) shifted the clock earlier (Khalsa et al., 2003). Wake time sets when that morning light can land.

Evening

  • Light falling before the temperature minimum shifted the clock later in the same study (Khalsa et al., 2003).
  • Ordinary room light before bedtime shortened the nightly melatonin signal by about 90 minutes in one study (Gooley et al., 2011).

NCCIH: “Being exposed to light at night can block melatonin production.”

Caffeine Timing

In a controlled study, a 400 milligram dose taken 6 hours before bedtime still reduced measured total sleep time (Drake et al., 2013).

The environment page covers the core temperature drop that precedes sleep onset (Harding et al., 2019).

What Comes Next

→ Continue to Sleep Stabilization & Recovery Reset.

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 or recovery problems, especially if symptoms are severe or ongoing.

Sources and further reading

  • Borbély et al., “The two-process model of sleep regulation: a reappraisal,” Journal of Sleep Research (2016). PubMed
  • NIGMS, “Circadian Rhythms.” NIGMS (read 2026-10-18 at nigms.nih.gov/education/fact-sheets/Pages/Circadian-Rhythms.aspx)
  • NINDS, “Brain Basics: Understanding Sleep” (sleep drive and adenosine; read 2026-10-18). NINDS
  • Khalsa et al., “A phase response curve to single bright light pulses in human subjects,” Journal of Physiology (2003). PubMed
  • NCCIH, “Melatonin: What You Need To Know.” NCCIH
  • Gooley et al., “Exposure to room light before bedtime suppresses melatonin,” Journal of Clinical Endocrinology & Metabolism (2011). PubMed
  • Drake et al., “Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed,” Journal of Clinical Sleep Medicine (2013). PubMed