Align your sleep window with the circadian gate

Go to bed when both systems are aligned: sleep pressure is high AND the clock is in its sleep phase.

Why it works

Process C creates a "sleep gate" during the clock’s nighttime phase and a "wake maintenance zone" in the early evening — a counterintuitive circadian alerting signal that prevents premature sleep. Trying to sleep during the wake maintenance zone (typically one to two hours before your natural bedtime) is why lying down early often produces frustrating wakefulness. The optimal sleep window is the hour following this zone, when both S and C support sleep.

How to do it

1. Identify the hour when you reliably feel genuinely sleepy without forcing it — that is near your circadian gate.
2. Avoid lying in bed earlier than thirty minutes before that time.
3. Expose yourself to dim light and low stimulation in the hour before the gate so the alerting signal has space to fade.

Evidence

The wake maintenance zone is well described in circadian physiology research; Edgar et al. (1993) provided key evidence for the circadian system’s active role in maintaining wakefulness before the gate opens. (rct)

Most precise characterization of the wake maintenance zone comes from controlled laboratory studies; in real daily life, it interacts with light, activity, and individual timing variation.

Sources

• Edgar et al. (1993), effect of SCN lesions on sleep in squirrel monkeys, Journal of Neuroscience

Common mistake

Lying in bed early "to rest" during the wake maintenance zone, which usually produces frustrating wakefulness and trains the brain that bed is a place for lying awake.