Process C — The Clock That Gates Your Sleep
The rhythm that says “now is a good time to sleep” or “absolutely not, it’s midday in here.”
Process C is the circadian process in the two-process sleep model — the brain’s timing signal that modulates when you feel naturally sleepy or alert over 24 hours. It’s driven by the same clock that underlies your circadian rhythm, and it’s heavily influenced by light, especially morning and evening light.
Even if Process S (sleep drive) is high, Process C can hold the “gate” to sleep partly closed at certain times, like mid‑morning or early evening, when your body prefers to stay awake. Later at night, as melatonin rises and core body temperature drops, Process C opens the gate wider, making it easier to fall and stay asleep — provided you haven’t confused it with late‑night light and erratic schedules.
When people have delayed sleep phase (DSPS) or advanced sleep phase (ASPS), it’s largely Process C that’s shifted — their internal night starts later or earlier than social clocks. Timed light exposure, melatonin, and consistent routines can gradually move Process C, but it’s stubborn and prefers gentle nudges over sudden flips.
Thinking in Process C terms helps explain why “just go to bed earlier” often fails: you’re trying to sleep in a circadian zone where your brain isn’t ready yet. Shifting the entire rhythm, rather than just the bedtime, is what makes change stick.
Why It Matters
Process C reminds you that sleep is not only about how tired you are, but also about whether your body clock agrees that it’s night.
Closing Line
Your sleep gatekeeper has office hours — working with them beats hammering on a closed door.