Sleep cycle calculators and circadian rhythm planners answer different questions. A cycle calculator estimates bedtime windows from wake time. A circadian plan shapes the daily cues that make a sleep schedule easier to repeat.
Cycles are useful for choosing a practical bedtime. Circadian cues are useful for moving a pattern earlier or later. Light is one of the most visible cues because morning brightness and late evening brightness pull in different directions.
The best Drift Light plan uses both: pick a realistic bedtime window, then use evening dimming and morning light to make that window easier tomorrow.
Where this guide fits
This page is part of the sleep-timing cluster. It connects the clock question to the bedroom question: when to start lowering evening cues, when morning light should anchor the next day, and how to choose a repeatable window rather than a perfect minute.
Practical inputs to compare: Use wake target, natural wake drift, time to fall asleep and morning-light access as the repeatable inputs.
How to read the result: Treat these inputs as a bedroom pattern, not a one-night verdict. If the same cue shows up on several ordinary nights, the next change is easier to choose and easier to reverse if it does not help.
- sleep cycle
- circadian rhythm
- sleep latency
- wake time
- chronotype
- morning light
- bedtime window
- sleep pressure
Keep it narrow: Do not change lamp type, screen cut-off, bedding, window opening and wake time on the same night. Hold the other cues steady so the page stays linked to one room question.
What to try tonight
- Choose one cue: light, screen boundary, temperature, humidity or airflow.
- Keep the sleep target and morning note simple.
- Repeat the change before judging it.
