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Glossary

Sleep Regularity Index

Defined in topic 41

A measure of how consistent sleep timing is from night to night. Across nearly 61,000 accelerometer-wearing adults it predicted death better than sleep duration did.

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Where this comes from

In the reference topic that owns this term

Reference topic 41, The Handrail II: Light, Sleep, Temperature, Nature, states the mismatch as a card: what the system evolved to expect, what it gets instead, and what happens in the gap.

Mismatch card

What it expects

Thousands of lux by day, near-total darkness at night, a temperature that falls after sunset, occasional cold and heat, and daily hours outdoors.

What it gets

Under 1,000 lux of waking light in the week the campers spent at home, evenings in the 30 to 300 lux band the clock reads most steeply, a thermostat that never moves, and most of a life indoors.

What happens in the gap

The clock drifts later and flattens, sleep timing scatters, and systems tuned by temperature and daylight have nothing to tune against.

The full card, and the topic behind it

What that chapter recommends

3 of the 9 graded recommendations in Reference topic 41, strongest evidence first. How the grades work.

  1. Get outside within about an hour of waking

    ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

    Outdoor light runs to thousands of lux, clear of the confusing indoor band. No trial has tested the hour; it follows from how the clock responds to morning light.

    Read it in full

  2. Dim the last two to three hours

    ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

    Lower overhead lights and screen brightness rather than chase a lux target, because sensitivity varies more than 50-fold between people.

    Read it in full

  3. Make the bedroom properly dark

    ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

    Cover standby lights, use curtains that work, put the phone face down or outside the room.

    Read it in full

Related terms

The argument behind this term, its studies and its notes are in Reference topic 41 of the reference library. The book gives the practical version. Get the book.