How much does sleep light min have to change before it stops being noise? The threshold from 650 nights

For a change in light sleep minutes to stop being noise and start being signal, it has to move at least 8.7% within a 28-night window, or 6.15% within a 56-night window. That threshold comes from 650 nights of a single body, the same row that backs the rest of this file. Below those figures, what you see on the morning app isn't new information — it's the variation this metric already produces when, in fact, nothing changed.

What sleep light min is, in the terms that matter here

Sleep light min is the number of minutes a wearable classifies as light sleep during the night — the stage that, for most consumer sensors, makes up the largest share of total time asleep. It's one of the numbers people watch most closely and contextualize least: a jump from one night to the next is read almost automatically as an event, when it can simply be the normal range this variable moves in on its own. The question this file answers isn't "did my light sleep minutes go up or down," but "did they go up or down by more than they go up and down for no reason at all?"

That distinction can only be made with your own data, over enough history. There is no universal threshold for sleep light min, because each person's background noise is different: it depends on the sensor, on routine, and on how much that specific person varies night to night. No one else's threshold gets imported here — it gets measured.

How it was measured: 650 nights of a single body

The file records 650 nights of sleep light min from a single body, inside a larger archive of 712 nights and 18483 total measurements across 31 variables. Across those 650 nights, the median sleep light min is 294 minutes: half the nights in the file sit above that figure and half below. That is the center of the distribution, the reference point against which any movement gets measured.

The coefficient of variation (CV) of the full series is 15.82%. That number summarizes how much sleep light min moves from one night to the next, relative to its own center, across all 650 nights. It's the base unit for everything else: if CV were zero, any change would be signal; at 15.82%, there is a band of normal movement — a notably wide one — that has to be subtracted before calling anything a real change.

Night-to-night correlation (rho) is 0.048, a number very close to zero. In practice: knowing last night's light sleep minutes tells you almost nothing about tonight's. Each night behaves, to a large extent, as an independent event — which is exactly why one low or high night is not enough to draw a conclusion, and why the threshold has to be calculated over windows of several nights, not a single data point.

The table: the threshold changes with the window

The change threshold isn't a fixed number: it drops as the observation window grows, because averaging more nights reduces the noise inherent to any single night. This table comes directly from the source row ruido.medido.json#sleep_light_min, without rounding or reinterpretation:

Window (nights)	Minimum change threshold
28	8.7%
56	6.15%
84	5.02%
168	3.55%

Read another way: to know whether your light sleep minutes truly changed, comparing two 28-night blocks, that change has to exceed 8.7% before you can rule out noise. Compare two 168-night blocks, with several months of history behind them, and the threshold drops to 3.55% — because there's far more averaging absorbing the night-to-night variation.

Beyond the window-based thresholds, the source row also includes a relative-noise measure (rcv) of 43.85%. It's another way of quantifying how much this variable moves relative to its own spread, and it's one of the higher figures across the 31 variables in this archive: it confirms that sleep light min is, from the outset, one of the noisiest metrics in the entire file.

Why this matters before reacting to a number

A threshold of 8.7% at 28 nights, or 6.15% at 56 nights, isn't a statistical quirk — it's the line that separates a morning reading from a real trend. Most of the decisions people make about their sleep — switching supplements, shifting schedules, changing routines — get triggered by a single number going up or down, without first asking whether that movement falls inside the range the variable produces on its own. With a CV of 15.82% and an rcv of 43.85%, sleep light min is exactly the kind of metric where this question matters most: it's among the ones that move most on their own, and therefore among the easiest to mistake for real change.

With 650 nights of a single body, that range stops being a guess and becomes a number: 15.82% CV, 0.048 night-to-night correlation, and a table of window-based thresholds that says, precisely, how much it takes for a change to stop being noise.

The limit

This threshold is measured on a single body, with 650 nights from one data source. It does not say what caused any specific change in that person's light sleep minutes, and it does not establish a cause-and-effect relationship between any intervention and the metric. It also does not generalize to another body: another person's background noise for sleep light min may carry a different CV, a different night-to-night correlation, and therefore a different threshold, even using the same sensor and the same definition of the metric. The threshold presented here is meant for reading this file rigorously — it does not replace someone else measuring their own series of nights before applying the same standard to it.

Keep going

This file is one piece inside a larger archive. You can review the rest of the sleep thresholds at Mental Work — all protocols, the related file on magnesium-for-sleep, or the full dataset at open science — the dataset.