Night work asks the clock to do what it isn't built for.

Why it's hard, and why it isn't your fault

The circadian clock sets itself by light. Working nights asks it to invert while it keeps receiving, every morning on the commute home, the strongest signal that exists for pushing it back the other way. This isn't a lack of habit or rigour: it is a conflict of signals, and it is treated at the level of the signal.

Which means most consumer sleep advice is beside the point here. "Go to bed at the same time" means nothing when the shift changes; "get seven hours" doesn't say how, at 9am, on a noisy street, in a bright bedroom.

The light plan, in three parts

An intervention study published in the Journal of Biological Rhythms in 2009 tested a combination of measures in permanent night workers — and produced measurable partial circadian adaptation where other strategies produced none. The three parts work together; separated, they lose most of their effect.

1. Intermittent bright light during the shift

Not a continuous wall of light: intermittent exposures, concentrated in the first half of the shift. That is what pushes the clock in the intended direction and supports alertness when it dips.

2. Dark glasses from clocking off to bed

The part everyone skips, and probably the most decisive. Morning light on the way home is exactly the signal that undoes the night's work. Dark glasses put on as you leave, kept until the bedroom, protect the shift you gained.

3. Strict darkness for sleep

Blackout, mask, phone out of reach. The human clock's sensitivity to light is high: ordinary levels are enough to move it. A bedroom that is "dark enough" isn't.

On rotating rosters: anchor sleep

When the roster changes every week, aiming for one regular night is unrealistic, and holding on to that aim mostly produces guilt. The anchor sleep strategy accepts split sleep and protects one thing: a block of about four hours at the same clock time every day, topped up by a second variable block wherever the shift allows.

The clock keeps a stable reference while everything else moves. It is one of the person-directed measures retained in the Cochrane review on shift work, alongside the prophylactic nap before the night shift — sleeping in advance rather than trying to recover afterwards.

The honest part

The Cochrane review of person-directed interventions for sleepiness at work and shift-work sleep disturbance concludes that they help without removing the problem. That is not a polite hedge: it is the finding.

The measures above reduce the avoidable share of the cost. They do not replace a sane roster — rotation direction, rest between shifts, number of consecutive nights — which is the employer's responsibility and weighs more than anything an individual can do alone. An app claiming otherwise would be lying to you.

One more point, for the shortened nights: the relationship between sleep duration and mortality, in a meta-analysis pooling more than 1.3 million people, is U-shaped — risk rises at both ends, with the more favourable zone around seven hours. Night work structurally pushes you toward the wrong side of that curve, which makes the defended sleep block less negotiable than it looks.

How Sillon handles it

"Night work" is one of the situations the app models explicitly: the relevant practices are offered only to people working nights, and the dedicated path sequences the light plan, anchor sleep and the prophylactic nap in order. These cards are not a general version to adapt yourself — that is precisely the failure they correct.