Delayed Sleep Phase and Your Mac Screen at Night
By Nikki NeislerCo-founder, Sundown
If your body clock runs late, your Mac is one of the few light sources you can fully control in the hours before you try to sleep, and warming and dimming it cuts the light it sends your way. That is all a screen setting does. It does not diagnose or treat delayed sleep phase syndrome, and no study cited here tested screen software for it, Sundown included.
This guide is for night owls who work or wind down on a Mac late in the evening, and for anyone who has been told, or suspects, that their sleep timing runs hours later than they want it to. It covers what the condition is, why evening light is part of the conversation, what the one glasses trial in patients found, and one example of how you might set a Mac screen for the evening.
What Is Delayed Sleep Phase Syndrome?
Delayed sleep phase syndrome, also called delayed sleep-wake phase disorder or DSPD, is a circadian rhythm sleep disorder in which your natural sleep and wake times sit hours later than the schedule you need to keep. The body clock itself runs late, which has nothing to do with discipline, and it is a medical diagnosis.
The Sleep Foundation's overview describes the usual picture: you cannot fall asleep at a socially normal bedtime, you struggle to wake up on time, and in some cases you are sleepy in the day. The American Academy of Sleep Medicine's patient site, Sleep Education, describes how a sleep doctor may assess it, starting with a thorough history, and suggests keeping a sleep diary to bring to the appointment.
If this sounds like you, see a doctor or a sleep specialist before you change any settings, because late sleep can have other causes and working out which one you have is a clinician's job. That is also why there is no quiz in this guide.
Why Does Evening Light Matter for a Late Body Clock?
Light reaching your eyes is the main signal your body clock sets itself by, and light in the evening tends to push the clock later. If your clock already runs late, the evening is when extra light pushes it the wrong way.
Three studies on our science page explain why this matters. In 2000, Jamie Zeitzer and colleagues at Harvard Medical School gave healthy young volunteers a single evening light exposure in the early biological night (Journal of Physiology, PMID 10922269). People were highly responsive to the clock-delaying effect of light at that time, and, against the authors' own expectations, ordinary dim room light produced a large share of the effect of very bright light. Their conclusion was that even small changes in ordinary late-evening light can move the clock.
The colour of the light matters as well. Steven Lockley, George Brainard and Charles Czeisler compared 6.5 hours of pure 460 nm light, which is blue, against 555 nm light, which is green, at equal photon density (Journal of Clinical Endocrinology and Metabolism, 2003, PMID 12970330). The blue light produced a two-fold greater delay of the circadian clock. That result is why warmer light, which carries less of the short-wavelength end of the spectrum, comes up at all.
A 2019 systematic review by Leena Tähkämö, Timo Partonen and Anu-Katriina Pesonen in Chronobiology International pulled 128 studies together (PMID 30311830). It found that light in the evening, at night and in the morning all shifted the timing of the melatonin rhythm, and that even long red wavelengths could produce a resetting response. So a warmer screen is still light, and brightness matters as well as colour.
None of these studies was run on people with delayed sleep phase syndrome. They were mostly laboratory experiments on healthy volunteers, so applying them to a late clock is a reasonable inference, but it is still an inference.
What Did the Delayed Sleep Phase Glasses Trial Find?
In a small open-label trial of nine patients with delayed sleep phase disorder, wearing amber blue-blocking glasses in the evening for two weeks was followed by actigraphy-measured sleep onset about two hours earlier. It tested glasses, not a screen, and it was a small study without a control group.
The trial was run by Esaki and colleagues at Fujita Health University in Japan (Chronobiology International, 2016, PMID 27322730). Nine consecutive patients were asked to wear amber lenses from 9 p.m. until bedtime every evening for two weeks, and the team measured the timing of their evening melatonin rise and their sleep with a wrist-worn activity monitor, before and after. One patient stopped early to switch to drug therapy.
Sleep onset measured by the wrist monitor moved about two hours earlier, and that change was statistically significant. The shift in melatonin timing, which is the more direct measure of the body clock, was not statistically significant. The authors wrote that amber lenses may be an effective and safe option and that the findings need repeating in a larger group with controlled observations.
So it is an interesting early result in the right population, and it is also nine people, open-label, with glasses.
Ostrin et al. (2017) found blue-blocking lenses raised nocturnal melatonin ~58% in healthy adults, who also slept ~24 minutes longer (PMID 28656675). Participants wore amber glasses in the hours before bedtime for two weeks.
One Example Warmth Setup for a Night Owl's Mac
This is one example of how you might step a Mac screen warmer and dimmer in the evening. The numbers are untested placeholders you can change. The idea is to count back from the time you plan to sleep tonight, and to let the screen get warmer and dimmer as that time gets closer.
If a clinician has given you a target sleep time, count back from that one. Whether and how to move your sleep time is a clinical question, so this setup does not try to answer it.
| Time before you plan to sleep | Example colour temperature | Example brightness |
|---|---|---|
| Daytime and early evening | Neutral, e.g. ordinary daytime white or a touch warmer | Whatever is comfortable |
| About three hours before | e.g. a warm white | Down a little |
| About one hour before | e.g. a deep orange, or any warmth you can read at | Lower |
| If you are still working past that time | e.g. a deep red | As low as you can read at |
Warming and dimming change two different things, and it helps to keep them apart. A warmer setting changes the colour, so there is less short-wavelength light at the same brightness, while lower brightness cuts the total amount of light, and doing both lowers each. Our guide to colour temperature explains the scale, and our two-hour evening routine walks through a similar ladder for an ordinary bedtime.
For reference, Apple's Night Shift stops at a warm white at its warmest, which matches the first example step and none of the warmer ones. Our guide on how to make Mac night mode darker covers what a Mac can do below that.
The screen is also only one lamp in the room. Overhead lights, a phone and a television all add light in the same hours, so a warm Mac in a brightly lit room still leaves you in a lot of light.
What a Screen Setting Cannot Do
A warmer, dimmer screen changes the light your Mac gives off and nothing else. It is not a treatment for delayed sleep phase syndrome and it does not replace anything a clinician may use.
Sleep doctors have clinical tools for this condition. The AASM's Sleep Education page describes carefully timed low-dose melatonin, with dose and timing to be discussed with a sleep doctor, and bright light therapy, which it describes as a proven way of shifting circadian rhythms whose specific use for delayed sleep phase has not been well validated. Chronotherapy, a supervised shift of the sleep schedule, is another approach clinicians describe. A clinician may use any of these with you, and this guide is not advice on them, so please do not start a melatonin supplement or a light box because a blog about screens mentioned it.
Morning light comes up in the same conversation because the Tähkämö review found that morning light also shifts the clock, just as evening light does. How much light, when, and for how long is exactly the kind of thing a clinician tailors, which is why this guide does not give you a morning plan.
If your late sleep is costing you work, school, driving safety or your mood, book an appointment instead of trying harder with settings.
How to Set This Up in Sundown
Sundown moves your Mac's colour from ordinary daytime white down to a deep red, in small steps, with its own brightness control.
You can set it by hand, opening Sundown from the menu bar at each step and lowering the brightness as the evening goes on, or build a custom schedule by time of day around the time you plan to sleep. Sundown moves your display's white point to the colour temperature you choose, down to a warmth Night Shift cannot reach.
Delayed Sleep Phase and Your Mac Screen: Common Questions
Can blue light make delayed sleep phase worse?
Lab studies in healthy volunteers found that evening light delays the body clock, blue light most strongly, and whether that applies to your sleep is a question for a clinician.
Is a warm screen enough?
No. A warm screen gives off less short-wavelength light at the same brightness and a dim one gives off less light overall, but neither is a treatment. Delayed sleep phase is a medical condition, so a doctor or sleep specialist should guide what you do about it.
When should a night owl stop screens?
One example, from the ladder above, is to start warming and dimming about three hours before you plan to sleep.
If your evenings run late on a Mac, try Sundown and set the screen by the number, and take the sleep question itself to a clinician.
