The most widely recommended guideline is to stop using screens at least one hour before bed. That window gives your brain enough time to ramp up its natural sleep signals after the stimulation of a backlit display. But the reason behind that number, and whether it’s enough for everyone, depends on what you’re using, how bright it is, and what you’re doing on it.
Why Screens Interfere With Sleep
Your brain uses light as its primary cue for deciding when to be awake and when to sleep. As evening approaches, a gland in your brain begins releasing melatonin, the hormone that makes you feel drowsy and prepares your body for rest. Light suppresses that release, and screens are particularly effective at doing so because they emit concentrated short-wavelength light in the 446 to 477 nanometer range. This is the blue portion of the visible spectrum, and it triggers the strongest melatonin-suppressing response of any wavelength.
The effect is dose-dependent: the brighter the screen and the longer you stare at it, the more melatonin gets suppressed. Research on room lighting found that even moderate indoor light around 100 lux (dimmer than a typical office) produced half the maximum possible melatonin suppression. At around 200 lux, seven out of eight study participants showed suppression rates between 51% and 88%. A phone or tablet held close to your face can easily reach these levels, especially in a dark room where your pupils are wide open.
What Happens When You Read on a Screen Before Bed
A well-known experiment published in the Proceedings of the National Academy of Sciences compared people who read on a light-emitting e-reader for several hours before bed with people who read a printed book. The results were striking. The e-reader group had their evening melatonin levels suppressed by about 55%, while the print group showed no suppression at all. The e-reader group also took nearly 10 minutes longer to fall asleep (about 26 minutes versus 16 minutes), got roughly 12 fewer minutes of REM sleep per night, and felt noticeably groggier the next morning.
Perhaps the most significant finding was that the e-reader shifted the body’s internal clock by more than 90 minutes. Melatonin onset, the point in the evening when the hormone first starts rising, occurred at 10:31 PM in the e-reader group compared to 9:01 PM in the print-book group. That kind of shift doesn’t just affect one night. It pushes your whole sleep schedule later, making it harder to fall asleep at your usual time and harder to wake up feeling rested.
Do Night Mode and Blue Light Filters Help?
Most phones and tablets now include a “night mode” or “night shift” setting that tints the screen amber to reduce blue light output. The logic is sound, since blue wavelengths are the biggest melatonin suppressors. In practice, though, the evidence for these filters is underwhelming.
A study evaluating blue light filter apps found no statistically significant improvement in sleep quality among users (the statistical test returned a p-value of 0.925, essentially no difference at all). One reason is that blue light is only part of the problem. Screens also emit other wavelengths that suppress melatonin, just less efficiently. And beyond light itself, the mental stimulation of scrolling social media, reading news, or watching videos keeps your brain in an alert state that works against sleep regardless of the screen’s color temperature.
Research on smartphone use with and without blue light filters did find some differences in next-morning cortisol patterns, suggesting the filters aren’t completely useless at a hormonal level. But the overall takeaway from the literature is clear: dimming and filtering help at the margins, but they don’t replace putting the device down.
One Hour Is the Minimum
Both the American Academy of Pediatrics and Canadian sleep health guidelines recommend eliminating screen use at least one hour before bed. This applies to children and adults alike. One hour gives your melatonin production time to recover from the suppression caused by screen light, though for people who are particularly sensitive to light or who struggle with falling asleep, a longer buffer of 90 minutes to two hours may work better.
Keep in mind that “one hour before bed” means one hour before you intend to fall asleep, not one hour before you get into bed. If you typically lie awake for 15 or 20 minutes, adjust accordingly.
How to Make the Screen-Free Window Easier
The biggest barrier to a screen-free hour isn’t knowledge. It’s habit. A few practical adjustments can make it more sustainable.
- Lower your ambient lighting too. Your phone isn’t the only source of melatonin-suppressing light. Overhead room lights at typical brightness (200 to 500 lux) cause significant suppression on their own. Switching to dim lamps or warm-toned bulbs in the hour before bed amplifies the benefit of putting your phone away.
- Move screens out of the bedroom. Charging your phone in another room removes the temptation to check it after lights out and eliminates notification-driven wake-ups during the night.
- Replace the habit, don’t just remove it. Reading a physical book, listening to a podcast or audiobook with the screen off, light stretching, or conversation all fill the same wind-down role without the light exposure.
- If you must use a screen, reduce brightness and increase distance. Light intensity drops sharply with distance, so holding a device at arm’s length rather than close to your face meaningfully reduces the amount of light reaching your eyes. Combine that with minimum brightness and a blue light filter for the least-bad option.
Not All Screens Are Equal
E-ink devices like basic Kindles (without a front light) reflect ambient light rather than emitting their own, so they behave more like paper than like a tablet. If your evening screen time is mostly reading, switching to a non-backlit e-reader lets you keep the habit without the melatonin hit. Front-lit e-ink readers fall somewhere in between: they emit less light than a tablet, but they’re not neutral.
Televisions, watched from across a room, deliver far less light to your eyes than a phone held 12 inches from your face. That doesn’t make late-night TV harmless for sleep, since the content itself can be stimulating, but in terms of raw light exposure, a dim TV at 10 feet is less disruptive than a bright phone at arm’s length. The worst combination for sleep is a bright, close screen in an otherwise dark room, because your dilated pupils let in the maximum amount of light.