There is no single cut-off time that fits every screen and every person. A phone held close to the face while scrolling needs a stronger boundary than a dim TV watched passively across the room.
As a practical rule, protect the final thirty to sixty minutes from active, close-range screen use. If work or family life makes that impossible, at least move the most stimulating task earlier and make the room light lower and warmer.
The goal is not purity. It is making the last part of the evening less bright, less close and less interactive.
Where this guide fits
This page sits in the screen-boundary cluster. It treats blue light as one part of a wider evening exposure pattern: brightness, distance, content, room light and whether the device keeps the brain in work or scrolling mode.
Practical inputs to compare: Measure hours after 7pm, device type, distance from the face, room lighting and the latest realistic stop time.
How to read the result: Treat these inputs as a bedroom pattern, not a one-night verdict. If the same cue shows up on several ordinary nights, the next change is easier to choose and easier to reverse if it does not help.
- blue light
- screen brightness
- phone distance
- night mode
- active scrolling
- screen cut-off
- close-range device use
- bedside charging
Keep it narrow: Do not change lamp type, screen cut-off, bedding, window opening and wake time on the same night. Hold the other cues steady so the page stays linked to one room question.
What to try tonight
- Choose one cue: light, screen boundary, temperature, humidity or airflow.
- Keep the sleep target and morning note simple.
- Repeat the change before judging it.
