There is strong clinical evidence that blue-toned light, such as "daylight" LEDs, and especially the UV radiation from white LEDs in phone and tablet backlights, triggers the brain into thinking it is daytime, even late in the evening when it is dark outside. Doing something like checking your email or watching YouTube videos while lying in bed right before sleep is the worst-case scenario.
An easy test is to turn off / blacken of all the screens around you for one hour before sleep. If you really want to read before sleep, read something not work-related, like an actual book, with an incandescent light.
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