"Stop using your phone before bed" is probably the most repeated piece of sleep advice there is. It isn't wrong, exactly — but for most people struggling with poor sleep, it is aimed at the wrong target. The evidence on blue light is real, but it's a much smaller part of the picture than popular advice suggests, and treating it as the whole explanation often means the actual cause goes unaddressed.
Blue light is real, but it's not the main event
Blue light does suppress the release of melatonin, the hormone that signals to the body that it's time to feel drowsy, and evening light exposure genuinely can push your body clock later. That much is well established. What gets left out of the popular version of this story is that light exposure across the whole day — not just the blue wavelength from a phone in the last hour before bed — is what most strongly shapes your circadian rhythm, and that phone use affects sleep through more than one channel at once.
What's actually keeping people up
In clinical practice, the pattern behind most chronic sleep difficulty looks less like "too much blue light" and more like: an irregular sleep and wake schedule that shifts the body clock around day to day; racing thoughts, worry, or unresolved stress that keep the mind active even lying still in the dark; scrolling emotionally engaging or stressful content — news, work email, arguments — which activates the same alertness system discussed in our article on anxiety, regardless of screen brightness; caffeine taken later in the day than realised; and simply going to bed later than the body is used to because a phone made "just five more minutes" easy to extend indefinitely. The phone is often a genuine contributor to poor sleep — just usually because of what it's doing to your mind and your bedtime, not because of the light itself.
The treatment with the strongest evidence
For people with persistent insomnia — difficulty falling asleep, staying asleep, or waking too early, several nights a week for weeks or longer — the American Academy of Sleep Medicine's clinical guidelines give a strong recommendation to cognitive behavioural therapy for insomnia, known as CBT-I, as the first-line treatment. CBT-I combines education about sleep regulation with specific behavioural techniques, such as stimulus control and sleep restriction therapy, typically over four to eight sessions. The guidelines are explicit that medication should generally be reserved for people who are unable to engage in CBT-I, who still have symptoms afterward, or who need short-term support alongside it — not as the default first step.
A more useful way to think about your phone at night
Rather than treating "no screens after 9pm" as a rule to feel guilty about breaking, it's more useful to ask what you're actually doing on your phone before bed, and whether your sleep and wake times are consistent from day to day. Reducing genuinely stimulating or stressful phone use in the hour before bed, and protecting a consistent wake-up time even on weekends, will generally do far more for your sleep than blue-light filters alone. If sleep difficulty has been persistent rather than occasional, it's worth having it properly assessed rather than treating it as something to fix alone with an app setting.
Sources: Sleep Foundation, overview of blue light and sleep; American Academy of Sleep Medicine, clinical practice guideline on behavioural and psychological treatments for chronic insomnia disorder in adults.