When you’re using any electronic device (TV, tablet, computer, or smartphone), you’re exposing yourself to blue light. Blue light tricks your brain into thinking it’s still daytime, halting the melatonin production and making it harder to fall asleep. Try to avoid any electronic devices for an hour or two before bed. If you need to scroll through your phone, use your night settings or the apps that filter out blue light.
Article source: https://www.huffingtonpost.co.uk/entry/this-how-much-sleep-you-actually-need-depending-on-age_uk_6411af84e4b00c3e607111a8