Blue Light Before Bed: Why Your Phone Is Making You More Tired, Not Less

Min Sung Kim  ‘26  • Feb 5, 2024

Most students think watching TikToks or scrolling Instagram at night helps them “wind down.” But biologically, it’s probably the biggest reason so many of us wake up exhausted.

Here is the science in one sentence: blue light from screens blocks your melatonin production.

Melatonin is the hormone that tells your brain it’s nighttime. It starts rising naturally around 9–11pm. When blue light hits your eyes, it delays that rise. This isn’t a tiny effect. Studies show even 30 minutes of bright screen exposure can push back your sleepiness by 1–2 hours.

And teenagers are more vulnerable to this delay than adults.

So even if you go to bed at midnight, your brain might not start the “sleep process” until almost 2am. That’s why you wake up feeling not “underslept,” but more like your sleep wasn’t “real sleep.”

This is also why so many students drink caffeine in the morning, which then disrupts the cycle even more.

One simple habit actually helps: never look up at your screen in bed. Keep the phone below eye level. The most light-sensitive cells for melatonin suppression sit at the bottom of your retina. The higher you hold your phone, the more direct blue light stimulation hits those cells.

Scrolling isn’t harmless. It is literally shifting your biological clock later each night.

The result is a kind of sleep jet lag—without ever switching time zones.