How Screen Color Temperature Affects Melatonin Production at Night

Melatonin is the hormone that rises in the evening and helps your body prepare for sleep. Light, especially bright light in the evening, slows that rise. Screens are a source of light, which is why people worry about using them at night.

How light affects melatonin

The eye contains special light-sensitive cells, separate from the ones you see with, that report light levels to your body clock. They're most sensitive to blue light. When they detect bright light in the evening, they signal the brain to hold back melatonin, telling your body it's still daytime.

What studies have found

• A 2015 Harvard study published in PNAS compared reading on a light-emitting e-reader with reading a printed book before bed. With the e-reader, people took longer to fall asleep, had less evening melatonin, and felt less alert the next morning.
• A 2021 Brigham Young University study found that the iPhone's Night Shift mode alone didn't lead to better sleep compared with not using it. People who got about seven hours of sleep slept better when they didn't use their phones before bed at all.

Color vs brightness

Warm screen modes reduce blue light, but brightness and how long you look also matter. A dim screen held further away gives far less light than a bright one close to your face, whatever the color. Many researchers now suggest focusing on overall light in the evening, not only on color.

What's in your control

• Lower brightness in the evening, on screens and room lights.
• Warm the color: Night Light on Windows, Night Shift on Mac and iPhone, and Android's equivalent.
• Use dark pages: mostly white websites give off a lot of light. Modern Dark Mode darkens websites, with a brightness slider.
• Warm websites: Blue Light Filter adds an amber layer over web pages, with adjustable intensity and warmth and a schedule (8 pm to 7 am by default). It only affects web pages, so use your system's night setting too.
• Stop screens earlier: 30 to 60 minutes before bed, if you can.
• Get bright light in the morning, which helps set your body clock.

Content matters too

Exciting games, work emails and stressful news keep you awake regardless of screen color. A calm activity matters as much as a warm screen.

When to get help

If you regularly can't fall asleep or wake unrefreshed, talk to a doctor. Sleep problems have many causes beyond screens. See whether blue light affects sleep and Night Shift vs a filter extension.