The study, reported by Scientific American, showed that two hours of iPad use at maximum brightness was enough to suppress people's normal nighttime release of melatonin, a key hormone in the body's clock, or circadian system.
Melatonin tells your body that it’s night, and helps make you sleepy. Delaying that signal could delay your sleep.
Researcher Mariana Figueiro says the dose of light is important. Brightness and exposure time, as well as the wavelength, determine whether it affects melatonin. The research, which included test subjects, showed that light in the blue-and-white range emitted by today's tablets can affect the release of melatonin.
Laptops and desktop computers, which emit even more of the disrupting light, can as well, but they are typically positioned farther from the eyes, which lessens the light's effects.
Figueiro told SA she hopes manufacturers will “get creative” with tomorrow's tablets, making them more “circadian friendly,” perhaps even switching to white text on a black screen at night to minimize the light dose.