Using a tablet or computer in the late evening disrupts the body's melatonin production [...] Melatonin tells your body that it is night, helping to make you sleepy. If you delay that signal, Figueiro says, you could delay sleep.[...] The dose of light is important, Figueiro says; the brightness and exposure time, as well as the wavelength, determine whether it affects melatonin. Light in the blue-and-white range emitted by today's tablets can do the trick—as can laptops and desktop computers, which emit even more of the disrupting light but are usually positioned farther from the eyes, which ameliorates the light's effects. [...]"