I found this over on the L.A. Times blog. It's true, by the way. The LCD screen is like looking into a flashlight, and it can mess up your sleep pattern. You really should set the iPad aside an hour or more before going to sleep.
...But staring at the screen before bed could leave you lying awake. That's because direct exposure to such abnormal light sources inhibits the body's secretion of melatonin, say several sleep experts.
If you've watched any late-night TV, you've no doubt heard the term thrown around in commercials for sleeping pills. Melatonin signals are sent through the brain as a response to darkness, telling the body to prepare to shut down for the night.
Light-emitting devices, including cellphones and yep, the iPad, tell the brain to stay alert. Because users hold those devices so close to their face, staring directly into the light, the effect is amplified compared with, say, a TV across the room or a bedside lamp, said Frisca Yan-Go, director of the UCLA Sleep Disorders Center in Santa Monica.