from the LISNEWS feed today http://lisnews.org/node/36824/ :
May 17, 2010 from CNN:
"Unlike paper books or e-book readers like the Amazon Kindle, which does not emit its own light, the iPad's screen shines light directly into the reader's eyes from a relatively close distance. That makes the iPad and laptops more likely to disrupt sleep patterns than, say, a television sitting across the bedroom or a lamp that illuminates a paper book, both of which shoot far less light straight into the eye, researchers said."
...Although you should read the rest of the story and see the video from CNN, because some people don't agree...go to http://www.cnn.com/2010/TECH/05/13/sleep.gadgets.ipad/