WANT A GOOD NIGHT’S SLEEP? READ A BOOK. But not an iPad:

RPI found that looking at a backlit screen, like those on iPads and other tablets, can lead to sleeplessness.

“Our study shows that a two-hour exposure to light from self-luminous electronic displays can suppress melatonin by about 22 percent,” said Mariana Figueiro, the lead researcher. “Stimulating the human circadian system to this level may affect sleep in those using the devices prior to bedtime.”

If this rather small study holds up, I suppose the e-ink screens on traditional (non-Fire) Kindles will benefit.