How Kindle’s Paperwhite Technology Works
The Kindle Paperwhite uses a unique lighting system to illuminate its electronic ink display. Rather than using a backlight as on LCD-based tablets, the Paperwhite uses a transparent light guide that directs light from four edge-mounted LEDs down toward the surface of the display. See how it all works!
Source: http://www.nytimes.com/interactive/2012/12/26/technology/light-reading.html?ref=technology