The great thing about the Kindle screen is that it doesn't use light to light up the pixels, but rather ink, or 'e-ink' as Amazon call it (hence why the screens are called 'e-ink' screens). The ink is then simply arranged on the screen where the pixels are and this creates the image.
The reason this is so good is that it doesn't require any light in order to light up – and that means that there are no changes in contrast that your eyes have to adjust to. At the same time there's no glass and the material of the screen is different and less reflective.