[mike463]

The science: - dilated pupils make focusing harder. - Higher contrast makes reading easier.

So: Reading on a kindle with a bright light closes down your pupils and makes it easier for your eyes to focus on the words without using the muscles in your eyes for focusing. This is especially important for readers over 40 who are starting to get farsighted.

An iPad has a glossy screen, which limits the contrast. (comparing signal to noise, well the reflection is all noise)

An e-ink screen has very high brightness and contrast, even (epecially) in bright sunlight.

I'm not saying it's impossible to read with the iPad or iPhone or a computer. Just realize it may take more unconscious effort for some people.

I have both an iPad and a Kindle and love both.