Anything lower produces less-crisp text and images. Screen quality: We gave preference to devices with a pixel density of 300 dots per inch, the highest available in any ebook reader and what most models offer.Because this feature is so prevalent, we didn’t test any readers without it. Unlike tablets such as the iPad, ebook readers use a side-lighting system that provides a glow across the screen, rather than from behind it. Built-in lighting: Most e-readers provide their own light for reading in dark environments.