The phrase "brightness range" refers to the difference in light intensity between the darkest and brightest parts of an image or scene. Full definition
Notion Ink claims the screen has a wide brightness range but there is no ambient light sensor to adjust brightness automatically (and there are no brightness shortcuts on the keyboard, for some reason), so you'll be blinded if you turn on the Cain at night after having used it during the day. (gadgets.ndtv.com)
The one point where the ZenFone 2's display comes up unnecessarily short is in brightness range, where it gets a bit washed out at its highest brightness — which still isn't all that bright — but just as importantly doesn't get dim enough in dark environments. (androidcentral.com)
Pocketbook has just released a new technical document that takes a look at high frequency ripples throughout the entire brightness range. (goodereader.com)