Swipe down from the top of the Echo screen for quick access to Settings and the Do Not Disturb (DND) function (or say "Alexa, do not disturb"). Using DND dims everything for a while, and it won't light up when you move in front of it.
More importantly, there is a slider for setting the screen brightness on a level of one to 10. This is the only way to set it to the max. If you say "Alexa, set brightness to 10," she'll just tell you to swipe down on the screen.
Source : pcmag.com