"Maximum brightness" refers to the highest level or intensity of light that an object or source can emit. It means that the light is at its brightest point or at its peak luminosity. Full definition
Turn on the lights using a light switch and the bulbs will come on full white at maximum brightness regardless of the settings in the app. (pocket-lint.com)
Quite understandable that, given we are playing high - end graphics on a full HD display with maximum brightness. (phoneradar.com)
Image quality is clear and sharp, with a high maximum brightness level. (zdnet.com)