That screen will default to dim when you turn the ignition key - the headlights come on, and the unit goes to nighttime mode. You'll have to manually change the brightness per bclemens post above. I have a top of the line Kenwood in one of my cars, and have the same problem with glare; this is common to any touch-screen unit. You can make a shield to fit into the space between radio and the surround that will keep sun off the screen. I've seen them advertised commercially, but don't know if they'll fit every radio, but if it's a standard double DIN they should work.
Ed (N4RWU) & Becky Taylor
Mistie (Walks 4-down)