All LCD displays will do that when they get overheated. They do not have to be in direct sunlight to fade, just get really warm.
It is not really a brightness thing, more of a contrast problem. The contrast will go back to normal after the display cools down.
Brian
My display screen went to about 1/2 brightness. It's happened a couple of times once it went back during a ride and the other time it went back to normal after stoping for a rest.
Anyone else see this? Or is it like the flashing F1 curse?
2010 C14