ios 4 dark screen in landscape mode

[rg2k]

Does anyone have the same problem: while outside in daylight, rotating my iPhone 3GS from portrait to landscape mode causes the screen to go considerably dark to a degree that I can not recognize anything on it. Going to the settings and bringing up the brightness doesn't change a thing and the screen remains dark. The only way to get back to a screen brightness under which I can see anything on the screen is to rotate it back to portrait mode. The really strange thing about this behavior is that it only happens in outside daylight. When I am at home I can rotate the screen without getting the dark screen. Going outside again - dark screen again. Any ideas? Thanks