ok i just found a solution with the help of the manual, but a bit with my brain too.
ambient
Light value (0..100, default 50) added to everything which is seen in this view. Can be used to change the overall brightness of the map.
Range:
0 .. 100 (default: 50)
Type:
var
Example:
camera.ambient = 100; // maximum brightness
tried camera.ambient = 100; => bright++
tried camera.ambient = 0; => change nothing
tried camera.ambient = -100; =>bright-- = what i needed
luck that i tried with -100, wonder why in the manual, there is "0 .. 100 (default: 50) for range"
