@ginggs + @Schturman: thanks for the idea about the autobrightness, but I'm afraid that in the old waze code there is no such feature and in addition to that nokia did not add way in qmobility (as far as i could find) to set the brightness level manually (or disable autobrightness).
Maybe after I'll finish rewriting the UI layer I'll reconsider, but in the meanwhile i still have a lot of other todos