private void setAlpha(int delta){
		int swing = 0;
		if (hours >= 20 || hours < 6){
			alpha = max;
		}
		else if (hours >= 6 && hours <= 8){
			swing = -1;
		}
		else if (hours >= 18 && hours < 20){
			swing = 1;	
		}
		else{
			alpha = min;
		}
		alpha += swing * rate * delta / 1000.0;
	}