Maximum number of hours like that appears to be ~166 a year, for a completely clear sky. About half of this time clouds will obscure the Moon, for regions where majority of mankind lives.

As the average length of such night, when natural vertical illuminance due to Sun is several centilux at most, is over 9 h, the proportion of almost deep night time, when Moon gives 0.1 lx or more, is below 3 %.

Strictly speaking, this concern direct illuminance. However, even total vertical illuminance including dispersed moonlight would give similar results, as most windows don't have an unobstructed sky view from them.

	Name	Last modified	Size	Description
	Parent Directory		-
	-9_30.txt	2012-09-19 13:02	26K
	-9_50.txt	2012-09-19 12:48	26K
	-9_60.txt	2012-09-19 13:00	26K
	2012_0_50.txt	2012-09-19 12:40	11K
	2012_30_40.txt	2012-09-19 12:38	9.5K
	2012_30_49.2.txt	2012-09-19 12:39	11K
	2012_30_60.txt	2012-09-19 12:35	9.8K
	example_night_length.txt	2012-09-19 13:01	42
	naut_40.txt	2012-09-19 13:13	26K
	naut_50.txt	2012-09-19 12:47	26K
	naut_60.txt	2012-09-19 13:03	26K
	win_dil.sh	2012-09-19 13:00	244
	win_dil.txt	2012-09-19 13:00	244