The script computes direct vertical illuminances by the Moon and filters out those, which are 0.10 lx at least. Its parameters are azimuth from the south and latitude.

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.

a working directory by Jenik Hollan
[ICO]NameLast modifiedSizeDescription

[PARENTDIR]Parent Directory  -  
[TXT]-9_30.txt2012-09-19 13:02 26K 
[TXT]-9_50.txt2012-09-19 12:48 26K 
[TXT]-9_60.txt2012-09-19 13:00 26K 
[TXT]2012_0_50.txt2012-09-19 12:40 11K 
[TXT]2012_30_40.txt2012-09-19 12:38 9.5K 
[TXT]2012_30_49.2.txt2012-09-19 12:39 11K 
[TXT]2012_30_60.txt2012-09-19 12:35 9.8K 
[TXT]example_night_length.txt2012-09-19 13:01 42  
[TXT]naut_40.txt2012-09-19 13:13 26K 
[TXT]naut_50.txt2012-09-19 12:47 26K 
[TXT]naut_60.txt2012-09-19 13:03 26K 
[TXT]win_dil.sh2012-09-19 13:00 244  
[TXT]win_dil.txt2012-09-19 13:00 244  

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