Light disturbance during your dark period... How does it happen?

I was just curious about something because I am building a new cab for flowering and I've always gone with the idea that absolutely noooo light should reach my girls during their dark period. So I got to thinking... how much light does it take to actually disrupt your plants at night? Since the moon can reflect a pretty good amount of light at times outdoors.. what type of light and how much of it and so on is acceptable for indoors?

Hopefully I worded that properly, its late and I'm a little disoriented right now. I'm sure its always best to go for no light at all during darkness periods but I was just curious as to how that works with the difference of indoor/outdoor lighting.

Anything under ~ 0.5 Lux will not disturb your plants.

I grew a plant about 10 years ago in a cupboard when I really didn't know what I was doing. I used to leave the cupboard door open sometimes during dark periods thinking it might help my plant to 'breath' so lighting from my lounge and also early morning light used to spill in to my cupboard at random times. The grow was quite slow under weak fluoro tubes but it gave me great results.

I found this...

http://boards.cannabis.com/growing-i...ark-cycle.html