[graeme]

What's the difference between 99.9% effective and 100%? I velcroed my blind to my window and turned off any light sources. J I can see a very, very, very faint glow in a couple spots around the blind, and if I look sideways I can catch a tiny bit under the door. Is there any benefit to going further?

[solarmist]

Probably not. As pointed out above in the open you'll usually have stars which, away from light sources, give off a fair amount of light on their own.

[AndrewKemendo]

That is a personal preference in my opinion and largely rests on how much you think your sleep would be impacted by those sources.