-viewing conditions. will you be watching in the evening with a sunset? or only by moonlight?
i tried my old projector(rated at 1600lumens, but after a few years of use, and comparing it to the jvc replacement, i'm guessing it was more around 500 lumens actual) on the white exterior wall of my house. the picture was barely visible until about an hour after sunset. then it was ok, not stellar, but not bad either. thing is, that was projecting about 2m wide, haha. so i'd GUESS you'd be looking at about 2000lumens minimum
regulations would obviously depend on your local laws, can't help there.
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