The OP didn’t specify that his neighbors were naked when he was looking. In my state, to be illegal the victim has to be in a place where they have a reasonable expectation of privacy, and the suspect has to be looking for the purposes of sexual gratification.
So, just looking at your neighbor eating dinner? Not a crime.
Looking at your neighbor getting out of the shower while you’re spanking the monkey? Probably illegal, but you could have a defense that they had no expectation of privacy when they leave the blinds open.