A few years back I was testing a set of night vision goggles we were reviewing. We picked a campsite that was really dark at night. The walking path by the sites, however, was clearly marked and had lights spaced an equal distance apart.
I was sitting in a camp chair with these goggles on, in as close to pitch black as I could get. I could see everything like it was daytime.
During the day we had seen a couple of people cut through the site. They knew we were there, but didn't care.
As I was looking around, I see this same guy turn off the path and come walking through the site. He didn't see me, until I said "Hi there. I'd stop walking right about now". Scared the you-know-what out of him. He couldn't see me. He said he was just walking through, and I explained that he was about to fall into the fire pit, and that I strongly recommended that he stick to the well marked and lit walking path. He turned around, and didn't cut through the site again. I think he was finally able to see me, or at least the really faint red glow of the IR illuminator that I had turned on.
For the record - those Bushnell Binocular Night Vision goggles worked quite well.