Recently I saw a commercial for Centrum that claims you can see the light of a single candle from ten miles away.
I was skeptical, but a trip to the internet claims that not only is that true, but you could actually see it from 30 miles away. Most of what I found simply repeated that claim (some had varying numbers, but in the 10-30 range) with nothing to back it up. One page detailed it a bit better, by giving some basic math based on the number of photons it takes to register a light in the eye. However, they still don't link to anything solid IMO.
Obviously these numbers assume line-of-sight, since any distance over a few miles would be blocked by the horizon if on the Earth's surface. I also assume that "the light from a single candle" means roughly one candela, but nobody cares enough to clarify that I could find.
The main reason I'm skeptical is because I've seen ceremonial (small) bonfires on mountains a few miles away. Even with a much larger light and closer distance, they're pretty faint.
Is there any empirical evidence that human eyes can see a light source that small from that distance? This seems like a simple thing for people to test.