NavList:

Antoine, you wrote of naval aviator (French and USN) night vision requirements:
"Under the darkest night, being able to detect / spot when a smoker inhales the smoke of his cigarette, i.e. the moment when his cigarette is "glowing" red.
By the way, I forgot the most important data ... from the "Fighter Pilot Candidate" Observer the "target smoker" is assumed to be a distance  ... of 20 km (11 NM, 12 SM)."

That's interesting! And back in the smoking era, it was probably a great choice for a "standard candle". I'm a bit surprised by the implied brightness though...

Suppose we start with a cigarette (in the middle of a "drag") at 20km distance, and let's suppose its apparent magnitude on the astronomers' magnitude scale is 6.5. That's faint and right at the limit of what people with good night vision (fully dark-adapted) can see. Now bring the light source closer by a factor of 10 to 2km distance. Applying the inverse-square law, that makes this cigarette brighter by a factor of 100 which is equivalent to 5 magnitudes brighter, so that gets us to magnitude 1.5. Repeat that process three times. At 200m distance, the apparent magnitude would be -3.5. At 20m, magnitude -8.5. And at 2m distance (about 6.6 feet) that would be magnitude -13.5. That's somewhat brighter than the Full Moon. I could see a candle flame or a (recently) lit match being that bright at short range, but do cigarettes, even when drawing a lot of air, get there? I need to find a smoker and test this out! :) 

Regardless, it's still amazing to consider: people with good vision can see light sources similar to a lit match from 20 kilometers distance at night.

Frank Reed