I'd like to see pics at various downrange distances, showing how bright it becomes for people at that range, and how looking towards the light appears.
Telescopes & binoculars lose a lot of brightness (proportional to the magnification and also the quality of the optics) so I don't suppose there is a way to take photos showing how bright the target would be when looking through optics, but pics showing the brightness at that range might give a clue.
I *think* that there are too many variables to be able to take representative pictures. Camera settings, f stop and time, film speed, etc, can make huge differences. Also, is the observer's eye, night adjusted? Is the scene already illuminated? And if so, at what level, 5 lumens, 650 lumens?
Certainly, someone smarter than me can do calculations maybe even logarithmic calcs to demonstrate what one may expect to see.
For example, a person with dark adjusted eyes, may be able to see fairly well with one to three lumens. But in full daylight, an additional 1-3 lumens would not be noticeable. Flashlight beam distances are calculated to give an increase of 0.25 lumens to the target. That is purported to be moon-light. Now cut that distance in half, and you'll have 4 times as much light.
It's been stated that lumens must be doubled for the human eye to be able to distinguish the difference.
You might experiment with a light that you have, with a known cd, and pace off 100 yards or so, and see how much more you can see with it on, vs with it off. Then pace off 50 yards, and note the difference. Consider doing the same experiment at different times of the evening/night, or with different ambient lighting conditions.
Have fun!