But a spot of light doesn't stay the same. The light spreads, and so the spot of light that is 2' wide at 50' will be 20' wide at 500'. It does not get apparently smaller to the eye. It stays the same.
Well, that depends on the beam angle of the light vs the apparent convergence of the boundaries at the distances in question.
I know in practice that the hot spot is typically small, and, the last vestiges of it that can reach the rated cd, etc, are not that much larger, as they were from the central part of the beam to start with.
So, sure, as we both agree, the spot does get larger with distance, but, it also gets dimmer, and the brightest spot of the hot spot, the part of the beam that can eventually hit the maximum range...will become harder to see at great distances.
If I use the 1.4º beam angle for the DEFT-X or TN31mb, longer range lights...and say that a 1,000 meters a 1.4º beam should be ~ 25.2 meters across.
At a km, 25 meters doesn't look as large as it does right in front of you, its a proportionally smaller part of your field of view.
If I extrapolate a bit, and call it 10,000 M (10 km), how large an object can you resolve at 10 km?
If using a beam of light to see it, that light is getting dimmer as it gets further away...so its harder to tell two objects from one object as you get further away...and its harder to resolve them with less light.
So the larger albeit dimmer beam is still far enough away that the objects you are trying to resolve appear as a smaller and smaller proportion of your field of view.
So, to put it another way (Maybe I was being confusing?) -
I have to tell if there are one or two men approaching, and whether they are armed.
The further away they are, the harder it is to resolve details such as if they are armed, or, even if I see one guy, or two close together, etc.
If they are right in front of me, I can see all the details clearly, and, they might be 50% of my total FOV.
If they are a bit further away, they might drop to 10%, 1% or even less of my FOV, and I will not have the resolution to make out details.
If my light beam hits them while they are close enough to not have their images merge/details blur...as in there's enough lux on target to resolve the details, it all works.
If they go 2x further away, there's 1/4 the lux, AND they are en even smaller proportion of my FOV, and, I might have needed more lux, not less, to help make out those details.
So, while the beam itself is traveling along regardless of what we need to see...the OBJECTS are getting smaller and smaller to our point of view...as with distance away, the apparent/resolvable distance between objects decreases (They look smaller to us when they are further away).
Now, your BRAIN will use context clues to try and "correct" this...so you will "know" that the man 500 M away is not really just a really small man...but, its can't SEE that the man is the same size, it SEES the man as smaller, and then, internally, says, well, he's a man, so he's probably ~ 5-6' tall, etc.
We know this happens, because we can take a really small man, put him a short distance away, and we will see him as further away.
We can draw lines on the ground that splay outwards, or inwards, but which LOOK like they are parallel when viewed on end....as our brain simply assumes they are like the RR tracks, and we PERCEIVE the splayed lines as ending closer to us, and the converging lines as ending further from us, etc.
So, objects do appear smaller when they are further away, as they are a smaller proportion of our field of view...but we mentally tend to adjust this to compensate. The compensation does NOT add resolution though...it merely tricks us into a correction for size/distance, a correction, at night, that can be severely fooled.
In boating for example, if you think a marker light is 12" across, and you see a marker light, you will run into it if it were actually a 3" marker light that was a lot closer than you thought....as, at night, you lose a lot of depth of field and other reference points....and your brain would tell you the 12" light was X distance away, but, not that it was a 3" light, your eyes can't really tell the difference.
You'd SEE a smaller light, mentally correct that image to your assumed 12" size, then, mentally adjust the projected distance to the marker....but, all you really saw was a smaller marker, but, assumed it was a larger marker further away.
