Minimum lux at target required to recognize a defined target?

[Genzod]

Perhaps one aspect that should be remembered is when a manufacturer will state (hopefully not overstate) maximum lux for a particular flashlight, it is when the battery(s) are fresh and before everything sags performance wise. Or maybe that is not germane to this discussion.

I view lux/range/lumen figures as "for comparison only". For example: Max range theoretical to 0.25 lux. Outputs are peak values after 1 minute run time. I'm aware of the reputation of certain manufacturers who are either not careful or exaggerate their numbers, and I take that into account. For those, I look for a consensus for data among reviewers.

Some manufacturers (a name is not my agenda here) assume the larger fraction of uneducated consumers will not understand these facts. Safe assumption, not a good one. I think it is a mistake for a manufacturer to treat the entire consumer base as "stupid" and potentially malicious. A simple legal disclaimer is sufficient to cover their sacred...well... you know... qualifying that the test data is according to a certain standard and is only for the purpose of comparison, not a measure of the full run time performance, and I think most everyone will get that much except the crankiest of "professional victims".

 

[BVH]

Spectrolab, the helicopter searchlight manufacturer, provides the figure of 32 Lux at 1 Kilometer output for their 1600 Watt light with a beam of 4 degrees and 40 Lux at 1 Kilometer output for their 500 Watt, 2-degree beam light. Maybe that gives you an idea of what they need to see a target from a typical 500 - 1000 feet away.

 

[Genzod]

Spectrolab, the helicopter searchlight manufacturer, provides the figure of 32 Lux at 1 Kilometer output for their 1600 Watt light with a beam of 4 degrees and 40 Lux at 1 Kilometer output for their 500 Watt, 2-degree beam light. Maybe that gives you an idea of what they need to see a target from a typical 500 - 1000 feet away.

Thank you. I would imagine that standard might set the upper limit for minimum lux requiring a much more detailed identification of target. A police chopper for example might be searching for a very specific suspect, what he's wearing, how he's moving, what he's up to, that sort of thing. Whereas my task is a whole lot less complex, being a simple, highly contrasted 2 x 6 inch rectangle on a much larger target, the base of a tree that is not moving.

I'm going to see if I can't do a little experiment tonight with a headlamp of known intensity and fresh batteries. I'll post a white 2x6 marker with similar reflectivity and contrast, then pace off a distance and approach the target until I can barely make out the target. I guess no formula will be a better substitute for my own eyes. Of course I'll be aware to take into account ambient light, full moon, that sort of thing. But I know of a few places where it's extremely dark (no street light) that will work.

Edit: BACK FROM THE FUTURE!

I configured the tool I devised much later for modeling blaze identification with the performance of the second copter lamp you mentioned--Plot. The 2 deg spotlight is 40 million candela, and the black line represents lux received at target vs. range. That curve intersects the yellow line (marginal identification of a highly contrasted 2x6 inch blaze) and the red line which is 32X more intense illumination, indicating the range and lux the lamp provides with those constraints. 32X above marginal is probably useful for identifying a moderately contrasted randomly located moving target the size of a man. You can see from the intersections the lux required is 776 lux (226m) for a man and 154 lux (509m) for a white blaze, about 52% and 10% the intensity of the average overcast mid day sun.

EDIT: I replaced the plot with more the accurate formulaic equation. (The 5th order polynomial curve was skewed by an inaccurate point at 175 meters during regression). I adjusted the acuity range needed for a 6 ft tall man rendering him with around 18x72 pixels with each pixel 1x1" (87.5m acuity limit). Sight represented in plot is 7.0mm dark adapted pupil with 20/20 vision (average 30 year old).

 

[archimedes]

....
I'm going to see if I can't do a little experiment tonight with a headlamp of known intensity and fresh batteries. I'll post a white 2x6 marker with similar reflectivity and contrast, then pace off a distance and approach the target until I can barely make out the target. I guess no formula will be a better substitute for my own eyes. Of course I'll be aware to take into account ambient light, full moon, that sort of thing. But I know of a few places where it's extremely dark (no street light) that will work. And of course I'll make sure the distance I select puts the target dimensions inside a 2 degree cone.

These types of practical real-world tests are very valuable. Detailed notes of your findings will be greatly appreciated, here on CPF.

Looking forward to hearing your results ....

 

[StarHalo]

But night vision ability declines with age, and women are typically better at it than men.

So get some women and go out into the forest with your flashlight..

 

[Offgridled]

I agree with arch.. I will be very interested in your experiment and results. Ive enjoyed your knowledge and humor. Great job.

 

[Genzod]

These types of practical real-world tests are very valuable. Detailed notes of your findings will be greatly appreciated, here on CPF.

Looking forward to hearing your results ....

One might compare my feeble attempt to establish a baseline for minimum lux required to identify a white blaze trail marker on a tree with "endeavoring to construct a mnemonic memory circuit using stone knives and bearskins", seeing that having a simple lux meter might have made my testing more precise. But then, with Spock as my inspiration, all things technical are possible even without the best of tools.

Nevertheless, my reasoning is, if I can get some kind of ballpark idea, and it is consistent with TEEJ's much posted expertise on this very topic, I think I can safely rest assured, there is very little fertilizer taking up space in TEEJ's shed.


I can come back later with explaining my stone knives and bearskins methodology, seeing that I'm very tired now, and would like to go to bed. But just to let you in on a little something I learned tonight. There is no fertilizer whatsoever in TEEJ's shed (as far as I am concerned). He is spot on with his minimum bound for simple, highly contrasted targets where aiming is the only concern.
I just have one question now. Just where in NJ do I send this smart fellow this booze?:drunk:

 

[Genzod]

But night vision ability declines with age, and women are typically better at it than men.

So get some women and go out into the forest with your flashlight..

One can explain the reason for being so "blind" at such an old age, and I can assure you it has nothing at all to do with women. But then, nothing flies over your head, because your reflexes are quick, and you will catch it, right?

 

[Genzod]

I agree with arch.. I will be very interested in your experiment and results. Ive enjoyed your knowledge and humor. Great job.

 

[StarHalo]

One can explain the reason for being so "blind" at such an old age, but I can assure you it has nothing at all to do with women.

The younger guys make themselves blind over women all the time, but as to the technical aspect of it, true story bro..

 

[Genzod]

The younger guys make themselves blind over women all the time, but as to the technical aspect of it, true story bro..

Never had an argument with me "bro"!

 

[Genzod]

I'd like to repeat the experiment later tonight before posting anything about the one I did last night. I'd also like to see how the requirement for target intensity varies with distance. I have three outputs on my lamp, so I can take three samples at three different distances. That might give me some kind of idea how much more intensity I would need at 100m.

 

[StarHalo]

Never had an argument with me "bro"!

But I'm arguing that "what I perceive" is not a good measure, since you're technically handicapped by gender from the start, not counting any other issues with your vision. Then there's the atmosphere, which is remarkably unpredictable in that no given weather condition ensures best visibility, since particulates in the area could be any range of local phenomenon like trees pollenating or nearby construction. I ran into this issue testing an HID light in the desert all the time; the distance would vary as much as 50% from night to night, and there was no meteorological parameter that could predict it.

 

[Genzod]

But I'm arguing that "what I perceive" is not a good measure, since you're technically handicapped by gender from the start, not counting any other issues with your vision. Then there's the atmosphere, which is remarkably unpredictable in that no given weather condition ensures best visibility, since particulates in the area could be any range of local phenomenon like trees pollenating or nearby construction. I ran into this issue testing an HID light in the desert all the time; the distance would vary as much as 50% from night to night, and there was no meteorological parameter that could predict it.

I'm not arguing, period!

This is for me. My eyes are the best test instrument for answering my question for what kind of light I need to get to search white blazes. Go back, reread the thread and see if you can pick up on that.

As for agreeing with the lux range TEEJ came up with, for me that range is relevant under similar conditions, and for his shooters. He seems to know what he is talking about.

As for weather, (and other variables) did you not read the assumptions in my OP? THERE ARE NO SKITTLES! REPEAT, THERE ARE NO SKITTLES!

I had a maturing puppy once who spied himself an opportunity in a loose thread on the fabric of a love seat. He was teething and his gums were irritating him. By the time I returned from a round trip to Maryland 12 hours later, that love seat was torn to sheds. Bad puppy...baaaaaaaaad puppy!:whoopin:

"You can't teach an old dog new tricks", but a young puppy might be able to teach us something.

 

[Genzod]

As noted above, a small target like that would be tough to identify without some sort of scope or binoculars. And using those, it changes all formulas and lux preferences anyway.

I should point out here to everyone that identifying a 2 x 6 white blaze on the Appalachian Trail is a very easy thing to do. You can't equate an object that small to some randomly varying micro-target that could pop up anywhere. That's not what is going on here.

White blazes are not randomly thrown wherever. As a general rule, the white blazes are anticipated about every 30-50 meters, (except in designated wilderness areas where spacing is between 160-400 meters) and they are found on trees at about head height along a well worn trail. Finding the next blaze on the trail is not like trying to target a camouflaged soldier in the bush, shooting chipmunks or searching for a needle in a haystack.

Although the standard blaze is 2 x 6 inches, sometimes they are a little wider due to tree growth, and then get painted over, but they tend to be the same sizes in such sections.

If you know what to expect, where to expect it and it's highly contrasted with the object it's painted on, it's very easy to recognize in very low light. No telescope or binoculars required! (with the obvious exception of said wilderness areas).

What is "hard to do" is spend $30 on a cheapy 4300 cd thrower and finding out what you really needed was the $50 compact 20,000cd thrower. :hairpull:

The clever ones figure out what they need first, then buy themselves one lamp for that one job. The simple ones buy many lamps for the same job, then proudly refer to themselves as "a flashlight collector".

 

[StarHalo]

As for weather, (and other variables) did you not read the assumptions in my OP?

Got that, it says "Atmosphere is clear," but what I'm telling you is that you can go out on two different nights that have what appear to be the exact same clear air, and the results can be wildly different. You will successfully see the target reflect one night, and then the very next night with every variable apparently the same, it simply won't reach. Living at the bottom of an ocean of air is an amazing thing..

 

[Genzod]

Got that, it says "Atmosphere is clear," but what I'm telling you is that you can go out on two different nights that have what appear to be the exact same clear air, and the results can be wildly different. You will successfully see the target reflect one night, and then the very next night with every variable apparently the same, it simply won't reach. Living at the bottom of an ocean of air is an amazing thing..

That's fine, but you're really preaching to the choir here. I'm already aware of these variables. That's the reason I posted assumptions.

When I ask a manufacturer to supply a range to 0.25 lux, I don't care about variables or being told it's a meaningless parameter. I just want to compare lamp performance between models and brands, not establish what I can see at that range. Likewise, I'm trying to establish a standard for myself through analysis and experiment at one consistent set of variables for the sake of providing some context for that particular parameter.

We have a computational standard for all things flight related moving through such an "ocean of atmosphere". It's called the US Standard Atmosphere. We use it as a model to provide consistent information for air density, temperature and pressure up to 86000m.

Of course this "ocean of air" is constantly changing, but that's not an argument for suggesting a standard atmosphere table isn't useful, especially when computationally designing flight vehicles. It's not a denial that the atmosphere is changing. No one is pretending that it isn't changing by having a standard. Neither is my exercise determining a personal range for what target intensities are useful and what are not.

Tonight I went out in the same clear atmosphere and was able to see the white blaze marker at a substantially greater distance than yesterday. Mystery? A reason to throw in the towel and say it's pointless to analyze? No, there was no direct moonlight hitting the bike trail in the foreground of my field of vision this time constricting my pupils requiring a greater intensity at target to see it. Atmosphere the same, variable for difference accounted for. No amazement or mystery to me whatsoever.

 

[Offgridled]

Current vision systems are designed to perform in clear weather. Needless to say, in any outdoor application, there is no escape from "bad" weather. Ultimately, computer vision systems must include mechanisms that enable them to function (even if somewhat less reliably) in the presence of haze, fog, rain, hail and snow.

Begin by studying the visual manifestations of different weather conditions. For thiS draw on what is already known about atmospheric optics, and identify effects caused by bad weather that can be turned to our advantage. Since the atmosphere modulates the information carried from a scene point to the observer, it can be viewed as a mechanism of visual information coding. We exploit two fundamental scattering models and develop methods for recovering pertinent scene properties, such as three-dimensional structure, from one or two images taken under poor weather conditions.

Next model the chromatic effects of the atmospheric scattering and verify it for fog and haze. Based on this chromatic model we derive several geometric constraints on scene color changes caused by varying atmospheric conditions. Finally, using these constraints we develop algorithms for computing fog or haze color, depth segmentation, extracting three-dimensional structure, and recovering "clear day" scene colors, from two or more images taken under different but unknown weather conditions.

 

[Genzod]

Current vision systems are designed to perform in clear weather. Needless to say, in any outdoor application, there is no escape from "bad" weather. Ultimately, computer vision systems must include mechanisms that enable them to function (even if somewhat less reliably) in the presence of haze, fog, rain, hail and snow.

Begin by studying the visual manifestations of different weather conditions. For thiS draw on what is already known about atmospheric optics, and identify effects caused by bad weather that can be turned to our advantage. Since the atmosphere modulates the information carried from a scene point to the observer, it can be viewed as a mechanism of visual information coding. We exploit two fundamental scattering models and develop methods for recovering pertinent scene properties, such as three-dimensional structure, from one or two images taken under poor weather conditions.

Next model the chromatic effects of the atmospheric scattering and verify it for fog and haze. Based on this chromatic model we derive several geometric constraints on scene color changes caused by varying atmospheric conditions. Finally, using these constraints we develop algorithms for computing fog or haze color, depth segmentation, extracting three-dimensional structure, and recovering "clear day" scene colors, from two or more images taken under different but unknown weather conditions.

That...or fly like a bat in an all weather capable EA-6B Prowler! (But, I'll settle for a neutral, minimized spill, narrow beamed light held low in the fog.)

 

[Genzod]

Experiment Update:

Sorry that I haven't posted yet. Data collection is still in progress and the procedure is getting better.

The first night was spent discovering a best location for the elimination of ambient light and glare (pupil contraction) and I want to minimize those effects if I can't altogether eliminate them.

Now that I had the ideal location, the second night I timed my experiment with the moon still below the horizon to eliminate its spill on the bike trail in front of me. I also was able to select and test three distances with the three output selections of my headlamp, up to about 50-60 meters, to give me some kind of idea how greater distances require more lux as the target virtually shrinks relative to the eye.

But I still didn't have good data for 100 meters, which is my desired constraint. My headlamp didn't have enough output to test at that range.

Today I realized all I have to do to get 100 m data is set the lamp on low, and paint the target with various approximate "measured" intensities --0.125 lux, 0.25, 0.5, 1, 2, 4 (determined mathematically by distance knowing intensity at 1 meter, then using a tripod at those distances). Then I walk my eyes over to a predetermined 100 m distance and see whether I can identify the target. The headlamp doesn't have to be with me when painting the target, it can be closer to emulate a stronger output.


That also eliminates spill light in my foreground and brings my perceived measurement closer to the "mechanical" one. I can then use that data as a ballpark "measured" reference that I can later modify with Stephens Power Law for foreground spill light).

So one more time guys. Hold tight. It's getting better.