Minimum lux at target required to recognize a defined target?

[Genzod]

Determination of PERSONAL Minimum Required Flashlight Intensity to Identify an Appalachian Trail White Blaze on a Tree as a Function of Distance Utilizing only Stone Knives, Bearskins and a Nerdy Girl with Glasses

EDIT: At the time of this experiment, subject had 20/40 vision and amazingly wide 8.5 mm dark adapted pupils. That acuity has since been corrected. Also, it was later learned that the experimental curve derived here could be adapted to all pupils and degrees of acuity with a convenient two equation piece-wise function discussed here in post #76 of this thread.


PREPARE TO BE AMAZED! (Probably how it will go, too) :laughing:




Abstract

Fast-packing the Appalachian Trail at night over long distances between trail towns requires a reliable headlamp, preferably one with a large enough boost mode that is able to see an appreciable distance when identifying trail markers for navigation (a vertical blaze of white paint, 2 x 6 inches in size, placed about 2 meters high on a tree and spaced about every 140 feet/43 meters). When such a boost is unavailable on the primary lamp because the manufacturer of your favorite headlamp model lost their minds and nixed lithium ion support, procuring a compact, lightweight secondary flashlight that has enough throw to find trail markers is necessitated. (Nah, this experimenter really would have needed redundancy for his lighting needs, either way).

Throw performance of a flashlight is defined by intensity in lux at one meter (e.g., candela) and/or throw distance to 0.25 lux. A minimum requirement to identify white blazes at a distance of 140 ft /43 m is straightforward, but various factors like weather and foreground spill light can impede both flashlight performance and perception. So it was decided a minimum constraint for marker identification at 100 meters under ideal conditions would be expedient. This choice provides brighter, easier identification under normal conditions, while providing some reserve capacity for performance robbing conditions.

An experiment was devised to determine the experimenter's personal minimum useful intensity required to meet this goal. A flashlight of known intensity was set at various distances from target so as to create intensity at marker of 0.5, 1, 2 and 4 lux. At each intensity, the experimenter attempted to identify target marker at 100 meters. The marker was discernible at 4, 2, and marginally discernible at 1 lux. At 0.5 lux, the marker was not discernible at 100 meters but was marginally discernible at 75 meters.

Experiment establishes that 1 lux provided the most practical minimum cutoff intensity for target identification at 100 m. 1 lux at 100 m is 10,000 lux/candela at 1 meter or 200 meters throw to 0.25 lux. A flashlight meeting those minimum requirements should provide the experimenter useful throw for identifying white blazes on the Appalachian Trail.

At a later date, a more useful set of data was collected at equally spaced intervals of 30 meters from target up to 180 meters. This new data allowed investigation of a suspected acuity limitation that began to deviate the required minimum intensity vs distance curve from the square law curve after about 85 meters. The equal spacing of data also allowed for easier handling of the regression curve fit.

The regressed curve becomes a useful tool for predicting target identification with various sized scopes at distances beyond the 180 meter range of this investigation. Although not discussed in this post, later posts in this thread demonstrate that feature. It was determined that as a rule of thumb, 0.5 lux is a practical minimum intensity for identifying the given target at any virtual sighting distance from an observation distance of 200 meters.

Methods and instruments

A makeshift white blaze, 2 x 6 inches in size was carefully cut from the poster-board rigid page of a spent spiral notebook (Did I not tell you this was stone knives & bearskins?). The surface color was white having a cool white tint, not flat and not entirely satin in sheen, either, providing a highly contrasted and highly reflective target for emulating white blazes. Duct tape was looped and placed at three points covering the entire backside of the marker, and placed on a pine tree of about 8-10 inches diameter at a bend in a forested section of a very wide bike path. (I'm taking the 5th on where exactly this was).


THAT TICKET WILL
COST YOU..............

1 MILLION DOLLARS!


A Princeton Tec Quad of current make was utilized for illumination, having the following characteristics and performance:

Three modes: low, medium and high.

Max output: 78 lm.
Range (high): 50 m @ 0.25 lux.
Range (medium): 24m
Range (low): 17m

(Note: Specifications in manual are no longer valid for this lamp. Correct data was derived from product package labeling.)


Maximum intensity of 625 cd was determined from maximum throw (I=(R^2)/4).

The low mode was used to generate predetermined target intensities for this experiment. The low mode intensity of 72.25 cd at one meter is determined from the 17 m throw and the maximum throw (I=Imax*(R/Rmax)^2).

The headlamp was secured to a tripod and aimed at the marker so the most intense part of the spot illuminated the center of the marker. The following table provides corresponding distances for the four tested target intensities:​

Table 1 Target intensities and corresponding distances of headlamp


​

0.5 lux....12.00 m
1.0 lux......8.50 m
2.0 lux......6.00 m
4.0 lux......4.25 m​

A set of three fresh AAA alkaline Duracell batteries were used for this test. The lamp on low mode has 10 hours of regulation, and the lamp was allowed to stabilize output before attempting to identify target.

A time of night was selected providing no moon and minor starlight due to high altitude haze (June 13, 2017 between 10:50 and 11:50 PM EDT). Temperature was about 80F and humidity was high at 71%. No rain, no fog, NO SKITTLES. Location had little ambient light and even less in the area where the tree with the marker was isolated by forest. Closest street lights impacting viewing zone while discerning target were 620 meters to the right of viewer. A hand was used as an effective visor to eliminate glare in peripheral vision due to the distant street lamps. The target marker was isolated by trees and bushes on all but the immediate viewing side and was not directly impacted by street lighting or residential light. The marker could be marginally discerned with the naked eye at 30.4 meters in this ambient light. The fox that passed by the target tree did not run off with the blaze marker, although, he may be the reason for the absence of ducks at the pond this year.


mmmmmm.....SNACKS!

The lamp on the tripod was set at a predetermined distance, turned on to low mode, aimed and locked, then the experimenter walked quickly to the 100 meter viewing line to identify target, starting with 4 lux and working down to 2, 1 and 0.5 lux. Identification at 100 m was successful for 4, 2 and 1 lux and unsuccessful at 0.5 lux. Identification with 0.5 lux was restored at 75 meters. The identification at 1 lux was considered marginal.

A 50 something year old male with corrected vision was utilized as a testing instrument. This instrument was ideal in that the investigation was conducted for the purpose of determining a useful minimum intensity at 100 meters as a constraint in procuring a magical flashlight for his own personal use. (And no, you still can't borrow it.)

Taken under advisement, a 40 something year old woman with corrected vision (allegedly superior to the geriatric male experimenter's vision) was asked to view the 0.5 lux case at 50 meters and 75 meters to render moot the assertions of love seat rending, irritable puppies once and for all. Identification was successfully made at 50 meters. At 75 meters, identification was successfully made but described by the woman as "marginal", just as it also was for the male experimenter--proving once and for all, that a man with a woman need not go blind. :huh: (This experimenter sees extremely well.)

No scopes or binoculars were used in this target identification. But please, do keep digging for a way to render this effort nebulous and pointless, I'm sure you'll come up with something. You did get an early start, after all.
​

​

Discussion and Conclusions

An intensity of approximately 1 lux was determined to be a boundary constraint for target identification at 100 m for the eyes of the experimenter. (Your results may differ.) Required intensity at target appears to closely approximate a quadratic function of the distance within the range of 0-88 meters. The farther the eyes are from the target, the higher the intensity at target is required in accordance to the square law.

After 88 meters the intensity as a function of range to target curve deviates noticeably from the square law primarily due to the acuity limitations of the observer (20/40--max range to acuity limit for this target is 88 m). Although suspected at first, there is no asymptote the required intensity approaches implying a limit to distance where no amount of light will resolve target.

Although one might imagine that looking for a white blaze marker is like hunting for chipmunks that move in and out of holes and blend in with their surroundings, the white blaze target is highly contrasted, easily anticipated, found typically on stationary trees (when they aren't being chased by a pack of marauding termites) spaced every 140 feet or so at an elevation of about 2 meters and is found more often than not along an easily identifiable, well worn path. But, if you still fancy the marker being an elusive chipmunk, don't worry--I won't interrupt your delusion. 1 lux as a limit will be fine for my purposes. (Your purposes may be different).


RUN, FORREST, RUUUUNNNN!

Ambient light: On June 11th in the same test location, phase angle of moon was about 27 degrees and Z = 39. Moonlight intensity was calculated at 0.11 lux The ambient light impinging on the isolated marker was substantially darker in comparison. On the following two test nights without moon, the marker was isolated in even less light. Distance for marginal marker visibility was measured on two moonless nights as 30.4 meters. Whatever the intensity of the ambient light impinging on the marker, it was perceived to be substantially less than the moonlight at 0.11 lux plus any background ambient light from the city. So ambient light impinging the marker was much, much smaller than the 0.5- 4 lux added by the lamp.

Perhaps a lumen stud could enlighten us on what that value is based on the distance needed to marginally identify the target without lamp. Go, Speed Racer, go! (In the mean time, see below for how I finally backed it out of the collected data.)

A new data set was collected on July 25th, 2017, 2-3:30am EDT. Crescent moon on opposite side of earth, no rain, very little cloud cover, no haze or pollen, no foxes, no Clint Eastwood running cattle between observer and target, no Skittles. A rectangular box visor was used this time to block the effect of ambient light above tree level, residences and street lights in the distance. Nevertheless, the new data was very similar to the old data with the exception that investigated range to target was extended from 100 meters out to 180 meters. The equally spaced data points made for better regression curve fit determination. Differences in regressed curves between old and new data were primarily due to the spacing of data points and initially imposing incorrect boundary conditions on the data during the regression. Those issues have been resolved and updated.
​

Table 2 Marginal target identification intensities* (less ambient light) and corresponding distances


​

..............DATA...............

​

Ia + 0.000 lux........30 m
Ia + 0.271 lux........60 m
Ia + 0.739 lux... ... 90 m
Ia + 1.640 lux .....120 m
Ia + 3.770 lux......150 m
Ia + 8.800 lux......180 m
​

*Ambient intensity at target, "Ia" is unknown at this point.

ACHTUNG! The data above represents the intensity from the lamp ONLY. It is not total intensity. Ia was later placed as a variable in the above data due to the fact that this forum is PREGNANT with looking for any false appearance of loose threads to pull to blow off neurotic steam. Future assaults by neurotic combatants vill face military tribunal und be shot.. den zent to zee Russian Front! ​

Ambient light intensity impinging target was determined by imposing the boundary condition I'(0)=0 and I(0)=0 on the data set and regressed curve. These constraints simply mean the minimum required light to see target approaches zero as the distance to target approaches zero. Since there is no other light but ambient in the interval between zero and 30 meters, and ambient light is the minimum required light to identify target from 30 m, less light than ambient is required at distances less than 30 m. The trick now is to guess Ia and bend the regressed curve with guesses for Ia until the shape of the curve at range equals zero has met the condition I'(0)=0

It is important to differentiate between ambient intensity and minimum required intensity at distances less than 30 meters, as ambient light is constant in the interval (lamp is off and not needed here), but minimum required intensity drops off as the target is approached from 30 m. The minimum required intensity curve from 0-30 m should theoretically follow a square law with approximately zero intensity at zero meters and ambient intensity at 30 meters--And indeed, as shall be seen, it does.

To find ambient intensity, a guess for ambient is provided as I(0)=-Ia. The data set of table 2 and this guess are regressed in a quintic polynomial regression (5th order polynomial), and the derivative is checked to see if I'(0) = 0. This involves monitoring the shrinking of the constant of the 1st order term of the polynomial with each progressive guess until it approaches approximately zero. Ia=0.085 lux when that requirement is accomplished. Once the curve has the proper shape with I'(0)=0, the constant term of the polynomial is truncated from the function, vertically moving the curve up the value of Ia so that the curve intersects the origin (0,0). The resulting curve represents all values for minimum required intensity to identify target at distances from 0 to 180 meters. Then we add the ambient intensity of 0.085 lux to each of the 6 collected data points and superimpose the curve over the data points.

The value of Ia makes sense as it is a small fraction of moonlight intensity plus background intensity (there was no moonlight during this data collection, therefore Ia is background from suburban light pollution and anything else in the atmosphere at the time--stars, light reflecting off clouds, etc--approximated as 0.39 lux*). Ambient light impinging on the target blaze in the shaded portion of the test area is 0.085 lux which is about 22% of the local suburban light pollution.


*Two nights prior to the first data collection, the moon was 39 degrees above horizon and estimated from a chart to be about 0.11 lux. Max sighting distance with only ambient light was found to be 34 m. On two test nights that followed much later with no moon, max sighting distance with only ambient light was 30 m. Unshaded suburban light pollution in the test area, P, can be backed out of the intensity square law equation (0.11+P)/P=(34/30)^2. P becomes 0.39 lux.


Boundary conditions: I'(0)=0 and I(0)=0

Table 3 Marginal target identification intensities and corresponding distances (with ambient light added)


​

...........DATA...............

0.000 lux.........0 m
0.085 lux*......30 m
0.356 lux........60 m
0.824 lux... ... 90 m
1.725 lux .....120 m
3.855 lux......150 m
8.885 lux......180 m**
​

​

*Artificial, guessed value used as a "bending point" to force and maintain a horizontal tangent in the regressed curve at point (0,0), i.e. I'(0)=0 . True value of ambient light is Ia=0.085 lux, which comes from the red regressed quintic (5th order) polynomial curve fit.

**EDIT: This one data point was in error due to the fact the correct location down range for marginal identification for 8 lux+ambient on target was over the surface of the lake. I apologize for not only being unable to walk on water like Jesus, but for also fudging this point by making an estimation instead of tossing it out altogether--be assured, it caused me no little grief. I discuss this in greater detail in post #76 where I describe the physics equation governing requirement for increased intensity beyond the acuity limit.​

Red Curve Regression:


​

Minimum Intensity to ID Target (lux) Vs. Observation Range to Target (meters)

I(x) = 7.3990e-05*x+6.5004e-05*x^2+1.4421e-06*x^3-2.1628e-08*x^4+1.1145e-10*x^5

(Intensity values valid only in the range from 0 to 180 meters. Notice I(0)=0 and that I'(0)<0.0001 which for our purposes is approximately 0.

PLOT*

We can determine from the plot, utilizing the point tool, that required intensity of the lamp at 100 meters is 1.0512-0.085 (ambient) = 0.9662 lux, which is consistent with 1 lux determined in the first data set, a deviation with relative error of only 3.4%.​

*Note: The blue curve is the square law curve for intensity and distance. The square law appears to be valid up to about 80-85 meters, which in terms of visual acuity represents a focus of 12 one inch square pixels filling the 2x6 inch target for a person with 20/20 vision, three 2x2" pixels for 20/40 vision which I had at the time of the data collection. As the target shrinks smaller than the 3x1 pixel resolution and focus blurs, the regressed curve increasingly deviates from the square law curve. At increasing distance, the target blends into the tree and dims, becoming a point source of light, ever diminishing.

​

EDIT: There is no vertical asymptote at a distance that no amount of light will resolve the target. I had suspected that at first, but it is not the case. Once the target rectangle slips inside the pixel dimension of 2x2", distance progressively dims the pixel, which stays the same size relative to the viewer.


Compact Flashlight: The 0.966 lux at 100 m constraint requires the performance of a flashlight with at least 0.966x100x100 = 9660 candela. (See plot of Range vs. Intensity for constant target lux of .5, 0.71, 1, 1.41) Since foreground spill can constrict pupils and require more intensity at target to identify it, it is necessary to minimize spill with a deep reflector, narrow beam spot, or impeding the spill light in some way without altering the spot, such as using a tube extended off the head of the lamp or using a sighting tube to isolate the pupil.

The Manker T01 II seems well suited for the job, capable of 10,000 cd with a primary AA (same battery as my headlamp) and 20,000 cd with an IMR battery for even greater throw. The Manker T01 II has output settings that make it also useful as a back up running light. Plus, it's empty weight is only 55 grams, which is desirable when wanting to keep things light running up hills.

Manker T01 II

​

 

[Offgridled]

Very well done here Genzod. I believe the numbers would have changed if SKITTLES were involved glad you used a females eyesight to keep all happy ( experimental reasons only) not to be taken out of context! I hope you enjoyed doing this as much as ive enjoyed reading it!! Ok back to my red button for now

 

[archimedes]

Nice work

As I know you'd be disappointed @Genzod if we didn't have at least something to criticize (lol) ... you might consider calling the "0.000 lux" data point, "no added light" / "ambient moonlight / starlight" or something similar, since truly without any lux you wouldn't be able to see anything at all

 

[Genzod]

Nice work

As I know you'd be disappointed @Genzod if we didn't have at least something to criticize (lol) ... you might consider calling the "0.000 lux" data point, "no added light" / "ambient moonlight / starlight" or something similar, since truly without any lux you wouldn't be able to see anything at all

I appreciate your smartalec humor, but you really should have waited to comment until after I removed the advisory that I was updating:

I am correcting some data points that were entered incorrectly. Please do not quote article while this advisory is still posted. I will remove it when the article is corrected, thank you

As you can see, the ambient light has been backed out of the data set and added into the data. I was doing that during your post.

I was aware of this issue as you could see from the request near the Go Speed Racer quote.

Perhaps you could have met the request and supplied a calculation method instead of just saying the data point was wrong? (That's the helpful way). I don't see that too often around these parts.

("Geniuses" with no answers, only red pens. (not you, haha) Reminds me of professors who mark tests wrong but don't tell you the correct answer.)

I've taken your advice and update the article.

 

[Offgridled]

Nice work

As I know you'd be disappointed @Genzod if we didn't have at least something to criticize (lol) ... you might consider calling the "0.000 lux" data point, "no added light" / "ambient moonlight / starlight" or something similar, since truly without any lux you wouldn't be able to see anything at all

Arch you always have me smiling.

 

[Offgridled]

Genzod the red pen is definetly safer than the red button.

 

[Genzod]

Genzod the red pen is definetly safer than the red button.

Oh, I know he was only "coarse jesting". And he did point out a way to protect myself from a loose thread that would attract sharks. That's been fixed.

His post simply brought up a lot of bad experiences on threads like this. Sharp people with a lot of technical saavy, and yet all the advice they seem to have gets invested in pointing out what is wrong with something rather than offering help with a solution, even when asked. I've asked such people for a little assistance, yet the only response after the request is unsurprisingly *silence*. Just another smart*ss on another bombing run trying to impress himself with shutting others down.

I'm trying to solve problems here that will help people with similar problems. I would hope people that are that technically saavy to see what is wrong could also be intelligent enough to figure out, there might be a solution they could contribute to.

If you want to be the exceptional rare bird, and not a "Debbie Downer" focused on only what is wrong, it's clear. Be a problem solver rather than a problem-pointer outer. The latter is as common as the litter of cigarette butts and can pull tops in the gutter of a highly trafficked street in the 70's.

 

[Genzod]

Ambient light is 0.0613 lux. Sheesh. That iteration was....well...you know...(and it took forever, too!)

(It took almost forever to realize the actual ambient on target is 0.085 lux and to correct the calculations that followed in later posts.)

 

[Offgridled]

Illuminance is a measure of how much*luminous fluxis spread over a given area. One can think of luminous flux (measured in*lumens) as a measure of the total "amount" of visible light present, and the illuminance as a measure of the intensity of illumination on a surface. A given amount of light will illuminate a surface more dimly if it is spread over a larger area, so illuminance is inversely proportional to area when the luminous flux is held constant.
The choice is ours....

 

[Genzod]

Open the two following links in your browser on two different tabs. Then click back and forth between tabs.

Camera 1 Camera 2 *

Lamp intensity only, lamp with ambient intensity added in.

I know, I know. It's fun, but don't over do it. (You might go blind).

*Note: these two graphs are no longer valid once I updated the old data with evenly spaced data more fit for regression analysis and corrected the boundary conditions. However, I left the post the way it is lest any of you OCD cases get panicked that your toy has been removed. See, I'm nicer than people give me credit for. Click away, you coo coo birds!

 

[scs]

...

The choice is ours....

Certainty of doom to the left and empty and unfulfilled promises to the right...

 

[ssanasisredna]

Certainty of doom to the left and empty and unfulfilled promises to the right...

 

[Offgridled]

Certainty of doom to the left and empty and unfulfilled promises to the right...

What flashlight would you take

 

[subwoofer]

Having made it through this thread so far, I'm still not sure if this is a serious question or just for fun. I'll guess fun.

The thread title is VERY interesting; as a night time hunter, target identification is absolutely crucial, and in some cases the only visible aspect are eyes reflecting back the gun lamp light. This is not sufficient to take a shot, even if you think you are confident that the colour, position and movement identify the target, you need more to be sure you are not making a big mistake.

For any one scenario there will be one equation, but with so many variables I can't see there being anything usable for real world situations. The 'observer' being the biggest variable (dark adaptation, spectacles, contacts, age, averted vision, binoculars, scope), not to mention their position relative to the target, the target's reflectivity, size and orientation. Perhaps using a camera with fixed lens and exposure might eliminate some of the variables.

Another major factor is glare. Glare from atmospheric factors (dust, moisture etc) and the spill light hitting the ground near the observer, so making the ground surface (grass, dust, wet etc) a big influence as it affects the relative brightness of target and the observer's immediate surroundings, so affecting target visibility.

Effectively for the best ability to identify a target, it means having the most collimated beam possible with as little spill as possible (a light-sabre like thrower). Very impractical for anything other than target identification. This is one reason the cheapy zoom lights are so popular as their lens can focus the LED's output to a very tight beam with no spill, and while this is very inefficient and the output is actually pretty low, the perceived brightness can be much higher.

An interesting subject to muse over, and one that had many practical uses, but will remain theoretical only. If you think about it in terms of the 'need' to identify a target, then 'minimum' is not really what it is all about, instead you throw as much light as you can and can either identify the target or not (S+R, LE and Military applications).

 

[scs]

Having made it through this thread so far, I'm still not sure if this is a serious question or just for fun. I'll guess fun.

The thread title is VERY interesting; as a night time hunter, target identification is absolutely crucial, and in some cases the only visible aspect are eyes reflecting back the gun lamp light. This is not sufficient to take a shot, even if you think you are confident that the colour, position and movement identify the target, you need more to be sure you are not making a big mistake.

For any one scenario there will be one equation, but with so many variables I can't see there being anything usable for real world situations. The 'observer' being the biggest variable (dark adaptation, spectacles, contacts, age, averted vision, binoculars, scope), not to mention their position relative to the target, the target's reflectivity, size and orientation. Perhaps using a camera with fixed lens and exposure might eliminate some of the variables.

Another major factor is glare. Glare from atmospheric factors (dust, moisture etc) and the spill light hitting the ground near the observer, so making the ground surface (grass, dust, wet etc) a big influence as it affects the relative brightness of target and the observer's immediate surroundings, so affecting target visibility.

Effectively for the best ability to identify a target, it means having the most collimated beam possible with as little spill as possible (a light-sabre like thrower). Very impractical for anything other than target identification. This is one reason the cheapy zoom lights are so popular as their lens can focus the LED's output to a very tight beam with no spill, and while this is very inefficient and the output is actually pretty low, the perceived brightness can be much higher.

An interesting subject to muse over, and one that had many practical uses, but will remain theoretical only. If you think about it in terms of the 'need' to identify a target, then 'minimum' is not really what it is all about, instead you throw as much light as you can and can either identify the target or not (S+R, LE and Military applications).

I guess it's a very vigorous mental exercise with real world measurements that has yielded results that might be useful as a rough guide for how many CDs a person should look for.

 

[Genzod]

I guess it's a very vigorous mental exercise with real world measurements that has yielded results that might be useful as a rough guide for how many CDs a person should look for.

No, maybe he's right. Maybe I shouldn't be advising people with guns to go out with 1 lux and shoot a living target at 100 meters. Maybe I did ignore spill light and atmospheric conditions and neglected the idea of collimation as a practical kind of light for this application. Maybe I do need to take a 490,000 cd/1400g cannon with me fastpacking for the absolutely best possible white blaze target identification. Indeed! My serious efforts must seem "amusing" to him in light of his superior knowledge as a professional lighting expert.

And here i was thinking the OP and my meant-for-mere-musing experiment was about learning my personal minimal lux requirement to see a white blaze trail marker at 100 m under ideal conditions, so I can get a bearing for selecting the most suitable compact flashlight for that need. I sure am glad there are professional lighting experts perusing this forum who can set us hokey amateurs straight!

:bow: My hat's off to him for his generosity and the obvious sacrifice of his time! His review of my "theory" has been considered, and I stand corrected!

Perhaps he could do one more thing for me? Recommend the heaviest possible collimated hand held thrower for my fast-packing? I want to make sure I'm lugging around the light that has the best ability to identify those white blazes. Don't want to accidentally shoot the wrong trail marker, you know!

SHHHH...BE VEWY VEWY QWIET,
I'M HUNTING TWAIL BWAZES!

 

[Genzod]

Continuing on with my musings...

I created a plot that bounds my candela requirements. It's based on the red curve which is the minimum lux for white blaze identification under ideal conditions (for my eyes). The horizontal axis is viewing distance to target in meters, and the vertical axis is measured target intensity in lux.

The pink line describes the candelas required at distance for that minimum constraint. Just multiply the left hand lux scale by 10,000. (2 lux on the scale would be 20,000 cd).

The blue line describes 4 times the minimum required lux at a distance, an intensity that makes identification very easy.

Since the pink line represents a flashlight with an intensity only strong enough to meet a minimum identification at that distance, the blue line will be 4 times that minimum, which is ample for making this identification under those conditions.

So lets pretend this is your data profile for a moment. You went to a trail and replicated my experiment with you as the viewer, and surprise surprise, you have big beautiful blue eyes that look exactly like mine. Mmm, you lucky guy.

Let's also pretend you are happy with viewing AT trail markers at a minimum constraint of 75 meters. That's about 32 meters beyond the typical average spacing. You use the point tool and click the pink line at 75 meters. The answer is 0.2670 lux, but that's the wrong scale. Multiply by 10,000, so the answer is 2670 cd. Now we're cooking with oil! You need a light with a mode having a minimum of 2670 cd to marginally make out a trail marker under ideal conditions.

Now follow a vertical rise to the blue line at 75 m. It resolves to 10,681 cd. To see the marker with 4 times that minimum intensity, you need a flashlight with an intensity of 10681 cd. Now move the pointer horizontally to the right until you hit the pink line again. You get between 102-103 meters. That is your max ideal range with a 10,681 cd flashlight capable of seeing 4x above minimum required intensity at 75 meters. So your idealized range is 75 meters to a potential 102 meters.

Let's say now the trees are 43 m apart most of the time as they are said to be. Most of the time you will only need about 177 cd to see with minimum required intensity. With 10681 cd, you are seeing the blazes at 43 m with target intensity about 60 times your minimum constraint at that distance.

Have fun with it, but please, if you're still clicking those two graphs back and forth--STOP IT already. You'll go blind!

 

[Genzod]

A lamp combination that I'm considering is the Zebralight H53w and the Manker T01 II. The intensity of the H53w is about 1200 lux @ 1 meter at 330 lm output. The intensity of the T01 II is 20,000 lux @ 1 meter.

If you start 1 meter away from the target and start stepping back, the lux value at target will diminish with the square of the distance. Add in any ambient light intensity and you have total target intensity.

The linked plot shows this target intensity for the Zebralight and Manker across distance to target in meters. The green curve is the Zebralight and the black is the Manker. The red curve is the OBSERVED not THEORETICAL minimum lux required at that distance to marginally see target.

One person in particular doesn't seem to understand the purpose of that minimum intensity to ID target boundary limit. I wouldn't question his understanding of the purpose of a throw to 0.25 lux figure for a lamp. He's a smart cookie. It's a figure that quantifies lamp performance. Maybe he'll eventually understand too what I am saying here. The red line is observed data obtained under specific conditions to establish a baseline that quantifies my visual performance. Not other people's visual performance--mine. No theories, no scopes, no contacts, no shiny wet grass, no Skittles, no glowy eyed out of season dead wabbits.

Well, the minimum lux to marginally identify target is a baseline from which we can create a frame of reference and talk about more useful light.

The "marginal" identification is subtle. I can tell there is a marker there, but it takes me a little effort to be sure. It's not something you would use to hunt a living thing. No one here is talking about hunting living things, except perhaps someone who has strayed off topic for some dark purpose. Maybe this 'expert' didn't read my OP (despite having said he read the thread up to that point). This confuses me. Why would a clever fellow rehash irrelevant issues and "variables" that have already been specified and dealt with in the thread, then dismiss the practical observations I made as mere musings and impractical theory? hmmmmm.

If you increase incident lux on target 4 times the baseline (red line), you get a decent, easy identification. The rectangle is focused. The identification is immediate. There is no question what it is.

So let's take a look at the plots.

The 330 lm max mode of the Zebralight intersects the red curve at about 60 m. Anything beyond that is useless. It's an upper limit. I can't go beyond that. A practical useful figure. Won't see target at that distance all the time, but I know I can't see beyond it. Useful, useful, useful. Mathematically speaking, boundaries are good.

Now we move toward the target. We want a useful amount of intensity on the target. We place a vertical line across the red and green curves and move it to the left. We come to the magic number 47 m. Let's check it out. We put the mouse over the graph and up come the orange buttons. Select the one that has a line with a point on it. Now click on the point of the green line at 47 m--0.5432 lux. Now the red line--0.2168 lux. (subtract ambient light from the red only which then becomes the required minimum lamp intensity and compare it to the thrown intensity of the lamp at that distance (green). We get (0.5432)/(0.2168-0.085)= 4.12. That's about 4X minimum required lux to ID target. So 47 m is a good distance that provides plenty of light for easy identification. So the max range of the Zebralight is 47m to a potential 60m. So with 330 lm max mode, the Zebralight can easily identify white blaze targets that have an average spacing of 43 m.

Now in the real world spill light is a problem. But any driver knows as well as I that the solution to glare is to block it out. We see cars coming toward us with their brights on and we put our hand up to cover the lights from our eyes to restore ability to see the road. Glare in the mirror? We turn the mirror up.

In the case of a trail, the spill light doesn't go very far in the kind of narrow beam lights I mentioned. You only need to see a narrow view and that down the narrow corridor of the spot where the spill doesn't reflect. Why not look through a tube at the target? You could alternatively put a tube on the lamp head to block spill; although, the eye tube visor could block glare from other sources like a moon on the horizon.

For the "Debbie Downers" who circle the forum in your AC130 gunship looking for an opportune moment to open fire with your negativity cannon: cease from making wet grass in foreground, close trees and glare from spill (and every other detail you can draw from your nix it bag) an issue just to win a warped and pointless argument.

And it is a pointless argument when it's a strawman argument. If you're going to debate, learn how to debate correctly--don't put arguments in my mouth I never made, then refute those arguments with contrary, irrelevant details to give the false impression you have shut my effort down--it's irrational-- stuff made for the "coo coo for Cocoa Puffs" box.

In fact, why not go look elsewhere for a debate? There's no debate going on here. I am pursuing the answer to a question, not asserting something that ruffles your chips--the topic is about answering a question about a very specific, well defined circumstance I am investigating for my needs. Here I am trying to answer my own question for lack of constructive help (TEEJ must be busy shooting wabbits) and all I get are discontented "Debbie Downers" negating me at every turn--providing no useful help--just reasons or exceptions for why I am "wrong". What kind of circus is this? Go back to reviewing lamps--you are apparently good at that. Reviewing my "theories" while I try to help myself isn't exactly your best forte.

Now we have seen that the Zebralight had a useful distance of 47 meters extending out to a possible maximum distance of about 60 meters. (For AT white blaze targets--no wascally wabbits allowed).

Now we do the same with the Manker. The intersection of black and red is at 115 meters--can't identify beyond that, not even on a good day--boundaries. Approaching target with the vertical line we arrive at 86 m and sample the two points on both lines. 2.704 and 0.7456 lux. Subtracting out ambient of 0.085 from the red and taking the ratio, we have 4.09 times the marginal identification intensity, again about 4X, which is plenty of intensity for easy identification. Thus we have a range of 86 meters to a potential 115 meters with the 20,000 cd Manker.

Now it can rain, it can fog we can stop to eat Skittles. We might even skin a wabbit. But none of those things change the performance capacity of the lamp's throw (in candela) and neither does it change the performance capacity of my eyes. We just tuck our head and deal with it until the miserable condition passes.

You can stick any lamp into the 2nd and 3rd equation to the right. Try 10,000 cd in place of 20,000, which is the AA primary battery performance for the Manker. I got 74-99 meters. (Your results may differ.)

You can check these results on the plot I posted earlier. In fact, it's probably a little easier to use it looking for a 4X lamp intensity difference because ambient light is already subtracted out of the pink and blue curves. Just take the intensity rating of the lamp, divide by 10,000 and use that number to draw a horizontal line across the pink and blue lines. The range is the intersection of the horizontal with the blue (low) and pink (max) curves. For 20,000 cd, the lux of 2 is used, and the intersections are 86 at the blue curve and 116 meters on the pink curve. Very close.

Now I have learned that the National Park System has estimated there are over 165000 white blazes over the 2189 miles of trail. I'm assuming that's ALL of them, both ways. A quick calculation yields an average spacing of 140 feet. Now that's good news to me because I read earlier that the spacing is on average 200 feet. That's a change from 61 meters to 43 meters. That cuts my intensity requirement for the flashlight in half. There are sections through designated wilderness areas and National Parks where the blazes are less frequent, even 0.1 to 0.25 miles apart at times (161m-404m and I would need a much heavier scope for that). Nothing I can do about that. But for the most part, the blazes are supposed to be set up so that one can see the next one from the former. If some areas are spread out that wide, the spacing in places it is not that wide is even closer together than 140 feet. The Zebralight H53w can deliver 4X intensity identification at 154 feet, so even without lithium ion boost, the Zebralight H53 can still work at finding blazes most of the time, except in places like national parks and wilderness areas where the blaze spacing is beyond the performance of any narrow beam compact flashlight. But I still need lamp redundancy, and it would be better to have a narrower beam for less spill and glare, especially for fog.

Hey review guy, how about this one? Would that be the best option for a fastpacker? Or should I go larger? Still haven't heard back yet. But then, things to do, bombing runs to complete....

 

[Genzod]

Taken under advisement:

"Effectively for the best ability to identify a target, it means having the most collimated beam possible with as little spill as possible (a light-sabre like thrower). Very impractical for anything other than target identification.... If you think about it in terms of the 'need' to identify a target, then 'minimum' is not really what it is all about, instead you throw as much light as you can and can either identify the target or not (S+R, LE and Military applications)."

I've decided that the best route to "have the most collimated beam possible" is to forsake the 490,000 cd/ 1400 gram hand held for a helo spot light. At $1000 an hr, I could rent a helo with a Spectrolab SX-16 Nightsun to follow me around on my next through-hike fastpacking expedition. Figure it will only add about $640,000 onto my hiking budget!

 

[archimedes]

... better rent two, 'cause "two is one" , and you don't want to risk having to hike in the dark without light ...