Lux, Throw, Beamspread, Inverse Square Law etc.

This is the split-off discussion from this thread about the Gladius flashlight:

https://www.candlepowerforums.com/threads/103320&page=1&pp=30

It contains good info and merits its own thread in order to avoid that is disappears in the archives without a trace in the search engine.

bernhard


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I'm with greenie on this one. The e2 is not a good light for comparison here. Too different. Not that this really matters much though.



joema:

The U2 has 45% more output than the Gladius but 37% less throw. Runtime is significantly less, 1 hr 4 min vs 3 hr 17 min.

Click to expand...

I've yet to see a true distance test that show the Gladius with more throw than the U2. My Gladius will kill the U2 on a light meter but outside, no comparison.

As for runtime, I don't seem to get anywhere close to 3hour before I see the Gladius blinking. With the U2, using the LGs, 1-1/2hours at full output. I'd bet at level 5 (6 being highest), it would be close to 3 hours and still more output than the Gladius. (I just did a ceiling bounce an using the inaccurate light meter, my eyes, it seems the level 4 is about the same as Gladius on high EDIT: oops, level 5 is closer. I just put fresh cells in the Gladius--which I thought were new )

My take, the U2 is a killer light that really shines when using LG2400s. It isn't flashy or impressive to none flashaholics but like everthing else, are you getting it because it is best for you or best to show off. The Gladius is a great light as well. The extra ,low level is the best feature to me. The wall shots are not as impressive in quality but it certainly shows bright and tight. The Gladius doesn't seem to be as robust. I like the quick change with the thumb operation (lockout could be easier). The lack of good rechargable support is what I dislike most(other than not using a Lux5).

That said, I've been carrying the Gladius the most. I can't say why.

Re: Gladius...What do you think about?

Luna said:

joema: The U2 has 45% more output than the Gladius but 37% less throw. Runtime is significantly less, 1 hr 4 min vs 3 hr 17 min.

Click to expand...

I've yet to see a true distance test that show the Gladius with more throw than the U2. My Gladius will kill the U2 on a light meter but outside, no comparison.

Click to expand...

The U2 definitely puts out more light, some U2s more than others. The one tested by Flashlightreviews.com actually seemed a little weak. To the extent I can tell doing wall and ceiling reflection tests with a lux meter, my U2 puts out more than 100 lumens.

However whether inside or outside, a Gladius should out throw it. Throw simply means the lux reading at the beam center point. It doesn't mean how visually bright the overall pattern looks at a distance. http://www.flashlightreviews.com/features/lux.htm

E.g, the SL Propoly Lux 4AA has great throw (lux reading at beam center), but it achieves that with a very small, bright hotspot. Despite having more measured throw, at many distances it looks dimmer than my U2 because the hotspot is so small.

Re: Gladius...What do you think about?

joema said:
However whether inside or outside, a Gladius should out throw it. Throw simply means the lux reading at the beam center point. It doesn't mean how visually bright the overall pattern looks at a distance. http://www.flashlightreviews.com/features/lux.htm


Unfortunately things are so simple. The reason is in this statement: "Any point source which spreads its influence equally in all directions without a limit to its range will obey the inverse square law" Our lights are not even close to being point sources and that is what is wrong with the assumption that nearfield readings will translate to distance readings. A Maxabeam is closer to approximating a point source but not these jokers. TIR will make these leds operate more like a point source down range.


Lux readings are normally measured by 'our type' at a typical 1meter distance. Problem with that is a beam is composed of light that is colminated and uncolminated. Upclose you will have a superposition of the two fields so that nearfield lux is greater. At a distance, the two beams will no longer be one, but rather travelling different paths. This is a consequence of lights not being point source emitters. The net effect is that down range performance cannot be estimated using inverse square and 1 meter lux measurements.

Or simply try it, my u2 and gladius have for the most part similar throw ( i.e. ~same lux at 45 yards at the brightest point) but at 1 meter the Gladius is much higher. Essentially, if distance didn't matter, we could measure lux at 1 inch and my L2 would have the greatest throw based on inv square.

---
Color temp is and issue too... I have a huge amount of scattering with the Gladius that is not an issue with my cooler U2. If you think keep in mind how thin lexan is contributes to about 10% loss, what do you think about 'ghostly image' I get on a cool night (high humidity). The u2 I have (obviously this works both ways) is almost incandescent in its ability to light up a target with low scattering.

Re: Gladius...What do you think about?

Luna said:

Unfortunately things are so simple...."Any point source..."...Our lights are not even close to being point sources and that is what is wrong with the assumption that nearfield readings will translate to distance readings...a beam is composed of light that is colminated and uncolminated. Upclose you will have a superposition of the two fields so that nearfield lux is greater. At a distance, the two beams will no longer be one, but rather travelling different paths...Or simply try it, my u2 and gladius have for the most part similar throw ( i.e. ~same lux at 45 yards at the brightest point) but at 1 meter the Gladius is much higher...

Click to expand...

Throw is the lux at the beam center. Comparing two different lights, it doesn't matter whether the reading is taken at 1 m or 10 m. The ratio between the two lights will be the same.

I've verified this on MANY different tests. If light "A" has 50% more throw than light "B" at 1 meter, it will also have 50% more throw at 10 meters.

E.g, my SL Propoly Lux 4AA has about double the throw of my HDS U60. Flashlightreviews.com's tests show that. My own lux meter tests at 0.5 meters, 1 meter and 10 meters also shows that. Same for various other lights I've tested. The ratio of one light's throw to another doesn't vary with distance. If one light has x% more throw than another, it will retain that advantage at any distance. At least regarding MEASURED throw, which may differ from your VISUAL impression of throw.

So that's NOT to say one light won't APPEAR to have more throw than another. My U2 has about the same throw as my Lux 4AA (it's a strong U2), and my lux meter shows this doesn't vary with distance. At 0.5 meters, 1 meter or 10 meters my U2 and PP Lux 4AA have about the same throw. But the U2 LOOKs like it throws much better because there's so much more light. The Lux 4AA obtains good throw through a "trick" -- the beam pattern is cleverly designed with a very small bright hotspot. The overall output is modest, but it really puts out big throw numbers. Yet the modest output makes the throw appear VISUALLY less.

If anybody has different test numbers I'd like to see them.

Re: Gladius...What do you think about?

QUOTE:joema
Throw is the lux at the beam center. Comparing two different lights, it doesn't matter whether the reading is

taken at 1 m or 10 m. The ratio between the two lights will be the same.

I've verified this on MANY different tests. If light "A" has 50% more throw than light "B" at 1 meter, it will also have 50% more throw at 10 meters.
...cut
one light's throw to another doesn't vary with distance. If one light has x% more throw than another, it will retain that advantage at any distance. At least regarding MEASURED throw, which may differ from your VISUAL impression of throw.

So that's NOT to say one light won't APPEAR to have more throw than another. My U2 has about the same throw as my Lux 4AA
(it's a strong U2), and my lux meter shows this doesn't vary with distance

...cut

If anybody has different test numbers I'd like to see them.

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my argumentative blather, not just at you joema

There is no subjective measurement. Throw is dependant on beamspread, why else do you think that divergence is a critical factor in reflector design? These are shaped beams plain and simple and in no way approximate a point source. (The fact that these are labertian and not isotrophic (radiating equally in all directions) further complicates things.)


The reflector and optics alter the beamspread yet these effects are seen very little when measurements are made close to the focus. Use a laser for instance as an extreme example. Focus it at 8inchs then focus it at 100meters. Now measure the lux at 100 meters of both systems. If focus had nothing to do with it then there would be no difference, but there is a large difference.


PS, Throw is not the lux, it is the distance at which a particular level will be maintained (typically 0.25 lux or so). To have double the throw, you will have to have a lot more than 2x the lux. To remove the divergence from the situation lets assume we have a Gladius and it is being driven at two levels 3200 lux and 1600lux @1m. We will calculate the distance at

which .25lux is hit:

d=sqrt(3200cd/.25lux)=113meters
d=sqrt(1600cd/.25lux)=80meters


just for giggles

Surefire L4=800cd


d=sqrt(800cd/.25lux)=57meters


This is typical inverse square. 4 times the lux to double the distance, ignoring divergence. So the Gladius only throws twice as far as the L4

With a U2, you can see a 1meter spread of 1900 to 2500 as reported. So on the high side (forgeting divergence) the u2 has a throw distance of 100m.(low of 87m) Mine is in the 2300range.

Given a particular reflector/source geometry, inv square law can be used to approximate downrange performance.




Conjecture all aside, My u2 and gladius have similar throw even though at 1meter the gladius registers a much higher lux level Does your Gladius show a distinct advantage over your U2? I find (just as the math above shows) the difference is so little that (even ignoring beamspread) they are similar. www.imagometrics.com has both review and only gives the Gladius a 10ft greater max. distance for object recognition. I've hear others report the same finding as me. Lux might give the impression of a much brighter light but it just doesn't pan out. In reality these lights are only good to about 45 yard anyhow and the U2s spill just really puts it into a different league. I still really like the Gladius and have been carrying it alot lately

Have a good one!



edit: weird word wrappin

Re: Gladius...What do you think about?

Luna said:

....My Gladius will kill the U2 on a light meter but outside, no comparison...my u2 and gladius have for the most part similar throw ( i.e. ~same lux at 45 yards at the brightest point) but at 1 meter the Gladius is much higher....There is no subjective measurement. Throw is dependant on beamspread, why else do you think that divergence is a critical factor in reflector design?...

Click to expand...

Of course throw is dependant on beam angle. That's not the point. Rather that two different lights (say a U2 and Gladius) with differing throws will retain that relative throw difference at ANY distance. When comparing two lights, the lesser throwing light at close range (say the U2) won't start having more throw than the other at long range.

Not only do my objective lux measurement show that, but simple trigonometry also does.

Consider two different 50 lux lights. Light "A" has a 6 degree beam angle, and light "B" has a 3 degree beam angle. To simplify things we'll assume a uniform beam pattern. We'll calculate the throw at 1 meter, 10 meters and 100 meters, and see if throw ratio between the two lights varies with distance.

Throw is simply lux taken at the beam center at a given distance. 1 lux = 1 lumen per square meter. Given a uniform beam pattern, lux (hence throw) is simply lumens / area. E.g, if the 50 lumen light makes a 0.1 m^2 beam spot at a given distance, that's 50 / 0.1 or 500 lux at that distance. That reading at the beam center is the "throw".

To calculate the throw (lux) at varying distances, we first calculate the beam cross sectional area at each distance.

To find that, we first take the tangent of the half angle, times the distance. E.g, for a 6 degree beam at 1 meter:

tan (3) = x / 1 m
0.0524 = x / 1 m
x = 0.0524 m

area = Pi * r^2
area = 3.14 * 0.0524^2
area = 0.00862 m^2

Lux (throw) = 50 lumens / 0.00862 m^2
Lux (throw) = 5800

We simply repeat the above for both lights at 1 meter, 10 meters and 100 meters, and compare the throw ratio between the two lights at each distance. I'll spare the math and just show the results below.

Throw at 1 meter:
=============
Light A: 5800 lux
Light B: 23222 lux
A:B throw ratio: 0.25 (light B has 4x the throw of A at 1 meter)

Throw at 10 meters:
==============
Light A: 58 lux
Light B: 232 lux
A:B throw ratio: 0.25 (light B has 4x the throw of A at 10 meters)

Throw at 100 meters:
================
Light A: 0.58 lux
Light B: 2.32 lux
A:B throw ratio: 0.25 (light B has 4x the throw of A at 100 meters)

As you can see distance has no impact on the throw difference between two lights.

Re: Gladius...What do you think about?

There are some problems with the throw & lux equations. Often the assumption being made is that
you are dealing with single light sources. As a multi LED fan I know from experience that some multi-led lights have such large hotspots lux meters do not measure the whole beam at one meter. My 3D mag with a 3 watt Diamond drop in module has a lux at one meter reading of 4700. My Quad bike light mod, when it had 4 Fraen LP's, had a lux reading at one meter of 3900 to 4000. At 102 yards the Quad with LP's was very noticieably brighter and the hotspot was huge in comparison to the dim pinpoint hotspot of the Mag.
There is also an issue with focus. Two of my six spotlights are 10 MCP Thors. One has a focus ring in it. At one meter it does not have a hotspot. It has a large dark hole. At 43 feet the lux readings are nearly identical.
Beyond 300 yards the Thor with the focus ring still has a nice identifiable hotspot and the stock Thor's hotspot looks noticeably wide and washed out in comparison, yet at one meter it was clearly the better of the two.


Also, not all U2's and Gladiuses are equal.
In spite of what Surefire says on their web sight, some U2 owners have reported the 5 watt donut. Others have U2's with perfect beams.
The same is true for Gladiuses. They do not have donuts, but do have differences in their beams from light to light. My wife's black Gladius has a lux reading at one meter of around 2300 to 2400 with very fresh batteries. My OD Gladius has a lux reading at one meter of 3000. That is a very dramatic difference. One is not better then the other. I actually prefer my wife's black Gladius's noticeably wider hotspot for up close (within 100 feet). The difference between two in terms of throw is not real noticeable till after around 200 feet. Since I like green and also carry a M60L and 3 Raws (2 U binned originals, 1 two level red) at all times, I have my wife carry the black Gladius with the wider hotspot. When my friend's HA III black Gladius arrives next week I plan to do comparisons of all three (beamshots, lux readings, etc.)

Now add to this the luxeon lottery and you end up with the following possibilities.

I personally believe that some people could have the right combination of U2 and Gladius and see very similar throw say they are equal in throw. Others could have another U2 Gladius combination and say there is no way in the world the U2 can throw as far as a Gladius. Both people will be speaking from personal experience and disgreeing with one another.

Yet both people will be right.

Take Care,
mtbkndad :wave:

Re: Gladius...What do you think about?

mtbkndad said:

...I personally believe that some people could have the right combination of U2 and Gladius and see very similar throw say they are equal in throw. Others could have another U2 Gladius combination and say there is no way in the world the U2 can throw as far as a Gladius...

Click to expand...

You're right, there's often significant variation between one U2 and other, or one Gladius and other.

However we were discussing whether two lights with different throws would remain equally different at varying distances. All my lux measurments plus the above calculations indicate they will remain equally different. One light with less throw at shorter range will not begin out throwing the other at longer range, at least from a measured lux standpoint at beam center.

Re: Gladius...What do you think about?

joema said:

You're right, there's often significant variation between one U2 and other, or one Gladius and other.

However we were discussing whether two lights with different throws would remain equally different at varying distances. All my lux measurments plus the above calculations indicate they will remain equally different. One light with less throw at shorter range will not begin out throwing the other at longer range, at least from a measured lux standpoint at beam center.

Click to expand...

I understand what you are saying that is why I made reference to two different examples in my stable of lights that do the opposite.

At one meter my Mag with 3 watt Diamond module has significantly more lux then my quad with 4 Fraen LP's. Yet at 102 yards the Quad has more throw (illuminating capability). Not just in the width, but also the brightness of the beam.

With my Thors, the unfocused Thor has a lux reading of 62,500 at 36 inches
(from my kitchen counter to the floor). at beam center
My focused Thor reads 4698 (yes I typed that right 4698) lux at the same distance to beam center. Remember the focused Thor has a dark center at this short distance.
The brightest part of the wide ring that will become a hotspot reads 22,390.

At 43 feet the lux readings are nearly identical. Beyond that the focused Thor gets better and the unfocused Thors gets proportionately worse.
At over 300 yards the difference is very dramatic.

My ELX-6 is another good example, it has nearly a 4" wide hotspot at one meter. I can turn the potentiometer down to have the same lux at 20 inches reading as my favorite 1 watt LED. Yet at longer distances will illumate objects better. The six 3 watt LED's that form its beam give a fuller light to the hotspot at distance then the single I watt LED. Plus the lux meter is measuring nearly the entire 1 watt led hotspot verses a small portion of the 6 LED hotspot. At approx. 9 inches the 1 watt LED registers around 5,800 lux and the ELX on low registers around 2300 lux. At around 20 inches the readings are equal. By 6 feet the 1 watt LED is around 70 lux and the ELX-6 on low is around 120 lux. The ELX-6 uses 20mm reflectors and the 1 watt has a 27 mm reflector so that helps the 1 watt light out a bit at longer distances (focus and reflector design becoming a factor again), but the ELX-6 is still brighter on low beyond 20 inches.

All of this is ultimately off topic, but good discussion for someone wanting to know if the Gladius is a good light.

Back to the original topic-
Gladius...What do you think about?

I think the Gladius is an amazing, tough, versatile light, it goes with me almost everywhere and gets used everyday.
Not to the exclusion of my favorite 5 watt light (modified M60L) or my Raws but as a very needed compliment to them.
The Gladius is made by a really good company that stands behind it's products.

Take Care,
mtbkndad :wave:

Re: Gladius...What do you think about?

joema said:

You're right, there's often significant variation between one U2 and other, or one Gladius and other.

However we were discussing whether two lights with different throws would remain equally different at varying distances. All my lux measurments plus the above calculations indicate they will remain equally different. One light with less throw at shorter range will not begin out throwing the other at longer range, at least from a measured lux standpoint at beam center.

Click to expand...

You don't get the focus issue. Take your U2 (put it on a low level if you wish to see the square with circles on the tips projection) and then project the beam onto a dark surface. At an inch or two a dark area will be seen at the beam center. Your lux measurement will be very low obviously. Now take it at a meter and it will be high. . This alone proves you do not have a linear relationship of lux vs distance. And again throw is not lux, it is distance. Lux is a variable to determine throw but they are not synonymous.

Re: Gladius...What do you think about?

mtbkndad said:

Thor ...cut
My ELX-6 is another good example, it has nearly a 4" wide hotspot at one meter. I can turn the potentiometer down to have the same lux at 20 inches reading as my favorite 1 watt LED. Yet at longer distances will illumate objects better. The six 3 watt LED's that form its beam give a fuller light to the hotspot at distance then the single I watt LED. Plus the lux meter is measuring nearly the entire 1 watt led hotspot verses a small portion of the 6 LED hotspot. At approx. 9 inches the 1 watt LED registers around 5,800 lux and the ELX on low registers around 2300 lux. At around 20 inches the readings are equal. By 6 feet the 1 watt LED is around 70 lux and the ELX-6 on low is around 120 lux. The ELX-6 uses 20mm reflectors and the 1 watt has a 27 mm reflector so that helps the 1 watt light out a bit at longer distances (focus and reflector design becoming a factor again), but the ELX-6 is still brighter on low beyond 20 inches.

Click to expand...

Great example but don't get me started on EL advertising the lux of his lights as a sum of the lux of all emitter/reflectors

Yes the gladius is a great light but in operation it has no throw advantage over the U2. A couple of meters at a distance is no big deal unless one wants to argue number alone without a real basis. I'm only arguing the numbers from an academic POV.

Re: Gladius...What do you think about?

joema side:Not only do my objective lux measurement show that, but simple trigonometry also does.

Consider two different 50 lux lights. Light "A" has a 6 degree beam angle, and light "B" has a 3 degree beam angle. To simplify things we'll assume a uniform beam pattern. We'll calculate the throw at 1 meter, 10 meters and 100 meters, and see if throw ratio between the two lights varies with distance.

Throw is simply lux taken at the beam center at a given distance. 1 lux = 1 lumen per square meter. Given a uniform beam pattern, lux (hence throw) is simply lumens / area. E.g, if the 50 lumen light makes a 0.1 m^2 beam spot at a given distance, that's 50 / 0.1 or 500 lux at that distance. That reading at the beam center is the "throw".

To calculate the throw (lux) at varying distances, we first calculate the beam cross sectional area at each distance.

To find that, we first take the tangent of the half angle, times the distance. E.g, for a 6 degree beam at 1 meter:


____________________________________________________________

Your model is incorrect because it assumes a set focal length for both lights among other factors. Divergence of the beam doesn't start at the same point in space for two different reflectors/emitter sources. A small difference in focus up close makes a big difference down range. These reflectors have different profiles too and that changes the result also. These are not point sources.... They do not have the same reflectors and they behave differently

Have you actually tried a Gladius vs U2 upclose and at a distance?


(ugg, quotes are still causeing lost posts. when will the vbulletin code be fixed)

Re: Gladius...What do you think about?

Luna said:

...Your model is incorrect because it assumes a set focal length for both lights among other factors. Divergence of the beam doesn't start at the same point in space for two different reflectors/emitter sources.

Click to expand...

The point is do two lights with differing throws, e.g, U2 and Gladius, maintain the relative throw difference at varying distances.

The answer is clearly yes, from both actual measurement and calculation. A light with less throw than another at 1 meter (say a U2 vs Gladius) will not start out throwing the other at 10 meters or 100 meters.

Yes it's true if you use absurd, non-meaningful distances such as 1 inch, that relationship breaks down. In that case you're measuring overall output, not throw. But over any realistic distance from 1 meter to infinity, the relationship holds -- the throw ratio between two lights will remain constant.

..Have you actually tried a Gladius vs U2 upclose and at a distance?

Click to expand...

I haven't tried a Gladius, but I've used a PP Lux 4AA that has identical throw, vs a U2. I've also measured many different lights at many different distances, and the results are always the same: the throw ratio between two lights remains constant at all meaningful distances.

Re: Gladius...What do you think about?

cy said:

...you are technically correct about gladius out throwing U2. but in real life U2's higher lumens give more effective throw...

Click to expand...

Yes, I've made that point several times already -- the Gladius has greater measured throw but the U2 output is sufficiently greater that it may have more "apparent" or "effective" throw from a visual standpoint. But the difference in measured throw between the two lights will remain constant at all meaningful distances, with the Gladius being greater.

They are both great lights. I personally got a U2 because I didn't need the tactical features, wanted maximum output, and liked the selector ring brightness control. However the Gladius will go much dimmer than a U2, has a smaller bezel (maybe easier to holster carry), is more amenable to one-hand brightness adjustment (esp in overhand grip), has the strobe feature, and is less expensive.

Re: Gladius...What do you think about?

joema said:

You're right, there's often significant variation between one U2 and other, or one Gladius and other.

However we were discussing whether two lights with different throws would remain equally different at varying distances. All my lux measurments plus the above calculations indicate they will remain equally different. One light with less throw at shorter range will not begin out throwing the other at longer range, at least from a measured lux standpoint at beam center.

Click to expand...

You did not specify distances and I gave three real world examples showing different. The most notable for your comparisons would be the two Thors
All things but the little focus ring behind one reflector are equal. That VARYING difference is most dramatic with them. From 36" to over 300 yards is a very wide and realistic span that I have used them in.
The measurements were even done at beam center as you specified.

Luna,
I had a frustrated chuckle when EL said "lux time # of LED's and reflectors myself.
:hairpull: :hairpull:


Personally, what I do not like about the U2 is I have such a hard time getting into it and can never see out of it's periscope, and it steers terrible. Surefire should have thought this out better.
I like the Gladius because I have never shied away from a fight. And the strobe enables me to contact my friends on Pluto without Saturn's rings getting in the way.

Seriously they are both very nice lights. As I inferred in another post, this thread was originally about what people think of the Gladius, it is a nice light and I own two. if you want a top quality 3 watt LED light with very innovative features and do not mind spending $234 on a flashlight it will serve you well. If you want a 3 watt LED light with only one bright level that is built real well you could save money and get a Pelican M6 or one of the other single power level 3 watt LED's available right now. If you do not need to get an LED, the new Night-Ops incans look very promising.
If you highly value a very wide beam then get a U2, or some other 5 watt light.

I personally think Night-Ops should take notice of all of the U2/Gladius comparisons as innapropriate as they are, comparing a 5 watt LED to a 3 watt LED. There seems to be some real user desire and therefore market potential for a 5 watt Gladius.

Take Care,
mtbkndad :wave:

Re: Gladius...What do you think about?

joema said:

Yes it's true if you use absurd, non-meaningful distances such as 1 inch, that relationship breaks down. In that case you're measuring overall output, not throw. But over any realistic distance from 1 meter to infinity, the relationship holds -- the throw ratio between two lights will remain constant.

Click to expand...

If you can find a discontinuity, regardless of where, then a model is not taking into account all variables.

If inchs bother you, What do you think a Maxabeam looks like on a close wall when it is focus for maximal throw?

Unfortunately, if your relationship were true, we could have a small reflector throwing as far as a spot light. There are just more factors involved.

joema said:

I haven't tried a Gladius, but I've used a PP Lux 4AA that has identical throw, vs a U2. I've also measured many different lights at many different distances, and the results are always the same: the throw ratio between two lights remains constant at all meaningful distances.

Click to expand...

You are once again using throw and lux interchagably.

If that were the case, a 100watt light bulb in free space would out throw a u2 on level 5. Do you really think it will?

Re: Gladius...What do you think about?

Luna said:

If you can find a discontinuity, regardless of where, then a model is not taking into account all variables...

Click to expand...

You have a point, I may have overlooked something, let me think about it a little...

bernhard,

Good work, this clearly took a bit of time and both threads are better for it. :thumbsup:

Take Care,
mtbkndad :wave:

Re: Gladius...What do you think about?

joema said:

The point is do two lights with differing throws, e.g, U2 and Gladius, maintain the relative throw difference at varying distances.

The answer is clearly yes, from both actual measurement and calculation. A light with less throw than another at 1 meter (say a U2 vs Gladius) will not start out throwing the other at 10 meters or 100 meters.

Click to expand...

This premise assumes that 1 meter is a sufficiently large distance to start making extrapolations based on an approximate 1/r^2 law. For most LED lights and the diffuse-beam incandescents, this is true. But for tight beams like you get from a Mag reflector (stock, Luxeon, or super-incan), 1 meter will not be enough. Other flashlights likely to fail this criterion are the Tigerlight, Dorcy 3D Luxeon, LEDbeam 3C, and all spotlights.

How do you know when you are far enough away? One approximation is the distance where the beam spot stops changing shape and only increases in size. Another approximation is the distance where the beam hotspot is much larger than the flashlight bezel--say, 2x.

For my Luxeon Mag mods, this threshold distance is about 3 meters. Instead of measuring the beam center lux at 1 m, it would be better to measure the lux a 3 meters and then multiply by 9. The resulting number would be incorrect for the actual lux measurement at 1 meter, but it would be a very good number for use in extrapolating the beam lux at large distances.