Basic xml vs xpg intensity question

[Joe Talmadge]

I understand the basic nature of reflectors and die sizes, that all things being equal, an xp-g (say) will out-throw an xm-l if the reflectors are the same size with similar engineering quality. My question is, given a relatively small reflector (let's say 25mm-35mm), and the xm-l's overall output of at least double over a comparable xp-g light, where does beam intensity falter? That is, if I only cared about beam intensity in the 5-10 foot range, and beyond that didn't care much about throw, would the xm-l's (bigger) hotspot still be brighter at this range, or is it already flooding out a little? Answers with particular lights are fine (e.g., "my SC600's hotspot is more/less bright than my quark xp-g at 10 feet"). Not having an xm-l light yet, I'm trying to figure out if, for a particular application I have in mind, a <35mm reflectored xm-l is a good fit, if I mostly only care about beam intensity in the first few yards, and after that just want lumens and floody is fine

 

[DM51]

There's a very good thread here about XP-G, XR-E and XM-L emitters in P60-size reflectors. I'm not sure it completely answers your question, though.

 

[hwc]

Just compare the beam shots in this review:

http://lygte-info.dk/review/Beamshot%20Quark%202011-08%20UK.html

Look at the Quark X AA2 (XM-L) next to the Quark AA2 (XP-G) next to the Fenix LD25 (floody, larger reflector XP-G). For the short distances you are talking about, I don't think there's any doubt the XM-L will provide brighter more useful light with the same package, batteries, and reflector.

 

[Chevy-SS]

I have numerous Quark 123*2 lights. I have one with XP-G R5 and I have a new one with XM-L. I will say that the LUX (intensity of light in the hotspot) seems to be lightly higher with the R5, but the hotspot is much smaller with the R5. The XM-L has a MUCH larger hotspot and casts out more overall lumens. But the R5 emitter will throw farther.

The Quark 123*2 XP-G R5 has been my EDC for over a year now. I bought the new XM-L version, thinking that would easily replace the R5 as my EDC. But after comparing the two lights, I am still using the R5 as my preferred EDC light.

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[tre]

Selfbuilt measures beam intensity at 5 meters (15 feet) and calculates back to one so you can use his measurements to get a feel for what the beam intensity would be at 15 feet in lights with different emitters.

ANSI standards for beam intensity specify that it should be measured at 2, 10, or 30 meters and we relaly don't know which one is used to get a manufacturers rating. I use 10 meters when I measure. I find that I actually get much closer to the manufacturers ratings for beam intensity when I measure at 10 meters vs closer distances. I get lower reading for all lights (XPG, XRE, and XML) when measured at closer distances.

 

[hwc]

ANSI standards for beam intensity specify that it should be measured at 2, 10, or 30 meters and we relaly don't know which one is used to get a manufacturers rating.

It doesn't matter which one they use because for formula for the canadela intensity (and for the beam throw) both factor in the absolute intensity of the hottest spot and the distance at which it was measured. The candela and beam distance numbers should be directly comparable between all lights measured under ANSI standards. A light with a higher candela or beam distance under ANSI will have a brighter center hotspot than a light with a lower number and, therefore will throw farther (or vice versa). If a light has a big lumen number and a smaller candela or beam distance number, it must have wider flood/splill characteristics -- which seems to be the case with all of these small reflector XM-L lights.

Seems like a really good tradeoff for a general purpose light. Your LD25 would be a great candidate for an XM-L version!

 

[Joe Talmadge]

Thanks guys, read through it all ... it seems like at (say) just a few inches, the hot spot of an xml would be about the same size, but much brighter, than a similar xp-g (all else being equal)... I'm still struggling with whether these extrapolated numbers tell me whether a particular xml light is as bright as a particular xpg light at shorter distance. The shots that hwc pointed out seem to indicate the xmls could be brighter at short distance, though selfbuilt's numbers don't always reflect that. I guess there's another way to ask: Chevy_ss, you have an xpg and xml model of the exact same light. At 5-10 feet away, to your eyes does the peak intensity of the hot spot of one differ much from the other?

 

[hwc]

At 5-10 feet away, to your eyes does the peak intensity of the hot spot of one differ much from the other?

These lights are all so bright that, on max output, their hotspots will set dry grass on fire at 5 or 10 feet. :) At really close range, the hotspots are probably too bright and you'll be most likely to go to something less than MAX.

 

[gcbryan]

Thanks guys, read through it all ... it seems like at (say) just a few inches, the hot spot of an xml would be about the same size, but much brighter, than a similar xp-g (all else being equal)... I'm still struggling with whether these extrapolated numbers tell me whether a particular xml light is as bright as a particular xpg light at shorter distance. The shots that hwc pointed out seem to indicate the xmls could be brighter at short distance, though selfbuilt's numbers don't always reflect that. I guess there's another way to ask: Chevy_ss, you have an xpg and xml model of the exact same light. At 5-10 feet away, to your eyes does the peak intensity of the hot spot of one differ much from the other?

If something is brighter at a long distance it's also brighter at a short distance. A beam can't go a certain distance and then suddenly get brighter.

The difference is that the hotspot of the XM-L is a lot bigger. The hotspot of the XP-G is a little brighter. Up close you will consider that the XM-L is brighter because the bright area is larger.

In reading your posts I would say that the XM-L is what you are looking for.

 

[tre]

It doesn't matter which one they use because for formula for the canadela intensity (and for the beam throw) both factor in the absolute intensity of the hottest spot and the distance at which it was measured. The candela and beam distance numbers should be directly comparable between all lights measured under ANSI standards.

This is actually not quite true. The beams on certain lights, a TK70 for example, are not fully converged at shorter distances. Yes, you are correct that in theory we can measure at any distance and calculate back to 1 meter (using the inverse square law) and the measurement will always come out the same. In practice this is not the case. My testing shows totally inaccurate beam intensity calculations at close distance. It is worse with certain lights.

 

[hwc]

Good point. Probably not an issue in real ANSI testing, which requires a selecting a test distance that it is at least ten times the diameter of the light source. I don't think 1 meter would be a "legal" test distance for the TK70 under ANSI testing.

I think that's why they had to offer multiple test distance options for the standard as a distance appropriate for a key chain light would not be appropriate for a search and rescue light.

In any case, I doubt that a TK70 on max would be the best choice for reading a book at 1 meter!

 

[Joe Talmadge]

If something is brighter at a long distance it's also brighter at a short distance. A beam can't go a certain distance and then suddenly get brighter.

That, honestly, is what I don't quite understand, and am struggling with whether I"m being stupid. Tre seems to address it somewhat below. But thinking about it from a different point of view: if I start at some point arbitrarily close to the lense -- say, 1mm away -- the hot spot sizes are going to be nearly identical, but the xml light may have 3x the photons of the xpe light. Right so far? We're measuring so close to the lense that it doesn't matter how focused, the hot spots are the same size -- the size of the lense (plus a bunch of accidentally measured spill). Now, go out 20 yards -- the angle of the beam is so much broader in the xml, that you still have the same amount of photons in the hot spot, but now the xml's hot spot is bigger, and so 3x the photons in 4x the total area yields a dimmer hot spot. I don't see what I got wrong in that description ... and if it's right, then you should be able to follow the beams from 20 yards out back to 1mm in, and somewhere along the line, you'll find that place where the xml's hot spot has tightened up enough that it's exactly as bright as the xpe's hot spot. Am I full of it?

 

[peterharvey73]

If we compare Nikon versus Canon camera lens quality from two post card size photos - you will not be able to tell the difference.
However, if we magnify and blow the print to 1 meter in size, then when you look at the edge of objects, you notice the extra sharpness - you will be able to tell that the Nikkor lenses are sharper!

Likewise with flashlights.
At a distance of 1 mm, there is a difference, but it is a tiny difference in hotspot size and hotspot intensity between R5 and XM-L emitters - not enough for the human eye to detect.
This is especially true for brightness.
At very short distances like 10 mm, though the R5 is brighter, the human eye's iris tends to shut this extra brightness out to compensate.
At 10 mm, you will notice that the XM-L's hotspot is a fraction larger.

However, at a distance of 10 meters, this difference is magnified, and much more obvious..

 

[jorn]

What you are seeing is lumens tured to lux. The xp-g should have more lux (throw) if you give them some range. But at 1 inch range the reflector has no function at all. So what you see is that the xm-l bombard a 1" area with 500lumens , and the xp-g has maby 270lumens on a 1" area. Lumens is the total output of light, lux is lumens pr square meters. Since the reflector has no room to focus any of the leds, the one with most lumens will give more lumens pr suare meter (lux). Give them some range for the reflector to work and youll se that the smaller and slightly more "intense glowing" xp-g will have the egde over a xm-l.

 

[JoVo]

If we compare Nikon versus Canon camera lens quality (...) you will be able to tell that the Nikkor lenses are sharper!

Not true.

At very short distances like 10 mm, though the R5 is brighter, the human eye's iris tends to shut this extra brightness out to compensate.
At 10 mm, you will notice that the XM-L's hotspot is a fraction larger.

Well, it's not necessarily a R5 but a XP-G. Also at short distance the XM-L should be brighter than the XP-G.
I think we should talk about measurements and numbers and not what your eyes do when you shine a light on a wall. Of course nobody will shine 300 Lumens at a white wall 10mm away and try to see a difference in intensity.

 

[jsalmika]

Just compare the beam shots in this review:

http://lygte-info.dk/review/Beamshot Quark 2011-08 UK.html

Look at the Quark X AA2 (XM-L) next to the Quark AA2 (XP-G)

Note that it's mentioned there that "The old Quark is a warm version." (-> lower output than in CW/NW).
I suppose it's still a XP-G version although it's called just as "4Sevens Quark AA-2 (old)".