OK, I think I get it, not all Lumens are created equal....right?

hotbossa · Jan 16, 2008

OK, I play guitar and I know about watts. 60 watts through a 1, 12" speaker combo amp isn't going to be as loud as 60 watts through a Half-Stack of Marshalls. It would actually make more sense to measure these amps in decibels. So are lumens the same way? I keep hearing that a "Surefire" lumen is more potent than a "Fenix" Lumen. When Fenix says they have a light that is 220 Lumens and it seems that Surefire's comparable models go to about half of that then the Fenix looks more appealing. What do you guys think? Am I on the right track? I have been trying to wrap my mind around this whole lumen game but have seemed to miss the boat.

Thanks!

:popcorn:

Marduke · Jan 16, 2008

Lumens are lumens. The difference is WHERE they are measured.

Most manufactures list emitter lumens, which is what the emitter puts out when driven at a given current. A few manufacturers list torch or "out the front" lumens, which is the lumens which leave the front of the flashlight.

Neither is more correct than the other (although emitter lumens are generally more accurate), it's just a different way of measuring them.

It depends greatly upon the specific light, but generally there is a 10-30% reduction from emitter lumens to torch lumens.

hotbossa · Jan 16, 2008

Marduke said:
Lumens are lumens. The difference is WHERE they are measured.

Most manufactures list emitter lumens, which is what the emitter puts out when driven at a given current. A few manufacturers list torch or "out the front" lumens, which is the lumens which leave the front of the flashlight.

Neither is more correct than the other (although emitter lumens are generally more accurate), it's just a different way of measuring them.

It depends greatly upon the specific light, but generally there is a 10-30% reduction from emitter lumens to torch lumens.

OK, that is making more sense.....It is like stating the horsepower of a car from the crankshaft rather than the rear wheels. Interesting.....

Is the Surefire rating thier lumes out the front or emitter?

woodrow · Jan 16, 2008

With their incan lights, SF usually measured them out the front, and often underestimated them. With their led lights....I would look at Chevrofreak's and other's runtime/output graphs.

violatorjf · Jan 16, 2008

hotbossa said:
It is like stating the horsepower of a car from the crankshaft rather than the rear wheels. Interesting.....

Very good analogy :thumbsup:

Kiessling · Jan 16, 2008

Neither is more correct than the other

Being a hair-splitter

... I have to disagree.

When talking about the output of a flashlight, you wanna know what comes out the front of the torch as usable light, and not what the theoretical luminous flux of the emitter is.
The problem is that measuring torch lumens is far from trivial, you need an integrating sphere to do it. Expensive and difficult process.

Most manufacturers quote the theoretical luminous flux of the LED emitter according to the data sheet. However, they do not take into account the losses of light transmission dues to the lens and reflector ... AND ... the heating of the die with the reduced efficiency ... etc.
Which means that you actually do not get just another way of measuring output ... but a number quoted from a data sheet that is known to be incorrect. There is no measurement. It is deception.

This situation makes a comparison of manufacturer claims difficult at best.

Manufacturers that measure true luminous flux out the front end (list not complete):
Arc
HDS
Novatac
SF

Then there are the "theoretical emitter lumens" manufacturers like Fenix et al. ... but the worst bunch are the liars, those that put marketing hype before everything else. Typically those are the cheap lights that you recognize right away so there's no real danger and just some annoyance. But there are others who play the game quite well. LED Lenser (Coast in USA) comes to mind. They sport some of the wildest claims in the industry.

If you really wanna know what is going on, you have to become a flashaholic and use CPF's resources.

bernie

Size15's · Jan 16, 2008

Marduke said:
Lumens are lumens.

This is the case when comparing two beams of light with the same wavelength spread and intensity of the various wavelengths of visible light spectrum under the same conditions.

The lumen is the unit of luminous flux, a measure of the perceived power of light. Luminous flux is adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light. The luminosity function describes the average sensitivity of the human eye to light of different wavelengths. For everyday light levels, the photopic luminosity function best approximates the response of the human eye. For low light levels, the response of the human eye changes, and the scotopic curve applies.

For flashlight users one may also consider mesopic vision - a combination of photopic vision and scotopic vision in low but not quite dark lighting situations.

What this means is that 100 lumens of red light is a different quantity of light to 100 lumens of green light - there needs to be more red light in order for the human eye to perceive it as the same. This is further complicated as the sensitivity of the eyes changes as the overall level of light decreases.

Marduke said:
Neither is more correct than the other (although emitter lumens are generally more accurate), it's just a different way of measuring them.

I disagree - the lumen output of a flashlight is correct when it is the measured light output from the flashlight. It doesn't matter what the output of the LED is unless you are working out the losses etc. Some companies base their output ratings on calculating the output based on specifications tables for the LED's. A flashlight is not hosting the LED in the same conditions as it was when the specs were determined.

Al

StarHalo · Jan 16, 2008

From the non-technical gallery: You can't perceive a difference of a few dozen lumens, so don't get too caught up in the numbers. Use advertised lumen numbers as a guideline. (It's usually the runtime numbers that are WAY off anyway)

[From the guitar tech gallery: 60 watts through a 1X12 combo will be louder than through a 4x12 half stack. In a 1x12, the speaker is getting 60 watts, in a 4x12, each speaker is getting 15 watts. The combo speaker will "break" earlier, whereas the speakers in the cab won't get enough power.]

LukeA · Jan 16, 2008

Kiessling said:
Manufacturers that measure true luminous flux out the front end (list not complete):
Arc
HDS
Novatac
SF

Pelican, too.

Rowrbazzle · Jan 16, 2008

hotbossa said:
It is like stating the horsepower of a car from the crankshaft rather than the rear wheels.

Yep, precisely. The only problem is that some of the companies advertise torch-lumens (rear-wheel horsepower) and some advertise emitter-lumens (crankshaft horsepower). And a few are advertise BS lumens. You've just got to keep track of which companies are which.

Seems like "drive-train losses" - the difference between emitter and torch lumens - generally run 20-25% or so. (The 5% or so that you might be off probably isn't too important, since your eyes won't be able to tell the difference.) Output from my old Fenix L2T (55 emitter-lumens) looks almost exactly the same as that from my HDS B42 (42 torch-lumens).

Size15's · Jan 16, 2008

StarHalo said:
From the non-technical gallery: You can't perceive a difference of a few dozen lumens, so don't get too caught up in the numbers. Use advertised lumen numbers as a guideline. (It's usually the runtime numbers that are WAY off anyway)

I agree - the output ratings of flashlights should be used as a guideline when comparing models from the same brand/manufacturer. Output ratings are not very useful for comparing different brands of flashlight.

Al

KeyGrip · Jan 17, 2008

Also, output is not the be-all end-all specification of a flashlight. To me, output is secondary or tertiary depending on other factors, especially intended use.

KenAnderson · Jan 17, 2008

Kiessling said:
Manufacturers that measure true luminous flux out the front end (list not complete):
Arc
HDS
Novatac
SF

Can add McGizmo's McLux lights to this list.

Also, some makers give runtimes at brightness levels that are flat for the full run, others give a runtime at a brightness that is declining through out the run.

Ken

MiniLux · Jan 17, 2008

hotbossa said:
OK, I play guitar and I know about watts. 60 watts through a 1, 12" speaker combo amp isn't going to be as loud as 60 watts through a Half-Stack of Marshalls. It would actually make more sense to measure these amps in decibels. So are lumens the same way?

Well, staying at your example, I would guess it's more the difference between watt PMPO and watt RMS. The first one is what you may get out at real max just before it goes :poof:

, while the other one is what you really may expect :devil:

DocBuckeye · Jan 17, 2008

:thinking:Along this line of thought...Is the percieved brightness of a light a linear relationship as lumens increase? (sorry if newbie question)

Size15's · Jan 17, 2008

DocBuckeye said:
:thinking:Along this line of thought...Is the percieved brightness of a light a linear relationship as lumens increase? (sorry if newbie question)

I very much doubt it. I'd guess it was more of a log relationship...
I guess it also depends on the beam relative to the ambient illumination as well as the targets being illuminated etc

Kiessling · Jan 17, 2008

Doc ...nope, it is logarithmic, making some few dozen luimens more or less really insignificant in the higher output lights of 80+ lumens.
bernie

mudman cj · Jan 17, 2008

It's geometrical, and follows Steven's power law. For an illuminated surface at a distance the exponent is about 0.33, so it takes 8 times more light intensity for us to perceive it as twice as bright. A point source is perceived with a power of 0.5, which would require 4 times the intensity to be perceived as twice as bright. Of course, this can vary depending on the situation (size of the lighted area and distance from it, reflective properties of the surface such as color, the photometric spectrum of the light, etc.).

Hitthespot · Jan 17, 2008

Size15's said:
This is the case when comparing two beams of light with the same wavelength spread and intensity of the various wavelengths of visible light spectrum under the same conditions.

The lumen is the unit of luminous flux, a measure of the perceived power of light. Luminous flux is adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light. The luminosity function describes the average sensitivity of the human eye to light of different wavelengths. For everyday light levels, the photopic luminosity function best approximates the response of the human eye. For low light levels, the response of the human eye changes, and the scotopic curve applies.

For flashlight users one may also consider mesopic vision - a combination of photopic vision and scotopic vision in low but not quite dark lighting situations.

What this means is that 100 lumens of red light is a different quantity of light to 100 lumens of green light - there needs to be more red light in order for the human eye to perceive it as the same. This is further complicated as the sensitivity of the eyes changes as the overall level of light decreases.

I disagree - the lumen output of a flashlight is correct when it is the measured light output from the flashlight. It doesn't matter what the output of the LED is unless you are working out the losses etc. Some companies base their output ratings on calculating the output based on specifications tables for the LED's. A flashlight is not hosting the LED in the same conditions as it was when the specs were determined.

Al

Did you want to talk about the weather or where you just making conversation.
.

Size15's · Jan 17, 2008

Hitthespot said:
Did you want to talk about the weather or where you just making conversation.
.

I don't want to talk about the weather - Over the last few days we've had Flood Incident Rooms open across the country. In my office we've been pulling shifts to provide 24 hour cover. We've shut the room this evening but more rain is expected tomorrow and at the weekend so we're on call.

OK, I think I get it, not all Lumens are created equal....right?

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