Why Lumens?

Roy

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Why is everyone hung up on the Lumen rating of a flashlight? It seems to me that the only time Lumens comes into play is when you're intrested in the spherical output of a light...and that is hard to get....even a minimag in candle mode is not spherical, its bulb sits on a flat surface. The measuring of Lumens requires very special measuring equipment that cost in the 5 figure range.

Generaly speaking, the light from a handheld flashlight (not a lantern) is projected as a cone of light and is thus measured in Candlepower(Fc), LUX or Candellas(cd). These measurments are made in the brightest part of the beam using calibrated lightmeters that generally cost in the $60-$300 range.

Which tells you more about a flashlight, the fact that it puts out 1,000cd or 100Lumens? IMHO knowing the cd and shape of the beam of light tells you more about a flashlight than knowing the total amount of light(Lumens) generated by that flashlight.

IMHO, a graphical system like that used by "Quickbeam" in his Flashlight Reviews website, when combined with beam measurments (Fc, LUX, Cd), tell you more about a flashlight than any other measurment.
 

JohnK

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Roy, you have been around the track here, I am surprised at the question.

The old anology of a very high candlepower laser (very narrow beam) with almost zilch lumens, compared to a flood beam high binned 3 watt Lux (wide beam), and a ton of lumens comes to mind.

You can't understand the beam without both measurements. You can't understand the usefullness of the light without both. Quickbeams (and others) beam shots give us this mix in an overall sort of way, and I find them most useful.

Another item of GREAT importance to me is a great and wide spill, combined with a bright hot spot. I love lights with BOTH, and candlepower ratings (lux) measurements don't tell me squat in the overall scheme of things.

I developed the "BB" method of thinking about light.

If "X" lumens is represented by 1,000 BB's (photons, if you wish, anyway a unit of radiated light), you can put the 1,000 BB's in a straight line (aka, laser) and you'd have a perfectly USELESS beam for walking through the woods, identifying most anything, or whatever.

Picture 500 of the BB's in a tight "hot spot" of larger diameter, and you wind up with medium CP, throw, or lux, but you have the other 500 BB's in the spill beam, to give you a wonderful visual picture of what is going around you.

We have the luxury of taking those 1,000 BB's (light units, photons, whatever) and through reflectors, optics, whatever, mix, and match the radiation of the light to suit us. BUT, you still start with "X" BB's (with that particular light source).

Lights are for SEEING, and perceiving visible objects.

Please don't think I am "talking down" to you. I'm still trying to understand the "big" picture also.

As an optometrist, I've spent a lifetime thinking about the facinating qualities of light, and our limited perception of it. This forum has just involved me further. What fun !

By the way, thanks for the excellent runtime charts, another facet to always consider.
 

FluffyGrunt

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Personally I find lumens with a description of the beam gives me a better idea of what to expect from a light. When I see: 1,700 lux, 2,200,334 mc, 8 billion candlepower or whatever I just ignore it because it means nothing to me.
With lumens I have several lights with reliable lumen measurements to compare to, with lux, cp and etc I don't have any light with a known cp,lux,candela measurement to compare it to so it's just a number.
 

VidPro

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i agree with you all :)
so far COMPARISONS are Very usefull. and beam patterns are usefull. and full info is usefull, but specs from the manufactures are :) ummm , not as usefull as CPF members evaluations.
center meter ratings to me arent usefull unless i need JUST a spot, and that is not very often. or if the thing will do a primo spot AND a primo wide.

spots to me are useless when your to close to the subject. when your out walking and trying to light the path.

both spot and wide are usefull when under the car doing maintainance.
spot is great when your distance trying to find something.

but when i am in the dark, and I want to light for my eyes, i want about 15-30* in front of me lite, because that is what i SEE, i dont see 2*, unless i got binoculars on :)
that is my area of concentrated vision.

my #1 most helpfull light is still a 1W with a standard luxeon optics, and no focus. it puts out a perfect blend, that doesnt mess up my iris, and just lights everything i see.

i want the LUMEN rating of the seperate components, that is for sure, how they rate the builds isnt as important to me, as long as they have the chart, the beam photo, and some standardized way of measuring any aspect of the beam.

the "led museum", and "flashlight reviews" stuff is very usefull.
 

LightObsession

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Quickbeam's total output measurement is probably just as useful as lumens measurement for comparing the total output of one light to another as long as to process is consistent and no light escapes from the lite box. It seems that many people focus only on the throw (brighness) numbers that he posts and ignore the total output measurements and mistakenly state that one measured light has more output than another measured light because it's throw (brightness) measurement is greater. This is only true if the total output measurement is also greater. This mistake is usually only made by those who haven't read the definitions of throw and total output.

An integrating sphere is usually coupled with a spectrometer which adds the capability of measuring the correlated color temperature (CCT) and color rendering index (CRI) which are very helpful in determining objectively if the output of a particular light is a color you're likely to desire or be willing to put up with. This may be more helpful than reports from individuls saying subjectively that one of their lights X is bluer than light Y, but light Y is bluer than light Z.

These setups require that the system be calibrated with calibration standards (light sources with known characteristics) periodically in order to maintain their believeability over time because of aging of the inner surface of the integrating sphere and the spectrometer electronics.

This is alot more work than Quickbeam's measurements and probably not worth the effort to most people just to get the additional CCT and CRI information. I personally would greatly appreciate this information when evaluating lights that I don't have the opportunity to handle personally before making a purchase decision.

I rely on Quickbeam's, Roy's and Craig's (and many other's)data and observations for evaluating lights because they are very good and have objective and consistent methods for comparing lights using consistent setups and equipment.

Keep up the good work guys.
 

MaxaBaker

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Well, a short answer from me is.........It wouldn't seem as impressive if the Ken5 was measured in lux or cd. Hearing that it is 16,000 lumens gives you a much better idea of how freaking bright it is.

my 1/2 cent......
 

Roy

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Max.....but how is your 16,000 Lumens being projected?..in a sphere?...in a 90 degree beam?...10degree beam? When you say Lumens, I think of a sphere of light NOT a beam from a flashlight.
 

LightObsession

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[ QUOTE ]
Roy said:
Max.....but how is your 16,000 Lumens being projected?..in a sphere?...in a 90 degree beam?...10degree beam? When you say Lumens, I think of a sphere of light NOT a beam from a flashlight.

[/ QUOTE ]

Isn't lumens total output regardless of it's direction or beam shape?
 

Roy

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Lumens tells me how much light the light SOURCE (led or bulb) is generating. It does not characterize how the light is being projected. Think about putting a MiniMag into "candle" mode...do the Lumens change when you take the head off the light?
 

LightObsession

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[ QUOTE ]
Roy said:
Lumens tells me how much light the light SOURCE (led or bulb) is generating. It does not characterize how the light is being projected. Think about putting a MiniMag into "candle" mode...do the Lumens change when you take the head off the light?

[/ QUOTE ]

A light meter doesn't characterize the beam either. If you used a light meter on a mini mag in "candle" mode, you'd think you were measuring a coin cell key chain light rather than a 2AA light. The integrating sphere should give similar numbers whether the light has the optics installed or is in candle mode, but should read higher in candle mode than with optics because most optics trap some of the light from the emitter.

Beam shots and verbal descriptions are still needed to describe how the light is being projected.
 

Roy

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Yes but, Fc/Lux/Cd does, to some degree, characterize how light is being projected by their definition...in a beam. It is true more than a single light measurment is needed to characterize the light output of a flashlight...some sort of beam description is also needed.

In reguards to my anology of the MiniMag....yes there will be some loss of light in the reflector and lens...I was just trying to make a point. Lets not pick nits. /ubbthreads/images/graemlins/icon6.gif
 

Mags

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Roy has a point there. Isnt lumens very general in measuring light? It doesnt demonstrate the throw of a light, but overall light. For example, a 100 lumen light. WOW as most would say. But how far does it throw? Like pretty much most 2 or 3 celled 5 watt luxeons are rated around or over 100 lumens right? But the lumens dont describe throw. Everyone here knows that right? 5 watters dont throw, they provide excellent flood. Since the light covers such a large area, the lumens rating is very high. Before I knew how useful lux was, I would simply be saying "LUMENS LUMENS LUMENS". Then I knew lumens wasnt everything, that it didnt measure throw, which is extremely important. Lux can do that, and the reviewer can give a nice beamshot and describe if the beam is exactly like the beamshot, or not. So I decided to depend on lux ratings instead. Besides, many, if not all distributors give dis-honest lumen ratings, and even if they were accurate ratings, I wouldnt know how much throw is provided by the product. And since the integrating sphere is so expensive, and lumens isnt that specific, why bother to depend on lumen ratings? I also read the overall output ratings that Quickbeam provides in his reviews. It helps me picture what the beam is like.
 

LightObsession

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I agree that lux measurements for total ouput at www.flashlightreviews.com are just as useful as lumens measurements in an integrating sphere for quantifying the total light out of the flashlight. Neither describes the beam characteristics and isn't expected too.

The main advantage I see gathering lumens data is that CCT and CRI data are usually collected along with the lumens data. Quantitative data on the color of the light is helpful, but usually not worth the extra investment.
 

MaxaBaker

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[ QUOTE ]
Mags said:
Isnt lumens very general in measuring light? It doesnt demonstrate the throw of a light, but overall light.

[/ QUOTE ]

Exactly what I'm talking about. Yes, it is a very general way of measuring light. BUT, It doesn't matter what the beam angle is for what I'm trying to say. For an example, if someone asked you how bright the Ken5 is, you dont tell them how far it throws or what the degree of the beam is, you just use a very simple unit that states the total amount of light it puts out (under normal circumstances); a lumen.

"How bright is the Ken5?"......."It puts out 16,000 lumens."

Now, if someone wants to have specifics, then go ahaead and tell them all of the details (fun,fun,fun). But, if you hear 16,000 lumens when you already know that 100 lumens is bright, you naturally say HOLY SH** and **** yourself......just because you know that 16,000 lumens is an incredable amount of light, no matter what the beam angle is.

edit:

[ QUOTE ]
Roy said:
Yes but, Fc/Lux/Cd does, to some degree, characterize how light is being projected by their definition...in a beam. It is true more than a single light measurment is needed to characterize the light output of a flashlight...some sort of beam description is also needed.


[/ QUOTE ]

Oops, I was speaking about the light being a flashlight in one piece (including whatever optics, reflector it is using, etc.) /ubbthreads/images/graemlins/blush.gif I now understand what you mean. Sorry.
 

soloco

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If had to choose between getting a cd or lumen rating, I'd want the lumens rating. I can get a basic feel for the shape just by looking at the refelctor/optic. Ideally, we would always get both.
 

SilverFox

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Hello Roy,

When I think of lumens, I think in terms of raw power. I think of horsepower the same way.

When I think of lux, I think in terms of performance. Kind of like quarter mile times.

Lumens gives me an idea of the possibilities, and also some idea of the power needed. Lux tells me how that power has been put to use.

Tom
 

raggie33

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i think a lumen like the amount a water ya have.i think a lux as the abilty to put the water where ya want it in a certain amout a time
 

Size15's

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You can map the beam of a flashlight with a goniophotometer. This coupled with the total output, colour temperature, how the output changes over time, how the output varies source to source, and battery to battery, and at various temperatures is useful information.

I think it would be interesting to see if the output/runtime curve was the same if intensity was measured or total output was measured.

SureFire uses Lumen ratings to help people decide between their different models - in a time when all the Lamp Assemblies (reflectors) were pretty much the same (size) and the beam profiles were kept similar. In such a situation the total output or their Lumen rating gave you a good impression of what an increase in light output was going to get you - larger central beam and brighter surround beam.

Now-a-days the significantly increased variety complicates things.

More than one "measurement rating" is required to get a good understanding of the beam. However, SureFire's Lumen outputs I feel give a better impression of what to expect (if you have already seen a SureFire that is).

Going in cold ratings are almost worthless in my opinion.

Al
 

Leeoniya

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so many threads that cover the same topic...so little time to copy and paste answers between them all, heh.

let just get this straight. keeping everything equal (reflector and emitter surface area). more lumens in that same surface area will increase the surface flux of the source and the intensity of the light. so say, you have 100 lumens will give more throw and lux than 10 lumens in the same configuration.

if the emitter surface area is not the same, and the flux density is different, the amount of lumens cannot be related to the throw of the other light.

so in comparison purposes, the directivity given by the reflector, the emitter surface area, and LUMENS/SURFACE AREA, will determine throw.

simply comparing lumens will never give you any sort of basis for comparing the throw of 2 different lights, even with equally efficient reflectors. to compare throw you must be certain that the more lumens is coming out of the same surface area, thus increasing intensity.

it's like comparing the volume to density. yes they're related. but without knowing mass, there is no way to relate the two, unless you know the mass is identical even without knowing what it is.

the total amount of light produced by a bright source can be reproduced by many many dimmer sources, which will never throw the distance of one source of the same lumens, even if each dimmer source had its own reflector and all the resulting beams were pointed in one target. thats why 1,000 inovas dont throw 100,000ft.

Leon
 

2dim

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[ QUOTE ]
This is alot more work than Quickbeam's measurements and probably not worth the effort to most people just to get the additional CCT and CRI information. I personally would greatly appreciate this information when evaluating lights that I don't have the opportunity to handle personally before making a purchase decision.

[/ QUOTE ]

Exactly! Comparing mere figures rather than actual lights in hand simply can't compare...even then, unless different options can be tested together under the identical circumstances in which they are meant to be used, mostly what we're left with is speculation and individual opinions. Light is definiely a very interesting subject and flashlights obviously quite fascinating, but surely the nature/means of communication itself limits comparisons of ANYTHING based solely on words. Although beamshots are always eagerly welcomed, still I'm left questioning just how much can be learned, especially if the pictures are posted primarily to encourage sales. Integrity of those providing info remains most significant, of course, but the medium to a large extent influences the message... Computers have their uses, however face-to-face with items-in-hand cannot be duplicated through figures of any kind IMHO. That's part of why CPF meets are so much fun, eh? Really sorry to have missed the Las Vegas show...
 
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