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Author Topic: Candlepower vs. Lumens (What's the difference?)  (Read 6787 times)
Heyimjack
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« on: January 28, 2008, 02:16:05 PM »

I get MANY MANY calls for this. Would someone or everyone explain the differences between the two. Both are measurements of light, but how are they different and which is a better (in your opinion) measurement for flashlights?...jP
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will
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« Reply #1 on: January 28, 2008, 04:16:56 PM »

try this

Summing it all up:

Candlepower is a rating of light output at the source, using English measurements.
Foot-candles are a measurement of light at an illuminated object.
Lumens are a metric equivalent to foot-candles in that they are measured at an object you want to illuminate.
Divide the number of lumens you have produced, or are capable of producing, by 12.57 and you get the candlepower equivalent of that light source.

this is from this web page.

http://www.theledlight.com/lumens.html
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nightcrawler
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« Reply #2 on: January 28, 2008, 06:03:26 PM »

Ummm....so 'candlepower' are like 'muzzle-velocity' and lumens are like 'blunt trauma', eh?


(And you all thought I couldn't talk guns!) grin
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AshA4
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« Reply #3 on: January 28, 2008, 06:23:23 PM »

Jack just ask your customers which two lights they are thinking about purchasing and tell them to buy the more expensive one!  grin
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speederino
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« Reply #4 on: January 28, 2008, 07:05:32 PM »

http://www.flashlightreviews.com/features/lux.htm

Candlepower/foot-candles/lux measures 'throw' of a light, or how good the light is at projecting at a distance. Lumens measures quantity of light produced. Both are worthwhile measurements needed to understand a light. IMHO one is useless without the other.
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« Reply #5 on: January 28, 2008, 11:32:26 PM »

From the Welcome Mat:

Q: What's the difference between "lumens" and "lux"?
A: Lumens measure the total amount of light output from a particular source. Lux measures the intensity of the light hitting a specified area. For example, an ordinary household lightbulb generates about 1000 lumens, but the intensity of its light at a particular point, such as on a book you're reading, will be comfortably low. Almost all flashlights rely on an optical device such as a reflector or lens to squeeze most of their output into a small area, which allows you to illuminate a point of interest with enough intensity, but without requiring a lot of power. To illustrate this concept, try the following: First, look at your room's ceiling light. In all likelihood, you can stare at it without much discomfort. Now, try looking into a weak flashlight like a traditional incandescent Mini-Maglite. You'll notice that it seems very bright. This is lux. Now, remove your Minimag's head to put it into candle mode. Try switching between its output and your ceiling light's output. Since they're now illuminating approximately the same area, the much higher lumen value of the ceiling light will provide much higher lux values at a chosen point. An extreme example of high lux and low lumens is a laser, which doesn't really create that much light, but focuses it into a tiny, brilliant point.
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« Reply #6 on: August 02, 2009, 08:09:09 AM »

The bottom line: candlepower is not very exact and most companies can make any candlepower claim, while lumen is a formular and more exact way to measure emited light and companies can't fudge the numbers as much.
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gswitter
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« Reply #7 on: August 02, 2009, 03:58:34 PM »

The bottom line: candlepower is not very exact and most companies can make any candlepower claim, while lumen is a formular and more exact way to measure emited light and companies can't fudge the numbers as much.

Unfortunately, there's no standardization for the usage of lumens, and the term can be (and is) just as easily abused.

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Handy
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« Reply #8 on: August 03, 2009, 07:07:40 AM »

The bottom line: candlepower is not very exact and most companies can make any candlepower claim, while lumen is a formular and more exact way to measure emited light and companies can't fudge the numbers as much.

Unfortunately, there's no standardization for the usage of lumens, and the term can be (and is) just as easily abused.



Lumen is quite standardized just like watts. The standards may not be readily accessible, but it is.  It's like watts in stereo systems.  Manufacturers don't always stick to the same rating standard. 

To express comparatively:
watts = pounds
candlepowers = pounds/sq.in


So, a pound of weight is a pound of weight.  A pound of weight focused to rest on a 1/100 of a square inch exerts a pressure of 100 lbs/sq-i.
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cjdelphi
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« Reply #9 on: August 03, 2009, 10:14:28 AM »

From my understanding it's pretty much as simple as....

Lumens = total light output
Candle Power = Measured by brightest intensity at the spot.

Candle Power makes no sense to me because how far away do you stand and measure it.

candlepowerforum.com

lumenpowerforum.com

Anyone made that site yet?
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gswitter
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« Reply #10 on: August 03, 2009, 01:30:27 PM »

The bottom line: candlepower is not very exact and most companies can make any candlepower claim, while lumen is a formular and more exact way to measure emited light and companies can't fudge the numbers as much.

Unfortunately, there's no standardization for the usage of lumens, and the term can be (and is) just as easily abused.



Lumen is quite standardized just like watts. The standards may not be readily accessible, but it is.  It's like watts in stereo systems.  Manufacturers don't always stick to the same rating standard. 

To express comparatively:
watts = pounds
candlepowers = pounds/sq.in


So, a pound of weight is a pound of weight.  A pound of weight focused to rest on a 1/100 of a square inch exerts a pressure of 100 lbs/sq-i.

That's not what I meant.

Lumens as a unit of measurement is absolutely defined, but there's nothing standard about the usage of the term "lumens" to define the output of a flashlight. Even ignoring the manufacturers/resellers that outright lie, the term "lumens" can refer to the spec'ed luminous flux for the emitter (typical, maximum, etc), an estimated out-the-front value based on the aforementioned spec (again - typical, maximum, etc), an actual measured value from an integrating sphere (and who knows how accurate it actually is), etc. Then there's the issue of luminous flux for a model/bin of LED being a range of values as opposed to a single value - and is a light recalibrated for specific output or is the current the LED sees consistent from unit to unit? And the same light can put out different values based on the type of lens, collimater, etc, and lights sometimes ship with multiple configurations. You can easily have dozens of lumens readings for the same light, all of which are technically correct.
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« Reply #11 on: August 03, 2009, 05:31:18 PM »


That's not what I meant.

Lumens as a unit of measurement is absolutely defined, but there's nothing standard about the usage of the term "lumens" to define the
output of a flashlight.
I'm with you there.  I was addressing the thread starter's question. 

Quote
Even ignoring the manufacturers/resellers that outright lie, the term "lumens" can refer to the spec'ed luminous flux for the emitter (typical, maximum, etc), an estimated out-the-front value based on the aforementioned spec (again - typical, maximum, etc), an actual measured value from an integrating sphere (and who knows how accurate it actually is), etc.

I think the popular trend is to "quote" off most favorable data based and pass it on as such and it is often preceded by the statement "maximum xxx lumens" or "up to xxx lumens", so they might pick the most favorable bin range from the datasheet, pick 25C junction temperature and maximum current to get their value. 

There is really no standard for flashlights.  A lot of cheap audio equipment uses PMPO watts.  It's not uncommon to see dry cell powered Chinese boomboxes with PMPO ratings in mid three figures. 

Cars often use consistent, protocol for defining output http://en.wikipedia.org/wiki/Horsepower


Quote
Then there's the issue of luminous flux for a model/bin of LED being a range of values as opposed to a single value - and is a light recalibrated for specific output or is the current the LED sees consistent from unit to unit? And the same light can put out different values based on the type of lens, collimater, etc, and lights sometimes ship with multiple configurations. You can easily have dozens of lumens readings for the same light, all of which are technically correct.
Hence the prefix "up to". 
Each manufacturer has its own definition.  It appears that Surefire has a reputation for at least meeting the spec lumens. 

Some speak equally favorably on CPF about Fenix products but as far as I know, the claims are based on amateur, home made light meters.  I think there was ten samples of one Fenix that was tested side by side with Arc, but for most models, I've yet to see data on Fenix from an integrating sphere with a current traceable calibration. 
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deusexaethera
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« Reply #12 on: August 03, 2009, 08:13:02 PM »

My understanding is that candlepower is the measurement of how bright the light is at any one point on a sphere surrounding the light source, making the assumption that the light is evenly bright around the entire sphere (as a candle would be). Of course, marketing being what it is, manufacturers usually choose to measure at the BRIGHTEST single point around the light source, which is why small lights with highly-focused beams can have seemingly impossible candlepower ratings.

Lumens, on the other hand, is a measurement of the total amount of light put out by the light source, regardless of which direction it emanates in, hence the need for an integrating sphere to reflect all of the light onto a measuring device, instead of just placing the measuring device in the path of the focused beam as is done when measuring candlepower.

Lux and foot-candles extrapolate on lumens and candlepower (respectively) by trying to determine the light's brightness at various standardized distances, whereas lumens and candlepower themselves don't account for diminishing brightness over distance, only absolute output.
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