Clarification of Candlepower and Lumens

[njs05]

I have been reading alot about different flashlights etc and I see that some are compared in lumens and some in candlepower. I have read alot at wikipedia about the difference between all of the different names and this is what I have come up with. So from what I can gather candlepower is basically the most intense spot of light given off from teh bulb, as in... the tighter the beam of the same wattage/lumen light... the higher the candlepower.. is that correct? Also, the lumens is basically the total amount of light given off by the light regardless of direction of light or tightness of beam... correct? and the wattage is the total amount of power used by the light and given off in some fashion (visible, infrared, heat, etc) So a 35w bulb can give off 1000 lumens or 3000 lumens and the only difference is the efficiency of the bulb? Am I getting this correct? And so from this... you cant easily convert a candlepower number from one light to a lumen number from another light?

 

[maxilux]

Welcome, we talked about this here:

http://www.candlepowerforums.com/vb/showthread.php?t=178070

there you find all you must know about this, but you are right

 

[jbosman1013]

I would say your on the right track but instead of candlepower most people measure the "intense spot" with a term called Lux

 

[njs05]

What is the difference between lux and candlepower? Is candlepower the same as candela? Isnt lux just candlepower on an object the light is projected onto instead of measured at the source of the light?

 

[KeyGrip]

What is the difference between lux and candlepower?

I always see Lux used as a measure of intensity at a given distance, usually one meter. I don't think CP has any restriction like that.

 

[njs05]

Ive read through the links, but Im still having a hard time grasping the lux/candlepower concept. I took classes with this information a while back... but its not coming back to me easily... can anyone offer any other insight into the lux/candlepower deal?

 

[SilverFox]

Hello Njs,

Welcome to CPF.

Both lux and footcandles (also referred to as candlepower) measure the same thing. Lux measure candela at 1 meter and footcandles measures candela at 1 foot.

You can convert between the two.

1 footcandle = 10.764 lux, and
1 lux = 0.0929 footcandles.

Tom

 

[leprechaun414]

Ive read through the links, but Im still having a hard time grasping the lux/candlepower concept. I took classes with this information a while back... but its not coming back to me easily... can anyone offer any other insight into the lux/candlepower deal?

I think what he is asking for is the conversion for when a light states lumens, he wants to know what it would be for candlepower.

Such as when the Magcharger states 30,000 Candlepower, how many Lumens would that be?
Or when a light states 100 Lumens, what candlepower that would be?

O and :welcome:

 

[Curious_character]

Ive read through the links, but Im still having a hard time grasping the lux/candlepower concept. I took classes with this information a while back... but its not coming back to me easily... can anyone offer any other insight into the lux/candlepower deal?

Candlepower (or candelas or candles -- all the same thing) measure the intensity of light being produced by a flashlight in a given direction, while lux is a measure of the illumination level at some measurement point. Candlepower tells you how brightly you can illuminate an object at a given distance (that is, how many lux of illumination you can produce at that distance). A light producing one candlepower of light intensity will light up an object one meter away with an illumination level of one lux. That same light will light up an object two meters away with an illumination level of 1/4 lux, and so forth. The number of lux a light produces at one meter is numerically equal to the number of candlepower it's producing in that direction. You need to know both the lux level and the distance from the apparent light source in order to calculate the candlepower that light is producing.

While candlepower describes the intensity of light in a given direction, lumens tells you the total light output in all directions. For a given number of lumens output, a light can be sharply focused to provide a large number of candlepower in a small range of directions, or it can be made diffuse to provide a lower candlepower value over a wider range of directions. If you want to know how brightly something will be illuminated at a particular distance (that is, the number of lux of illumination at that distance), you need to know the candlepower. You can't determine it if all you know is the total lumen output. (Unless, of course, you also know exactly how the light is distributed with respect to direction, from which you can calculate the candlepower.)

c_c

 

[KROMATICS]

Candlepower measures the brightest part of a beam while Lumens measures overall light output. Since different lights have different beams (flood, spot with spill, spot only) lumens is the best indicator of light output. The more light concentrated into a smaller area the brighter it will appear.

EDIT: See post above this

 

[njs05]

So it is precisely as I said in the beginning?>

 

[Curious_character]

So it is precisely as I said in the beginning?>

Just about spot on. . .

. . . So from what I can gather candlepower is basically the most intense spot of light given off from teh bulb, as in... the tighter the beam of the same wattage/lumen light... the higher the candlepower.. is that correct?

Yes. Technically, the candlepower a light can produce isn't a single number, but a different value in every direction. However, it's almost universally used to mean the candlepower in the most intense direction, as you've said.

Also, the lumens is basically the total amount of light given off by the light regardless of direction of light or tightness of beam... correct?

Yes.

and the wattage is the total amount of power used by the light and given off in some fashion (visible, infrared, heat, etc)

"Wattage" is of course power, and unless explicitly specified, you can't be sure quite what it's indicating. It could be the power being consumed from the battery. Or it can be the power being delivered to the bulb or LED. It could even be the light power being emitted from the bulb or LED. And frequently, it's simply a completely fabricated number intended to make a flashlight seem more "powerful" to a gullible buyer.

So a 35w bulb can give off 1000 lumens or 3000 lumens and the only difference is the efficiency of the bulb?

Yes, if the bulb is consuming 35 watts in both cases.

Am I getting this correct? And so from this... you cant easily convert a candlepower number from one light to a lumen number from another light?

That's about the only statement I'll take issue with. In practice, you can't do it at all. It would only be possible if you knew exactly the relative intensity in all directions of each light. One final comment is that we seldom have decent candlepower or lumen values to work with. Like power "specifications", lumen values are often highly exaggerated and sometimes purely fictitious. And it turns out that really accurate lux measurements are much harder to make than they seem (as was recently brought home to me with some passaround reference lights). So it's sometimes impossible even to convert "lumen numbers" to real lumens and "candlepower numbers" to real candlepower.

c_c

 

[njs05]

So basically there is no way to compare two different lights by the numbers advertised, be it candlepower, candela, lux, lumens, or wattage? I also have seen wildly ridiculous numbers advertised... particularily on walmart spotlight models....

 

[Curious_character]

So basically there is no way to compare two different lights by the numbers advertised, be it candlepower, candela, lux, lumens, or wattage? I also have seen wildly ridiculous numbers advertised... particularily on walmart spotlight models....

There are a very few manufacturers which seem honest with their lumen figures, but they seldom or never quote candlepower. There are a few more which seem to consistently overstate the lumen output by a fairly constant exaggeration factor. Then there are the ones who just make the numbers up. By far your best source of information is right here at CPF, where people have tested various lights against each other and reported the results. There are also several review web sites which give good quantitative information, most notably Flashlight Reviews. Sadly, the information there is rapidly getting out of date because no new reviews are being done. Another site with an extremely large number of reviews but in less depth is the LED Museum. There are also several others which I'm sure other folks can recommend.

c_c

 

[LuxLuthor]

Although it has been alluded to previously, most people want to know the "torch lumens" that are coming out the front of the light to be able to compare one with another. This takes into account the shape, size, voltage, current powering the bulb/LED, and also the shape, surface coating (texture), & size of the reflector, and the lens. If the light allows a focus movement of the reflector, the deck of cards just got thrown up into the air again.

As CC mentioned, very few companies even give you a practical value like the "Torch Lumens," and the supposed "Gold Standard" of testing light output is sticking it inside of an "Integrating Sphere." But, the I.S. does not measure a hotspot, nor all these other factors I just mentioned, necessarily.

All of these complexities are why you see talking about "Bulb Lumens" with incandescents, "Lumens" with LED's, Candlepower with spotlights, with very little standardization of exactly how the numbers were arrived at.