# How Many Lumens in a Camp Fire?



## Cataract (Mar 24, 2010)

Just wondering how does a camp fire compare with a non-collimated light.

Anyone ever taken a light meter outdoors at camp? If not, it might be interesting to evaluate how much light comes out of a fire. Obviously, it's pretty much impossible to measure the total output (lumen) for practical reasons, but at least a directional output average in lux would be interesting. I think we'll all agree that all camp fires are not created equal, but an average would be interesting to have. If no one's willing to bing out their precious light meter, a guesstimate would be interesting thing to come up with, since there are so many lights with low settings and infinite variability. Here are some parameters:

There's the obvious relatives, like: 
-How much woods in the fire
-How dispersed or close together are the logs
-How much humidity in the wood
-Log width, length, type of wood
-Anything else than wood in the fire?

We obviously can't control most of these, and I really wonder who would bring a calibrated balance to weight the wood... 
so let's just try to keep the parameters within reason and say it's a standard camp fire (20 to 30 inches in diameter), the wood is relatively dry (not cracking dry), the logs are 4 to 6 inch in diameter, the starter wood and paper has burnt out (only wood in the fire by now). Your fire would probably have 5 or 6 logs, some of them already burned, so you put 2 or three more fresh ones and wait for the luminosity to peak out... 

At the opposite end, it would also be interesting to have an idea of the Lux output of the gigantic bonfire as well. Problem here, I dare anyone to take a measurement at 1 meter!

I'll try to come up with my own guesstimate this summer, I just hope I don't get stuck with wet wood like last year... it really sucked! All the fires I started had to be ignited 2 to 4 times each, just to dry the wood enough to burn... I'd say I had a 5 lux camp fire all summer long!


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## StarHalo (Mar 24, 2010)

A candle flame is ~13 lumens, so if you extrapolate the area of the camp fire flames, that would give you an idea of the number of lumens.


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## Cataract (Mar 24, 2010)

Interesting info. I'm not 100% sure that wax candle luminosity is the same as for wood: higher temperature burn should translate in more light, but I could be wrong on that one... there's the whole chemical reaction involved which could actually mean less


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## saabgoblin (Mar 24, 2010)

Grab a number of lights with varying lumen output and shine each one into the fire, if you can see the hot spot in the fire, then shine one of your lower lumen output lights into the fire until the hot spot disappears and you will have an approximation of the lumen output in that given area of the fire.

If you aren't happy with that method, you can fork over quite a few thousand dollars for a mobile integrating sphere to take on your next adventure and then you can measure the output of any given number of fireflies in a given area.:nana:

Good question by the way and there are numerous variables so there would of course be no constant value but a campfire is enough to abolish many stars from your view.


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## Cataract (Mar 24, 2010)

saabgoblin said:


> Grab a number of lights with varying lumen output and shine each one into the fire, if you can see the hot spot in the fire, then shine one of your lower lumen output lights into the fire until the hot spot disappears and you will have an approximation of the lumen output in that given area of the fire.


 
I was thinking more in the line of holding the flashlight at equal distance from a tree (unless you want to try with one of yours directly into the fire:nana and try to get the same illumination on the tree... but that definitely would be a LUX equivalent rather than a lumen equivalent... then again, make a sphere out of the flames and figure how many times the surface of the business end of your light fits on the surface of that sphere and get out your pocket calculator... 

...but I do like the idea of measuring the lumen output of fireflies! maybe that could be extended to burning marshmallows and firecrackers as well.


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## SmurfTacular (Mar 24, 2010)

StarHalo said:


> A candle flame is ~13 lumens, so if you extrapolate the area of the camp fire flames, that would give you an idea of the number of lumens.



does that mean a 1 million candle power spotlight is 77,000 lumens?


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## John_Galt (Mar 24, 2010)

SmurfTacular said:


> does that mean a 1 million candle power spotlight is 77,000 lumens?



There is no possible correlation between candlepower and lumens. Rough estimates are possible (but probably not accurate) if you know certain specifics like beam divergance angle, etc. Candlepower is a measurement of the concentration of light at a certain distance (but not the same as lux), not a measurement of total output.

Besides, do you really think the battery in a spotlight is capable of providing x# of watts to produce 77,000 lumens? No way, no how...


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## SmurfTacular (Mar 24, 2010)

John_Galt said:


> There is no possible correlation between candlepower and lumens. Rough estimates are possible (but probably not accurate) if you know certain specifics like beam divergance angle, etc. Candlepower is a measurement of the concentration of light at a certain distance (but not the same as lux), not a measurement of total output.
> 
> Besides, do you really think the battery in a spotlight is capable of providing x# of watts to produce 77,000 lumens? No way, no how...




I knew that was impossible. I just don't really get the relationship between lumens, candle power, and lux.


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## Thujone (Mar 24, 2010)

SmurfTacular said:


> does that mean a 1 million candle power spotlight is 77,000 lumens?



No


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