lumens vs candlepower

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vhyper007

Enlightened
Hear Ye, Hear ye,

can anyone amongst you tell me if there is a meaningful relationship between lumens and candlepower.?

I googled one site which said you convert candlepower to lumens by multiplying CP x 12.566. This would make my 10,000,000 cp Thor have
125 billion 660 million lumens. Another way of looking at this is my L2 with 100 lumens has only 7.957 CP or the beast with a "sizzling" 2000 lumens has only 159.16 CP.

My math is correct so where lies the problem?

Curiously,
vhyper

MaxaBaker

Flashlight Enthusiast
There is NO conversion of lumens to candlepower or candlepower to lumens. I don't know what that website is talking about. /ubbthreads/images/graemlins/duh2.gif /ubbthreads/images/graemlins/thinking.gif

jtivat

Flashlight Enthusiast
Nope there is not, think of it this way. If you go from spot to flood on a Mag light the CP will change by a lot but the lumens will stay the same. Lumens is the total light output where CP is a measure of intensity at one point in the beam.

SilverFox

Flashaholic
Hello Vhyper,

I do not believe anyone has been successful in measuring 10000000 candlepower from a Thor. I think that claim has been derived from the velocity and arc of meteors falling through the sky during ancient Greek mythology... /ubbthreads/images/graemlins/evilgrin07.gif

Your Google search failed to inform you that as the solid angle of the light changes, your multiplier gets smaller. The conversion is difficult and makes all kinds of assumptions that will get you in trouble. It would be better to heed to what Baker and JT have presented...

However, to figure the whole thing out you need to know:

the distance involved that the Candle Power measurement was taken at
the Lumens per square foot
and the solid angle of the lamp

This should keep you Googling for a while... /ubbthreads/images/graemlins/smile.gif

Tom

beezaur

Flashlight Enthusiast
The definitions I found by Googling were highly obfuscated, so be careful about web-available information. According to the CRC Handbook of Chemistry and Physics, 79th ed.,

- the candela (cd) is the SI unit of luminous intensity;
- the lumem (lm) is the unit for luminous flux, cd sr,

where the steridian (sr) is the unit solid angle.

What?

Flux is like how many people you have leaving a building per minute. It gives the big picture, but no specifics about any one door.

Intensity is like how many people are going through a certain door every minute. It gives the specifics for one point, but tells you nothing about the big picture.

There can be a meaningful relationship between the two. For example, if light is given off equally in all directions, you can take an intensity measurement in cd and multiply it by however many steridians are in a sphere to get lumens.

However, flashlight beams are not so even. You would have to measure cd at lots of points and assign a solid angle to each measurement before you can get lumens from that.

It can be done. It just isn't a conversion. The site you found is in error.

Scott

PS: you guys beat me while I was looking all this stuff up!

dano

Flashlight Enthusiast
Closed...This topic comes up several times a week. Please do a search for lumens and candlepower, and you'll receive a ton of info.

-dan

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