Sailingsaves
Well-Known Member
Trying to find a simple explanation...
Had a headache when I woke up and still have it, so not thinking too well.
There was time I would have been able to explain it in one sentence, but not today.
I'm sure someone else will be along and be able to explain it better than I have.
This is a pretty ok explanation though:
http://www.flashlightuniversity.com/lumens-vs-candlepower/
OR
Lumens are a measure of the total amount of light emitted in all directions, and while not entirely appropriate when applied to directional light sources like flashlights, it still can be used to measure all the light poured out the end of your torch, regardless of what direction it`s going in.
Candlepower or Candela is a peak spot measure- the intensity of the very brightest point of light within the focussed beam, usually the very center. It does relate with Lumens, to the half angle of the beam- in other words, the angle from the centre at which the brightness is exactly half of the peak value at the centre. For an identical intensity light source (ie, lumen value is the same) the narrower the beam the higher the Candlepower rating. But the dispersion of the beam plays a big role. It depends largely on the width of the hotspot, what portion of the light goes into the main beam, and what portion spills off to the side.
Unless you know the precise dispersion of the individual beams, with an accurate 2 dimentional plot of intensity (or a simple 1-dimention graph if the dispertion is perfectly circular and not lopsided or oval), and then apply advanced mathematics that would make most highschool students heads spin, you cannot convert between the two. Can`t be done, sorry.
Regrettably there is not a simple home-friendly way to measure lumen outputs. A simple photographic Lux meter can be used to give you candela (candlepower) readings but Lumens require advanced methods. You need lots of space, lots of money and lots of Barium Sulphate paint in order to do it. Hence why most manufacturers just use candlepower. Additionally (and maybe more influencially), candlepower figures are often high and look great on fancy packaging and web sites- that thing about narrow beams again. Many Pelican lights and all Maglites for example, are rated quite highly as far as cp goes, but the overall light output is low compared to some, just the fact that they can focus pretty narrowly. A narrow beam is not always a useful beam so candlepower ratings cannot be soley relied upon. Similarly Lumen ratings cannot be soley relied upon either. A high-lumen beam could be so wide and dispersed that it does not throw more than a few feet, or a low lumen beam could be so narrow that it shines a very long way.
It`s all down to what you`re looking for in a lignt and until flashlight manufacturers get their act together and embrace a universal, standardised and informative rating method they will all use, the only real way to tell if one torch is better for you than another is to try it out yourself. Hence the official CPF motto "Get them both
". We reviewers try our best but however detailed we try to be in our writeups, you still cannot beat seeing the thing for yourself.
OR
http://en.wikipedia.org/wiki/Lumen_(unit)
OR
http://www.ransen.com/Photometric/Candelas-Lumens-And-Lux.htm
Had a headache when I woke up and still have it, so not thinking too well.
There was time I would have been able to explain it in one sentence, but not today.
I'm sure someone else will be along and be able to explain it better than I have.
This is a pretty ok explanation though:
http://www.flashlightuniversity.com/lumens-vs-candlepower/
OR
Lumens are a measure of the total amount of light emitted in all directions, and while not entirely appropriate when applied to directional light sources like flashlights, it still can be used to measure all the light poured out the end of your torch, regardless of what direction it`s going in.
Candlepower or Candela is a peak spot measure- the intensity of the very brightest point of light within the focussed beam, usually the very center. It does relate with Lumens, to the half angle of the beam- in other words, the angle from the centre at which the brightness is exactly half of the peak value at the centre. For an identical intensity light source (ie, lumen value is the same) the narrower the beam the higher the Candlepower rating. But the dispersion of the beam plays a big role. It depends largely on the width of the hotspot, what portion of the light goes into the main beam, and what portion spills off to the side.
Unless you know the precise dispersion of the individual beams, with an accurate 2 dimentional plot of intensity (or a simple 1-dimention graph if the dispertion is perfectly circular and not lopsided or oval), and then apply advanced mathematics that would make most highschool students heads spin, you cannot convert between the two. Can`t be done, sorry.
Regrettably there is not a simple home-friendly way to measure lumen outputs. A simple photographic Lux meter can be used to give you candela (candlepower) readings but Lumens require advanced methods. You need lots of space, lots of money and lots of Barium Sulphate paint in order to do it. Hence why most manufacturers just use candlepower. Additionally (and maybe more influencially), candlepower figures are often high and look great on fancy packaging and web sites- that thing about narrow beams again. Many Pelican lights and all Maglites for example, are rated quite highly as far as cp goes, but the overall light output is low compared to some, just the fact that they can focus pretty narrowly. A narrow beam is not always a useful beam so candlepower ratings cannot be soley relied upon. Similarly Lumen ratings cannot be soley relied upon either. A high-lumen beam could be so wide and dispersed that it does not throw more than a few feet, or a low lumen beam could be so narrow that it shines a very long way.
It`s all down to what you`re looking for in a lignt and until flashlight manufacturers get their act together and embrace a universal, standardised and informative rating method they will all use, the only real way to tell if one torch is better for you than another is to try it out yourself. Hence the official CPF motto "Get them both
OR
http://en.wikipedia.org/wiki/Lumen_(unit)
OR
http://www.ransen.com/Photometric/Candelas-Lumens-And-Lux.htm
