Your highest candlepower spotlight?

That_Guy said:

What's wrong with candlepower? It is one of the most useful measurements we have for describing flashlights, second perhaps only to lumens. The abuse by most manufacturers is unfortunate but doesn't make candlepower useless or candlepower measurements any less valid. It just means that one has to be careful when using candlepower to compare different lights. It is the best method we have for measuring and comparing throw. It is certainly a hell of a lot better than the stupid lux @ 1m standard which most of CPF uses.

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Given some of your previously useful & scholarly posts, I'm a bit surprised by your post above.

To answer your question, technically nothing is wrong with candlepower or lux or lumens or candela or foot-candle or foot-lambert, or bulb lumens, or torch lumens, Steradian, or Nit. The problem is that these terms are all poorly understood, changed over time, not used correctly, measurement standards not followed uniformly, or measurements not done properly for them to be all that useful.

How many threads and resources do you wish me to post to make my point? How about we start with some CPF oldies:
Or we could glance at some less formal:
Or get into the FAQs at International Light Technologies

Or better yet, let's all go to the 64 page PDF of The Light Measurement Handbook by Alex Ryder.

Whew, that got tedious....I know let's assume perhaps a simple strategy and look at the original definition of Candlepower and see if that is straightforward (from Wiki):
Hmmmm....that really cleared things up...except I don't have any sperm whale heads handy. I know....let's go to the pure, modern redefined International System of Units (abbreviated SI from the French "Le Système International d'Unités") hitting up Wiki once more (Oh & ignore the pesky rounding up from 0.981 to 1.0 candela)

But a bit more concise and accurate is Candlepower defined as:
OK, now we're talking!!! Oh but wait, what exactly do they mean by candela? Damn....let's hope for the best and see what that is:
Curses....foiled again!

OK, slight sarcasm aside, and assuming some modern definition can be accepted and agreed upon, it is still nearly impossible to take into account (with any standardized accuracy) the variations in various light (luminous flux) source, reflector, focus, lens, distance from light source, position & placement of beam when measurement taken, quality/accuracy/calibration of light tester (including sensor design, size, material, spectral design, conversion circuitry, etc).

As far as I am concerned, the only truly useful way to evaluate complete lights are side by side personal viewing, and to a lesser degree a series of quality beamshot photographs done by the same team, with the same camera, witnessed and verified by a number of respected flashaholics.

I actually do not even consider an Integrating Sphere to be all that useful when evaluating a complete flashlight, HID, spotlight, etc., since what people most care about (the hotspot, artifacts, corona, spill, color, throw) are not addressed in an Integrating Sphere.

Since you mentioned with a twinge of negative spin:

It is certainly a hell of a lot better than the stupid lux @ 1m standard which most of CPF uses.

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I will say that I stand by my "stupid" destructive point source incan bulb testing by a relatively inexpensive Meterman LM631 Lux measured at 1 Meter linked in my sig, but with full awareness that it is at best, a comparitive review that was not witnessed, and does not reflect the cases of a huge dropoff of Lux measured as the overdriven bulb aged.

Lux,
I agree that many terms are "poorly understood, changed over time, not used correctly, measurement standards not followed uniformly, or measurements not done properly." I also admit that the scientific definitions of candlepower and candela are very confusing and difficult to understand. Even I don't properly understand the scientific definition of candlepower. "The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian." How the hell is anyone supposed to know what this actually means? It may be useful to a scientist, but to someone who just wants to understand the 10 million candlepower figure stamped on the side of the box of a light he just bought it is utterly meaningless.

Despite this however I do still believe that the candlepower is a very useful unit. I started writing about why I believe this, but I ended up just saying the same things I did in this thread which you've already read. I can't really add much more without repeating myself. In that thread I also explain my comment about lux @ 1m being stupid. I wasn't criticizing your destructive incan bulb tests, they are about the one situation where using lux @ 1m is acceptable because you are measuring the bulb naked without a reflector.

it is still nearly impossible to take into account (with any standardized accuracy) the variations in various light (luminous flux) source, reflector, focus, lens, distance from light source, position & placement of beam when measurement taken, quality/accuracy/calibration of light tester (including sensor design, size, material, spectral design, conversion circuitry, etc).

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Most of this doesn't matter, at least if candlepower is measured properly. The "variations in various light (luminous flux) source, reflector, focus, lens" don't matter because the candlepower measurement takes all these into account, which is pretty much the whole point of measuring candlepower in the first place! The "distance from light source" doesn't matter because it is included in the candlepower calculation. The "position & placement of beam when measurement taken" doesn't matter because candlepower only refers to the hottest part of the beam (hence peak beam candlepower). "quality/accuracy/calibration of light tester (including sensor design, size, material, spectral design, conversion circuitry, etc)" certainly is an issue, but it doesn't really matter that much. Even an inaccurate light meter is still a lot better than the human eye for quantifying the differences between lights.

As far as I am concerned, the only truly useful way to evaluate complete lights are side by side personal viewing, and to a lesser degree a series of quality beamshot photographs done by the same team, with the same camera, witnessed and verified by a number of respected flashaholics.

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That is certainly true if you want to know "the big picture". However if you are only interested in a specific thing about a light, such as its throw or total light output, then scientific measurements such as candlepower or lumens are best.

I dont think we should be arguing about how it is measured and all that. We need to get back on bluebeam's topic. lets just call it "what candlepower is you spotlight overated?" I think we all know that none of our spotlights are realy 10 million candle power. {WWII spotlight owners cant say the same :devil: } but we are talking about what the box says it is, or what it would say. just my two cents.

SilentK, just ignore us, and your point is valid.

That_Guy said:

Lux,
I agree that many terms are "poorly understood, changed over time, not used correctly, measurement standards not followed uniformly, or measurements not done properly." I also admit that the scientific definitions of candlepower and candela are very confusing and difficult to understand. Even I don't properly understand the scientific definition of candlepower. "The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian." How the hell is anyone supposed to know what this actually means? It may be useful to a scientist, but to someone who just wants to understand the 10 million candlepower figure stamped on the side of the box of a light he just bought it is utterly meaningless.

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Exactly my point....and to illustrate that your method is not taking the defined terms into account properly to promote it as you are. What I am actually saying is that you are not measuring candlepower with your method of measuring Lux at farther distances. There are too many variables between how you are extrapolating and measuring (especially with reflector spotlights) and the actual definition of a candela.

Is what you are doing "more useful" (contrasted with "accurate") in certain applications? Perhaps, but you cannot call them candlepower or candela unless you comply with how those scientific terms are defined. You should call your measurements: "That_Guyumens" :laughing: and then if we all want to use our own version of measurements, they could be called "This_Guyumens" or "LuxLuthorumens."

Going back to the Ryer Manual, this statement on p. 17, under "Collimation" section jumped out at me:

Lenses and reflectors can drastically distort inverse square law approximations, so should be avoided where precision distance calculations are required.

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IMHO, the biggest source of mischief is the lack of validity when comparing your light meter readings (represented as actual candlepower--which they are not--using the inverse square law) with a particular light, light meter, technique, and room--vs. everyone else using their own version of measurement, beam/reflector angle, focus, light hardware variations, power source fluctuations, ambient conditions, reflected light (i.e. from your body standing next to hotspot; surface & color of walls & ceiling; any table or furniture that may be obstructing). Surely you can see that there can be no "standard candela" among all of us flashaholics allowing agreement upon that precise scientific term.

That_Guy said:

Most of this doesn't matter, at least if candlepower is measured properly.

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There's the rub....and ergo, if it is not measured properly, consistently, and with all the controls among all those using candlepower...it is not significantly more useful than some of the other measurement terms/methods.

That_Guy said:

The "variations in various light (luminous flux) source, reflector, focus, lens" don't matter because the candlepower measurement takes all these into account, which is pretty much the whole point of measuring candlepower in the first place! The "distance from light source" doesn't matter because it is included in the candlepower calculation. The "position & placement of beam when measurement taken" doesn't matter because candlepower only refers to the hottest part of the beam (hence peak beam candlepower).

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I'm sorry but I just cannot agree that all of these assumptions in your list don't matter. Read p 22 chapter 8.2 to 8.22 here, and again 8.3 to 8.8 of The International Lighttech IL-1400 meter manual, and see comments below.

That_Guy said:

"quality/accuracy/calibration of light tester (including sensor design, size, material, spectral design, conversion circuitry, etc)" certainly is an issue, but it doesn't really matter that much. Even an inaccurate light meter is still a lot better than the human eye for quantifying the differences between lights.

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Well my Meterman says it uses the "CIE Photopic" spectrum (vs. Scotopic, etc.) described on Ryer p.11. I'm not exactly sure how that relates to your meter, and how the known detection inaccuracies using it with LED's applies to HID bulbs which can have UV, etc. The various unique light sources have specific, properly designed equipment referenced in the IL-1400 manual....so I have reason to believe it does matter.

That_Guy said:

That is certainly true if you want to know "the big picture". However if you are only interested in a specific thing about a light, such as its throw or total light output, then scientific measurements such as candlepower or lumens are best.

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Referring to the Ryer Handbook....note how they used the "5 times" rule on page 25 to address what Curious_Character appeared to be trying to resolve at the start of his post you linked, in terms of finding the true "point source" which is mandatory for using the inverse square law. Thereafter, reading chapters 6 & 7 explains what the Steradian is (Fig 7.1), and why it is important. Figure 7.4 does a nice job (with section text) of explaining and comparing other confusing terms.

Then reading on page 36, they start a discussion of some new terms that applies to spotlights, and go into some practical examples.

The biggest source of confusion regarding intensity measurements involves the difference between Mean Spherical Candela and Beam Candela, both of which use the candela unit (lumens per steradian).

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I actually took some of the ideas from chapter 8 when doing my destructive incan testing, and found it worth reading.

I finish with a repeat quote from p. 17 of Ryer:

Lenses and reflectors can drastically distort inverse square law approximations, so should be avoided where precision distance calculations are required.

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