#### TripleDouble

##### Newly Enlightened

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- May 15, 2001

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- Thread starter TripleDouble
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Help Support Candle Power Flashlight Forum

- Joined
- May 15, 2001

- Messages
- 66

He's done CP measurements for both LED & Incans but I don't know how to test "lumen" output.

Lumens ratings are measured in a Kubrick Sphere or something.

Al

You need a Flux Capacitor to measure lumens.

Here's a helpful cut and paste from Carley's Web site definition page.

Notice that Radio Shack's catalogue and many bulb catalogues show the MSCP of a bulb running at rated voltages and amperages.

Multiply the MSCP by 12.57 to get lumens.

I simply extrapolate the MSCP of overdriven or underdriven bulbs to estimate the MSCP and Lumens of any given combination I consider.

"Mean Spherical Candlepower - MSCP (or CP candlepower for short) is the total light output of a lamp in all directions.

Foot Candles - Total light output of a lamp when the light is compressed by a lens or reflector. Foot candles is a "directional specific" light measurement.

Filament Temperature - The operating temperature of the filament measured in degrees kelvin.

Lumens = MSCP x 4 x pi

1 MSCP=12.57 Lumens

Wattage - The amount of electrical power of a lamp. Volts x Amps = Watts"

- Joined
- Oct 13, 2001

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Multiply the MSCP by 12.57 to get lumens.

Mean Spherical Candlepower - MSCP (or CP candlepower for short) is the total light output of a lamp in all directions.

Foot Candles - Total light output of a lamp when the light is compressed by a lens or reflector. Foot candles is a "directional specific" light measurement.

Filament Temperature - The operating temperature of the filament measured in degrees kelvin.

Lumens = MSCP x 4 x pi

1 MSCP=12.57 Lumens

Lemlux,

I still find the candlepower/lumen subject somewhat confusing. I thought that lumens referred to the total amount of light emitted

by a light source, and candlepower was a measurement of "brightness" taken at a specific point or defined area within a beam, and that lumens was a more reliable measure than candlepower because, among other examples, a high lumen lamp could give a less impressive candlepower reading than a low lumen lamp depending on the dispersion of the beams.

But evidently, when I (and most people) use the term "candlepower" we are actually referring to "foot candles" and not MSCP which is a type of measurement identical to lumens but expressed in different numbers?

So that on the one hand we have Lumens and/or MSCP and on the other hand we have foot candles? Is that correct? If not, could you please explain all these terms in math-challenged layman's language or refer me to a simple source? I have heard people arguing about these terms for years and would love to clear up my own misconceptions.

Best regards

Brightnorm

Your interpretation of bulbmaker Carley's definition is the same way I read it.

I assume that Carley speaks authoratatively. Certainly, they are better versed than I am in this field. Then, the first thing College taught was to challenge an assertion until you were convinced that it was defensible.

Carley's language seems logically consistent to me. I've heard "foot candles" used over the years but I suppose it's a cumbersome word for the marketing hacks to use. It wouldn't be the first time advertisers have corrupted the language. Obsfucation is their job!

The _candela_ is a measure of intensity of light, how 'bright' the light is in one particular direction.

The lumen is a measure of total flux of light, meaning how much light is going in a range of directions.

Going back to the pond analogy, the candela is like the meter, and you can use it to measure how deep the pond is below a point on the surface. If you move your meter stick a bit to the side, you may measure a different depth. As you get to the edge of the pond, the depth reaches zero.

The lumen is like the liter. You can measure the total volume of the pond, say by bailing it out with a container. But you can also calculate the volume if you know the depth of each point of the pond, and the conversion for depth and area to volume.

If you measure the intensity (candela) of a light source in all directions, you can convert that set of values into total flux of light (lumen) by doing the appropriate math (integration).

The mean spherical candlepower is the _average_ intensity of a light source in all directions. It is akin to the _average_ depth of the pond. If you know the average depth of the pond (in meters), and the surface area (in square meters), and you multiply, then you will get the volume of the pond, in cubic meters, which you will then have to convert to liters.

The equation converting MSCP to lumen then falls out of the definitions. A candela is the intensity of a light source which produces a flux of 1 lumen per steradian.* Since there ar 4*pi steradians in a full sphere, the conversion from MSCP to lumen is to just multiply by 4*pi.

The lumen is then defined in terms of watts and the measured characteristics of the human eye. You measure the lumen output of a light source with a tool that measures the candela output from a bunch of different directions, and then integrates.

-Jon

*(Sounds circular, I know. Back to the pond analogy: a meter is the depth of a pond which produces a volume of 1000 liters per square meter. It works because the steradian is a different sort of unit from the candela, and the steradian is a basic unit.)

I can see where the "mean" adjusts for elements like the opaque base of the bulb. In your analogy, the base would be a zero depth island in the pond.

I wonder if it manufacturers actually adjust for shadowed portions of the beam blocked by filament support structures.

This question is motivated by Carley's apparently accurate claim that their attention to filament placement reduces filament shadows.

That's a great way of explaining it!

But, if foot candles = CP for the following:

BTW, I'm likely to write rubbish here.

Lets assume that manufacturer's CP rating are accurate, and not inflated for marketing.

They aren't going to give an average CP rating are they? They'll record the highest value they can. Where that is in the beam, we don't know. How much of the beam that value applies to, we don't know. What the rest of the beam is like, we don't know.

So we can't convert CP to Lu because we don't have enough information. Assuming that that what we do have is accurate in the first place.

I was thinking that if we know the Lu rating for a SureFire, and we know the beam angle of the main beam and total beam angle, and we know the percentage of Lu in the main beam, we could work out the 'CP' for the main beam.

So, we know the total amount of water. We know the depth and area of the deep end, and the depth and area of the shallow end. We assume that there is a clean break between the two, or that what gradient there is, is insignificant...

Converting a SureFire Lu output to CP would be easier on some beams then others. The percentage of main beam Lu concentration is usually taken as ~70% of total.

I suppose the N2 lamp would be a good beam to try this out on.

I don't have any reason myself to try this since why would I need to have a CP value for a SureFire?

Al

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