## Light Measurement Confusion (Geek Alert)

I'm trying to understand how to compare flashlights and my sums just don't seem to work out.

What am I missing ?

I use a Minolta photographic meter that is quite accurate (matches camera meters). I go to the ANSI formulae for calibrating these meters 18% gray card and ANSI light meter standard and I can easily back footcandles out of this.

One candela (candlepower) is supposed to produce one footcandle at one foot.

OK, I measure some lights as
Inova X5 73 fc 10"
Lambda Illuminator 222 fc 8"
MiniMag AA 273 fc 3"
Double Barrel 4AA 547 fc 3"
Mag 6D 2515 fc 4"

The numbers above marked "fc" could also be candela or candlepower.

I realize that the diameter of the beam is also related to the overall luminous flux produced by the lamp (lumens) but the peak brightness of the beam in candela (or fc at one foot) is independent of coverage area. More light over a larger coverage area equals the same illuminance.

Now where I get confused is
(1) Maglight states that the 6D is 20,000 CP - let's say 8X my measurement

(2) Craig at the LED MUSEUM in his BEAUTIFUL plots and reviews states the Lambda Illuminator is 256,000mcd. That's millicandela or let's call it 256cd (candela). My measurement was 222. Well, Craig's measurement was 15% brighter. I had used the LI for a little bit he might have used really fresh batteries for this measurement (other posted tests show a falloff in the first few minutes) I'm not worried. Essentially Craig's and my measurements were the same. Craig probably takes more time and is more accurate in positioning the lights than I was and that could make a difference (do you measure from the emitter or front of light to the dome or the cell?

(3) Also in Craig's wonderful reviews, he uses that high tech ProMetric system that gives great graphs. BUT it shows a peak illuminance of 796 Cd. Now 796 vs 256 is a BIG difference. Not as big as 2500 to 20,000, but still big.