Those prices are "staggering." I'm not sure I agree with their lumens vs candlepower argument. The purpose of a flashlight is spot, not general illumination. Either total lumens or candlepower alone is an incomplete spec leaving you unable to determine whether it meets your needs. You also need a specification of beam angle (or range of beam angles if it has a "focusing" mechanism.
With beam angle, you can define the relationships between the parameters, although there is an issue of uniformity of illumination across the beam. The candlepower should not be the "very tallest grain of sugar" but some average across the central part of the declared beam angle. The industry would have to standardize, so the beam angkle is the point where the light is some percentage down from maximum, and then the candle power computed as an average across, lets say, half that beam angle (or a third.) Without a beam angle, I really can't use lumens for purpose, except in general purpose lighting. With candlepower and distance, I may not know the diameter of the spot, but I know the illumination at the brighest point. The electrical analog is that I need both transmitter power and the gain of the antenna (or beamangle) to determine whether I adequately illuminate the receiving antenna. ________________________________ From: James R. Frysinger <j...@metricmethods.com> To: U.S. Metric Association <usma@colostate.edu> Sent: Wed, August 4, 2010 9:49:15 PM Subject: [USMA:48324] Use of lumens for flashlights I came across an interesting product catalog that describes the products (flashlights, etc.) made by SureFire. Page ICF12 of this discusses "candlepower" [candelas] versus "lumens". http://www.armory.sk/pdf/2007-Illumination-Catalog.pdf CAUTION: This is a 7.5 MiB file, more or less. I like their "pile of sugar on a table" analogy! All in all, they present quite a dazzling level of technological discussion in this catalog. The products go for dazzling prices too, alas. http://www.surefire.com/Flashlights Jim -- James R. Frysinger 632 Stony Point Mountain Road Doyle, TN 38559-3030 (C) 931.212.0267 (H) 931.657.3107 (F) 931.657.3108
