js
Flashlight Enthusiast
The time has come . . .
The time has come to talk of many things --but not in this case of cabbages and Kings and sealing wax and why the sea is boiling hot and so on,
but rather the time has come to talk of the CPF established 65 percent rule of thumb for converting bulb lumens from published specs and re-rating formulas, into torch lumens, or in other words, into lumens out the front of the light.
And the time has come for those of us who have used and defended the 65 percent figure all along to say a very loud and obnoxious "nya nya na nya na! I told you so!"
OK. Just kidding about that last part. But seriously, it does feel pretty good to find out that your back of the envelope calculations and amateur estimations turned out to be correct after all.
Now, I was one of the people who inherited the 65 percent figure. I did not derive it myself, but rather was given it by Ginseng, who suggested that it was more or less the best we could hope for and was in his experience as accurate as possible given our limited measurement capabilities. I am told that PaulW was the first person to come up with this rule, and also that NewBie/Jarhead did some calculations and basically said "Yup. That's about right."
But however that may be, I came to uphold and believe in the 65 percent transmission efficiency figure for lamps in reflectors in flashlights. It seems crazy at first glance that so much light would get lost, but there it is. It does. And after a lot of experience with incan modding and comparing lights and outputs, I no longer doubted it, but rather spent too much time and effort going around CPF trying to get people to start comparing apples to apples instead of to oranges.
Because, you might ask, "why use torch lumens at all? Why don't we all just talk bulb lumens?" and the reason is that SureFire lights are all quoted in terms of torch lumens, and the SF M6 seems to be the Lion whose tail is always being pulled. People just LOVE to talk about their 1,234 lumen Mag85's, and feel very cool when thinking that an M6 is only 500 lumens.
Now, I've given up my official position as CPF lumens ogre. I no longer care if people want to quote their bulb lumens and yet compare them to the torch lumens of other lights. More power to them! Those who know, know. And those who don't probably don't care anyway. And the whole thing just wastes my energy.
However, I still get sucked into arguments and most recently this happened in LuxLuthor's thread L2==>M4==> ? M6 Help a new member right around post #38 with Luna and his badgering about the 65 percent figure. (Not that I was faultless in these exchanges--far from it; check out the actual exchanges and judge for yourself).
So, now to the point --to wit, the evidence:
A smooth, vacuum aluminized reflector with a Welch Allyn 01274 lamp potted into it was sent to an integrating sphere to be measured for total beam lumens, or MSCP (=total lumens/4 pi). This lamp is rated at 553 lumens at 7.2 volts. 7.2 volts was applied at the pins and 391 lumens was measured in the sphere.
391/553 = 70.7 percent.
However, this was the lamp module only. Add in a lens and angular losses due to the lip of the reflector being recessed down into the head of a light and you probably have at least another 5 or 6 percent. Plus, if you consider that an OP or stippled reflector means more internal reflections of the light versus a smooth reflector, then you maybe have even more losses, but how much I couldn't say. But in any case, you end up with something close to --wait for it--
65 PERCENT
Taking a step back, I will readily admit that this is only a single piece of integrating sphere evidence. However, it still carries a lot of weight even so.
What really annoys me about all of the recent turmoil over this is the notion that if you don't have an IS, you can't say anything at all. I believe that our ingenuity and inventiveness here at CPF have proven otherwise. From the lumens estimator box, to our very own PaulW :bow: :bow: :bow: and his ceiling bounce tests, we have shown that there really is something in between an arbitrary, off the cuff uninformed random guess, and hard numbers from an integrating sphere.
So it's time for people like myself and Ginseng and PaulW and bwaites to pat ourselves on the back and do a little victory dance and (maybe) say "I told you so."
I would never do this, of course, being far too mature. *cough* I told you so! *cough*
Hmmm? What? Oh, no, I didn't say anything. Just a bad cough. Sorry. :devil:
The time has come to talk of many things --but not in this case of cabbages and Kings and sealing wax and why the sea is boiling hot and so on,
but rather the time has come to talk of the CPF established 65 percent rule of thumb for converting bulb lumens from published specs and re-rating formulas, into torch lumens, or in other words, into lumens out the front of the light.
And the time has come for those of us who have used and defended the 65 percent figure all along to say a very loud and obnoxious "nya nya na nya na! I told you so!"
OK. Just kidding about that last part. But seriously, it does feel pretty good to find out that your back of the envelope calculations and amateur estimations turned out to be correct after all.
Now, I was one of the people who inherited the 65 percent figure. I did not derive it myself, but rather was given it by Ginseng, who suggested that it was more or less the best we could hope for and was in his experience as accurate as possible given our limited measurement capabilities. I am told that PaulW was the first person to come up with this rule, and also that NewBie/Jarhead did some calculations and basically said "Yup. That's about right."
But however that may be, I came to uphold and believe in the 65 percent transmission efficiency figure for lamps in reflectors in flashlights. It seems crazy at first glance that so much light would get lost, but there it is. It does. And after a lot of experience with incan modding and comparing lights and outputs, I no longer doubted it, but rather spent too much time and effort going around CPF trying to get people to start comparing apples to apples instead of to oranges.
Because, you might ask, "why use torch lumens at all? Why don't we all just talk bulb lumens?" and the reason is that SureFire lights are all quoted in terms of torch lumens, and the SF M6 seems to be the Lion whose tail is always being pulled. People just LOVE to talk about their 1,234 lumen Mag85's, and feel very cool when thinking that an M6 is only 500 lumens.
Now, I've given up my official position as CPF lumens ogre. I no longer care if people want to quote their bulb lumens and yet compare them to the torch lumens of other lights. More power to them! Those who know, know. And those who don't probably don't care anyway. And the whole thing just wastes my energy.
However, I still get sucked into arguments and most recently this happened in LuxLuthor's thread L2==>M4==> ? M6 Help a new member right around post #38 with Luna and his badgering about the 65 percent figure. (Not that I was faultless in these exchanges--far from it; check out the actual exchanges and judge for yourself).
So, now to the point --to wit, the evidence:
A smooth, vacuum aluminized reflector with a Welch Allyn 01274 lamp potted into it was sent to an integrating sphere to be measured for total beam lumens, or MSCP (=total lumens/4 pi). This lamp is rated at 553 lumens at 7.2 volts. 7.2 volts was applied at the pins and 391 lumens was measured in the sphere.
391/553 = 70.7 percent.
However, this was the lamp module only. Add in a lens and angular losses due to the lip of the reflector being recessed down into the head of a light and you probably have at least another 5 or 6 percent. Plus, if you consider that an OP or stippled reflector means more internal reflections of the light versus a smooth reflector, then you maybe have even more losses, but how much I couldn't say. But in any case, you end up with something close to --wait for it--
65 PERCENT
Taking a step back, I will readily admit that this is only a single piece of integrating sphere evidence. However, it still carries a lot of weight even so.
What really annoys me about all of the recent turmoil over this is the notion that if you don't have an IS, you can't say anything at all. I believe that our ingenuity and inventiveness here at CPF have proven otherwise. From the lumens estimator box, to our very own PaulW :bow: :bow: :bow: and his ceiling bounce tests, we have shown that there really is something in between an arbitrary, off the cuff uninformed random guess, and hard numbers from an integrating sphere.
So it's time for people like myself and Ginseng and PaulW and bwaites to pat ourselves on the back and do a little victory dance and (maybe) say "I told you so."
I would never do this, of course, being far too mature. *cough* I told you so! *cough*
Hmmm? What? Oh, no, I didn't say anything. Just a bad cough. Sorry. :devil:
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