# Bulb Re-rating & Torch Lumens Questions



## TBrogden (Oct 20, 2005)

All,

Are there any formulae or rules of thumb for "re-rating" of incandescent bulbs? I'm finding that Welch Allyn's website doesn't offer re-rating for all its bulbs and, even when it does provide that info, it doesn't extend to voltages in which interested.

Also, I often see here in the forums that torch lumens have been calculated at 65% of bulb lumens. If not too much trouble, I would very much like to know how that number was derived and the weighted contributions of those things making up the 35% "loss".

Many thanks,

Tony


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## Lurveleven (Oct 20, 2005)

See my signature for WA re-rating.

For bulbs from other manufacturers you can use the following formulas for re-rating:

The formula for halogen lumens re-rating is as follows:

Lr = (Va/Vd)^3.5*Ld, where Lr is re-rated lumens, and Ld is design lumens, and Vd is design voltage and Va is applied voltage.

The formula for halogen lamp life re-rating is as follows:

Lr = (Vd/Va)^12*Ld, where Lr is re-rated life, and Ld is design life, and Vd is design voltage and Va is applied voltage.

The formula for halogen current re-rating is as follows:

Ar = (Va/Vd)^0.55*Ad, where Ar is re-rated current, and Ad is design current, and Vd is design voltage and Va is applied voltage.

The formula for halogen CCT re-rating is as follows:

CCTr = (Va/Vd)^0.317*CCTd, where CCTr is re-rated CCT, and CCTd is design CCT, and Vd is design voltage and Va is applied voltage.

To find voltage sag:
Va = (Aa/Ad)^1.818*Vd, where Aa is applied current, and Ad is design current, and Vd is design voltage and Va is applied voltage.

To find applied voltage from lamp life:
Va = Vd/((Lr/Ld)^(1/12)), where Lr is re-rated life, and Ld is design life, and Vd is design voltage and Va is applied voltage.

To find applied voltage from lumens:
Va = (Lr/Ld)^(1/3.5)*Vd, where Lr is re-rated lumens, and Ld is design lumens, and Vd is design voltage and Va is applied voltage.

I'll let JS chime in on how they arrived at 65% for the torch lumens.

Sigbjoern


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## bwaites (Oct 20, 2005)

Sig,

Thanks for those formulas again!

I lost them with my computer crash and hoped someone would post so I wouldn't have to go looking!!!

Bill


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## TBrogden (Oct 20, 2005)

Sig,

This is great!

Thanks very much,

Tony


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## Phaserburn (Oct 20, 2005)

dummy question: what does ^ mean?


:duh2:


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## Haesslich (Oct 20, 2005)

That's the Exponent sign: So in other words, the equation 'Lr = (Vd/Va)^12*Ld' can be rewritten as so:

Lamp Rating is equal to the product of the design voltage divided by the applied voltage of a lamp, to the power of 12 times the design life of a lamp.


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## Phaserburn (Oct 20, 2005)

Thanks, Haesslich!

:thanks:


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## JimH (Oct 20, 2005)

Sig,

Thanks for the formulas, but, unless I missed it, you forgot one. Carley lists the output of their lamps in Mean Spherical Candlepower, which is directly convertable to lumens.

MSCP (mean spherical candle power) 

lumens = MSCP X 4 Pi = MSCP X 12.566 



If you don't mind, I'd like to copy those formulas over to the CPF Wiki where it's easy to find them.


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## Lurveleven (Oct 20, 2005)

Thanks Jim.

Btw, it should be: Lumens = MSCP x 12.566 
I guess you don't have Pi on your calculator so you must have miss-entered 3.1715 instead of 3.1415 when using your calculator.

Sigbjoern


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## JimH (Oct 20, 2005)

Lurveleven said:


> Thanks Jim.
> 
> Btw, it should be: Lumens = MSCP x 12.566
> I guess you don't have Pi on your calculator so you must have miss-entered 3.1715 instead of 3.1415 when using your calculator.
> ...



I did enter it from memory but made a typo




- damned fat fingers



. 

Good catch, I'll correct it.


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## PaulW (Oct 20, 2005)

Tony,

To address your second question:



TBrogden said:


> . . . Also, I often see here in the forums that torch lumens have been calculated at 65% of bulb lumens. If not too much trouble, I would very much like to know how that number was derived and the weighted contributions of those things making up the 35% "loss". . . .


As far as I know, the 65% figure came from empirical tests. That is, when measuring the light from a torch using a WA bulb, it seemed generally to be about 65% as bright as a Surefire torch with the same designated lumens. This led to folks making "total light output" tests designed to comare two torches.

Such tests are designed to get a measure of total light rather than direct light in the beam center. The light reflected from a wall or corner is measured for each torch. Some folks have even constructed little chambers, such as milk bottles to collect the light.

No one knows exactly where the other 35% of the light goes. It has been guessed by some of our smarter CPFers that it is probably lost within the torch's head -- in reflection at the lens surfaces, absorption by the reflector surface, and capture in the hole in the reflector near the bulb's base.

Paul


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## bwaites (Oct 20, 2005)

Actually, that 65% figure was arrived at with a little more objectivity and research than just comparisons. It took into account aluminum coating reflectivity, window loss, etc.

I suspect that Ginseng (and probably js!) has it logged away where we came up with that figure, but it is pretty widely aknowledged on the board that it is close to correct.

Another interesting factoid:

Surefire rates their lights with a very conservative "torch lumens", or actual lumens out the front, while most companies rate their lights with "bulb lumens" or lumens produced by the bulb, before reflection. 
Bill


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## PaulW (Oct 20, 2005)

bwaites said:


> Actually, that 65% figure was arrived at with a little more objectivity and research than just comparisons. It took into account aluminum coating reflectivity, window loss, etc.
> 
> I suspect that Ginseng (and probably js!) has it logged away where we came up with that figure, but it is pretty widely aknowledged on the board that it is close to correct.
> 
> Bill


Thanks, Bill. It's always a good day when I learn something new. I had no idea you guys had been working on that.

Paul


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## bwaites (Oct 20, 2005)

No credit on my part!! When I say "we", I mean those of us who quote it, not that I had anything to do with the number!!

Someone on CPF, and I don't remember who it was, but I'm sure js or ginseng or both will, came up with that number and it has proven pretty reliable when we compare it with the "known" numbers from Surefire. 

Bill


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## Size15's (Oct 20, 2005)

bwaites said:


> Another interesting factoid:
> 
> Surefire rates their lights with a very conservative "torch lumens", or actual lumens out the front, while most companies rate their lights with "bulb lumens" or lumens produced by the bulb, before reflection.
> Bill



To follow what Bill has written, SureFire's rating is not the peak output over the course of the unregulated runtime but a value more representative of the light output over the course of the runtime of the batteries.

For example, SureFire rates it's E2e at 60 lumens. Independant rate put the output in the order of 80 lumens I believe.

Comparing lumen ratings between manufacturers is almost as pointless as comparing candlepower ratings. At least that's my opinion.

Al :shrug:


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## andrewwynn (Oct 23, 2005)

manoman thanks so much for the formulas.. my 'master database' of WA lamps running from every possible battery combination just took a huge step up in performance.. it automatically recalculates everything you just put in the switch (circuit) resistance and blamo.. i even figured out how to have it resolve circular references so that it recalculates the ending current after considering voltage drop.

I think i'll makes a quick n dirty re-rater spreadsheet that i can post. 

the WA re-rater will let you use any bulb you just have to put it in manually.. i've been told and it makes sense that re-rating can only bet trusted maybe 20% +/- but the formula is what you have to go with, and i'm sure that certain bulbs can be pushed a lot harder than 20% overdrive..

One thing i've adeed to my re-rating spreadsheet: the ability to track how close to the melting point the filament is.. i'm finding that 4-5% away from the melting point is a really nice place to run WA bulbs.. you end up with low 30s for lumen/watt and the color is spot-on gorgeous. 

I think i'm going to go make a simplified version of my spreadsheet now i'm betting it'd be very helpful to hotwire folk. 

-awr


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## andrewwynn (Oct 24, 2005)

OK.. here it is: 






That is a screen shot of the re-rater spreadsheet.. 

here is the spreadsheet itself

(right click and save target). 

the key is right inside the file just scroll down to read it. 

I have a couple bulbs in there...my 'master spreadsheet' has a different theme to it... it's broken down by host light.. i.e. has all the bulbs that work well from a 7.2V source and also has all the battery combinations that work in that voltage.. it would take an hour just to explain how to use it, but it is awesome. 

This is a much more simple design.. has spots for two bulbs.. and will let you either put in the bulb voltage you desire and it will show you the input voltage required.. or you can put in input (battery) voltage and it will show you the bulb voltage you will get based on a resistance value you put in (there is a chart included for all the basis possibilities). 

As you can see from the sample. .the 1111 is a kick butt bulb.. in a 7.2V source you can expect 834 bulb lumen nominal with the KIU socket! 

If you put the 1274 in a 2D-3bore with 9 CR123 primaries.. regulate to 8V and get 800 lumens.. the Vbulb and Vbat are entered as well as the 'blue' values for the design values of the bulb. 

My favorite part is now everything is calculated including current.. it actually is a circular reference since the current is based on the voltage but the bulb voltage depends on the current.. it just 'finds the answer' automatically.. gotta love computers sometimes. 

This spreadsheet takes into account the voltage losses on the switch.. put in your favorite bulb and change the resistance value from 30 (KIU socket) to stock pr bulb (177) and watch the dastardly effect it has on the lumen output! 

Hope people find it useful, please post if you grabbed it and it helpd you out.

-awr


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## Nereus (Oct 24, 2005)

Thanks, Lurveleven, for _very_ useful bulb re-rating formulas! I noticed that they produce very similar results with WA's site when re-rating 01185 and 01166 bulbs. I would not be surprised if WA used them directly. Now I have two questions for you (or for anyone who knows the answer):

Where did you get those formulas?

Sometimes people say that bulb is running xxx% from the (tungsten?) melting point. How do you calculate that percentage?

WBR, Nereus


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## Lurveleven (Oct 24, 2005)

The two first formulas have previously been posted on CPF, but the rest I had to create myself. To do that I collected a few data points from the output from the WA rerater and used those to reverse engineer the formulas.

Sigbjoern


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## andrewwynn (Oct 24, 2005)

Kelvin temperature is an abolute scale.. 0K is absolute zero it's a direct fraction. W melts at 3695K. the formula is: (1-bulbtemp-3695) (and x100 if you want to read %).

the formulas Lurveleven posted are what WA's re-rater uses.. the results from the formula that i included from lurve into my spreadsheet match to the decimal point exactly what the results show from the WA re-rater... they might go more than 3 sig. digits but it's a moot point.. they are perfect.. i love that the current calculations even though 'circular' i was able to let the spreadsheet iteratively calculate 'til it finds the solution that is my favorite part... you have no idea how many times i used a calculator to estimate the current at a different voltage! (which of course.. changes as soon as you change the current. aaaaah)

-awr


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## js (Oct 26, 2005)

AWR,

Quick note about temperature of the tungsten filament and CCT: they are NOT the same. The CCT is the Correlated Color Temperature, and reflects the "best fit" of an ideal black body radiator to the actual output of the light source. Tungsten is really a "grey" body, so the filament temp and CCT are different by about 80 to 100 K, with CCT being higher than actual temperature.

As for the 65 percent figure, Ginseng is the one who quoted it to me way back when I was first doing the TigerLight Upgrade Thread. So I didn't originate it, but I have verified it over time by doing comparisons of lights with known outputs. It is only a rule of thumb to be sure, but it is one that I will hang my hat on, so to speak. I have found it to be within the measurement error bar of the only optical measuring device I own: my eyes.

A calibrated integrating sphere would be necessary to really test out the rule of thumb in each particular case, and over a wide range of total outputs and lamp types and reflector sizes, and so on. But I'm not about to drop 6 or 8 large on one of those!


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## andrewwynn (Oct 26, 2005)

good to know about the CCT.. probably explains how bulbs can run 'so close' to the melting point. 

-awr


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## Nereus (Oct 26, 2005)

Thank you for your quick answers, guys! JS, you answered my next question before I even asked it... I was also wondering if CCT and real filament temperatures are the same.

When it comes to degrading bulb lumens to torch lumens, have a look on WA's 10 watt HID datasheet. It's said that the 10 watt SEL hid produces 500 lumens and the same 10 watt hid with built-in reflector produces 450 lumens - that's only 10% decrease in light output due to (aluminium ?) reflector.

WBR, Nereus


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## LuxLuthor (Aug 27, 2007)

A great old thread worth bumping at least once every few years. I found this linked on Lurveleven's sig in some other thread. This is also a more recent short discussion on calculating lumens.


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## Aircraft800 (Aug 27, 2007)

I was always wondering where you guys were coming up with the bulb lumen outputs that were beyond the graphs at WA site.

Thanks for the bump! I'll subscribe to this one so I don't loose it.


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## FILIPPO (Aug 27, 2007)

Hi thanks for your formulas!
I have just put all of them in Excel...

I was thinking is there a formula to calculate the volt at bulb pins from battry pack volt and resistance?:candle:


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## LuxLuthor (Aug 27, 2007)

FILIPPO said:


> Hi thanks for your formulas!
> I have just *put all of them in Excel.*.



It appears you did not carefully read post #17 above.


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## FILIPPO (Aug 27, 2007)

LuxLuthor said:


> It appears you did not carefully read post #17 above.


 
OMG, I have missed the most important post!
my bad! excuse me for the stupid question!:shakehead


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## LuxLuthor (Aug 27, 2007)

There are actually several improvements/enhancements to AWR's hotrater...but that link is a pretty good start.


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## Icebreak (Aug 27, 2007)

Excellent bump, LuxLuthor.


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## drew2001 (Oct 16, 2007)

Bump again for new readers ... like me !

thanks Great thread !


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## js (Oct 17, 2007)

Since this thread got bumped, it deserves a link my thread on the subject of bLu vs. tLu:

 bLu vs. tLu: IS confirms 65% conversion factor


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