# ANSI lumens vs OTF lumens?



## JustinTime (Jan 6, 2013)

I searched ANSI lumens looking for my answer but was overwhelmed with how many results the search presented. Basically, for a newb like myself; when I read from a manufacturer that one of their light is rated at 375 ANSI lumens as an example. I perceive that as they are saying it is 375 lumens OTF. I'm sure this is a common newb assumption. So, my first question; is that a correct analysis? I'm betting (to my disappointment) that ANSI lumens are really just a rating showing that the manufacturer has gone through the steps to accurately rate the lumens output of their light. On the other hand what makes me think that ANSI lumens are in fact OTF lumens is companies that advertise ANSI lumens also advertise the led lumen output of the light as well.


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## x2o (Jan 6, 2013)

I'm not 100% sure if CPF will allow a link to the flashlight wiki, but I'll give it a try http://flashlightwiki.com/ANSI-NEMA_FL-1#The_FL-1_Standard

There is some great info there about the Ansi FL-1 standard and will likely answer all of your questions.


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## JustinTime (Jan 6, 2013)

Thank you. I saved it to favorites just in case.


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## JustinTime (Jan 6, 2013)

Thank you. It does explain ANSI lumens but it really didn't clarify what the difference is between the terminology of OTF lumens in correlation to ANSI lumens. I'm really trying to figure out what the difference is between the two terms.


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## 2xTrinity (Jan 6, 2013)

JustinTime said:


> Thank you. It does explain ANSI lumens but it really didn't clarify what the difference is between the terminology of OTF lumens in correlation to ANSI lumens. I'm really trying to figure out what the difference is between the two terms.



American National Standards Institude (ANSI) is a group which does standardized testing for light output in lumens from devices like flashlights, computer monitors, and projectors.

Light output in all these cases is measured by placing the light inside an integrating sphere (see: wikipedia), which gives the actual amount of lumens coming out the front (OTF) of the flashlight. 

In some cases vendors of lights etc may exaggerate their lumen output by quoting the gross from the emitter based on the datasheet of the LED, often not considering losses in the optics or due to the LED heating up (why ANSI waits 30 seconds from start up time). Or in some cases I suspect they just make a number up. (eg small junky chinese lights that claim 900+ lumens)

While you could measure or estimate OTF lumens yourself (assuming you have a calibrated integrating sphere), sending it off to ANSI is different in that they're an unbiased third party with well calibrated gear that allows objective comparisons between one product and another.


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## enomosiki (Jan 6, 2013)

*Emitter output*: The amount of output produced directly at the emitter determined by calculating the amount of electrical current being fed into the emitter by the driver.

*Out-the-front*: The amount of output projected immediately upon activation measured inside of an integrating sphere, which incorporates efficiency ratings from the optics, lens and/or reflector has been calculated.

*ANSI/NEMA FL-1*: Out-the-front lumens calculated after 30 to 120 seconds after activation, which incorporates not only the optics/lens/reflector efficiency ratings from OTF but thermal and voltage stabilization as well.


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## twl (Jan 6, 2013)

Okay, you have to start at the beginning to get the terminology.

First, there's "emitter lumens" or "LED lumens", which is what the emitter is theoretically capable of producing at the drive current used, and sometimes it might be also what it actually does produce in the light at the emitter ONLY.

Then, there are losses in the reflector system or the optics, and also in the lens and possibly from reflections, so how many lumens actually comes OUT THE FRONT of the light is where we get this "OTF" term. It is typically somewhere around 15% less than the emitter lumens, although it can be more or less than that, depending on how good of a job was done with the light and its parts.

The ANSI lumens are OTF lumens which are measured at 30-120 seconds after the light is turned on.
The emitter starts to heat up almost immediately after turn-on, and the output starts to sag. Depending on how good the thermal management design of the light is, it might only sag a few lumens, or it might sag a hundred lumens or more. So, the ANSI lumens figure gives you some insight into how well the light can sustain its OTF output for some short time after turn-on, at least. 

A light with good thermal management will sustain a very high percentage of its OTF lumens at turn-on, for most of the run-time of the battery that's in it. As lumen outputs get very high, and the lights are not very big, then it gets harder to manage this thermal load, and the light may start to show rapid decline of lumen output shortly after turn-on, and the light gets excessively hot. This shows that the light was designed with too much output for it to manage its thermal load properly, and the typical manufacturer's method to deal with this is a "step-down" of the output automatically, to a level that it can much more likely sustain, such as half-power.

There are games played by manufacturers with this step-down function, and they typically try to time the step-down at a time just after the time specification for the ANSI measurement, so that they can claim maximum OTF lumens at turn-on, and then automatically step-down the output after 2 minutes or so, and then they can advertise an "ANSI lumens" rating that is actually much higher than the light can sustain, and will pretty much only be useful at that level in a short burst function. They will tell you it is a "750 lumen light", when it actually is a 750 lumen light for 2 minutes, and then it's a 480 lumen light after that.
This is extremely common to the point that it is almost standard procedure on Chinese made lights, so you have to watch out what you are buying. They do it because it is much cheaper to put in a timer to step-down the light after a couple of minutes, than it is to design a light with proper thermal management characteristics. Basically, you can have the worst thermal design in the world, and still get a high "ANSI Lumens" rating with a step-down after 2 minutes. And that's exactly why they do what they do. The Chinese lights almost all essentially side-step the ANSI ratings with this scheme, and the ANSI Lumens spec is basically meaningless in Chinese lights because of this.
If you know that's what it's going to do, and you are okay with it doing that, then there's no problem.


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## subwoofer (Jan 6, 2013)

2xTrinity said:


> American National Standards Institude (ANSI) is a group which does standardized testing for light output in lumens from devices like flashlights, computer monitors, and projectors.
> 
> While you could measure or estimate OTF lumens yourself (assuming you have a calibrated integrating sphere), sending it off to ANSI is different in that they're an unbiased third party with well calibrated gear that allows objective comparisons between one product and another.



I don't think ANSI do any actual testing for manufacturers as:

"Every flashlight company that participates in this rating system can conduct their own tests, adhering to very specific guidelines, or use an outside test agency."

They just specify the standard others must follow, like the BSI.


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## tam17 (Jan 6, 2013)

twl said:


> (...) Chinese lights almost all essentially side-step the ANSI ratings with this scheme, and the ANSI Lumens spec is basically meaningless in Chinese lights because of this.(...)



I wouldn't generalize on this. Not every Chinese manufacturer is dishonest. This is the point where neutral, non-biased flashlight reviews really begin to matter: everyone can draw conclusions for himself and vote with his wallet. 

Regarding the stepdown caveat, there's an example of a recent flashlight model (made by a reputable Chinese manufacturer, which I'm not going to name) that has almost unbelievable ANSI lumen rating and throw for its size, number and type of batteries used. Some of the exhilarated new owners expressed their praise for this light by calling it a dedicated searchlight. "Dedicated searchlight", which allows only _three minutes_ of operation before reverting to 2/3 of its initial output by timed stepdown! If something seems unbelievable, it probably is. Use your knowledge and common sense... BTW don't forget to check out Flashlight Reviews section before you spend your hard-earned cash...

Just my two cents


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## JustinTime (Jan 6, 2013)

Man, everyones replies here are extremely informative and helpful. TWL and Trinity, than you so much for your in depth posts. tam17, I believe I just received the light from the manufacturer you are not naming.  . I am happy with it. It is a bright sob. I do believe what TWL said though as it is a way to put inadequate heat sinking into the light and get a higher output rating that will attract buyers. It attracted me for sure. 

I can turn the step down off on my light. I wonder what the output drops off too with the step down off. I can certainly feel this light is noticebly warmer than my older less driven torches.


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## subwoofer (Jan 7, 2013)

tam17 said:


> Regarding the stepdown caveat, there's an example of a recent flashlight model (made by a reputable Chinese manufacturer, which I'm not going to name) that has almost unbelievable ANSI lumen rating and throw for its size, number and type of batteries used. Some of the exhilarated new owners expressed their praise for this light by calling it a dedicated searchlight. "Dedicated searchlight", which allows only _three minutes_ of operation before reverting to 2/3 of its initial output by timed stepdown!



Does the light that steps down after 3 minutes run on 4 x AA by any chance?


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## tam17 (Jan 7, 2013)

subwoofer said:


> Does the light that steps down after 3 minutes run on 4 x AA by any chance?



Yes it does.


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## reppans (Jan 7, 2013)

The ANSI standards are so loose, and each companies' adoption of them so different, that comparing spec sheets between different companies can actually be quite misleading. If you want to compare lights on an apples-to-apples to basis, there are only two ways I know of 1) mine through Selfbuilt's reviews and 2) test them yourself - and you don't need an integrated light sphere, I just use a DSLR and a couple of walls to bounce off of.

Unfortunately, both methods are less than ideal since Selfbuilt does not test every light, or every mode, and you cannot return lights you test yourself. But what you do find from both methods, is that manufacturers tend to be consistently good, or consistently bad, with their spec sheets, so it gives you a very good sense of who to trust, and who to take with grain of salt.

Here are some things to look out for, where companies play games, and what I've personally come across, now with the ability to objectively, and accurately, measure my lights:

- Step-down function (as mentioned above) but at least the step-down has a purpose, is usually noted, and/or a good manufacturer will only quote the stepped-down number if not noted in the specs.
- Cliff drops - Lights shooting for ultra-high performance tend to crash hard a few minutes after, for example, it's ultra-freshly charged NiMh drops below 1.4V... it still gets the higher ANSI lumen though.
- Battery used - Some don't list, some use Alks, and then there's a whole host of different capacity rechargeables with which to choose from.
- Output/Runtime curves - a perfectly regulated light that produces 100 lms for 5 hrs straight (100 avg - flat line) would be rated the same as one that started at 100 and ended at 10 (55avg - downward sloping line) by ANSI
- Manufacture conservatism.... or different ANSI scales? - if you look through Selfbuilt's reviews, and use his lumen scale, many manufacturers are significantly under-rating their lights (eg, a 140 lumen manufacturer spec is rated 240 by SB)
- Misrepresentation of lows - some misrepresent this number to get good runtime numbers. Do you think you can tell the difference between 3 lumens and 1.5 lumens? A company using the latter will double its runtime specs.

I gotta say, I've seen plenty of quality control issues among my lights, but all of them pale in comparison with certain manufacturers that exaggerate their spec sheets. Guess it's just that I feel my QC issues are random/isolated instance, while BS spec sheet mean 100% defective products.... and that the manufacturer cleanly gets away with because most people can't tell otherwise.


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## MichaelW (Jan 7, 2013)

I think the way to end these ANSI games is to change the rating time period from 30-120 seconds to 30-1200 seconds.


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## ozzywalker (Jul 16, 2013)

http://darksucks.blogspot.fr/2011/05/integrating-sphere-up-and-running.html

on this blog you can see how o.t.f. lumen are measured..i believe this measurement it's more accurate than Ansi fl1 for the part of lumen.


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## subwoofer (Jul 17, 2013)

MichaelW said:


> I think the way to end these ANSI games is to change the rating time period from 30-120 seconds to 30-1200 seconds.



Whatever the standard, the manufacturers will make the light fit that standard. Say the measurement is at 1200s from turn on, then instead of a step down at 3 or 5 minutes, there will be a step up at 19m55s just in time for the measurement. With the advanced drivers being used, the timing of maximum output can simply be triggered to fit the standard.

Maybe a better measurement would be to take an average reading over 10 minutes or even 30 minutes as this might stop the 'peak output' war.


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## bluemax_1 (Jul 19, 2013)

subwoofer said:


> Maybe a better measurement would be to take an average reading over 10 minutes or even 30 minutes as this might stop the 'peak output' war.



That would be a novel idea. How about 60 minutes? That's a common figure for usable continuous runtime at maximum output. The manufacturers would then list the lumen rating as the maximum average lumen setting that the light can maintain at 70f ambient temps for 60 minutes and listing whatever battery type was used for testing. They could then also list Burst modes, their lumen ratings and durations, eg. a 600 lumen light (maintains a regulated 600 lumens for 60 minutes), with a 1000 lumen Burst mode for up to 5 minutes.


Max


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