Oh, it's a tricky one!
"Divide 30 by half" = 30 / 0.5 = 60. "and add 10" = 60 + 10 = 70.
"Divide 30 in half" = 30 / 2 = 15. "and add 10" = 15 + 10 = 25.
It says divide 30 BY HALF (30/.5) = 60 rather than saying to divide 30 in half which would be 15. Very literal instructions following is necessary for the correct answer (70). Just two little words, BY and IN, make a total difference in the correct answer.
Darn: You beat me to it!
ok,I just went back!!! I also got a degree in English for these tricky questions!
Neither answer can be considered correct. “divide 30 by half” is ambiguous and improper english. Should be “divide thirty by one-half” or “divide thirty in half”.
i was going to say… divide 30 by half of WHAT? but you beat me to it
Also just what are you adding 10 to? If you divide 30 in half, do you add 10 to one of the halves? both halves? the sum of the halves?
Tastes great! 
Less filling!
t is difficult to get perfectly accurate readings i agree.
I don’t even like posting numbers but I get bugged over and over to do it. All I do is test lights that are considered to be “known” and then I test mine in the exact same way and do the math. It’s as close as I’m going to get or even bother getting. I have tested hundreds of lights so I have a pretty good idea of what is up. But in all honestly I think a meter is really best used for making an educated guess and to test one light against another. If light A is 30% more lumens on my meter than light B it’s 30% brighter and that is all I really need to know.
So instead of trying to get everyone on the same page why not simply expect the numbers to be a useful tool in comparing one light to the next? If Tom E or “The” or anyone else says that light A is 50% more lumens or twice the LUX of Light B then that is what you should be looking at. Not how many lumens or how many lux. because those numbers are NEVER going to be consistent from person to person.
I have been asked by a few members the same question. Should I buy a light meter and which one? I say go for it, buy a cheap one and do yourself a favor and use it to compare one light against the next. Did your mod increase the light by 20% or add 10,000 Lux. Whooo Hooo that’s what it’s all about. Is your new SRK brighter than your old SRK etc etc etc.
Also I don’t need the weatherman to tell me it’s hot outside. If I turn on a light and it lights up my entire yard it’s a lot of lumens. Heck I still use my wife as a light meter all the time. I turn them on so she can’t see which is which and ask her which one is brighter. If I check her eyes against the light meter it’s the same 99% of the time.
Oh and I have gone on CPF enough to know that modded lights over there get exaggerated lumens all the time and lux numbers are worse. So it’s not just this forum.
In short I’m more interested in a comparison than the numbers. Is light A brighter than light B. That is all I really want to know and a 10 or even 20 percent difference isn’t going to be enough for most eyes to tell anyway.
The exact reason I bought mine was to test lux. Take a base reading, and then swap the driver, led, ar lens, aspheric maybe... See what kind of improvement I got. Or for a flooder, bounce it off the ceiling, do my mods, and do another ceiling bounce and see what kind of improvements I got. I'm pretty confident that my lux readings are pretty close, but I wouldn't say they are absolute. Same with my flooder test, any numbers I get will be useless to someone else trying to reproduce my readings.
When you read a review, and person "A" measures a light to have 58mm wide reflector and person "B" writes in another review that the reflector of another light is 68mm wide. You expect that person "B"`s reflector is 10mm wider right? Or do you only think that person A`s measurement of 58mm should only be compared to other measurements person A have done?
I certainly think its nice that person A and person B`s numbers are as comparable as possible. I would like lumen and lux numbers to be more like that as well.
In the world there are lots of common tools for precision measuring. Its useful. Why settle for inaccuracy between different people when you can settle for accuracy?
Ok, I cant get peoples lumen/lux numbers to be dead accurate. Actually, not even within 10%. But if we could make numbers that on average are maybe as high as 20% off become closer, that would certainly help.
Usually when something is calibrated to a well defined standard, measurements should be spot on or very close to eachother. That is not the case with ANSI numbers from different manufacturers. So when people calibrate their lights towards ANSI rated flashlights they will not be on the same page depending on what flashlights they used for calibration.
Example. JM just posted a review of Fenix TK35 Ultimate edition. His lumen number on turbo was 5% lower compared to Fenix.
You can read in his review that he is using a calibrated Sphere. Now, if rdrfronty measured that light with his calibrated sphere would you expect 5% lower compared to Fenix? No, you would expect his number to probably be 10% higher or more. That is what I expect from his calibrated sphere, and its what he is expecting based on an earlier post in this thread.
Ill admit, I have not compared enough data to see that JM are generally close to Fenix, or maybe on the low side. But I based on my observations, I would expect him to measure well below rdrfronty and his lightbox, which is also calibrated.
@rdrfronty
When it comes to lux, I can see that Im not going to get you are anyone with similar meter to try and get closer to people with lower calibrations/reading meters simply because there are too many examples where your measurements or similar measurements are too close to calibrated meters.
When it comes to lumen, its a different story.
Its is clear to me, and you that in general, compared to Fenix, your numbers are typically 10%+ higher, and there are cases where your calibration is 20% higher. For the record, Im not saying your numbers are wrong, or that Fenix is closer to what is right, you have clearly done a great job with the calibration based on ANSI rated lights. I just want peoples numbers to become closer, and try to avoid a big gap.
Im just observing various peoples numbers who have also been through a calibration process. Compared to your box these guys are as far as I can see lower.
-Selfbuilt (Up towards 17% lower. At least on TK61)
-Johnnymac (His numbers seems fairly similar to selfbuilt. So lower)
-_the_ (His numbers seems fairly similar to selfbuilt. So lower)
-UpZ (I believe his calibrated sphere are based on Fenix, or close. So Im assuming his numbers are up towards 17% lower too.)
-Relic38 (Based on memory I believe he`s numbers were quite comparable with the above. Certainly closer to them. So lower. )
-jmpaul320 (Cant say for sure, but certainly seems lower. Example earlier in this thread showed Tom E measured about 8% higher on the exact same light)
-Match (1200 lumen OTF at 3A with XM-L2 U2 on copper does not seem possible based on his graphs. Which is basically what you see on a TK61. So I would have to say lower.)
-djozz (1200 lumen OTF at 3A with XM-L2 U2 on copper does not seem possible based on his graphs. Which is basically what you see on a TK61. So I would have to say lower.)
I think you will find that many people have Fenix lights close to their calibration. You can find several threads about that. That means, there are many more who are lower compared to your lumen numbers.
Id like to include this link. A person got to test 68 flashlights at Led-Lensers Calibrated sphere. They got a big nice expensive sphere!
NSFW, lumen sphere porn:
Lights were measured at 5 sec instead of 30 (since they wanted to save time).
According to google translate it was said that Fenix were the manufacturer that were closest with their ANSI numbers.
So, once again, I have an example that shows lower compared to your box.
The point of all this. Your numbers are generally higher compared to most others. Up towards 20% higher compared some. Im not aware of anyone who consistently shows higher lumen numbers compared to your box`s calibration. Do you? Ive asked the question to others earlier in the thread, and have not seen anyone been able to point at others with higher numbers. As seen, many others does seem to have lower numbers. When I say many, I mean, basically everybody who often share numbers except the ones with similar box to you.
I may be off on a several details and numbers in the list above. Its not supposed to be anything exact. So please, no need to nitpick. And sure, there will be examples where maybe you quite similar results. But I think that on average you fill find that most others are.... lower.
Im not capable of doing this precisely, but if we made a list of all the people who have "calibrated" integrating spheres or numbers that are supposed to be similar to spheres and often share them. If we then tried to extract an average (or median if you prefer) lumen number from all of them. Then that number should be what everyone should calibrate towards in order for everybody to "get the same page". That number does not exist. And will never exist. But that would have been my idea of getting everybody on the same page... If you followed that logic... Either way, I think its clear that you would have to adjust your lumen number lower.
As I believe you can see. I can not say that people with "Fenix numbers" should adjust their numbers up in order to get closer to yours. There are too many of them, and they are too close to calibrated equipment. And many of them are too close to each other.
But, as far as I can see, if you (rdrfronty) adjusted your lumen numbers down a bit, that would certainly help to get everybody a bit closer. I believe you could just talk to your brother and send a PM to Tom E, DBCstm, RMM on how to lower their calibration accordingly. That way more people would be closer when it comes to lumen numbers and you guys would still have as comparable numbers as before. Its just a suggestion. Feel free to share your thoughts why that would be a bad idea...
I want my numbers to be comparable with you, your brother, Tom E, DBCstm, RMM. Simply because we are all into high output modified lights, and all of you share a good amount of numbers. Id say you guys are responsible for a very high amount of the numbers that are being posted on modified lights here on BLF. And all of you guys have comparable numbers. But I would like to see that my numbers were not consistently a good step higher compared to "everybody else".
Standards are a beautiful thing. There are so many to choose from!
But more seriously, there’s an article by Peter Norvig about how to become an expert at programming. It may not be directly applicable, but some of his advice still makes a lot of sense for other endeavors.
http://norvig.com/21-days.html
The part I want to point out is where he gives a recipe for becoming really good at it. I’ll summarize it here, in more general terms. On BLF, we do most of these:
- Get interested in the topic.
- Do it. A lot. Learn by doing.
- Talk with others who do it.
- If you want, take school courses about it.
- Work on projects with others who do it.
- Work on projects after others who did it, picking up where they left off.
- Learn a bunch of different ways of doing it.
- Learn how it works at a low level, so you’ll have a better intuition for how to “cut with the grain”, so to speak.
And then at the end of his list he gives two additional steps — steps which seem particularly relevant right now:
- Get involved in a standardization effort. It could be the ANSI measurement committee, or it could be a matter of determining the optimal strobe timings. Either way, you learn about what other people like in a light, how deeply they feel so, and perhaps even a little about why they feel so.
- Have the good sense to get off the standardization effort as quickly as possible.
Can’t forget that last part.
First if all.... I am drunk and your example is comparing a lot of people lower than you expect. And second of alll, your example to compare it to was taking readings st 5 seconds instead of the industry standard of 30 seconds... You want consistent results, but you at comparing results taken out of industry standard time frames.
If 15 people you are comparing to are getting numbers lower than you expect them to be, maybe your numbers are higher than realistic? Just something to think about.
You want consistant numbers, but really not proving your point in that last post. You are kind of contradicting yourself...
Hobbyist results are to be taking as comparison, not absolute. Andbyiu just proved to us that even people with top of the line equipment can't even take reliable tests by doing them at 5 seconds instead of 30.
You name 9 people that are nice enough to take readings of lights and say they are all lower. And name one person using a high dollar integrating sphere but they can not even follow spec and take readings at 5 seconds instead of 30. How is that reliable? You cant even acknowledge his results as they are taken 25 seconds before they should have been. So you mine as well just erase them from your mind, right?
Wow, access to an official calibrated sphere and then not use the standard 30seconds, but measuring after 5seconds when even the battery sag has not been settled!!
What a waste.
Waste? Certainly not. But yes, it certainly would have been much better if they measured at 30sec. As can be read, they said that was not according to ANSI.
It does not change the fact that also that sphere were more in line with Selfbuilt and most reviewers. I compared a couple of lights with Selfbuilts numbers, and they were quite similar if not lower. And if they were measured at 30 sec instead of 5 sec. Measured numbers would have been even lower.
I think this is quite reassuring for guys like JM, who wondered if his numbers are a bit too low, since he measured a Fenix light too low. According to rdrfrontys calibration, Fenix lights should read 10-20% too high. But that calibrated sphere mostly showed that Fenix lights should be quite close to their ANSI ratings. If anything, they should read a bit lower.
> Is the exact same type of white cardboard/posterboard/paint
> available everywhere in the world, all with the same reflectivity?
http://www.ohio.edu/people/schneidw/vico222/gray_card_musings.html
I actually followed that link. It’s a surprisingly interesting read! Thanks! I’m not sure we can really apply that last piece of advice - to get off the standardization effort - in the context of this conversation. In fact, it doesn’t fit at all. That advice was given to a person seeking to become an expert in their chosen endeavor. We’re not talking about becoming experts here. An expert may very well be expected to balk at the idea of being merely comparable to others. But, we’re talking about a place where sharing information about our chosen subject is the very reason we gather. Making the information more meaningful by standardizing to a point of repeatability would be the higher goal. In this case, excellence requires being relevant.
As has been said before, the measurements we take are only going to be good enough to compare light “A” with light “B”. But, shouldn’t we have a reasonable expectation that one person’s light “A” will shine as brightly as another’s? If the readings on light “A” can vary by as much as 20% from person to person, then how do we compare it to light “B” reliably without each person having to possess each light? With thousands of lights in the world, can anyone afford to own them all? In most studies, polls, elections, and other such collections of data, the outliers are usually considered irrelevant. They aren’t given consideration. Nobody cares if the one guy whose measurement is 30% higher or lower is more accurate or less so. They go with the consensus. Don’t we do the same thing here - try to reduce spill and make a tighter beam? Even when trying to make a flood light, is it not more desirable to make it somewhat uniform? Does anyone intentionally make a light with 3 emitters aimed in three directions, and not rather aimed in unison at one target?
I hear you guys that are saying that dead-on accuracy is impossible because of so many irregularities in the flashlights themselves. I know what you’re saying, and you’re right. But, that doesn’t mean we can’t try to get as close as possible. And it doesn’t need to be as hard as some people suggest. For instance, if one person’s measurements really are reliably ~20% higher than everyone else’s, then all we need is a correction factor for that person’s numbers. Let’s say we have 10 people testing lights and their numbers vary from person to person typically by the same amount each time. We take that amount as a correction factor and apply it so that their numbers are closer in line with each other for the “same” lights. Then, when we see differences, we call those actual differences in manufacture from one light to another.
DavidEF;
Fine but who is going to skin the cat? Unless and until a large number of THE SAME LIGHTS are tested by all the people with Lumens spheres within a relatively short period of time with the same batteries charged on the same charger and then all the data is processed from each person and a correction factor assigned coming up with common readings is not going to happen. The logistics are a killer and this is the type of thing that needs to be repeated regularly as measuring equipment ages etc. That is why in industry there are calibration companies and labs set up to do periodic calibration of test and inspection equipment, and even a lot of production equipment including torque wrenches. In industry if it measures anything it has a calibration sticker on it.
Based on the evidence cited by people who have done the measurements even different manufacturers cannot agree on Lumens out for a given light so to expect a bunch of hobbyists to do better is asking the impossible it appears to me.
This thread has been an education and I would like it to be a sticky as it is so educational but I also think that the subject has been discussed to death and should be closed. Unfortunately those who want perfection will never get it just as even manufacturers have not done so based on info regarding test results presented here. Discussing it ad nauseum is not going to change the situation that currently exists.
I think the reason Norvig suggested getting involved in standardization is to better understand the things which matter to other people, and why and how deeply they care. It’s not about actually standardizing anything. And the reason to stop is to keep one’s sanity… to keep this from happening:
Take soda, for example. Er, no. That’s too complex. Take cola, for example. Or just Coke.
At the Coke factory, the product is pretty consistent. But by the time it gets into a customer’s mouth, the taste and formula vary wildly. The syrup they produce has a limited shelf life, so the taste changes by time since manufacture. It goes into a bunch of different types of soda machines which all behave a little differently, and may or may not have been cleaned recently. The soda machine must be calibrated and maintained by a person, and nobody is quite the same as anyone else. The machine mixes varying amounts of water and CO2 in with the syrup, based on the machine itself, the charge level of the CO2 container, the amount of syrup left, etc. The local water source changes the flavor too. CO2 retention varies greatly based on temperature of the liquid, and the overall taste changes quite a bit with temperature too. A bunch of CO2 is lost immediately based on the velocity of the liquid when it lands in the cup. People add different amounts of ice. The ambient temperature changes the rate of decay once the product is dispensed, and it doesn’t taste the same after it has been sitting for half an hour. And so on.
I bet Coke would really love to make sure each person gets exactly the same beverage experience, and probably goes to great lengths to standardize as much as possible. But how often do people complain that their drink’s CO2 level is off by 20%? How often do they even notice? There’s a point where one must either decide it’s “good enough” or leave sanity behind. Diminishing returns transforms the effort into something of an entirely different nature, a matter of philosophy rather than practical application.
I mean, if you think there are a couple of restaurants where the Coke really doesn’t taste right, then definitely let them know. But try to keep in mind that the goal is better-tasting soda, not convincing them to stop serving beverages.