Basically what I’m asking is, when these companies (a.k.a. ‘Lumens Liars’) state ‘such-and-such flashlight’ has 1000 Lumens, how many true Lumens does it really have? Now, I realize true Lumens vary due to different battery strength (i.e. 2700ma; 3000ma), and so on; but, there must be a way to pin down an accurate range (i.e. a company states 1000 Lumens = 500 to 700 range of true Lumens) of true Lumens in a flashlight that claims 1000 Lumens.
And to expand on this, if and when (hopefully soon) this accurate information is revealed, we could help our BLF brothers and sisters make informed decisions on future purchases which are truly suited to their needs. Thanks and have a great day guys and gals
There are a few ways reported on here how you can measure actual lumens. For the simplest one you need a lux-meter, a dark room and a torch with lumen ratings which you know for sure are accurate e.g a well-known brand which reports ANSI standard ratings that have been independently verified by someone else. Then you put the lux-meter in a specific place and the torch next to it shining at the ceiling, then record the amount the meter reads, this is a ‘ceiling bounce’ test.
Then you just divide the known lumen output of that light by the reading you got, the result of that will tell you how many lumens each unit on the meter is worth. Then you can test all of your lights in the same way and multiply the readings you get by that number to get the actual lumen values.
Of course you can’t work it out until you own the actual light in question and can test it. Then there may well be variances between individual batches and samples of that light so you can’t be sure that number will generalise.
Thanks R. F. for an answer. That sounds like something that should be left to someone who knows what they’re doing. Are these lux-meters expensive; what’s the cost?
It’s not too difficult to get the hang of, you can get a decent lux meter for under $20 from chinese websites.
On a side note battery capacity (in mah) doesn’t affect lumens, but measures the capacity of the cell, so how long it will run at a particular current draw.
You can work out rough lumens OTF of a light from current measurements…
Current to the emitter (in ma) can tell you roughly how much a light will put out the front if you look at the LED used. You can’t measure current to the emitter without taking the light apart so people do ‘tailcap’ measurements from which we can approximate it based on the circuit used: for example in a 2 cell li-ion light you might measure 1.5 amps at the tailcap. First you multiply that by the cells’ voltage at the time of measurement ( e.g. 4.0 would = 6) then multiply by number of cells (so 12) this number is equivalent to watts input to the circuit. Next you minus that reading for estimated driver inefficiency (e.g. if 80% then /100 x 80 = 9.6), then divide that number by the forward voltage of the particular emitter at the estimated current (e.g for XM-L about 3.2), and in this case you get exactly 3 amps going to the LED.
Then you just look up how many lumens that emitter gives out at that current (probably around 900) and take account of loss in the optics for OTF values (e.g. 20% losses would take 180 off, leaving 720 lumens OTF).
Btw sorry for all the editing, I added this to my 1st post but it’s probably better seperately so I moved it.
Isn’t going to happen because there is too much variation in build quality/ quality control with shady manufacturers, and because people want a cool deal, they will not pass up the spurious buys. So they will keep coming. That is the problem. The best resource is this forum where those who know what they are talking about can steer one toward legit offerings.
Thank you. You posted, “…those who know what they are talking about can steer one toward legit offerings” My Q. to you is, where are the sites that you’ve found to sell “legit offerings”.
There are some brands for which you can know the readings are pretty accurate e.g. Fenix/Sunwayman/Nitecore etc. Otherwise you have to rely on the dealer to give you more accurate readings than the manufacturer claims, it’s the same with battery capacity.
Fasttech is one of the best for this although many are still exaggerated so you need to search for reviews if you are unsure.
Intloutdoors is pretty honest, but most stores with budget offerings have items that come from various manufacturers and so none can guarantee all ratings. Since the things that affect brightness are: 1) pill size, 2) current draw, and 3) emitter efficiency, it’s just not possible to regulate those factors on the budget scene.
You can use a DSLR if you have one. It’ll measure down to 0.10 lumens +/- ~10%. Just use a trusted light to calibrate it once any it’ll spit out a lumen measurement for any light/mode.
It really is surprising how far out some respected manufacturers are on their marketing claims. Downside is that knowing the truth can sometimes spoil the ownership experience for what are actually very good lights.
digital single lens reflex? not sure… but thats from the top of my head.
Thats a digital camera, a digital version of the SLR, something like the Canon EOS series.
they are expensive… better buy a lux-meter… much cheaper
That is the simplest way and in effect you’re using the room as a lightbox. But relying on the ratio of a single light’s known output at one setting divided by its ceiling bounce reading is most valid for that specific light at that brightness and can be way off when applied to different lights over a range of brightnesses.
You can refine this and get greater accuracy by making a regression formula from ceiling bounce readings (independent variable) and their corresponding ANSI lumens (dependent variable) of multiple lights at multiple settings. Very easy to do in excel and once you have the formula you simply plug in ceiling bounce readings to get estimated lumens.
You can refine this even further by making a lightbox or IS and applying the above.
Remember (AFAIK at least) lumens are a ratio scale, so while differences between lights in things like beam profile can act as a confounding variable, levels of lumen output should remain directly proportional to the reading of the luxmeter without the need for a more complex regression formula.
