What is a Lumen???

[fluoronator]

I've been reading over several posts trying to understand the meaning of the lumen ratings quoted on the spec sheet. Here is a summery of the main questions being asked along with the typical answers…

• What is a Lumen? (This question is usually answered pretty well, there's also typically a discussion of why this rating doesn't tell the whole story.)
• Do flashlight manufactures all use a standard method of measurement? (Answer is almost always "No").
• How do I know I'm comparing apples to apples when comparing lumen ratings? (You rarely can, and only then with a little inside knowledge about the companies methods.)
• Is there a group of reputable manufactures that you can rely upon to report good faith ratings based on standard practices within the industry? (What Standard Practices?)

So here's my question… Does anyone know of any past initiatives or attempts to urge manufacturers to write a set of standards, comply with the standards and note the standard test method along with the lumen rating on the spec sheet?

 

[paulr]

1. http://en.wikipedia.org/wiki/Lumen_(unit)

2. no

3. you are too concerned about lumens, it's like comparing wines by focusing on how the alcohol content is measured

4. No, lumen ratings from manufacturers are often simply pulled out of their butt. It goes way beyond the bulb lumen vs. torch lumen thing.

Re your question: some cpf'ers have wanted this but basically nobody else gives a damn. Manufacturers don't think of flashlights as scientific instruments, so if putting bigger numbers on them sells more of them, that's what they do.

 

[EntropyQ3]

Re your question: some cpf'ers have wanted this but basically nobody else gives a damn. Manufacturers don't think of flashlights as scientific instruments, so if putting bigger numbers on them sells more of them, that's what they do.

Then again, if nobody actually gave a damn, the manufacturers wouldn't spec it at all, now would they?

So there are interested parties, and while there may not be any hope for an industry standard that would actually be upheld, that doesn't mean that we couldn't do something of the kind here on CPF, similar to what was done with the lightmeter standard pass-around project.

While I agree that a flashlight has more than one quality of interest, light output and battery lives are pretty damn relevant for how you can use a light. Furthermore they are readily quantifiable properties. It makes sense to measure them, since other qualities are quite subjective - one mans "solid" is another mans "clumsy", one mans "firm" is another mans "stiff" and so on.

The existance of the objective does not imply a devaluation of the subjective.

 

[paulr]

What I mean by nobody gives a damn, is not that mfgrs think publishing numbers is unimportant, they just think it's unimportant that the numbers mean anything. At best it's just an indication of where the difference lights in a single mfgr's line-up compare. There are a few exceptions but basically it's best to ignore all mfgr claims and go with independent measurements.

Anyway there have been various CPF'er efforts to make uniform measurements, acquire integrating spheres, etc. Informal light box testing is the most common approach and is a lot better than nothing, though still dubious in some cases. Doug at flashlightreviews has done a lot of these in the past and they are very useful, though he hasn't been adding many new ones recently.

 

[LuxLuthor]

Recognizing that exact question, I have sacrificed many light bulbs to get some relative comparisons at various voltage overdrive values using this setup of a shielded light meter at 1 meter.

I'm not sure about this thread being in the battery section of the forum though.

 

[jirik_cz]

So here's my question… Does anyone know of any past initiatives or attempts to urge manufacturers to write a set of standards, comply with the standards and note the standard test method along with the lumen rating on the spec sheet?

There is a proposal of Standards for Measuring Flashlight Output by HDS systems. http://www.hdssystems.com/MeasuringFlashlightOutput.pdf

 

[DM51]

I think this thread belongs in 'General Flashlight Discussion', so I'll move it there now.

 

[MrAl]

Hi there,

Since the application has a lot to do with why you are asking this,
it makes sense to start there.
You seem to be looking for a way to compare different lights advertised
on the web as to their light output so you can judge what you are
getting for your money. Since the total amount of light can be measured,
it makes sense to want to get the light with the most light output for a
cost that seems reasonable or is better than another light with the same
light output.
There are however many more points about a light that come into question
besides light output. I dont bring this up to cloud the issue, but to convey
the concept of how to measure the total quality of a flashlight, not just
the light output. The light output is just one quality point, and there are
others such as how well the switch works and how long it lasts.
Again, im not trying to cloud the issue of light output which is important to know,
but leading up to another more important point that encompasses not only
the light output but the total quality of the light.

The total light output spec can indeed be falsified, as others have alluded to,
but even so, there are other things that can be misleading or even
malfunctioning, to the point that makes the light undesirable for you to own
or want to use for your intended purpose, even with the best light output
for the money.

Because of this is it wise to think about what the return policy of a particular
light is before you buy it, just in case it turns out that it doesnt fit your
need very well. It could be the light output, the switch, the style, even
the number or chemistry of the cells used in it (although you should be able
to find this out before you buy it). There's always something that comes
up, so be prepared to return it for either a refund or another light.
That's my advice, i hope it helps a bit.

Since we are on the subject of what can cause a light to function in a way
we dont like (including light output), recently i discovered that one of my
lights does not work very well once the battery runs down a little. By
"a little" i mean for 20 minutes or so. What happens is the light output dies
down very quickly with a new cell so that instead of putting out a nice
bright beam of light in the night it puts out the same as an ordinary lower
quality lower output lower priced LED !! This means i have to either accept
the lower output after maybe 15 minutes or be prepared to swap out the
battery at any given time to get the light output back to normal.
This is what i mean about things coming up.
Also, if the connection between the battery and light is not almost perfect,
the light output also dies down to match the next LED size *down*. This
is a bit nasty too.

I quess what this all means is that you should only buy from a manufacturer
that allows returns without too much question, which should be most of them.

 

[Jimmy H]

I think flashlight ratings and advertising has parallels to cars.

Lumens (horsepower)
Horsepower can be measured at the drive shaft, without accessories such as alternator, a/c compressor, power steering pump, or it can be measured at the rear wheels. Which one do they use when they tell you?

Beam throw, or beam spread (torque)
Torque, especially at lower speeds, will give you a feeling of more power than the car may really make, and it will taper off as you gain speed.

Run time (EPA fuel economy)
You probably want to know the miles/gallon, too. Your mileage will vary, depending on how much horsepower you use. Keep your foot on the floor, and you won't go as far as if you drive more conservatively.

Luxeon, Cree, etc. (Hemi)
Do you want a 4-cylinder, 6-cylinder, 8-cylinder, turbocharged, supercharged, etc.