How to easily measure lumens

[Jeff Liebermann]

How to easily measure lumens without an integrating sphere.

The correct way to measure total light output from a bicycle headlight
or flashlight is with an integrating sphere:
<https://www.google.com/search?q=integrating+sphere&tbm=isch>
<https://www.youtube.com/watch?v=mvyptpA-BmY>
These are not cheap, although they can be home built. There are also
other ways to do it (lumen tube):
<http://s1074.photobucket.com/user/mrsdnf/media/stuff/IMG_3226.jpg.html>
<https://www.youtube.com/watch?v=xOE1ykJ5WAU>

My method is far from accurate, but good enough for estimating and
comparing the light output of flashlights and bicycle headlights. To
make it work, you'll need a tape measure and a lux meter. I'm using
this one:
<http://www.ebay.com/itm/381903904643>
It's main advantages are that it does auto ranging, has a max hold
feature, and is cheap.

First, the math:
1 lux = 1 lumen per square meter.
That means if I project a circular spot on the wall, with an area of 1
square meter, the indicated brightness in lux equals the approximate
lumens output, which can be read directly from the lux meter. Notice
that it is NOT important to know the beam width or the distance
between the light source and the wall.

How big is a 1 square meter spot?
Area = Pi * radius^2
For Area = 1 square meter the radius of the spot is:
r = sqrt(1/Pi) = 0.564 meters
The diameter of the spot is 1.12 meters (44 inches).

Find a darkened room with a suitable wall, and put two pieced of
masking tape on the wall separated by 1.12 meters (44 inches). Notice
that the wall does not need to be flat or painted white. Half way
between the two markers, hang the lux meter.

To measure, turn on the lux meter and punch the max hold button. This
will display and hold the highest reading. Start well back from the
wall, turn on the flashlight, and slowly move towards the wall until
the edge of the light spot lands on top of the two markers. Turn off
the light and read the meter. The meter reading in lux will be equal
to the lumens output of the flashlight or bicycle headlight.

I bought various flashlights on eBay and tested them at maximum
brightness with new batteries.
This one claims 5000 lumens but delivers 200 lumens.
<http://www.ebay.com/itm/322447023467>
This one claims 300 lumens but delivers 97 lumens.
<http://www.ebay.com/itm/391639378962>
This one claims 6000 lumens, but delivers 212 lumens.
<http://www.ebay.com/itm/201457081072>

There are plenty of problems with this method. Putting the lux meter
at the center of the circle causes the meter to favor lights with hot
spots in the middle. A properly designed bicycle light or flashlight
should have an even and equal brightness distribution across the spot
on the wall, but this is rarely the case. I'm working on a more
accurate way to measure and calculate the average light output.
Probably, it will be measuring the light in the center and along the
edge, and taking an average or estimating the total based on a
gaussian light distribution. Or maybe not putting the lux meter in
the center of the circle. That's for later.

Another error is the color temperature of the light. LED's come in a
variety of color temperatures. The lux meter has a different
sensitivity at each of these colors where the sensitivity curve
follows the sensitivity of the human eye.
<https://image.slidesharecdn.com/ivanperrepresentationfor24-141008071626-conversion-gate02/95/pls-2014-is-measuring-led-illuminance-with-a-lux-meter-accurate-19-638.jpg>
Comparing lights with different color temperatures will be a problem.

There is also a problem in dealing with the 1 square meter area when
the spot is not a perfect circle, but rather an ellipse as in many
bicycle headlights.
Area = Pi * major_axis_radius * minor_axis_radius
This can be easily measured, but will be different for each headlight
with an elliptical beam pattern and will therefore be a bit more
complicated to measure.

I also do not yet have a calibration illuminance standard. Therefore,
I don't know how accurate this method might be until after I get or
build one.

Good luck, have fun, enjoy, and please post some test results for
various bicycle headlights.


--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[Frank Krygowski]

On 3/24/2017 2:22 AM, Jeff Liebermann wrote:
> A properly designed bicycle light or flashlight
> should have an even and equal brightness distribution across the spot
> on the wall, but this is rarely the case.

A properly designed bicycle light should not have a round spot at all.
See http://peterwhitecycles.com/plight.php for some information on
headlight optics.

Alternately, face your favorite motor vehicle toward a wall, turn on the
lights (low beam) and observe the beam pattern.


--
- Frank Krygowski

[Sir Ridesalot]

Much is made about different methods of measuring bicycle lights. I think the best thig is to asctually try the light in the conditions you ride in.

If I'm going to or have to test a light only AFTER BUYING it then I'll just wait until night time, ride to where I need to know how the light works for me and then simply turn on the light. Does it light up the road enough and far enough ahead for me at the speeds I ride? Yes, then I'll keep the light. No, then I'll return it for something better.

Cheers

[Sir Ridesalot]

Opps. Sent too soon.

I meant to add that lights can have very similar outputs but widely varying beam shapes/road illumination and therefore widely varying usefullness. I was aastounded at just how poor the hub dynamo light I tried outside a bicycle shop on a very dark section of road actualy was. Ditto for some battery lights.

Some people will tell you that their light illuminates a sign X-distance away. What they fail to tell you is that that's about all the light does iluminiate.

Cheers

[Joerg]

Yup! This is similar to what I have (2nd part, with diffuser lens) on
both bikes:

https://www.youtube.com/watch?v=5J9zIGTfgGw

After installing them I never looked back. No need to measure any
lumens. It simply does the job at night even north of 25mph and makes me
very visible to motorists during the day. Only on singletrack I have to
keep it below 15mph at night but that's fine.

[...]

--
Regards, Joerg

http://www.analogconsultants.com/

[Doug Landau]

Yer FIRED! FIRED!, I tell ya!

[Mark J.]

Huh. My experience was the exact opposite. I suspect we've used
different dyno-lights. I'd been a die-hard battery-light disciple for
years, and had several different models (each better than the last, as
tech improved.)

But I was persuaded to try a dyno-hub for my 2 mile suburban commute,
where light _to see by_ just wasn't needed, or hardly, and the dyno
convenience was a factor.

I so liked my B&M Luxos, I tried it on a recreational ride in the _dark_
countryside, and within a month, put another Luxos on my rando bike.

On my first long dark ride with it, I continually annoyed my riding
partner with "I really LOVE this light" - because of its useful beam
pattern. The Luxos has no more lumens than my last few LED battery
lights, (at least not on the settings I used) but it enables me to see
much better. No central "hot" spot to affect my night vision, just an
incredibly wide field of even light.

(Paired with Shutter Precision dyno-hubs).

Mark J.

[Jeff Liebermann]

On Fri, 24 Mar 2017 13:30:06 -0400, Frank Krygowski
<frkr...@sbcglobal.net> wrote:

>On 3/24/2017 2:22 AM, Jeff Liebermann wrote:
>> A properly designed bicycle light or flashlight
>> should have an even and equal brightness distribution across the spot
>> on the wall, but this is rarely the case.

Oops. That's wrong. I didn't think of the vertical gradient.

>A properly designed bicycle light should not have a round spot at all.
>See http://peterwhitecycles.com/plight.php for some information on
>headlight optics.

True. A properly designed bicycle headlight should belch more light
near the horizon than it does for light pointing downward to
compensate for beam spreading at longer distances. When pointed at a
vertical wall, the upper part of the spot should be brighter than the
lower part. The horizontal light distribution should be even.

At least, that's the theory. I've been playing with this cheap light:
<https://www.rei.com/product/769616/planet-bike-blaze-1-watt-front-bike-light>
which seems to produce a circular spot with no obvious vertical
gradient. I'll see if I can borrow something better and see what it
looks like on the wall. Meanwhile, I've been using cheap flashlights,
which all produce roughly circular spots and have no need of a
vertical gradient (unless one uses it on a bicycle).

Even with a vertical gradient and an elliptical spot pattern, it
should be possible to determine the average luminance by taking lux
readings at the center, and at 0, 90, 180, and 270 degrees, and
averaging the values (somehow). A straight line average would
probably be sufficient, but I would like to try Gaussian for better
accuracy:
<https://en.wikipedia.org/wiki/Gaussian_beam>

>Alternately, face your favorite motor vehicle toward a wall, turn on the
>lights (low beam) and observe the beam pattern.

<https://www.google.com/search?tbm=isch&q=headlight+beam+pattern+on+wall>
Yep. Brighter at the top than at the bottom and roughly elliptical,
but not very well controlled.

[Jeff Liebermann]

On Fri, 24 Mar 2017 11:09:08 -0700 (PDT), Sir Ridesalot
<i_am_cyc...@yahoo.ca> wrote:

>Much is made about different methods of measuring bicycle lights. I think

>the best thing is to actually try the light in the conditions you ride in.

Sigh. I forgot to include a statement of purpose. I didn't write the
procedure to provide a means of selecting a suitable bicycle light.
Lumens is just one factor among many, some of which are intangible,
subjective, or cannot be quantified. What I was trying to do is
provide an easy way to get an approximate measurement of the lumens
output using a cheap lux meter, tape measure, and the simplest
possible procedure. The idea is that the average cyclist or
flashlight enthusiast can run a quick sanity check on bicycle light
and flashlight output to verify any advertised claims. Hopefully, the
trend towards ever increasing exaggerated lumens claims will end if
the buyer is able to verify the numbers.

Of course it's best to try a headlight under the expected operating
conditions before buying. However, part of what one pays for any
light is its ability to deliver some total amount of light, as
measured in lumens. This also impacts the battery runtime, dynamo
loading, heat dissipation, output loss as it gets warm, etc. Once the
lumens are known, all of these can be calculated or at least
estimated. If the resulting numbers look sane, then the light is
worth trying. If something in the numbers appear to be wrong for your
expected situation, such as insufficient runtime, then you can save
yourself the time and effort testing the light. (Actually, the last
time I road tested a light, I didn't bother letting the battery run
down because I was tired).

>If I'm going to or have to test a light only AFTER BUYING it then I'll
>just wait until night time, ride to where I need to know how the light
>works for me and then simply turn on the light. Does it light up the road
>enough and far enough ahead for me at the speeds I ride? Yes, then I'll
>keep the light. No, then I'll return it for something better.

That's a good description of how one should test a headlight. With
the variety of beam patterns available, a field test is a necessity.
Such a test does nothing for testing lighting under adverse conditions
(rain, snow, fog), mechanical construction, and assembly failures. Of
course, my lumens measurement also does nothing for these problems.
Like I said, lumens are just one part of the puzzle.

Drivel: The parts for a integrating PVC pipe just arrived. We'll
soon see if the two methods produce similar numbers.
<https://www.flickr.com/photos/77239986@N00/albums/72157650137883291>

[John B.]

On Fri, 24 Mar 2017 19:19:19 -0700, Jeff Liebermann <je...@cruzio.com>
wrote:

>On Fri, 24 Mar 2017 11:09:08 -0700 (PDT), Sir Ridesalot
><i_am_cyc...@yahoo.ca> wrote:
>
>>Much is made about different methods of measuring bicycle lights. I think
>>the best thing is to actually try the light in the conditions you ride in.
>
>Sigh. I forgot to include a statement of purpose. I didn't write the
>procedure to provide a means of selecting a suitable bicycle light.
>Lumens is just one factor among many, some of which are intangible,
>subjective, or cannot be quantified. What I was trying to do is
>provide an easy way to get an approximate measurement of the lumens
>output using a cheap lux meter, tape measure, and the simplest
>possible procedure. The idea is that the average cyclist or
>flashlight enthusiast can run a quick sanity check on bicycle light
>and flashlight output to verify any advertised claims. Hopefully, the
>trend towards ever increasing exaggerated lumens claims will end if
>the buyer is able to verify the numbers.
>

I would have to ask. Is it important to verify the advertising claims?
Or is it important to verify that you can see sufficiently well to
cycle?

--
Cheers,

John B.

[cycl...@gmail.com]

Frank, if you aim a light straight at something it should throw almost a perfect circle. When you aim you bike light up the road it strikes at an angle forming an oblong circle. If you try to form a light in any other manner you cannot have equal illumination within the beam.

[cycl...@gmail.com]

If you observe his beams you can see just as I stated - that there are bright and dark spots within the beam so that you can mistake potholes for dark spots in the beam.

You should pay closer attention to what Jeff is trying to say and not what you are trying to think.

[cycl...@gmail.com]

You were correct the first time Jeff. With the tilted beam you get an oblong pattern that shows a wider pattern in the distance and a brighter smaller coverage up close. The photos showing the lighting patterns demonstrate what happens if you try to vary from that.

Modern LED lighting is MUCH brighter per watt and so a good round light will give you the best and most understandable coverage. Remember that the rider does a very large part of understanding his pathway through peripheral vision so you cannot have dark and light spots randomly throughout your coverage.

[Jeff Liebermann]

On Sat, 25 Mar 2017 12:32:55 +0700, John B. <sloc...@gmail.com>
wrote:

>I would have to ask. Is it important to verify the advertising claims?
>Or is it important to verify that you can see sufficiently well to
>cycle?

Are those the only choices available? How about:
1. Is it important to buy from a vendor that doesn't lie about the
performance of their lights?
2. Is it important to verify lumens if the light tends to fade in
output as it gets warm and as the battery becomes depleted.
3. Is it important to filter out ridiculous lumens claims so that
selecting a light does not become an exercise in buy, try, return, but
something else, try, return, ad infinitum[1].
4. It is important to recognize that there might be a relationship
between lumens output and visibility?
5. Is it important to correlate the relationship between lumens and
selling price?
6. Is it important to also verify other advertised numbers, such as
beam pattern, weight, battery life, and compatibility with available
batteries and dynamos?

I believe that you're asking me to choose between two extremes,
neither of which is useful or optimum. At one extreme, we have the
test ride as the sole determination of a suitable headlight
accompanied by totally ignoring the data sheet. Yes, trial and error
will eventually result in something worth buying, but methinks the
process might be shortened if the buyer looks at the numbers first.

At the other extreme, we have buying blindly, usually online and
solely from the advertised claims. This is become more common thanks
to online shopping, where the buy, try, return cycle is not very
effective. The problem is that *ALL* the advertised specifications
tend to be exaggerated well beyond reason. If online vendors can't
handle the buy, try, return cycle, then 2nd best would be honest
numbers.

There's a third extreme in the form of buying from reviews. Most
reviews simply recycle the advertised lumen claims from the
manufacturers data sheet. A few reviewers attempt to make comparative
measurements. A tiny number borrow an overpriced integrating sphere
and actually make measurements. I would think that if the
manufacturer or reviewer is willing to buy, rent, or borrow a $20,000
instrument just to deliver one accurate number, they would consider
this number rather important.

Buying from reviews also has its hazards. If the reviewer makes a
procedural error, misinterprets the results, or misrepresents the
products, it's quite easy to make a bad decision. In effect, the
buyer is purchasing by proxy, where the reviewer actually makes the
selection.

What I've done is provide a possible procedure needed for mere mortals
to verify advertised brightness claims. Whether you choose to use
those tools is your decision. If it inspires Chinese manufacturers
and resellers to provide honest light output figures, then I have
achieved my goal and can then move on to dealing with inflated battery
capacity claims.


Drivel:
[1] Buying a headlight without looking at the numbers is much like
buying clothes without looking at the marked sizes and making the
choice based on how it feels, looks, or fits. The somewhat standard
clothing sizes cover wide ranges of size, fit, body shape,
proportions, ethnicity, etc which require a fitting room to make the
final decision. While it's still a trial and error process, without
looking at the marked sizes, shopping for clothes would be rather
tedious and time consuming without first narrowing down the available
candidates. One runs the risk of buying something too large or too
small (or in lighting too bright no too dim).

[Jeff Liebermann]

On Fri, 24 Mar 2017 14:12:52 -0700, Joerg <ne...@analogconsultants.com>
wrote:

>On 2017-03-24 11:13, Sir Ridesalot wrote:
>> On Friday, March 24, 2017 at 2:09:12 PM UTC-4, Sir Ridesalot wrote:
>>> On Friday, March 24, 2017 at 2:22:08 AM UTC-4, Jeff Liebermann
>>> wrote:
>>>> Another error is the color temperature of the light. LED's come
>>>> in a variety of color temperatures. The lux meter has a
>>>> different sensitivity at each of these colors where the
>>>> sensitivity curve follows the sensitivity of the human eye.
>>>> <https://image.slidesharecdn.com/ivanperrepresentationfor24-141008071626-conversion-gate02/95/pls-2014-is-measuring-led-illuminance-with-a-lux-meter-accurate-19-638.jpg>

>Comparing lights with different color temperatures will be a problem.

It might be a problem, but I don't think so. The light meter follows
the color sensitivity of the human eye. Lux (brightness) is also
weighted for human eye response. Therefore, I believe that equal
brightness (lux) numbers, of different color temperatures, would
appear as identically bright to the human eye. I'm not an expert on
optics and need to do some remedial reading first.

>>> Much is made about different methods of measuring bicycle lights. I
>>> think the best thig is to asctually try the light in the conditions
>>> you ride in.

>Yup! This is similar to what I have (2nd part, with diffuser lens) on
>both bikes:
>
>https://www.youtube.com/watch?v=5J9zIGTfgGw
>
>After installing them I never looked back. No need to measure any
>lumens. It simply does the job at night even north of 25mph and makes me
>very visible to motorists during the day. Only on singletrack I have to
>keep it below 15mph at night but that's fine.

Perhaps we should consider changing the "tech" part of the newsgroup
name to "feel"? No need for technology when we have expert opinions
and impressions. I seem to recall that "tech" is partly an exercise
in quantifying poorly understood phenomenon into repeatable tests and
measurements so that meaninful comparisons can be made. I guess not.
Does passing a road test now means that you can now throw away all the
measurements and numbers?

Grumble... I'm disappointed.

[Frank Krygowski]

You make some good points above. Two things I'd like to see come out of
your experiments:

1) A comparison of your methods results with those of an integrating
sphere for several different bike lights. Obviously, it would be good
to show your method is reasonably accurate.

2) Some examination of the correlation between lumen output and
usefulness as a road lighting bike headlight. (That's as opposed to a
"be seen" light.)

The point of #2 is that I believe there is far too much emphasis on
lumen count. IME a light with relatively low lumen count can do an
excellent job of lighting the road, and often do a better job than
lights with higher lumen outputs.

And IME any headlight that adequately lights the road is perfectly
capable as a "be seen" light.

--
- Frank Krygowski

[Frank Krygowski]

Nope. In fact, that's pretty much backwards. Re-read the article
linked above. Or examine your car's headlight beams. They are
absolutely not circular, for reasons that should be easily understandable.


--
- Frank Krygowski

[Joerg]

On 2017-03-25 10:18, Jeff Liebermann wrote:
> On Fri, 24 Mar 2017 14:12:52 -0700, Joerg <ne...@analogconsultants.com>
> wrote:
>
>> On 2017-03-24 11:13, Sir Ridesalot wrote:
>>> On Friday, March 24, 2017 at 2:09:12 PM UTC-4, Sir Ridesalot wrote:
>>>> On Friday, March 24, 2017 at 2:22:08 AM UTC-4, Jeff Liebermann
>>>> wrote:
>>>>> Another error is the color temperature of the light. LED's come
>>>>> in a variety of color temperatures. The lux meter has a
>>>>> different sensitivity at each of these colors where the
>>>>> sensitivity curve follows the sensitivity of the human eye.
>>>>> <https://image.slidesharecdn.com/ivanperrepresentationfor24-141008071626-conversion-gate02/95/pls-2014-is-measuring-led-illuminance-with-a-lux-meter-accurate-19-638.jpg>
>
>> Comparing lights with different color temperatures will be a problem.
>
> It might be a problem, but I don't think so. The light meter follows
> the color sensitivity of the human eye. Lux (brightness) is also
> weighted for human eye response. Therefore, I believe that equal
> brightness (lux) numbers, of different color temperatures, would
> appear as identically bright to the human eye. I'm not an expert on
> optics and need to do some remedial reading first.
>

I think Sir wrote that. I do not know much about color temps and stuff
but have a relative who is an expert in that field (not for lighting but
cameras).

>>>> Much is made about different methods of measuring bicycle lights. I
>>>> think the best thig is to asctually try the light in the conditions
>>>> you ride in.
>
>> Yup! This is similar to what I have (2nd part, with diffuser lens) on
>> both bikes:
>>
>> https://www.youtube.com/watch?v=5J9zIGTfgGw
>>
>> After installing them I never looked back. No need to measure any
>> lumens. It simply does the job at night even north of 25mph and makes me
>> very visible to motorists during the day. Only on singletrack I have to
>> keep it below 15mph at night but that's fine.
>
> Perhaps we should consider changing the "tech" part of the newsgroup
> name to "feel"? No need for technology when we have expert opinions
> and impressions. I seem to recall that "tech" is partly an exercise
> in quantifying poorly understood phenomenon into repeatable tests and
> measurements so that meaninful comparisons can be made. I guess not.
> Does passing a road test now means that you can now throw away all the
> measurements and numbers?
>
> Grumble... I'm disappointed.
>

Tech does not always mean everything is best described by hard numbers.
Take audio noise, for example. Shannon's theorem and measurements may
show that information in a certain noisy environment cannot possibly be
deciphered yet then people can do it.

With light there are just too many factors. Spectral distribution,
illumination to the side and slightly up, and so on. For example, a
StVZO light which gets stellar reviews in scientific testing can perform
horridly on a bicycle with a suspension. In a nutshell, when it comes to
lighting I strongly believe there is nothing better than to actually try
it out. I have, and I had found a light I really like that way (after a
slight mod).

[John B.]

On Sat, 25 Mar 2017 09:57:15 -0700, Jeff Liebermann <je...@cruzio.com>
wrote:

>On Sat, 25 Mar 2017 12:32:55 +0700, John B. <sloc...@gmail.com>
>wrote:
>
>>I would have to ask. Is it important to verify the advertising claims?
>>Or is it important to verify that you can see sufficiently well to
>>cycle?
>
>Are those the only choices available? How about:
>1. Is it important to buy from a vendor that doesn't lie about the
>performance of their lights?
>2. Is it important to verify lumens if the light tends to fade in
>output as it gets warm and as the battery becomes depleted.
>3. Is it important to filter out ridiculous lumens claims so that
>selecting a light does not become an exercise in buy, try, return, but
>something else, try, return, ad infinitum[1].
>4. It is important to recognize that there might be a relationship
>between lumens output and visibility?
>5. Is it important to correlate the relationship between lumens and
>selling price?
>6. Is it important to also verify other advertised numbers, such as
>beam pattern, weight, battery life, and compatibility with available
>batteries and dynamos?
>

Ultimately the only test that makes sense is "does it work", and I
would even add the amendment "does it work"+"for me!"

James, for one, and probably many others, ride faster than I do and
likely need see the road much further ahead than I do so logically
they probably need a stronger light than I do and a light that
fulfills my requirements may well not suit their needs. Thus a light
that fulfils my needs may not fulfil theirs.

As for claims by makers or distributors I generally disregard them as
I am fully aware that they are intent on selling as much of their
product as possible.

I am, this moment, looking at a smallish, black, LED flashlight
equipped with the usual 3.7V battery that states, in black and white,
right there on the body of the light "UltraFire XB 8000W". But that
was the cheap one. I have another that says "CREE T6 15000W". I might
comment that I did not purchase either of these two, very handy,
lights based on the maker's claims or data sheet :-)

In fact after reading some claims made by various testers or testing
institutes I tend to disregard them to a great extent. I remember one
magazine downgrading a Winchester single shot .22 rifle.... because it
was a "single shot". Sort of like downgrading a Bi-cycle because it
only has two wheels :-)

>I believe that you're asking me to choose between two extremes,
>neither of which is useful or optimum. At one extreme, we have the
>test ride as the sole determination of a suitable headlight
>accompanied by totally ignoring the data sheet. Yes, trial and error
>will eventually result in something worth buying, but methinks the
>process might be shortened if the buyer looks at the numbers first.

I'm not asking you to do anything. I am commenting that the ultimate
test is "does it work for you"? Regardless of what the data sheet says
or does not say.

I have from time to time commented on my bike riding in Japan. In the
1960's I was a lowly Airman at an airbase outside of Tokyo and resided
(illegally) off base with a convivial young lady. I bought a
2nd/3rd/who knows what/hand bicycle fitted with a bottle generator and
a rather anemic incandescent light. I rode that bicycle back and forth
every day for a year or more with no problems what so ever.

No maker's data sheet, no advertisement. No nothing. Just get on and
pedal. Had I purchased a super, dooper, very powerful, magnificent,
bicycle light, would I been better off?

>At the other extreme, we have buying blindly, usually online and
>solely from the advertised claims. This is become more common thanks
>to online shopping, where the buy, try, return cycle is not very
>effective. The problem is that *ALL* the advertised specifications
>tend to be exaggerated well beyond reason. If online vendors can't
>handle the buy, try, return cycle, then 2nd best would be honest
>numbers.

There is a very old adage that states "a fool and his money are soon
parted" that I have always taken to heart. The only unknown quality
item I would even think of buying on line would be from an individual
that I trust to tell me the truth, of a specific make that I already
know is of sufficient quality to suit my needs.

But of course, living in a relatively primitive country I am not
restricted to buying on line. I have the advantage of a "whole bunch"
of shops that I can visit and compare prices and quality.

Cheers,

John B.

[Barry Beams]

This is the first time I've ever seen a thread about lighting speak about the taboo truth, that the eye does _not perceive brightness based solely on raw lumens, but also by the chromaticity and evenness of the beam.
When designing the Oculus, I made identical lights of the same lumen output (+/- Cree's 7% standard tolerance for production LEDs) using identical LEDs but from from different bins, in order to test what color temperatures people considered brighter.
Without fail, the cool/cold white on the ANSI curve is seen as brightest. Above or below the line, where the output may appear with a blue or red tint, is not seen as bright, nor as easy on the eye, despite being the same overall color temperature as the bins right on the ANSI curve.
Lux is a frivolous measurement, because it can only measure how bright the light is at a given point. There is not a spec for the distance lux should be measured at. This a light claiming 80 lux is a meaningless value. See the Bush and Muller website for useless irrelevant overstated claims made in lux, without any distance given, nor lumen for their lights.
Evenness is the most often overlooked element of usable visibility. Bright spots cause the eye to stop down, lowering the sensitivity for everywhere dimmer. The Oculus beam in the lights I currently sell actually has a slight measurable dimmer region where other lights would have a bright center spot. The evenness all around makes the eye able to see better everywhere in the beam, because the eye doesn't need to stop down to filter overly bright spots.
Other ray trace images from other lights all have hot red areas. My beam has none, yet also has very high efficiency. Simulations in Zemax showed 1 watt of light into the optic results in .97 watts out. That's independent of color temperatures or wavelengths, based only on ray traces.

That DIY lumen tube can be improved greatly by spraying the inside with a bright white reflective coating. Try Rustoleum white gloss protective enamel. Still not close to an accurate measurement.
Some light test labs use stopped down filters with spheres too small to get a good measurement of higher powered beams. Cutting the light in half doubles the tolerance of the measurement.

Bike light type beams are most accurately measured in an integrating tube, not an integrating sphere. I got some free testing from Gamma Scientific at the Strategies in Light LED trade show. Much better accuracy at capturing projected beams. Spheres are best for a omnidirectional beam such as a light bulb.

[Barry Beams]

On Thursday, March 23, 2017 at 11:22:08 PM UTC-7, Jeff Liebermann wrote:

Forgot to add that I've made 2200 lumen versions of the Oculus, but with lower bins because my bins aren't available yet in the LEDs I built the 2200 units with.
Side by side, in a meeting room where I gave a presentation, everyone answered that my current retail 1800 unit was brighter than the more room color temperature 2200.

Problem with commercial lights is that LED companies sell large quantities in what they call kits. The kits that the big light companies order have a wide variation of LED color temperatures. So you can take a dozen of the same light from a competitor, and some will visibly look clearly brighter or dimmer due to different color temperature, even if they all would measure the same number of lumens.

[Frank Krygowski]

On 3/25/2017 11:45 PM, John B. wrote:
>
> Ultimately the only test that makes sense is "does it work", and I
> would even add the amendment "does it work"+"for me!"
>
> James, for one, and probably many others, ride faster than I do and
> likely need see the road much further ahead than I do so logically
> they probably need a stronger light than I do and a light that
> fulfills my requirements may well not suit their needs. Thus a light
> that fulfils my needs may not fulfil theirs.

BTW, vaguely related: Last night, friends and I played as part of a
benefit concert in a tiny town over an hour's drive away. Before the
event started, I stepped into a side room away from the stage to tune my
fiddle.

A bike was parked in the side room, sort of a classic steel bike from
the early '80s, with a rack and bags. And ... hey, what's this? A
dynamo hub? A B&M Led headlight? Whose bike is this?

We played our way through the concert, then were invited to eat with the
organizers. Eventually, just as my friends and I were leaving, I
remembered to ask about the bike. I assumed it belonged to Tom, the
organizer who lived in that town.

Wrong! The bike belonged to a young, pretty French woman, a friend of
Tom' son. I said "Oh! I was interested, because I have a similar dynamo
hub and headlight. I don't see many of them around here." She said
"Yes, I bought the hub and built the wheel myself. I like it very much!"
I said "I build my own wheels too!" Tom said "She rode to the concert
from ..." some little town which turned out to be over 30 miles away.

<sigh> Sadly, my friends were already out the door, waiting for me. I
think I missed some really pleasant conversation.

--
- Frank Krygowski

[Joerg]

On 2017-03-26 09:08, Frank Krygowski wrote:
> On 3/25/2017 11:45 PM, John B. wrote:
>>
>> Ultimately the only test that makes sense is "does it work", and I
>> would even add the amendment "does it work"+"for me!"
>>
>> James, for one, and probably many others, ride faster than I do and
>> likely need see the road much further ahead than I do so logically
>> they probably need a stronger light than I do and a light that
>> fulfills my requirements may well not suit their needs. Thus a light
>> that fulfils my needs may not fulfil theirs.
>
> BTW, vaguely related: Last night, friends and I played as part of a
> benefit concert in a tiny town over an hour's drive away. Before the
> event started, I stepped into a side room away from the stage to tune my
> fiddle.
>
> A bike was parked in the side room, sort of a classic steel bike from
> the early '80s, with a rack and bags.

Peugeot? I am still riding my old Gazelle Trim Trophy steel frame. Also
with rack and bags which I just packed for the next ride.


> ... And ... hey, what's this? A

> dynamo hub? A B&M Led headlight? Whose bike is this?
>
> We played our way through the concert, then were invited to eat with the
> organizers. Eventually, just as my friends and I were leaving, I
> remembered to ask about the bike. I assumed it belonged to Tom, the
> organizer who lived in that town.
>
> Wrong! The bike belonged to a young, pretty French woman, a friend of
> Tom' son. I said "Oh! I was interested, because I have a similar dynamo
> hub and headlight. I don't see many of them around here." She said
> "Yes, I bought the hub and built the wheel myself. I like it very much!"
> I said "I build my own wheels too!" Tom said "She rode to the concert
> from ..." some little town which turned out to be over 30 miles away.
>
> <sigh> Sadly, my friends were already out the door, waiting for me. I
> think I missed some really pleasant conversation.
>

Now, now ... hey, I think you are married :-)

--
SCNR, Joerg

http://www.analogconsultants.com/

[Frank Krygowski]

I'm married. But I'm allowed to converse!


--
- Frank Krygowski