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How to easily measure lumens



 
 
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  #1  
Old March 24th 17, 07:22 AM posted to rec.bicycles.tech
Jeff Liebermann
external usenet poster
 
Posts: 4,018
Default How to easily measure lumens

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 sphe
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
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Ads
  #2  
Old March 24th 17, 06:30 PM posted to rec.bicycles.tech
Frank Krygowski[_4_]
external usenet poster
 
Posts: 10,538
Default How to easily measure lumens

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
  #3  
Old March 24th 17, 07:09 PM posted to rec.bicycles.tech
Sir Ridesalot
external usenet poster
 
Posts: 5,270
Default How to easily measure lumens

On Friday, March 24, 2017 at 2:22:08 AM UTC-4, Jeff Liebermann wrote:
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 sphe
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
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558


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
  #4  
Old March 24th 17, 07:13 PM posted to rec.bicycles.tech
Sir Ridesalot
external usenet poster
 
Posts: 5,270
Default How to easily measure lumens

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


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


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
  #5  
Old March 24th 17, 10:12 PM posted to rec.bicycles.tech
Joerg[_2_]
external usenet poster
 
Posts: 6,016
Default How to easily measure lumens

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


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.

[...]

--
Regards, Joerg

http://www.analogconsultants.com/
  #6  
Old March 24th 17, 10:35 PM posted to rec.bicycles.tech
Doug Landau
external usenet poster
 
Posts: 1,424
Default How to easily measure lumens

On Friday, March 24, 2017 at 11:13:50 AM UTC-7, 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:
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 sphe
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
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558


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.

  #7  
Old March 25th 17, 12:45 AM posted to rec.bicycles.tech
Mark J.
external usenet poster
 
Posts: 840
Default How to easily measure lumens

On 3/24/2017 11:13 AM, Sir Ridesalot wrote:
On Friday, March 24, 2017 at 2:09:12 PM UTC-4, Sir Ridesalot wrote:
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


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.


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.

  #8  
Old March 25th 17, 02:17 AM posted to rec.bicycles.tech
Jeff Liebermann
external usenet poster
 
Posts: 4,018
Default How to easily measure lumens

On Fri, 24 Mar 2017 13:30:06 -0400, Frank Krygowski
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
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
  #9  
Old March 25th 17, 03:19 AM posted to rec.bicycles.tech
Jeff Liebermann
external usenet poster
 
Posts: 4,018
Default How to easily measure lumens

On Fri, 24 Mar 2017 11:09:08 -0700 (PDT), Sir Ridesalot
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

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
  #10  
Old March 25th 17, 06:32 AM posted to rec.bicycles.tech
John B.[_3_]
external usenet poster
 
Posts: 5,697
Default How to easily measure lumens

On Fri, 24 Mar 2017 19:19:19 -0700, Jeff Liebermann
wrote:

On Fri, 24 Mar 2017 11:09:08 -0700 (PDT), Sir Ridesalot
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.

 




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