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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 |
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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
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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 |
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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 |
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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/ |
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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. |
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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. |
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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 |
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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 |
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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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