Following on the work by Lasersaber, Lidmotor, Peanutbutter and Burgess in particular, my son and I constructed a "light-box" to permit repeatable measurements using TWO light meters -- and a triplet of power and voltage meters to monitor input power. Pls see attached photos from my home
electronics bench today.
I found that the meters agree quite well -- one of them is the SAME as used by Lidmotor in vids (orange-color around it). The black one is cheaper on Amazon.
However -- the meters do not measure LUMENS but rather Lux -- as would be expected actually. (See wiki Lumen (unit) - Wikipedia, the free encyclopedia )
So we have to be cautious regarding colors, also the difference between lux measured on the meters and lumens.
So I ran various "bulbs" in the box and kept track of the input voltage, input power via two meters, and lux via the two light meters. As long as the bulbs were designed to put out light more-or-less isotropically (in all directions -- not beam-like), I found a GOOD correlation in my box between lumens and the measured lux on the meters.
That is -- I assumed the lumens as listed on the packaging with each bulb is reasonably accurate. I found that the voltage in town varies from about 117 VAC -- then the power on the meters agrees well with the rated power on the bulb -- and about 124.7 VAC. The lux meters show a sharp RISE in output lux when the voltage in town jumps UP. (I was surprised the voltage varies so much... good thing I'm keeping track of it! so I can make sense of my readings.)
So, when the power for a 40 W bulb showed 42.5 W with the higher voltage, I made two separate measurements of lux output, and I assume the given lumens output scales roughly linearly for a small change in input voltage.
Likewise for the various bulbs, 90W, 100W incandescent; 13 W fluorescent; and 9.5 W LED bulb.
I found that to within a few percent, I could find a conversion factor between what I read on the flux meters IN THE LIGHT BOX and lumens as given on the packaging! That is, I was able to calibrate the light-box-plus-light-meters system. Without given all the data here (tedious, its all in my logbook) -- here is the conversion:
Lumens = 0.059 * Lux (+/- about 7% with the various measurements involved) with my light-box.
This is actually the value using just the top watt-volts-kW-hour meter (it is cheaper and I like the increased digits for kW-hours) AND the cheaper black light-meter. The conversion factor found by averaging both power-meters, and also averaging the light meters is about the same, so I'm simplifying measurements by focusing on two meters, one for input power and one for output light. (But I do have redundancy to check things; part of my scientific training I guess... )
I would be leary of using this system to try to establish ou, there are more reliable measurements IMO, but -- this is a very interesting way to compare lumens/watt for various bulbs AND for various circuits -- like the SJR -- for the same bulb.
Peanutbutter and Burgess pls note -- one may get more lumens/watt (Lm/W) due to higher frequencies in the output circuit, for example; that is, higher Lm/W does not NECESSARILY MEAN that you are getting more POWER in the output circuit, it may just be there is more efficient light -output than is rated on the bulb for 60 Hz.
electronics bench today.
I found that the meters agree quite well -- one of them is the SAME as used by Lidmotor in vids (orange-color around it). The black one is cheaper on Amazon.
However -- the meters do not measure LUMENS but rather Lux -- as would be expected actually. (See wiki Lumen (unit) - Wikipedia, the free encyclopedia )
The difference between the units lumen and lux is that the lux takes into account the area over which the luminous flux is spread. A flux of 1000 lumens, concentrated into an area of one square metre, lights up that square metre with an illuminance of 1000 lux. The same 1000 lumens, spread out over ten square metres, produces a dimmer illuminance of only 100 lux. Mathematically, 1 lx = 1 lm/m2.
A source radiating a power of one watt of light in the color for which the eye is most efficient (a wavelength of 555 nm, in the green region of the optical spectrum) has luminous flux of 683 lumens. So a lumen represents at least 1/683 watts of visible light power, depending on the spectral distribution.
A source radiating a power of one watt of light in the color for which the eye is most efficient (a wavelength of 555 nm, in the green region of the optical spectrum) has luminous flux of 683 lumens. So a lumen represents at least 1/683 watts of visible light power, depending on the spectral distribution.
So I ran various "bulbs" in the box and kept track of the input voltage, input power via two meters, and lux via the two light meters. As long as the bulbs were designed to put out light more-or-less isotropically (in all directions -- not beam-like), I found a GOOD correlation in my box between lumens and the measured lux on the meters.
That is -- I assumed the lumens as listed on the packaging with each bulb is reasonably accurate. I found that the voltage in town varies from about 117 VAC -- then the power on the meters agrees well with the rated power on the bulb -- and about 124.7 VAC. The lux meters show a sharp RISE in output lux when the voltage in town jumps UP. (I was surprised the voltage varies so much... good thing I'm keeping track of it! so I can make sense of my readings.)
So, when the power for a 40 W bulb showed 42.5 W with the higher voltage, I made two separate measurements of lux output, and I assume the given lumens output scales roughly linearly for a small change in input voltage.
Likewise for the various bulbs, 90W, 100W incandescent; 13 W fluorescent; and 9.5 W LED bulb.
I found that to within a few percent, I could find a conversion factor between what I read on the flux meters IN THE LIGHT BOX and lumens as given on the packaging! That is, I was able to calibrate the light-box-plus-light-meters system. Without given all the data here (tedious, its all in my logbook) -- here is the conversion:
Lumens = 0.059 * Lux (+/- about 7% with the various measurements involved) with my light-box.
This is actually the value using just the top watt-volts-kW-hour meter (it is cheaper and I like the increased digits for kW-hours) AND the cheaper black light-meter. The conversion factor found by averaging both power-meters, and also averaging the light meters is about the same, so I'm simplifying measurements by focusing on two meters, one for input power and one for output light. (But I do have redundancy to check things; part of my scientific training I guess... )
I would be leary of using this system to try to establish ou, there are more reliable measurements IMO, but -- this is a very interesting way to compare lumens/watt for various bulbs AND for various circuits -- like the SJR -- for the same bulb.
Peanutbutter and Burgess pls note -- one may get more lumens/watt (Lm/W) due to higher frequencies in the output circuit, for example; that is, higher Lm/W does not NECESSARILY MEAN that you are getting more POWER in the output circuit, it may just be there is more efficient light -output than is rated on the bulb for 60 Hz.
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