Easy to Understand Lumens Vs Lux Explanation
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TennesseeTony
Newly Enlightened
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- Jun 2, 2014
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Great explanation. Really clears that up. Thanks so much. This is a great forum for someone new. I've learned so much in the last few days.
This place is like that...if you read the threads, every day you learn something new.
thedoc007
Flashlight Enthusiast
You sure that isn't all the tritium you have around you?
Seriously, though, this is a great thread. Well explained, and a good reference for anyone who is just learning the concepts.
Full Power
Newly Enlightened
Sorry, I think I missed that explanation ... one needs to take it slow in order for all this info to make a little sense without risking overload! I had no idea a Flashlight could be so interesting, and most of all -- is more than just a Flashlight!
Sent from my iPhone using Candlepowerforums
Sure, that's one way. I prefer to overload, reset, overload, reset....
Keeping my brain fried on too much data is how I roll. But beware of any posts I may make during a reset. There have been more than a few....Great thread, TEEJ,
Ken
Danielsan
Enlightened
I always think about a firefighter and a fire hose, the lumens is the total amount of water shooting out of that thing and the lux is jox concentrated the water jet is. Thats why even a low amount of water can be compressed to a powerful water jet, that would be a low lumen thrower flashlight. A high lumen light with low lux is when the fire hose sprays huge a fountain
That's pretty much the analogy in this thread.
The qualification would be that the UNITS need the depth of the resultant puddles to be analogous to how bright the target would look, so that the actual level of illumination would follow, and be able to be applied to what you'd see over a larger vs smaller surface area, etc.
Brianalaman
Newly Enlightened
You just made a whole lot of sense. Thanks for the detail and explanation. :thumbsup:
Skyraider59
Newly Enlightened
Is there a direct link between OTF lumens & lux readings out of an integration sphere
Hi Guys
Can any one answer this question? Would an out of the front lumen figure relate to a lux figure obtained from a DIY integration sphere?
May be an odd question, but like many I always like to know if the lumen figure given by the manufacturer are close or a long way away from reality!
I give you a random example
Let say that you have a Gloworm x2 claimed at 1500lms which have been tested at approx 1400lms,
if you would check it in an integration sphere got let say 1000 lux (fictitious figure for easy calculation)
Cloud you then assume that any light showing let say 500 lux in the same sphere would have an OTF output of roughly 750 lumen? and a light showing 2000lux would have a guesstimated out put of 3000lms?
If this assumption is correct would the light have to be of the same design ie single led versus twin or would this not matter?
I understand that this may be a very rough way of estimated OTF lumen, but this could be useful to many to just have a very rough idea of the actual lumen, specifically for the over claimed outputs found on some Chinese lights!!
Any idea on this?
Hi Guys
Can any one answer this question? Would an out of the front lumen figure relate to a lux figure obtained from a DIY integration sphere?
May be an odd question, but like many I always like to know if the lumen figure given by the manufacturer are close or a long way away from reality!
I give you a random example
Let say that you have a Gloworm x2 claimed at 1500lms which have been tested at approx 1400lms,
if you would check it in an integration sphere got let say 1000 lux (fictitious figure for easy calculation)
Cloud you then assume that any light showing let say 500 lux in the same sphere would have an OTF output of roughly 750 lumen? and a light showing 2000lux would have a guesstimated out put of 3000lms?
If this assumption is correct would the light have to be of the same design ie single led versus twin or would this not matter?
I understand that this may be a very rough way of estimated OTF lumen, but this could be useful to many to just have a very rough idea of the actual lumen, specifically for the over claimed outputs found on some Chinese lights!!
Any idea on this?
Re: Is there a direct link between OTF lumens & lux readings out of an integration sp
Well, the way an integrating sphere WORKS is that it homogenizes the total lumens so that they evenly cover the interior of the sphere, so a LUX reading on that surface would be representative of the lux present across the surface area.
As lumens are lux per square meter, if the interior is 1 square meter in surface area, and your representative lux reading = 1, it means you have 1 lux per square meter, or, 1 lumen.
IE: The way the IS works is exactly how your asking if it COULD work...so, yes, its actually its primary reason to exist.
The sphere is CALIBRATED to get the readings to be representative. So the actual sphere interior surface area and, baffles to prevent emitter light from shining directly ON the lux sensor, etc, are taken into account. KNOWN lumen sources are used to adjust the IS's response until the IS's equation is known, and you can then count on a calibration curve you can plot UNKNOWN lumen sources against...and find their value.
If its a DIYS IS, the distribution will NOT be homogeneous, and, the beam angle and other characteristics WILL cause the IS to be wrong by some amount. IE: The light will NOT be evenly distributed, and the lux will be higher or lower in some areas inside it...so a single lux measurement will be ONE of the lux levels, but may not be representative of an average of all of them, etc.
Its not realistic to expect a homemade $100 IS /Light box to be as good as a several thousand dollar laboratory made IS. There are REASONS the "Real One's" are so expensive and difficult to make.
That said, with enough tweaking, many people have managed to get pretty close, at least for the lights THEY measure. The problem is that they have no good way of knowing for sure how a different light might be read, say due to multiple emiters or a really floody, or more typically, more throwy, beam pattern.
For example, the super expensive crystal impregnated IS coatings and perfectly round IS interiors with ports and surfaces designed to also evenly distribute impacting photons - CAN integrate the light from a powerful thrower, as the beam will hit the wall, and BE evenly distributed.
When a powerful beam hits your cardboard paper mache or Styrofoam box's white paint or interior, etc...some light might be absorbed and not reflected back, and be lost from the measurements...and some might reflect back in a very narrow band on on part of the box, but not others, so that the one (ONE) lux reading you have could be in a darker, or lighter, area...and your reading will be shy or inflated as a result.
Some home made IS tend to over estimate throwers and under estimate flooders, and some do the opposite. If people use a "Known Lumen Output" light, say a Surefire they trust the specs on...it might have a throw oriented beam, and, when they calibrate the IS, its therefore calibrated to represent the out put of the Surefire's beam pattern. They might then test another light of unknown output's lumen claims, and get a false low, or high,...making them assume the unknown brand's claims are inflated....or understated.
There are also "Wait Times". MANY lights start out brighter, and get dimmer with time. SOME are so dramatic, that their CLAIMED lumen outputs are based upon the max reading, say the first 30 seconds or so....and they then drop to half or less seconds later. So, if you put in the AA powered 1,000 L claim light, and it takes you more than 30 seconds or so to turn it on, and get a reading, the out put might have been 1,000 L, but, by the time you got a reading, it was 400 L....or, you GOT the 1,000 L, but didn't wait to see what it dropped to later, etc.
So, sure, what you ask is not only doable, its what its for....but, on a DIYS IS, YMWV...and you simply need to remember it if counting on the readings.
Well, the way an integrating sphere WORKS is that it homogenizes the total lumens so that they evenly cover the interior of the sphere, so a LUX reading on that surface would be representative of the lux present across the surface area.
As lumens are lux per square meter, if the interior is 1 square meter in surface area, and your representative lux reading = 1, it means you have 1 lux per square meter, or, 1 lumen.
IE: The way the IS works is exactly how your asking if it COULD work...so, yes, its actually its primary reason to exist.
The sphere is CALIBRATED to get the readings to be representative. So the actual sphere interior surface area and, baffles to prevent emitter light from shining directly ON the lux sensor, etc, are taken into account. KNOWN lumen sources are used to adjust the IS's response until the IS's equation is known, and you can then count on a calibration curve you can plot UNKNOWN lumen sources against...and find their value.
If its a DIYS IS, the distribution will NOT be homogeneous, and, the beam angle and other characteristics WILL cause the IS to be wrong by some amount. IE: The light will NOT be evenly distributed, and the lux will be higher or lower in some areas inside it...so a single lux measurement will be ONE of the lux levels, but may not be representative of an average of all of them, etc.
Its not realistic to expect a homemade $100 IS /Light box to be as good as a several thousand dollar laboratory made IS. There are REASONS the "Real One's" are so expensive and difficult to make.
That said, with enough tweaking, many people have managed to get pretty close, at least for the lights THEY measure. The problem is that they have no good way of knowing for sure how a different light might be read, say due to multiple emiters or a really floody, or more typically, more throwy, beam pattern.
For example, the super expensive crystal impregnated IS coatings and perfectly round IS interiors with ports and surfaces designed to also evenly distribute impacting photons - CAN integrate the light from a powerful thrower, as the beam will hit the wall, and BE evenly distributed.
When a powerful beam hits your cardboard paper mache or Styrofoam box's white paint or interior, etc...some light might be absorbed and not reflected back, and be lost from the measurements...and some might reflect back in a very narrow band on on part of the box, but not others, so that the one (ONE) lux reading you have could be in a darker, or lighter, area...and your reading will be shy or inflated as a result.
Some home made IS tend to over estimate throwers and under estimate flooders, and some do the opposite. If people use a "Known Lumen Output" light, say a Surefire they trust the specs on...it might have a throw oriented beam, and, when they calibrate the IS, its therefore calibrated to represent the out put of the Surefire's beam pattern. They might then test another light of unknown output's lumen claims, and get a false low, or high,...making them assume the unknown brand's claims are inflated....or understated.
There are also "Wait Times". MANY lights start out brighter, and get dimmer with time. SOME are so dramatic, that their CLAIMED lumen outputs are based upon the max reading, say the first 30 seconds or so....and they then drop to half or less seconds later. So, if you put in the AA powered 1,000 L claim light, and it takes you more than 30 seconds or so to turn it on, and get a reading, the out put might have been 1,000 L, but, by the time you got a reading, it was 400 L....or, you GOT the 1,000 L, but didn't wait to see what it dropped to later, etc.
So, sure, what you ask is not only doable, its what its for....but, on a DIYS IS, YMWV...and you simply need to remember it if counting on the readings.
Last edited:
Skyraider59
Newly Enlightened
Re: Is there a direct link between OTF lumens & lux readings out of an integration sp
Thanks very much TEEJ for your in depth answer to my question.
So the bottom line is unless you have a lab IS, making assumptions of actual lumen outputs of several different lights(flooder/thrower/single/twin led etc) using a DIY IS which has been "roughly" calibrated with a know lumen output light is not a reliable way of quantifying an output!
I did kind of expected this, so claimed lumen output given by manufacturer will have to stay unverified for many lights!
Thanks again
Thanks very much TEEJ for your in depth answer to my question.
So the bottom line is unless you have a lab IS, making assumptions of actual lumen outputs of several different lights(flooder/thrower/single/twin led etc) using a DIY IS which has been "roughly" calibrated with a know lumen output light is not a reliable way of quantifying an output!
I did kind of expected this, so claimed lumen output given by manufacturer will have to stay unverified for many lights!
Thanks again
dc38
Flashlight Enthusiast
Re: Is there a direct link between OTF lumens & lux readings out of an integration sp
I developed a cheap way to ballpark it the lumen output using a cheap luxmeter...it works on the preface and assumption that an integrating sphere takes a cross section of total distributed dispersed light. I figured there qould be a coincidental point at which the luxmeter could be placed from a diffuser that would do the same thing. Ill pm you
I developed a cheap way to ballpark it the lumen output using a cheap luxmeter...it works on the preface and assumption that an integrating sphere takes a cross section of total distributed dispersed light. I figured there qould be a coincidental point at which the luxmeter could be placed from a diffuser that would do the same thing. Ill pm you
Skyraider59
Newly Enlightened
Re: Is there a direct link between OTF lumens & lux readings out of an integration sp
Sound good, looking forward to hear, thanks
Sound good, looking forward to hear, thanks
Re: Is there a direct link between OTF lumens & lux readings out of an integration sp
That could be a problem.
The diffuser would need to make the light coming out evenly distributed, and, to get the beam to hit it, and diffuse evenly, such that a reading anywhere would be representative, would be difficult to achieve. So, while a diffuser is supposed to DO that, in practice, it tends to be brighter in the middle....even if MORE evenly distributed.
Multiple diffusers might be a way to further homogenize the output, albeit each optic interface will cause losses, and your calibration curves would need to account for that percentage. This would include the parts of the spectrum that were being filtered out...as the lumen is a wavelength weighted value, etc.
That could be a problem.
The diffuser would need to make the light coming out evenly distributed, and, to get the beam to hit it, and diffuse evenly, such that a reading anywhere would be representative, would be difficult to achieve. So, while a diffuser is supposed to DO that, in practice, it tends to be brighter in the middle....even if MORE evenly distributed.
Multiple diffusers might be a way to further homogenize the output, albeit each optic interface will cause losses, and your calibration curves would need to account for that percentage. This would include the parts of the spectrum that were being filtered out...as the lumen is a wavelength weighted value, etc.
silvercookie
Newly Enlightened
- Joined
- Nov 19, 2014
- Messages
- 7
I can honestly say that is the first time in a long time i have read a good thread.
OldNick
Newly Enlightened
Integrating sphereLux to lumens, final conversion confusion
So you get an integrating sphere as described elsewhere on these forums. You make sure you surce cannot directkly strike the meter sensor. The whole idea is to make the light source as diffuse as possible. You measure the lux. Then what? One thread said you divide by 36. Why? Doesn't the ratio of the entire sphere's area to the area seen by the sensor (or the area of the sphere) come into play here? That was what I could not find, either here or looking elsewhere.
Thanks for any help
So you get an integrating sphere as described elsewhere on these forums. You make sure you surce cannot directkly strike the meter sensor. The whole idea is to make the light source as diffuse as possible. You measure the lux. Then what? One thread said you divide by 36. Why? Doesn't the ratio of the entire sphere's area to the area seen by the sensor (or the area of the sphere) come into play here? That was what I could not find, either here or looking elsewhere.
Thanks for any help
Last edited:
Re: Integrating sphereLux to lumens, final conversion confusion
This is explained earlier in this very thread...
..But, to summarize:
The reason its an INTEGRATING Sphere (IS), is because the light is spread out evenly across the SURFACE AREA of the sphere's interior.
This is SO that a reading of the lux, taken anywhere inside the sphere, will be representative of the average lux.
So, the SIZE of the sphere is what dictates the MATH you'd use to interpret that lux reading.
So if the lux is the lumens per square meter (m2), and the interior surface area of the sphere is 1 m2, then a reading of 1 lux means that there must have been 1 lumen to create that reading.
If the sphere is larger for example, then the surface area inside it might be 10 m2, so a reading of 1 lux would have required 10 lumens to achieve, or, the original 1 lumen source would have yielded 0.1 lumens as a result, and so forth.
To further calibrate the IS, known sources are measured and compared to the actual measurements by the IS to see if they agree, and, if they are off, the INTERPRETATION of the reading itself is adjusted by correction factors that allow the reading to be INTERPRETED correctly. (Or at least more correctly, etc)
So, the sphere has a shape and coating that evenly integrates/distributes the light across its interior surfaces, and a baffle that prevents the sensor from being in the direct path of the source, so it reads an integrated/smoothly distributed average of the lux.
When you see a lux reading, you need to know the surface area it is representative of, and, the correction factors that were determined for that IS, to calculate the lumens that that lux READING would indicate.
Does that help?
This is explained earlier in this very thread...
..But, to summarize:
The reason its an INTEGRATING Sphere (IS), is because the light is spread out evenly across the SURFACE AREA of the sphere's interior.
This is SO that a reading of the lux, taken anywhere inside the sphere, will be representative of the average lux.
So, the SIZE of the sphere is what dictates the MATH you'd use to interpret that lux reading.
So if the lux is the lumens per square meter (m2), and the interior surface area of the sphere is 1 m2, then a reading of 1 lux means that there must have been 1 lumen to create that reading.
If the sphere is larger for example, then the surface area inside it might be 10 m2, so a reading of 1 lux would have required 10 lumens to achieve, or, the original 1 lumen source would have yielded 0.1 lumens as a result, and so forth.
To further calibrate the IS, known sources are measured and compared to the actual measurements by the IS to see if they agree, and, if they are off, the INTERPRETATION of the reading itself is adjusted by correction factors that allow the reading to be INTERPRETED correctly. (Or at least more correctly, etc)
So, the sphere has a shape and coating that evenly integrates/distributes the light across its interior surfaces, and a baffle that prevents the sensor from being in the direct path of the source, so it reads an integrated/smoothly distributed average of the lux.
When you see a lux reading, you need to know the surface area it is representative of, and, the correction factors that were determined for that IS, to calculate the lumens that that lux READING would indicate.
Does that help?
