Talk:Lumen (unit)

Needs clarification or at least referencing
A standard 100 watt incandescent light bulb emits approximately 1700 lumens in North America and around 1300 lumens in 220 V areas of the world. See luminous efficacy for the specific efficiency of various types of electric light sources.

At first glance, it makes absolutely no sense as to why a 100 watt bulb would be 1700 lumens in North America and why a 100 watts elsewhere would be any different. Voltage as the only controlled parameter has absolutely no affect on lumens per watt!

Lumens per watt is affected by filament temperature and envelope transmissiveness, but neither of those are controled by geographic location or voltage.

Thanks! -Jesse —Preceding unsigned comment added by 64.146.180.232 (talk) 18:32, 4 December 2007 (UTC)


 * The voltage is not the only controlled parameter. The thickness of the filament is another. Light bulbs designed for 220 V are designed differently than those made for 110 V. Be aware also that light bulbs are nonlinear devices. The resistance of the filament varies with voltage.--Srleffler (talk) 00:10, 5 December 2007 (UTC)


 * I realize that voltage is not the only controlled parameter -- but it's the only one that the article mentions as being the cause of less efficient lumens/watt. I also realize that incandescent light bulbs are non-linear, although it would be slightly more exacting to say that the resistance of the filament is affected by temperature, which is affected by wattage and dissipation, and wattage is affected by resistance and voltage, and so on. The only controlling parameters I can think of which control lumens/watt would be envelope transparency, filament surface temperature, and filament material, and none of those are tied only to voltage or operating in other parts of the world. There is no reason that an equal surface temperature, filament composition, and bulb transparency could not be done on both 110v and 220v lamps.


 * Is the article saying that 220v filaments are designed to run cooler, thus putting out more of their total energy in non-visible regions? or is it saying that they are running so hot that the same happens?


 * I'm not saying that the average 220v bulb is or is not the same efficiency as the average 110v bulb -- I do not know -- but I guess I'm saying that the article is dreadfully ambiguous, and it makes a statement that doesn't even make sense, and it doesn't give a cause for the phenomenon, nor does it cite any references. I'd say it is closer to "whimsical banter" and doesn't even rise to the level of "Original Research."


 * Does anyone mind if I remove that statement in a week or two if nobody finds some references? Thanks & Keep up the good work. -Jesse —Preceding unsigned comment added by 64.146.180.232 (talk) 03:30, 6 December 2007 (UTC)


 * I rephrased it to remove the impression that we are talking about the same bulb being run on two different voltages. It would be helpful to add a citation to support the two values. Removing the statement would not be appropriate unless you have strong reason to think it is untrue. Note that all of the discussion above is original research, and cannot be used to justify changing the article. Even if we obtained an explanation for why the efficiencies are different, there would be no reason to add that to the article. It's beyond the scope. The bulb outputs are given as a practical example of lumens. They don't need to be explained here. --Srleffler (talk) 06:26, 6 December 2007 (UTC)


 * I suspect the solution to this puzzle has to do with bulb lifetime. From some searching I did online, it appears that bulb lifetime changes very dramatically with voltage (proportional to the twelfth power). They probably have to sacrifice efficiency to get decent bulb lifetime at the higher voltage.--Srleffler (talk) 06:40, 6 December 2007 (UTC)


 * Removing (or moving to talk pages) is quite appropriate for material for which there is no reliable source. See (which at the time of my writing) says: "Any material that is challenged or likely to be challenged must be supported by a reliable source. "Original research" is a claim for which no reliable source can be found. Producing a reliable published source that advances the same claim taken in context is the only way to disprove an assertion that a claim constitutes original research. If there is a source, but the source or claim is disputed, that is not original research but rather of a question of reliable sourcing or undue weight. However, using information from references out-of-context or to forward claims not directly supported by the sources is original research."


 * I don't know who made the claim that 220v bulbs produce less lumens per watt then 110v, but I don't take it to be true. I know that it's certainly not always true (for example, the most efficient incandescent 220v bulb is better then the least efficient 110v. The reverse is also true.) WP Official Policy is that the only way to counter the claim of original research is to provide reliable sources. I don't know who made the claim, and I don't know if they were correct -- maybe they were, maybe they weren't. But they provided no references, so an average reader has no way of knowing. By the way, in my comments here, I am challenging the afore mentioned statement as being "Original Research."


 * I would propose that the comparison of incandescent bulb efficiencies be replaced with a simple statement like "The ability of lightbulbs to produce visible light is measured in lumens. Some types of lamps, like incandescent, tend to produce more of their output energy in non-visable regions and less in the visible, and so produce less lumens per watt, then, lets say, a flourescent or sodium vapor lamp, which tend produce more visible light per watt." (If lamp efficiency even needs to be discussed here -- since I think lamps have their own section..) Can anyone give me a single reason that removing an unreferenced statement of questionable accuracy would be somehow not appropriate?  Having that unreferenced OR statement there is inappropriate, according to WP Policy.. The statement is not always true, and I'm not convinced that it's even "usually true."


 * By the way, I forgot to ask before, but is this article someone's pet project? If so I understand how you could feel intruded upon by my wishing to effect WP Policy compliance and meaningfulness to this article. If it's someone's pet project, just say so, and I'll go away and not bother you any more! I wouldn't want someone else trying to edit my personal webpages..! Otherwise, there is A) No reason whatsoever that a disputed unreferenced statement should exist on WP, and B) No reason whatsoever that said disputed unreferenced statement shouldn't be removed. Thanks and keep up the good work! -Jesse


 * PS:The fact that our conversation is original research is besides the point. The point is that the material in question is original research, and according to WP policy should not even exist to begin with (unless with valid references) -- you make it sound as if unreferenced statements can only be removed if they are proved wrong using valid references. But that of course is exactly the opposite of WP Policy which says they may be removed unless proved TRUE with valid references. -Jesse —Preceding unsigned comment added by 64.146.180.232 (talk) 05:31, 7 December 2007 (UTC)
 * I completely missed this reply (and your subsequent edit to the article). You are quite right that unsourced material can in general be deleted from the article. However, deleting material that is not really in doubt or that can be easily sourced might be seen as disruptive editing. The reason I brought up the fact that the conversation above involves original research was to point out that argument about why a 230 V bulb might be less efficient than a 120 V bulb is completely irrelevant to whether that "fact" should be in a Wikipedia article. Either the claim can be sourced or it can't. Argument about why it might or might not be true is interesting, but irrelevant.--Srleffler (talk) 04:08, 27 May 2008 (UTC)
 * Just for fun, I looked up some 230 V bulbs. Philips has a 100 W 230 V bulb that puts out 1380 lm. My favorite local industrial supply company, McMaster-Carr, stocks 3 standard "general purpose" 100 W bulbs: a 230 V model that produces 1270 lm, rated for 1000 hours, a 120 V model that produces 1600 lm, rated for 750 hours, and a long-life 120 V model that produces 1470 lm, rated for 1500 hours. A survey of 120 V bulbs' package statistics gives output ranging from 1585 to 1750 for standard bulbs. So, a quick survey seems to support the statement that standard 230 V bulbs are less efficient than standard 120 V models.
 * Having done some reading and thinking on this since we last talked, I've learned that one can produce bulbs that are much more or much less efficient, at any given voltage. There is a tradeoff, though, between efficiency and bulb life. Standard ("general service") 100 W light bulbs are designed for bulb life in the 750–1000 hour range. Designing a bulb to run for this length of time at 230 V requires a cooler filament temperature, and therefore less efficiency. One can design a bulb to be more efficient but last for a shorter time, but that wouldn't be a "general service" (standard) bulb. Projector bulbs take that approach. Alternatively, one can design a bulb for longer life but at the expense of reduced efficiency, as in the example of the 1500-hour "long-life" bulb above. At any given rated lifespan, though, a 230 V bulb will be less efficient than a 120 V one with the same power rating.--Srleffler (talk) 05:31, 27 May 2008 (UTC)

This issue about bulb construction is pointless in an article about lumens and in my opinion it should be removed. The original sentence was inserted as reference for a luminous flux from a typical standard bulb. Rather than a US-EU standard bulb competition, it would be more useful adding also halogen and fluorescent lamps data. BTW these standard bulbs burns all at 2700°K and as you can see the us version has higher luminosity than eu, but shorter life. There are no free-lunches or 120v miracles. -- Basilicofresco  (msg) 14:05, 2 January 2009 (UTC)


 * The article doesn't discuss bulb construction, and doesn't seek to compare US and EU bulbs. Rather, the article illustrates how much light a lumen is by telling the readers how many lumens are produced by a common light source with which they will be familiar. Because it is so common in the home, the incandescent lamp is the obvious example to provide. Since European bulbs don't produce the same light output as North American ones, the article needs to give both values so it meets the needs of readers both in Europe and in North America. The article does not explain why European bulbs are dimmer than North American ones, nor should it. If we were going to make a change, I would recommend removing the less-familiar sodium lamp, and replacing it with compact fluorescents, since these are rapidly replacing incandescent bulbs. I would still keep the incandescent bulb values, though, since this is a very familiar light source.


 * I'm not sure what you thought those two datasheets prove. The numbers agree well with those in the article and cited by me above. The 130 V bulb is brighter and more efficient than the 240 V model. Note also the long-life 120 V bulb I mention above, which is rated for 1500 hours with an output of 1470 lm—still brighter than the 1000-hour 230 V bulb you mention. --Srleffler (talk) 17:53, 2 January 2009 (UTC)

I moved the 230 V case out of parentheses. The article should not presume that the reader is in a place with a 120 V grid. The 120 V and 230 V cases are of equal importance. I removed the halogen lamp because I don't think we need three examples and because consumer halogen lamps vary a lot more in output than the others. Where I happen to live, the commonly available medium-base halogens are not significantly more efficient than a typical incandescent bulb, but they have long bulb life. The purpose here is to provide common examples, such that a reader can look at a light bulb in their own home, not think too much about the technical details, and get a feel for what a lumen is (or what 1500 lm is). I rephrased the CFL example to make the emitted lumens clearer, and added references for 120 V CFLs.--Srleffler (talk) 19:14, 4 January 2009 (UTC)


 * Just to clarify the original point. A 120 volt 100 watt incandescent lamp does give more light than its 220/240 volt counterpart.  This comes about because the temperature at which the filament is run determines the efficiency of the lamp - the higher the temperature the better the efficiency (more Lumens per watt).  The temperature is determined by a number of compromises but generally, the temperature is aimed to give a 1000 hour life on average.  The life is determined largely by the surface area of the filament, as it is from here that the tungsten evaporates.  A 120 volt bulb requires a filament with one quarter of the resistance of a 240 volt bulb (half the voltage time twice the current for the same wattage).  As such the filament is half as long and twice the cross sectional area giving one quarter of the resistance.  But the resultant 120 volt filament has a smaller surface area than the 240 volt filament and can thus be run hotter for the same life giving a 30% gain in efficiency.


 * This principle is exploited in 12 volt low voltage halogen lighting where the very thick filaments coupled with the halogen cycle allows the filament to be run even hotter giving nearly a 70% gain in efficiency compared with a 240 volt lamp and the lamp still has a 4000 hour life. 20.133.0.13 (talk) 13:52, 9 September 2009 (UTC)
 * Great explanation, thank you! The world has to know it - passer-by — Preceding unsigned comment added by 194.44.247.146 (talk) 10:39, 14 June 2013 (UTC)

Differences between lumens and lux: This section has some poor grammar and is quite confusing to the reader. —Preceding unsigned comment added by 211.30.168.79 (talk) 12:43, 19 July 2009 (UTC)

More clarification
What is the purpose behind this strange equivalency string?

1 lm = 1 cd·sr = 1 lx·m2

How is it useful or informative? What is the meaning of "cd x sr" or "lux x m2"? Wouldn't it be more useful to say that the lumen is defined by reference to a source with intensity of 1 cd in a given direction, where 1 cd = 1 lm/sr? An isotropic 1 cd source then emits 4pi lumens... Cluginbuhl (talk) 02:12, 21 August 2009 (UTC)


 * It's usual for articles on SI units to provide the equation for the unit in terms of SI base units, in the introduction. The expression is there for those who need it. If it doesn't help you then you aren't the target audience for that equation. :) The article does go on to say that this means a light source that uniformly radiates one candela in all directions radiates a total of 4π lumens.


 * One can approach defining the lumen the way you suggest, but it isn't very clear unless the reader has a good understanding of solid angles already. A source that emits with an intensity of 1 cd into a solid angle of 1 sr emits a total of 1 lm. You have to specify the solid angle that is illuminated by the source for the definition to be correct. Isotropic sources are convenient because it's easier to visualize an isotropic source than a source that emits only into a solid angle of 1 sr.--Srleffler (talk) 02:49, 21 August 2009 (UTC)

The whole detailed discussion about lumen output of 120V vs 230V lamps is off-topic for this page defining and discussing lumen. Take it to a luminous efficacy page, if there is one. Here just give an example like a "typical" candle at about 10 lm, a 100W bulb at about 1500 lm, a streetlight at 20,000-50,000 lm. That's it. Don't get distracted. Cluginbuhl (talk) 02:20, 21 August 2009 (UTC)
 * That's pretty much how it started out. The article initially gave the lumen output of a typical 100 W bulb, because that is a light source that would be familiar to most readers. This had to be adjusted because European 100 W bulbs are dimmer than American ones. I'll see if it can be simplified a bit.--Srleffler (talk) 02:53, 21 August 2009 (UTC)

One more clarification
The reason that higher-voltage incandescent lamps have fewer lumens per watts is very simple. This was alluded to in the earlier ″Light output and lifetime″ section of this article. The following is a more explicit description of the difference in lumens versus operating voltage.

The main failure mode is evaporation of the tungsten filament. Evaporation causes the filament to become thinner. The higher-voltage lamp is designed start with a thinner filament than that of a lower-voltage, or it would draw too much wattage, operate at a much higher temperature and have a very short life. Thinning alone is not enough to make a product acceptable because that would make the life too short and also make it fail too easily from a minor mechanical shock. Dmc7 (talk) 23:35, 18 August 2017 (UTC)

Not correct methinks.
"That is, a light source that uniformly radiates one candela in all directions radiates a total of 4π lumens. If the source were partially covered by an ideal absorbing hemisphere, that system would radiate half as much luminous flux—only 2π lumens."

I don't believe that this is correct. If the hemisphere is absorbing the light over half the sphere over which it radiates, then the light flux over the remaining half must be the same at 4π lumens. If the hemisphere redirected the light into the system forcing it to combine with the unshielded half, then it would become 8π lumens, but the source would remain a 1 candela source. 20.133.0.13 (talk) 13:57, 9 September 2009 (UTC)


 * It is correct. Candelas are a measure of intensity, but lumens are a measure of the total flux emitted. If you block half the emitting area with an absorber, the amount of lumens emitted are cut in half, but the intensity in candelas remains the same over the unblocked portion of the source. (The intensity is of course zero where the source is blocked.)


 * If you used a reflecting hemisphere instead of an absorbing one, the intensity would double over the unblocked half of the source, but the total lumens emitted would remain the same. (This assumes, of course, that the source does not absorb any of the reflected light, and that the reflected light is uniformly distributed. In practice, the source would have to be much smaller than the diameter of the hemisphere for this to work.)--Srleffler (talk) 16:27, 9 September 2009 (UTC)


 * Thanks for the responses. I had a think about it and it did make sense after all.  I wonder if the article requires some clarrification? 20.133.0.13 (talk) 12:41, 10 September 2009 (UTC)

Plural
As the plural in English language is usually adapted from the language the word comes from e.g. radius -> radii, I changed that. Hope you're fine with that, otherwise please discuss here. example of a lighting firm's homepageThanks, Saippuakauppias ⇄ 23:48, 28 October 2009 (UTC)
 * "Lumens" is correct, at least in American English.* If you want to assert that "lumina" is the correct plural in English somewhere else, you are going to have to provide a reference to support your claim. I believe that "lumens" is the correct English plural everywhere.
 * --Srleffler (talk) 03:10, 29 October 2009 (UTC)
 * --Srleffler (talk) 03:10, 29 October 2009 (UTC)


 * NB: Dictionaries are not much help, because the unrelated biological term lumen does have plural "lumina". As a result, many dictionaries list both "lumens" and "lumina" as plurals for "lumen"; the distinct meanings of "lumen" have different plurals.--Srleffler (talk) 03:35, 29 October 2009 (UTC)

I reverted you again today, because you still have not provided a reliable source to support your claim that "lumina" is a valid English plural for "lumen", in the context of the unit of luminous flux. Wikipedia's verifiability policy allows uncited and disputed material to be removed by any editor. Such material must not be re-inserted unless a citation to a reliable source is provided.--Srleffler (talk) 00:11, 30 October 2009 (UTC)


 * The word "lumen" is from Latin, meaning "light". Therefore latin plural applies. Now your NIST dpcument doesn't provide any evidence for anything as far as I can see, as there are no plurals mentioned. Provide a valid source for "lumens" first please. Otherwise: "disputed material to be removed by any editor. Such material must not be re-inserted unless a citation to a reliable source is provided." --Saippuakauppias ⇄ 02:38, 31 October 2009 (UTC)


 * Since the plural "lumens" is regular in English, it never gets mention. If you're in doubt, compare searches for "lumens per watt" versus "lumina per watt" or something of that sort.  There is nothing in the literature to suggest that lumina is a plural of a unit of luminous flux, so you probably ought to drop it. Dicklyon (talk) 05:25, 31 October 2009 (UTC)


 * It doesn't matter what the plural is in Latin, only what the plural is in English. The NIST document states on the page cited that the plurals are formed regularly, except for lux, hertz, and siemens which don't change in the plural. --Srleffler (talk) 05:54, 31 October 2009 (UTC)

Plurals aside, would it be appropriate to mention, in the introduction, the etymology of the name, "lumen (the Latin for light)" ? 84.215.6.238 (talk) 14:46, 9 February 2013 (UTC)
 * No, certainly not in the introduction. Wikipedia is not a dictionary. In general, etymology is off-topic. It is almost never relevant enough to mention in the introduction, and in most cases is not worth mentioning at all.--Srleffler (talk) 00:33, 10 February 2013 (UTC)

Photons per second?
Shouldn't Lumen be expressible in terms of photons per second (of a given wavelength)? Obviously the eye's spectral response and the energy per photon will make this depend on wavelength, but still, an order-of-magnitude number would be useful. According to Luminous efficacy, 100% efficiency would be 683 lm/W, so 683 lm = 1 J/s. Taking a value near the peak spectral response, &lambda;=550, gives 3.61e−19 J/photon by the Planck relation. Dividing by that gives
 * $$683\,\mathrm{lm} = 1\, \mathrm{J}/\mathrm{s} = 2.77\times 10^{18} \mathrm{photons}/\mathrm{s}$$
 * $$1\,\mathrm{lm} = 4.05\times 10^{15} \mathrm{photons}/\mathrm{s}$$

or
 * $$2.47\times 10^{-16} \,\mathrm{lm} = 1 \mathrm{photon}/\mathrm{s}$$

Again, this is just for 550 nm green light. Does that sound right? —Ben FrantzDale (talk) 13:01, 13 September 2010 (UTC)


 * It's misleading to talk about expressing lumens "in terms of photons per second". It implies a general relation where there is none. Obviously if you know the spectrum of a source you can calculate one from the other. When you do this you are not "expressing" one in terms of the other. Rather, you are describing the source in two different ways.--Srleffler (talk) 04:22, 14 September 2010 (UTC)


 * Sure. My motivation is to try to get a ballpark sense of photon-limited shot noise, at least to get some bounds on that. Since I rarely work with lumens, I'd like a little confirmation that the above calculation is about right :-). —Ben FrantzDale (talk) 11:35, 14 September 2010 (UTC)

This is frustrating and the article is a terrible article. What is misleading about giving the reader a way to relate wavelength, lumens, and photons per second? Nothing does this, and the article gives volumes of useless information that are supremely confusing. Along the same lines as the question above, could we not write this?


 * $$lumens = E N$$

Where E is the energy of a photon and N is the number per second? For heavens sake someone please explain this in the article because it's terrible without it. -Theanphibian (talk • contribs) 18:18, 28 September 2011 (UTC)


 * The article doesn't give a relationship between lumens and photons per second because there is no general relationship between the two. In order to get from photons per second to lumens you have to know the spectrum of wavelengths emitted by the source. The expression relating the two would involve an integral over wavelength, of the product of the number of photons per second times the luminosity function. For the very special case of monochromatic light, one can write an equation of the form you propose, but it would be misleading to include that in the article because it would suggest to naive readers that the simple relation for this special case applies more generally. Also, this special case is pretty much worthless, since photometric units like lumens are typically used for broad-spectrum sources, not monochromatic ones. --Srleffler (talk) 03:15, 29 September 2011 (UTC)


 * Some quick synthesis gives:
 * $$\phi_\mathrm{v} = 683.002\ \mathrm{lm/W}\cdot \int_0^\infin \overline{y}(\lambda) N(\lambda)\frac{h c}{\lambda}\mathrm{d}\lambda$$,
 * where $$\phi_\mathrm{v}$$ is the luminous flux, in lumens,
 * $$\overline{y}(\lambda)$$ is the luminosity function,
 * $$N(\lambda)$$ is the number of photons per unit wavelength, per second,
 * $$h$$ is the planck constant,
 * $$c$$ is the speed of light, and
 * $$\lambda$$ is wavelength.
 * The integral is effectively just over the visible spectrum, since the luminosity function is zero for wavelengths outside the visible range. I do not feel that this equation has sufficient value to merit being in the article.--Srleffler (talk) 03:36, 29 September 2011 (UTC)


 * Article aside, that is a rather helpful equation. -Theanphibian (talk • contribs) 14:03, 17 October 2011 (UTC)

Example Table?
As a reader of this page, I didn't find the thing I was looking for: a table relating incandescent bulb wattage to lumens. —Preceding unsigned comment added by 192.132.94.130 (talk) 17:10, 11 January 2011 (UTC)


 * You want Incandescent light bulb.--Srleffler (talk) 03:30, 12 January 2011 (UTC)

Kitchen example
I removed the mostly-redundant kitchen light example, for two reasons: first, the flux given seemed a bit high for an actual fixture. Four 4' T8 fluorescent tubes output about 10 klx. More importantly, putting the same fixture in a larger room does not uniformly reduce the illuminance. Assuming the same ceiling height, the illuminance right under the fixture might be almost the same but the illuminance near the walls of the larger room would be lower. One could think about average illuminance, but that would be pointless. You don't measure the average illuminance across a whole room, nor is that what is important for use. --Srleffler (talk) 17:26, 23 June 2011 (UTC)

NITS
This is an article about lumen. There should be a related link, or a small paragraph about the comparison to nits too! — Preceding unsigned comment added by 98.254.64.146 (talk) 14:01, 25 June 2011 (UTC)
 * They are not so easy to compare. Lumens are units of luminous flux, while nits are units of luminance. Nits are discussed at Candela per square metre. We could probably say something about them here, but I'm not sure what.


 * You may find Photometry (optics) interesting...--Srleffler (talk) 16:19, 25 June 2011 (UTC)

Clarification of the Introduction
This sentence (from the Explanation section) should be put in the introduction:
 * The lumen can be thought of casually as a measure of the total "amount" of visible light in some defined beam or angle, or emitted from some source.

It immediately and clearly explaines what Lumen is. The introduction of this article is too complex as it is. While an in-depth explanation is needed, I think that the first paragraph should be easier to understand. - GeiwTeol 22:58, 15 July 2011 (UTC)


 * Good idea. I reworked the intro based on your suggestion.--Srleffler (talk) 23:36, 15 July 2011 (UTC)


 * I reworked the paragraph with the equation. Hope it's more clear now.  (not less clear!!) OsamaBinLogin (talk) 16:36, 25 May 2017 (UTC)

History?
I came here looking for a section about the history/origin of the unit. --  oKto  siTe   talk 09:29, 27 September 2011 (UTC)
 * You might be interested in Candela, which has a little bit of relevant history.--Srleffler (talk) 04:26, 28 September 2011 (UTC)

Lots of people looking for something like this?
Can we work some of this in under Lighting?

http://www.lvrj.com/sponsored/lumens-cfls-and-leds-a-light-bulb-guide-for-new-regulations.html?ref=498
 * . . . the following light bulbs all produce roughly the same amount of light (450 lumens): 40-watt incandescent, 29-watt halogen, 11-watt compact fluorescent (CFL) and 9-watt LED. It's still important to pay attention to wattage to make sure you don't exceed the recommended level for your lamp, but it's increasingly unlikely that you'll exceed that level as you purchase more efficient bulbs.

Thanks -- Jo3sampl (talk) 04:49, 8 November 2011 (UTC)


 * The text I quoted above is labeled as "promotional". I'll look for similar info from a more reliable source (although there's no obvious reason to misstate what's essentially how-to-buy data). I think a lot of people get to this page looking for a rough quide to the new labelling standard -- we think we know what a 100w bulb will do, and we want to know if a 1600-lumen bulb is essentially comparable for our purposes. I didn't find conversion help at the Incandescent light article. -- Cheers/Jo3sampl (talk) 12:56, 8 November 2011 (UTC)

Conversion chart for those who think in watts
There's a nice table at http://www.energy.ca.gov/lightbulbs/lightbulb_faqs.html. -- Jo3sampl (talk) 13:19, 8 November 2011 (UTC)

This is a dead link Try this one https://www.rapidtables.com/calc/light/lumen-to-watt-calculator.html Jokem (talk) 01:02, 30 October 2021 (UTC)

Expired source
The source 3 "OSRAM DULUX energisparepærer" (pdf). Osram.dk. Retrieved May 25, 2013. is now a 404 error. Napishtim (talk) 09:52, 22 July 2014 (UTC)
 * Marked.--Srleffler (talk) 04:14, 23 July 2014 (UTC)

Isn't it misleading to measure lamps for lighting in lumens?
I have one LED lamp rated 420 lm at 8 W energy consumption and another one rated 806 lm and 9,5 W. So the second lamp seems to be much more efficient. But when you look a little closer, the second lamp only lights up 160 degrees while the first one has an emitting angle of 330 degrees (which seems also much closer to the characteristics of a standard incandescent light bulb). Wouldn't it be more appropriate to rate those lamps according to the total amount of energy they emit as visible light? BerlinSight (talk) 22:52, 30 September 2014 (UTC)
 * That's essentially what rating them in lumens does. Lumens are a measure of the total "amount" of visible light emitted by the bulb per second. The advantage of using lumens rather than "energy emitted as visible light" is that lumens take into account the fact that the spectrum of the light affects how bright it appears.--Srleffler (talk) 04:40, 1 October 2014 (UTC)

External links modified
Hello fellow Wikipedians,

I have just added archive links to 1 one external link on Lumen (unit). Please take a moment to review my edit. If necessary, add after the link to keep me from modifying it. Alternatively, you can add to keep me off the page altogether. I made the following changes:
 * Added archive https://web.archive.org/20120301182202/http://www.osram.dk/osram_dk/Forbrugere/Lystyper/Energispareprer/brochure_DK_DULUX.pdf to http://www.osram.dk/osram_dk/Forbrugere/Lystyper/Energispareprer/brochure_DK_DULUX.pdf

When you have finished reviewing my changes, please set the checked parameter below to true to let others know.

Cheers.—cyberbot II  Talk to my owner :Online 19:17, 11 February 2016 (UTC)

Assessment comment
Substituted at 22:36, 29 April 2016 (UTC)

External links modified
Hello fellow Wikipedians,

I have just modified 2 external links on Lumen (unit). Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
 * Added archive https://web.archive.org/web/20081014010312/http://www.energyfederation.org/consumer/default.php/cPath/25_44_784 to http://www.energyfederation.org/consumer/default.php/cPath/25_44_784
 * Corrected formatting/usage for http://www.cpilive.net/news_ver2_old/guides_2004/projector_guide_issue_04/office.htm

When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.

Cheers.— InternetArchiveBot  (Report bug) 20:24, 27 May 2017 (UTC)

Why not define candela in terms of lumen instead of the other way around?
I get that the SI base unit is the candela, defined as: "The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×10^12 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian." But why perpetuate that, when, unless I made a mistake and not encumbered by a lot of experience in practical applications, the lumen can equivalently and far simpler be defined as: "The lumen is the luminous flux of a source that emits monochromatic radiation of frequency 540×10^12 hertz and that has a radiant flux of 1/683 watt." From there the candela can be defined as lumen/sr and the lux as lumen/m^2, instead of one's mind having to trampoline from candela, over lumen (by integrating over a sphere), and only then to lux. I don't think that a putative accident of history should bind us forever to have the issue presented to us along the same roundabout course, only making us wonder whether there is any logic to such madness, if the alternative is so much clearer, and it seems to me that the current direction of the SI derivation deserves little more consideration than a footnote. — RFST (talk) 09:27, 7 February 2018 (UTC)
 * The SI definition of the candela is what the candela is. We can't avoid that or work around it. It's wrong to say "the lumen can equivalently...be defined as...". What you mean is "the lumen could have been defined as...". It could have been, but it wasn't so we're stuck with the definition that we have.--Srleffler (talk) 13:02, 8 February 2018 (UTC)
 * Not good enough. Without a good rationale, the current definition is just rubbish. Nothing is anything simply because some idiot or committee of idiots said so, and if you need 50% more words than absolutely necessary to say something you're an idiot. — RFST (talk) 18:41, 8 February 2018 (UTC)
 * Ultimately, it doesn't matter whether you feel it is good enough. The SI definition of the candela is what the candela is. No other definition matters. The unit exists only because it was defined by the SI. You could create another system of units with the lumen defined as proposed above, and a "candela" based on it, but in doing so you would have created an entirely new set of units that are almost but not quite the same as the SI ones. A big part of the purpose of creating standards is to avoid this. It's confusing having the same unit defined in several different ways, or having lots of different units for the same thing. It leads to inaccuracy and error.
 * Something you may be missing: the definitions of the base units are not just words. The definition of a base unit describes a physical experiment that can be performed. The derived units are related to the base unit by mathematics, but each of the base units is defined by a physical measurement. The definitions of the base units are chosen such that the measurements described can be performed with high precision. I don't know for sure why they chose the candela over the lumen, but it may well be that radiant intensity can be measured more accurately than total radiant flux.--Srleffler (talk) 03:41, 9 February 2018 (UTC)
 * But the simplification is entirely equivalent, and you can do the same experiments! I didn't even replace a specific object or set of objects with a recipe to make a new object, like for the kilogram, I just left out a bunch of useless words that only served to obfuscate (unless you can give me a good purpose for them?). Does the definition of the candela hinge on an exact steradian that's stored in a vault somewhere because nobody can reconstruct it? Of course not, and other definitions aren't followed to the letter either, so... — RFST (talk) 11:37, 9 February 2018 (UTC)
 * You've changed the apparatus that would be needed to make the measurement. A setup to measure radiant flux is different from one for measuring radiant intensity. I don't know which would be more accurate, but they are not the same.
 * You didn't leave out any useless words. The only words I see that you left out were "in a given direction" and "in that direction". These are necessary because luminous intensity is directional. A real source is not going to emit equal intensity in all directions. The definition says that this doesn't matter: all that matters is that in some given direction, the radiant intensity is 1/683 W/sr. The lack of directionality in luminous flux might actually be the reason it wasn't used as the base unit. To measure the luminous or radiant flux of a source, you have to collect all the light it emits, in all directions. If you miss any, you affect the result of your measurement. That might not sound like a big deal, but when people are working on official standards measurements, they are trying to measure quantities to many decimal places of precision. Remember that the accuracy of your base unit measurement is the limit on accuracy for all other measurements in the world. If you can only measure the base unit to four digits of precision, than no other measurement of a luminous quantity anywhere in the world can exceed four digits of precision, because the unit itself is not defined better than that. You would be surprised at the effort that goes into making standards measurements accurate. Scientists spend their careers on this.
 * The official Kilogram is not stored in a vault because nobody can replicate it. It's stored in a vault because by definition there can be only one. You have to have one, single reference to which everything else is compared. One definition of the kilogram. One definition of the candela. If you have more than one, than whatever tiny discrepancy exists between the two reference standards becomes the absolute limit on the accuracy of all measurements of that physical quantity.--Srleffler (talk) 12:43, 9 February 2018 (UTC)
 * The definitions are equivalent, and the extra words are useless, because there's no difference beyond the application of fairly basic mathematics. You are entirely free to choose between considering all the light (integrated view), or only the light intensity in a given direction (differential view). Suppose an experiment can be devised in the integrated view that is more accurate by an order of magnitude: would you vilify it because it does not directly measure the current SI base unit, or embrace it because with a relatively simple mathematical transformation you get the same accuracy also for the SI base unit? And that kilogram in a vault will be given the same treatment as the prototype metre bar as soon as something better is accepted that matches within the margin of error associated with usage of the prototype. This is a silly discussion, going nowhere; you can have the last word if you want. — RFST (talk) 17:21, 9 February 2018 (UTC)
 * This is not math. This is not a thought experiment where you are free to simply "consider" an integrated or differential view. You have to actually perform the experiment and obtain the result. Yes, if a different experiment were able to get us a more accurate measure of the candela, the SI base unit definition would be revised exactly as has been done with the meter and as they are trying to do with the kilogram. The fact that the definition of the candela has not been changed is an indication that the experiment described in its definition is still the best measurement available.--Srleffler (talk) 07:58, 10 February 2018 (UTC)
 * There is no comparison between differential/integrated (mathematically equivalent, as are the experiments, you should just go to where the accuracy is) and prototype/description (world of difference), so stop bringing that up. If there were or is a better integrated measurement, changing the definition for that reason alone (and not just as an excuse for something long overdue) would be the height of stupid; not changing the SI definition now is regrettable but understandable (it's their job to be conservative); not changing the Wikipedia approach because of an existing SI definition is again in the realm of stupid. Can we conclude that you know of no valid reason for the current contorted definition other than an attempt to stay close to the state of the art in measurement, which you think is great (definition should be uncompromisingly experiment-driven) and I think is stupid (definition should not be slavishly experiment-driven, but rather mostly insight-driven)? — RFST (talk) 14:37, 12 February 2018 (UTC)

There isn't really an option here. The term "candela" has no meaning outside the definition given to it by the SI. The official definition defines what a candela is, and the definitions of other units follow from that. Presenting some other "definition" of the units would simply be incorrect. "Mathematical equivalence" is irrelevant, because this is not a math problem. Units are about physical measurement of the real world, and in the real world it very much does matter how you measure things. The purpose of standardized units is to enable measurements performed in widely-separated places to be compared, using units that are known to be the same everywhere. This is done by a chain of calibration that stretches from the equipment used to perform the measurements back to an actual implementation of the base unit measurement. This is fundamental to what standardized units are for.--Srleffler (talk) 05:19, 13 February 2018 (UTC) Mathematical equivalence is irrelevant?! I give up... — RFST (talk) 11:47, 13 February 2018 (UTC)

Good news: lumen is no longer defined in terms of candela. Why? I will explain below, but first let me explain why it used to be like this until 19 May 2019. Until 1979, photometric units were defined in terms of "standard candles" (Black Body, Candlepower, Hefner lamp). For calibration, luminous intensities were compared. That's why candela had been declared as base unit in 1954. With the new definition as of 1979, the photometric units got based on luminous flux, i.e. power weighted by a photobiological factor. "Lumen" became a special expression for "Watt" weighted by luminous efficacy. (Like the sievert, which is J/kg times a biological factor). When this change was made, everybody agreed that lumen was now more "basic" than candela. There was also serious doubt whether there could be any base unit at all for photometry. (For details see, the minutes of the CIPM meeting of 1977, 66th session, especially pages 14 and 143 - all of this in French). The CCPR (Consultative Committee for Photometry and Radiometry) proposed candela to be replaced by lumen as base unit. However, this proposal was rejected, because people were afraid that any change in the list of base units would undermine the acceptance of SI and endanger the reform of photometric units planned for (and done in) 1979. Now let's come my statement above that today lumen is no longer defined in terms of candela. The change came with the 2019 redefinition of the SI base units. In fact this was not just a redefinition of the base units but of the system itself. Previously, there had been 7 base units (including candela), each one them having its own, separate definition: "Base unit X is ...". As of 20 May 2019, there have been seven new definitions - but definitions of constants rather than base units. The seven fundamental definitions read: "Constant X has the value Y when expressed in SI units." The SI brochure clearly states (Chapter 2.3): "[...] this distinction [base units vs. derived units] is, in principle, not needed, since all units, base as well as derived units, may be constructed directly from the defining constants. Nevertheless, the concept of base and derived units is maintained because it is useful and historically well established [...]". So, the lumen is now defined directly as Watt × luminous efficacy. The intro of this acticle should be update accordingly. (by a native speaker, i.e. not by myself) -- Wassermaus (talk) 13:13, 1 September 2019 (UTC)

ISO standard
There is no mention in the article of the ISO 21118 standard for a lumen - only the ANSI standard. There is confusion about the difference in methodology and in comparing the units. Gpurinton (talk) 07:52, 22 July 2021 (UTC) Gpurinton

What is a lumen in base units?
The article lists the lumen, expressed in base units, as lm = cd sr. But it seems to me it should either simply be lm = cd or lm = cd m^2/m^2. Certainly the steradian is not a base unit, it's a dimensionless quantity derived by dividing 1 square metre by 1 square metre, though dividing the square of any arbitrary unit of length by itself would give exactly the same quantity of solid angle. Ava Eva Thornton (talk) 17:28, 29 August 2022 (UTC)


 * Good point. I agree it cannot be cd sr, but I don't know what should replace it. My suggestion is to correct the obvious error now (by replacing it with one of your suggestions) and then continue the discussion here. What do the sources say? Dondervogel 2 (talk) 12:51, 31 August 2022 (UTC)
 * The article does not refer to "base units". It does correctly say that 1 lm = 1 cd·sr. Writing either lm = cd or lm = cd m^2/m^2 would be idiotic; I oppose putting either expression in the article. Photometric units are confusing enough without that nonsense.--Srleffler (talk) 04:35, 1 September 2022 (UTC)
 * Ah yes, there is indeed no mention of base units. I missed that. Best left unchanged after all? Dondervogel 2 (talk) 12:47, 1 September 2022 (UTC)
 * This is one of the "uncomfortable" areas of the SI: its failure to separately manage angle as a quantity dimension, while encouraging the use of redundant use of rad vs. 1, cd vs. lm, etc. for clarity of intent, that is, as a "fake" dimension. If we were to include an "in SI base units" entry, it would simply be that lm is equal to cd.  I think  is an excellent way of expressing it.  172.82.47.242 (talk) 23:16, 3 September 2022 (UTC)
 * The current (9th) edition of the SI Brochure is explicit: lm = cd sr. It's not for us to replace that with WP:OR. NebY (talk) 14:10, 5 September 2022 (UTC)
 * The SI brochure is schizophrenic (it has some small errors and oversights, as well). But you have a point: the brochure does say "Unit expressed in terms of base units".  However, this is clearly not entirely satisfactory as is, so perhaps we should follow the brochure's lead: put in a footnote to forestall the "Uh ..." reaction.  172.82.47.242 (talk) 16:50, 6 September 2022 (UTC)
 * I have added an explanatory footnote that will hopefully address this. See what you think.  172.82.47.242 (talk) 16:58, 6 September 2022 (UTC)
 * The second part of that footnote, "The steradian is not an SI base unit, but may be regarded as the multiplier 1, leaving only the base unit candela in this expression" is basically a statement that the lumen is a candela mutiplied by one. That's worse than confusing, it's wrong. The first sentence in "Explanation" is much better: If a light source emits one candela of luminous intensity uniformly across a solid angle of one steradian, the total luminous flux emitted into that angle is one lumen. The solid area is an essential multiplier; a candela over an entire sphere is an emission of 4π lumens. NebY (talk) 17:23, 6 September 2022 (UTC)
 * The passage in the SI Brochure "it is a long-established practice in mathematics and across all areas of science to make use of rad = 1 and sr = 1" is in section 2.3.3 Dimensions of quantities, and applies to performing Dimensional analysis. NebY (talk) 17:45, 6 September 2022 (UTC)
 * OK, I've rewriiten the footnote, explaining that we're following the brochure despite its (understandable) apparent self-contradiction, quoting it on the steradian and citing it (at last!). NebY (talk) 18:20, 6 September 2022 (UTC)
 * I like what you have changed it to. I'm not sure what you mean by "it's wrong", though this is totally unimportant.  I really hope that the SI gets sorted with regards to angle before long; it is not as though this is difficult to clear up in principle, though it would need an extended transition phase.  (I must be off my head: the fight about dimensional angle in the SI is not getting anywhere close to consensus within metrological circles, with none that I've seen presenting a fully coherent picture.)  172.82.47.242 (talk) 20:34, 6 September 2022 (UTC)
 * Thanks! I haven't kept up with the fight. Is our hardly-optimistic description at Radian any good? NebY (talk) 23:06, 6 September 2022 (UTC)
 * As an interested non-expert bystander, I periodically see what papers I can access on the topic, and I see that there are recent papers that I have not read. I have not seen a clear and comprehensive presentation from the perspective of a framework of dimensional quantities in general, which simplifies argument and gives additional insight – instead, there remains the unhelpful unit-centric approach.
 * The linked section (at a glance) seems to serve quite well to give the reader some insight into the issue. IMO it does not make that the SI radian convention is merely that obvious enough (see, for example, ).  The heading "Dimensional analysis" is not ideal for what the section is about: with that heading, one expects an exposition of the dimensional status, not a perspective of the status of angle as an independent dimensional quantity.  There are some issues: The radian is defined as $θ = s/r$, where ... should read Angle is defined as $θ = s/r$, where ..., and the inclusion of the date 2019 is irrelevant and misleading in In SI2019, the radian is defined accordingly as 1 rad = 1, since this has been part of the SI since at least 1995, as is evident from .  172.82.47.242 (talk) 13:58, 7 September 2022 (UTC)