Talk:Luminous efficiency function

message: This needs some kind of disambiguation page -- "luminosity function" in astronomy means the number of objects of a given luminosity per unit volume of space.  It's used in the context of stars, galaxies, and even quasars, so it's very broadly used.  I'm not in a position to write such an article at the moment, but maybe someone could write a stub with just that info and create the disambiguation page? -- JThorstensen —The preceding unsigned comment was added by 67.142.130.36 (talk) 03:06, 3 May 2007 (UTC)
thread_title:  Astronomical definition 

message: Please provide the complete un-normalized response curves of the three types of humans color receptors, and show how this adds up to (or differs from) the Luminosity function.-69.87.203.133 02:23, 25 May 2007 (UTC)
replies: text: The cone responses are physical; I'm not sure where to find good data on them, but I'll see.  The luminosity function, on the other hand, is derived from psychovisual measurements.  So there's not necessarily any simple relationship, is there?  Presumably, though, the luminosity function is a linear combination of cone curves, since the XYZ color space is supposed to span the same 3D subspace of spectrum space that human color vision does.  What are you hoping to get out of this exercise? Dicklyon 02:44, 25 May 2007 (UTC)

text: I found a bunch of cone datasets at the CVRL.  Most seem to been constructed from color-matching functions, and based on some measurements that you'll have to chase down in the refs.  They seem to be normalized.  It's not clear what you can get from "un-normalized", but maybe there's something there.  Some indicate the weights needed to get the (modified) photopic luminosity function, like this one, which indicates no weight at all for the short-wavelength cones. Dicklyon 04:40, 25 May 2007 (UTC)
replies: text: Are there any plans to add a graph to the article showing response levels for the three normal cone types? Atamido (talk) 19:17, 19 March 2010 (UTC)

text: This graph has the same problems I noted at Talk:Cone_cell#The_picture_in_the_infobox.  — Preceding unsigned comment added by 77.61.180.106 (talk) 02:46, 8 March 2021 (UTC)
thread_title:  Human cone response 

message: I removed the following from the article, since it is clearly identified as speculation/original research, and is uncited.
An argument can be made that the difference between rod and cone response is an evolutionary adaptation to survival under star-lit skies.  The apparent-magnitude-weighted average spectrum of stars in the Earth's sky is bluer than the spectrum of the Sun (this statement is based on conversations with other professional astronomers and needs verification and a reference), hence the optimal vision for predation - and avoiding predation - at night is bluer than the optimal for daylight. P.r.newman (talk) 09:36, 3 April 2008 (UTC)
thread_title:  Uncited speculation removed. 

message: Quick comment: The last section says that the lower spectral limit for eye responsivity is 507 nm.  I assume that this should be 407 nm, to be consistent with the plot.  128.111.74.4 (talk) 21:53, 14 March 2008 (UTC)
replies: text: You seem to have misread it. The last section (on scotopic vision) says that the peak of the eye's sensitivity in dim light is 507 nm. This is the green curve on the graph.--Srleffler (talk) 02:23, 15 March 2008 (UTC)
thread_title: Lower limit

message: Is it necessary to use "discretized" to refer to the standard tables?  Apparently common usage since the 60s, but I came to this page as a curious user, not a mathematician. Jabberwoch (talk) 12:46, 31 October 2011 (UTC)
replies: text: That paragraph had a lot more abstract mathematical language than was necessary. I rephrased it a bit.--Srleffler (talk) 03:41, 1 November 2011 (UTC)
thread_title: Details

message: For common calculations, it would be really helpful to have a list of some weighted average values. For example, for "white" light (both tungsten and daylight).  i.e. integral (photopic luminosity d color)  
For example, if a light bulb emits 10 Watts of "average white" light, how many candelas is that?  — Preceding unsigned comment added by 87.194.171.29 (talk) 03:13, 20 February 2012 (UTC)
replies: text: You're looking at the wrong article. See Luminous efficacy for that.--Srleffler (talk) 05:49, 20 February 2012 (UTC)
thread_title:  Can we have some average values ? 

message: At what output interface is this "sensitivity" exactly measured?  Output of the rods? Optical nerve fibers? Which fibers? There are many types of fibers differing in color channel and spatial frequency. In subjective perception of "brightness"? In that case it's not a measurement of the eye, but eye+brain, which may be very subjective, vary from person to person and time to time.
I didn't find this specified anywhere in the article so unfortunately the article is meaningless for me. 
"Under photopic conditions, the actual spectral performance varies significantly from the smoothed function V(l ) adopted by the CIE for a "Standard Observor." Although not often noted in the literature, the Standard Observor is neither a real observor or an average human observor. The accuracy of V(l ) has often been criticized, even by the Chairman of the Committee that adopted it. These variations will be discussed in abbreviated form below."
http://neuronresearch.net/vision/files/photopiceffic.htm
From this article I get an impression the Luminosity curve is complete bullshit and little to do with reality - would like that its explained in the Wikipedia article what exactly it actually is
— Preceding unsigned comment added by 77.58.143.68 (talk) 00:36, 25 June 2012 (UTC)
replies: text: It’s not bullshit; it’s actually pretty good, considering the original methods used. As mentioned, it’s a description of eye/brain sensitivity to different wavelengths of light. Everything about color is subjective and varies from person to person and circumstance to circumstance. That doesn’t mean we shouldn’t try to make approximate models. More recent corrections have been suggested by several other scientists, including most recently Sharpe, Stockman, et al., based on measurements of the cones. You can read their several papers about it for technical details. –jacobolus (t) 01:19, 25 June 2012 (UTC)

text: Yeah, it's a little complicated.  [Here's a book] with some explanation.  For the cones, "sensitivity" makes more objective physical sense, and it's not about the "output", but about how different wavelengths of input are weighted, and the data can come from exact matching of color sensations.  For luminance, you can't do it without a human having to make judgements about which of two different-colored regions is "brighter", which is a trickier test to get consistent results from.  It depends on the individual's proportions of cone types, retinal wiring, and other stuff, so is more variable and less physical than the pigments in the opsins.  But, as Jacobolus notes, it's not bullshit.  Improve the article if you can.  Dicklyon (talk) 03:21, 25 June 2012 (UTC)

text: I see you removed your comments & Dicklyon put them back... we’re not upset w/ you or anything for the "bullshit" label; I agree that this article is kind of a stub, and could be expanded and more fully explained, and I also agree that some of the models of vision are radical (over?)simplifications of vision, based on some really strong assumptions – they describe what a non-colorblind observer sees when in standardized light conditions, properly adapted to the lighting, and looking at a small patch of color on a standardized background, and especially how they match the appearance of one patch of color to another by twiddling knobs, under the assumption that Grassmann's law applies. All of these assumptions at best hold contingently and approximately. There’s good reason to be skeptical of models that are so persnickety and limited! –jacobolus (t) 07:08, 25 June 2012 (UTC)
thread_title:  "Sensitivity" ambiguous for me 

message: The current version says the wavelength corresponding to the frequency of 540 THz is 555.016 nm, but it seems wrong. 299792458 / 540e12 = 555.17e-9. — TAKASUGI Shinji (talk) 01:55, 8 November 2013 (UTC)
replies: text: Ah, it’s okay, as it is the wavelength in the standard air at 20°C. — TAKASUGI Shinji (talk) 01:57, 8 November 2013 (UTC)
thread_title:  Wavelength of 555.016 nm ? 

message: Isn't it colored wrong? Scotopic means dark, so scotopic should be black, and the photopic has maximum efficiency at green color, so it should be green.
:The color is completely arbitrary. It's common, though, for the most important curve on a graph to be black, and for less important curves to be in lighter colors.--Srleffler (talk) 02:11, 12 June 2015 (UTC)
thread_title:  Main graph problem 

message: I think the link in the first section text to power spectral density should actually be spectral power distribution, since it is over wavelength and not time.  --- squeen
:Agree.  "Density" is not per se wrong, but the link is to a different meaning which is wrong for the usage in this article. North8000 (talk) 21:22, 8 January 2019 (UTC)
replies: text: I second that the SPD is also a density function, but I think SPD is the more common term (and proper link) in this usage case.  Not a regular editor or definitive subject expert (just an engineer doing spectral ray tracing), I do not feel "empowered" to make this change unilaterally.  Is there consensus? --- squeen 10 January 2019  — Preceding unsigned comment added by 2601:154:C100:240:DE4A:3EFF:FE70:2F8A (talk) 13:30, 10 January 2019 (UTC)
replies: text: Go for it! North8000 (talk) 15:36, 10 January 2019 (UTC)
thread_title:  PSD or SPD? 

message: The CIE calls this the luminous efficiency function, and has not called it "luminosity function" since the 1930s. It is occasionally referred to as luminosity function in some papers on color vision deficiency into the 1950s/60s.
But the use of "luminosity function" in this context leads to the frequent and incorrect use of luminosity instead of the correct term luminance. 
In modern colorimetry, luminosity means light over time, and is used often in astronomy, and is less correct in this context. Luminous efficiency function is the less ambiguous, less confusing terminology. Myndex (talk) 05:50, 22 February 2021 (UTC)
replies: text: Done.--Srleffler (talk) 03:28, 1 March 2021 (UTC)
thread_title:  Name change to luminous efficiency function 

message: I strongly believe that the lead of an article should be representative of the subject matter. Not just because it makes an article easier to read if it starts with a kind of summary, but also because many readers will just read the lead and maybe one of the sections if they're interested in something in particular. Keeping that in mind, let's look at the lead:
:A luminous efficiency function or luminosity function describes the average spectral sensitivity of human visual perception of brightness.
And then right next to it is a picture of the CIE 1931 1 nm curve. The impression is given that this is a more or less exactly known quantity, but that's false, see Talk:Cone cell#The picture in the infobox for details. There's a noticeable ripple on the graph; this isn't caused by a deficiency in our SVG renderer, it's present in the 1 nm data and caused by the interpolation method used. But that's a minor issue compared to the fact that more recent research seems to indicate that the overall shape of the graph is off, especially towards the blue end of the spectrum. And of course there's some individual variation and age plays a role as well; showing thin solid lines doesn't communicate this fact well.  — Preceding unsigned comment added by 77.61.180.106 (talk) 14:11, 8 March 2021 (UTC)
replies: text: The fact that it begins with the article "a" rather than "the", plus the fact that the graph shows three different photopic functions ought to give the reader a clue that this is not an exactly known quantity. If there are problems with the published sources that are documented in other reliable published sources, the article should discuss those issues. If you have the time, you could try adding something. I recommend starting with adding something to the body of the article. We can then condense that for the lead afterward.--Srleffler (talk) 00:33, 14 March 2021 (UTC)
thread_title:  About the lead 

message: I notice the article doesn't really discuss methods of measuring luminous efficiency, such as flicker photometry or direct brightness matching, or how to interpret the sometimes significant differences between results obtained through different methods.  — Preceding unsigned comment added by 77.61.180.106 (talk) 14:17, 8 March 2021 (UTC)
replies: text: That might be better placed in the article Spectral sensitivity. You're certainly welcome to add a section on that. Wikipedia is open to everyone to edit.--Srleffler (talk) 00:34, 14 March 2021 (UTC)
thread_title:  Measurement