Talk:Standard illuminant

Series D
Regarding illuminant series D, why is it that when I plug an x value of 0.31271 into -3*x^2 +2.870*x - 0.275 I get a result of 0.3291150677 instead of a result of 0.32902? —Preceding unsigned comment added by 142.161.241.193 (talk) 22:14, 19 October 2008 (UTC)


 * It's probably a mistake. The CIE has a well-defined procedure for rounding off but I did not follow it when preparing the table (so the accuracy might be impaired). There are several citations so if you have the time you can correct the chromaticities from them. --Adoniscik(t, c) 22:53, 19 October 2008 (UTC)


 * Color Vision and Colorimetry By Daniel Malacara claims the relationship between xD and yD is 2.870*yD^2 - yD - 3.000 * xD^2 - 0.275 = 0. This disagrees with the current wikipedia entry.  I'm hesitant to make any corrections without another source or the original CIE document.  And now that I check, this formula also seems to diagree with the (widely cited) chromaticities for D65  —Preceding unsigned comment added by 142.161.241.193 (talk) 02:49, 20 October 2008 (UTC)


 * Malacara is wrong. The first variable should be $$x_D$$, not $$y_D^2$$. (Lindbloom has it right.) --Adoniscik(t, c) 03:26, 20 October 2008 (UTC)


 * Okay. I looked at a few other sources and they all agree with the wiki page.  I still find it strange that the calculated chromaticity differs from the widely given values.  —Preceding unsigned comment added by 142.161.241.193 (talk) 04:29, 20 October 2008 (UTC)


 * I'm not saying the chromaticities are absolutely right, but the D-series formula is. I calculated the chromaticities from the CMS and SPDs, if I remember correctly. I neglected to implement the rounding off procedure so the last few digits may be off. I'll take a look at my code when I have spare time. In the meantime you can follow the references. --Adoniscik(t, c) 13:34, 20 October 2008 (UTC)


 * Okay. I'm starting to suspect the issue is that the formula given for computing the chromaticities from temperature is only an approximation. To get the exact value, one must calculate the chromaticities from the entire SPD.  —Preceding unsigned comment added by 142.161.241.193 (talk) 18:31, 20 October 2008 (UTC)


 * The formula is correct, but if are starting from a CCT you have to remember that Planck's constant has been revised since the definition of the series, as explained in D65. This affects the chromaticity of the canonical illuminants (D50, D55, D65, D75). For the rest, just substitute the CCT. --Adoniscik(t, c) 19:18, 20 October 2008 (UTC)


 * Sorry if I'm still confused. What do you get when you evaluate let x = 0.312713 in -3*x^2 + 2.87*x - 0.275 ? I don't get 0.329016.  My result differs by more than 10^-4!  —Preceding unsigned comment added by 142.161.241.193 (talk) 23:25, 20 October 2008 (UTC)


 * The quadratic relation is a best-fit curve. I suppose the most precise results derive from the SPD itself. If you are going to be exacting you may be interested in following the recommended rounding off procedure, as explained in Appendix 2 (Uncertainties in Spectral Color Measurement) of Schanda's Colorimetry book. For D65, Schanda lists x=0.31272, y=0.32903. This agrees with the formula; if you set T=6500x1.4388/1.438, you get x=0.312720... Substitute that into the quadratic equation and you get y=0.329125... Truth be told, the difference is indistinguishable. --Adoniscik(t, c) 01:09, 21 October 2008 (UTC)
 * I came to this talk page because I noticed the discrepancy between this page and Illuminant D65. When I follow the official procedure from page 62 the standard, using the referenced formulae from page 3, and plugging in 6504 K from the article, I get the following:
 * -4.6070e9/T³+2.9678e6/T²+0.09911e3/T+0.244063 with T=6504 yields x=.312714
 * -3x²+2.87x-.275 where x=.312714 yields y=.329119
 * The procedure doesn't say these values should be rounded at this stage.
 * The wording of the text then implies that the constants in the formulae to calculate the factors for the S distributions should be carefully calculated such that the coordinates of the final sum are the ones put in.
 * Is it possible the colour coordinates listed on the D65 article are wrong? Let's hope not, but we need to get to the bottom of this.
 * One might say that in practice it might not matter since when one plugs in these x and y values into a converter using the other white one gets 254.886, 255.000, 254.899 in terms of sRGB colour values, but I think it does matter because it raises questions about how D65 is actually defined, why Wikipedia seems to contradict itself, and similar worries. — Preceding unsigned comment added by 77.61.180.106 (talk) 22:51, 30 December 2020 (UTC)
 * I have figured out where the 0,32902 figure comes from and it isn't just slightly off, it's wrong, by which I mean that it isn't the result of a rounding error or something but of a mistaken thought process.
 * Note: I'll be using commas rather than periods in this post.
 * To establish a baseline, I first measured the x and y coordinates of the spectral distribution table provided by the CIE using CIE's 1931 standard observer tables at 10 nm intervals. I also calculated the D65 white point at 6503,61613351878 K. (I realise I'm stating more figures than are actually significant. I believe it will help people checking my work.) The two sets of coordinates matched to four digits. I also calculated the spectrum myself using the S0, S1 and S2 tables provided by the CIE and the constants M1 and M2 rounded to three digits and this spectrum aside from a few rounding errors matches the table provided by the CIE and has essentially the same x and y coordinates. Then I calculated it without rounding the Ms, but still using CIE's coefficients and got an even better match. Now, mathematically it should be the case that if all the coefficients are carefully recalculated using CIE's procedure, and then the Ms without rounding the intermediate results, the exact coordinates of the white point should be obtained again. I decided to check this, if only to judge if numerical issues were going to be a big problem, and I got a perfect match.
 * Trying to figure out where the strange x and y coordinates might come from, I tried measuring the table linearly interpolated to 5 nm intervals with the observer Lagrange interpolated to 5 nm intervals. One might object this doesn't make any sense, but remember I'm looking for anomalous coordinates. When I saw the 0 after the 0,329 I felt I was on the right track. It turns out that whoever calculated the 0,32902 measured the x and y coordinates of a spectrum calculated from the S tables linearly interpolated to 5 nm intervals using unrounded Ms calculated using CIE's coefficients, using the Lagrange interpolated observer.
 * Now what this does effectively is subtly change the characteristics of the observer. The S tables act a bit like primaries, although they can have negative coefficients, which wouldn't be possible when using physical primaries. When the observer changes, the observed colours of these primaries change as well. Now, D65 isn't a physical light source and the final D65 tables are only informative; rather it's a mathematical construct designed to yield a specific white point. So when the colours of the primaries change, the coefficients must be adjusted and whoever calculated the 0,32902 value didn't do that.
 * The CIE provides a method to calculate these adjusted coefficients. I have verified that their method makes mathematical sense and when I use it without rounding to calculate matching coefficients and Ms I get the D65 white point again, as expected. I am certain that the coordinates now listed in Illuminant D65 are wrong.
 * For reference, here's a table of values I calculated. I didn't round any to significant figures.

!Description!!M1!!M2!!x!!y
 * D65 calculated white point||n/a||n/a||0,312720273260374||0,329125276333145
 * D65 table||-0,295||-0,689||0,312731939052615||0,329131248432228
 * D65 calculated with CIE Ms||-0,295||-0,689||0,312731962657572||0,329131499046731
 * D65 calculated without rounding Ms||-0,294649462789131||-0,689128185456599||0,312720046938127||0,329119493351070
 * D65 calculated without rounding any of the coefficients||-0,294886815462621||-0,690323252084450||0,312720273260374||0,329125276333145
 * D65 table with interpolation||-0,295||-0,689||0,312720521360332||0,329030683518559
 * D65 calculated with interpolation and unadjusted, unrounded Ms||-0,294649462789131||-0,689128185456599||0,312708546823219||0,329018914033498
 * D65 calculated with interpolation and proper Ms||-0,298920590019293||-0,709397376927945||0,312720273260374||0,329125276333145
 * }
 * D65 calculated without rounding any of the coefficients||-0,294886815462621||-0,690323252084450||0,312720273260374||0,329125276333145
 * D65 table with interpolation||-0,295||-0,689||0,312720521360332||0,329030683518559
 * D65 calculated with interpolation and unadjusted, unrounded Ms||-0,294649462789131||-0,689128185456599||0,312708546823219||0,329018914033498
 * D65 calculated with interpolation and proper Ms||-0,298920590019293||-0,709397376927945||0,312720273260374||0,329125276333145
 * }
 * D65 calculated with interpolation and proper Ms||-0,298920590019293||-0,709397376927945||0,312720273260374||0,329125276333145
 * }
 * }

Series A
The text has x=0.44758 but the white point table has x=0.44757. --User:Copyeditor42 23Apr2010 —Preceding undated comment added 13:32, 23 April 2010 (UTC).


 * I assume it’s a rounding error? The difference between those is irrelevant for practical purposes. –jacobolus (t) 04:48, 24 April 2010 (UTC)

Incomplete references for Series F illuminants
I cannot find any references that point to the 5-digit accurate chromaticities given in the table. Only F2, F7 and F11 are given in Equivalent White Light Sources, and CIE Illuminants (ref 21), but not for the others. Background: I have reproduced the CIE 1931 chromaticities numerically and can confirm the accurate values for all but F4 with about 4 digits accuracy and F2, F7 and F11 with almost 5 digit accuracy with respect to ref 21. But for F4 I get (x,y) = (0.43987, 0.40314) instead of (0.44018, 0.40329). I have used two sources for the spectra which list identical data. So the values given for F4 in the table are inconsistent with the spectral tables listed in the reference list (some of which had to be retrieved from the Internet Archive, however).

Another point worth mentioning is that the chromaticities only match the table data if a finite summation in 5-nm steps is used rather than (linear or spline) interpolation and more accurate quadrature schemes. Therefore, it should be mentioned somewhere if there is an 'official' numerical calculation method.--SiriusB (talk) 14:29, 15 November 2012 (UTC)


 * I’ve read several sources that recommended using the finite 5-nm step summation, starting w/ the Handbook of Colorimetry from the 30s. The whole CIE system is based on the 1931 5-nm increment definitions of X, Y, Z. I’ll see if I can track down a modern source. I’m sure this kind of thing is covered in Wyszecki/Stiles (including chromaticity coordinates for F illuminants, etc.), but I don’t have a copy and am not currently near any libraries. –jacobolus (t) 18:29, 15 November 2012 (UTC)


 * To 4-digit precision, here are the chromaticities of F illuminants from Colorimetry: Understanding the CIE System edited by Schanda (from chapter 3, by Schanda). http://i.imgur.com/I9yqU.png It’s not clear to me what precision was used for summing tristimulus values here, but quoting from that book, ‘Values of the CIE 1931 standard colorimetric observer have been standardized. The color-matching functions are given in the standard as values from 360 nm to 830 nm at 1 nm intervals with seven significant figures. For almost all practical applications an abridged and coarser set of data is adequate. CIE Publication 15 states “In the case where more coarsely sampled data will produce no significant calculation error selected values taken from the standard at 5 nm intervals, rounded to six decimal places, and reproduced in the above publication both in printed and electronic form will be sufficient.”’ –jacobolus (t) 18:38, 15 November 2012 (UTC)


 * Thanks. The chromaticities are the same as in Wikipedia. However, what I am looking for is an independent table of the spectral power distribution of the F illuminants since there might be some misprint in the commonly cited sources. It cannot be by chance that all F1 to F12 with the only exception of F4 can be precisely reproduces. Therefore I suggest some typo, transposed digits or unintented truncation of values (or even only one value) given in the F4 column of the common reference of F.txt, the Excel spreadsheet and its host site (available through Wayback Machine).


 * For the 5nm discritization I can look up in W&S since I have a copy in reach (but not at this moment).--SiriusB (talk) 08:18, 16 November 2012 (UTC)

Update: I have solved the riddle of deviating chromaticities: The spd of FL4 in the official CIE.15.2004 table (see this Excel Spreadsheet) differs at 600 nm by -0.76 units from the table cited here. The CIE.15.2004 table gives the x,y values given in the article. Some of the other FL spectra do also differ at a few points.--SiriusB (talk) 09:19, 15 April 2013 (UTC)

CIE standard illuminant A is intended to represent typical, domestic, tungsten-filament lighting
represent typical! "domestic" Please define domestic! — Preceding unsigned comment added by 188.62.58.119 (talk) 20:25, 29 May 2015 (UTC)
 * lol* can not be taken serious?

Domestic is not only used to mean 'from this country', but can also mean 'in/around the house'. Knowing that, the need of defining "domestic" vanishes, IMHO.Muxarin (talk) 13:27, 31 January 2017 (UTC)

CCT of Illuminant E
The quoted CCT for Illuminant E is 5455K, but it is apparently unsourced. I see various references to 5454K and 5455K (as well as one outlier to 5500K). Is there a good source for a precise value? Chconnor (talk) 22:18, 2 September 2016 (UTC)

RGB Colors
It seems to me, just by eyeballing, that the provided example RGB colors in the table are *not* the colors of the illuminants, but just RGB renderings of the given color temperature. Case in point, the RGB color for D65 (assuming the rendering was done for sRGB) should be just white, since by definition, that is the white point of sRGB. But you see that the color is slightly purplelish. If you then compare the graphs of the Planckian locus with the location of D65, you'll see that, indeed, D65 should have more green in it than the blackbody color of the same CCT. So I'd recommend to revise these colors, whoever did them. 2A01:598:B003:91C7:345D:9B77:CF5F:7054 (talk) 19:30, 11 April 2019 (UTC)
 * Trying to figure out what specifically you mean and are suggesting. To get it started, could you tell us which specific diagram you referring to? Thanks. North8000 (talk) 15:56, 12 April 2019 (UTC)
 * He's referring to the section ‘White points of standard illuminants’ and he's right. Since colours in HTML are sRGB and the sRGB white point is D65, the colour should be #FFF but it isn't.
 * By the way, I don't really understand why there's a column called Hue and a column called RGB. Both colours displayed have a hue, intrinsically, and both are delivered to the browser as hexadecimal sRGB values. — Preceding unsigned comment added by 77.61.180.106 (talk) 02:57, 30 December 2020 (UTC)

How it got this way
Looking into this, I find two main problems. First in this edit the RGB values were added without explanation. The previous Hue values made a certain logical sense that was explained in the caption, that is, that they all had the intended chromaticity represented at a Y value of 0.54 (but that's not what Hue means). I haven't checked to see if the numbers were accurate, but at least the D65 chromaticity was a neutral at #c2c2c2", which the new RGB #fff9fb was not (a bit purple; the later conversion to use Template:Color temperature didn't help that, and is probably where the numbers came from (at least from the same formulae). Second, those colors came only from the CCT, not from the whitepoint xy coordinates given.

At another point, illuminant A at 2856 K, the Hue is #ffb263 and the sRGB #ffb662. This is the lowest hue used at Y = 0.54, which is why the red is at ff. The sRGB value from the template always has the highest primary at ff, so they should match in theory. They're close, but not the same. I'm inclined to believe the Hue value (I'll plan on checking).

This should be easy to fix, since a mapping of xy to XYZ to sRGB is much simpler than modeling CCT. If someone knows how to write templates, I'll be happy to assist in coming up with a good fix. In the meantime, I suggest just removing the sRGB column, and completing the missing Hue values (for CCT below the lowest one there now, 2856, it will not be possible to maintain Y = 0.54, so we'll need to let them get darker, e.g. by approximating them with the existing sRGB numbers). Or I can calculate values in Matlab and plug them in, maybe. Dicklyon (talk) 03:37, 22 October 2021 (UTC)

You guys had something to do with this. Got an opinion? Dicklyon (talk) 03:53, 22 October 2021 (UTC)

Hex values
OK, I made this little function in Matlab: and tested it with the whitepoint of illuminant A: which yielded the #ffb263 that's in the Hue field. So I can run the rest of the numbers and check them... Dicklyon (talk) 09:30, 22 October 2021 (UTC)

Reducing the Y value in the code to 0.52, the whitepoints all fit with values up to 255, yielding this table of colors (in order by name): faaf62 d3bba8 c3bdc7 cdbda5 c7beaf bfbfbf b9bfcb b1c0da cfbab7 bbc0ba d9ba93 eab57b f8b068 b7c2b5 d8bb8a bfbfbf cdbda5 dcb994 cdbda4 dfb88f f6b169 ffad5d f6b16c ddb894 cebcab c1bec2 fbaf62 f9b053 ecb731 ddb990 . Dicklyon (talk) 09:48, 22 October 2021 (UTC)
 * Thank you for your contribution! I appreciate the work you did with the mathlab formula. I guess your values are more precise than the current used ones. I suggest to replace the old values with your newly calculated ones.
 * I also moved the disc to here, where the template is located. --Angerdan (talk) 16:51, 22 October 2021 (UTC)
 * I moved it back to the article, where other editors may see it. The template should be deleted, in my opinion, but should certainly not be the focus of discussion. Dicklyon (talk) 18:29, 22 October 2021 (UTC)
 * Which values do you propose to replace? I think we should have one column, and call it "Color", not "Hue" or "RGB".  Yes? Dicklyon (talk) 18:29, 22 October 2021 (UTC)
 * Color is unprecise and it is much more useful with offerung both values (Hue and RGB). Since you posted the HEX RGB values, of course i proposed to use your nex values there. --Angerdan (talk) 18:44, 22 October 2021 (UTC)

I made the proposed change. Let me know what you'd do differently. How is Color less precise or correct than Hue or RGB? Dicklyon (talk) 18:57, 22 October 2021 (UTC)

FYI, the script that printed the hex values uses numbers scraped from the article/template, thus: Dicklyon (talk) 06:11, 24 October 2021 (UTC)

Series D Calculation and Tabulated Values
The final sentence states:
 * In order to match all significant digits of the published data of the canonical illuminants the values of M1 and M2 have to be rounded to three decimal places before calculation of SD.

If you do this with the 107 tabulated D65 values at 5 nm interval (300 nm - 830), you will find that the CCT temperature needs to be reduced from 6504 to nominally 6502.5 and you will need to round the return value to 4 places (the precision of the tabulated values) in order to minimize the number of values in error. Even then, 27 of the values are in error in the range [-0.0004 .. 0.0008]. If in addition you subtract 0.0002 from the calculated value prior to final rounding, the errors balance in the range [-0.0006 .. 0.0006] but now 100 of the values are in error. The rounding here rounds the halfway point away from zero. Final truncation instead of rounding gives 32 errors in the same range.

I tried various other rounding schemes and get worse matching. Rounding M1 and M2 to four places produces the same values as rounding to three places, due to the small deviation of M1 and M2 from an exact three place fraction. I took my equations from Bruce Lindbloom's page, referenced in footnote 19. Those equations are identical to the equations in the wiki page, if you can disregard the unsightly comma dividing the decimal fraction into 3 digit groups. The latter really needs to be removed - nobody anywhere uses commas in decimal fractions, and it is very hard to read.

The bottom line is this: either the tabulated data can not be reproduced with modern physical constant values utilized in the black body calculations, or the coefficients in the equations do not offer adequate accuracy, or there is some error in the formulation. I was unable to find any reference other than Lindbloom's, and while his attention to detail is excellent, he is lax on citing references for his formulations. That said, I have found his site to be an excellent and accurate reference regarding the standards.

For reference, the D65 tabulated data may be found at the following links. I verified that the 5 nm values are identical. The 1 nm values at the first link appear to be linear interpolations of the 5 nm data, rounded to 4 places.

http://www.npsg.uwaterloo.ca/data/illuminant/d65.txt

https://raw.githubusercontent.com/hughsie/colord/master/data/illuminant/CIE-D65.csv

Recommended correction: change the wording of the final sentence to indicate that exact fidelity with tabulated values is not possible. Additionally, it would probably be useful to cite variations in CCT (apart from the usually cited variation, e.g. from 6500 to 6504) that are necessary to minimize deviation, and to point out that rounding the final calculation to tabular data accuracy (4 places) is necessary.

From the perspective of new work, these deviations are trivial. From the perspective of replicating old work that relied on tabular data, these variations prohibit the substitution of calculated data for tabular data.

I have also looked into performing these verification calculations with D50. Suffice it to say, similar problems arise, but with different error variations and CCT adjustments. — Preceding unsigned comment added by 216.251.133.187 (talk) 21:35, 23 July 2019 (UTC)

There are only two standard illuminants: A and D65
There are only two standard illuminants: A and D65

All other illuminants are just CIE Illuminants, they are NOT "standard" illuminants.

AS SUCH, this article should be named "CIE illuminants" and not "Standard illuminants". Myndex (talk) 23:29, 20 October 2021 (UTC)
 * This book at section 8.9 says that the others were "previously denoted as CIE standard illuminants", but doesn't say when or why that changed. Do you know?  It would seem relevant to deciding what to change here. Dicklyon (talk) 23:55, 20 October 2021 (UTC)
 * Hi The CIE states that only A and D65 are the standard illuminants in Colorimetry Pub15-3, 2004, and I believe the 1986 edition, so the change I think was before that, possibly in the 1976 iterations?? It was long enough ago that I do not have a "before" example. All I can say for sure is that at least since 2004, The CIE has stated the standards are only A and D65... thank you...Myndex (talk) 02:11, 21 October 2021 (UTC)
 * I don't dispute what's a current CIE standard. But tons of recent books still talk about "standard illuminants" B and C and "standard illuminant" D55.  So we should probably state that these are no longer CIE standards, but we can still cover them under the current topic. Alternatively, a  move to CIE illuminants as you suggested might be OK.  Dicklyon (talk) 07:22, 21 October 2021 (UTC)
 * Hi so, A B and C were created in 1931. B fell out of favor quickly, C is still occasionally in use but depreciated and no longer standard. D65 was created in 1964, and in 1967 CIE (1967) Recommendations on standard illuminants for colorimetry indicated keeping only 2 as STANDARD: A and D65  So I vote for calling this article CIE illuminants, as the only other "standard illuminants" ever were B and C — B rarely used (the chemicals to make it being very toxic) and C being depreciated in the 1960s. Thank you... Myndex (talk) 20:57, 21 October 2021 (UTC)
 * Whatever the current official status, people still regularly call these "Standard Illuminant B" or "Standard Illuminant C". The name "Standard Illuminant" also does not necessarily imply that the illuminant in question is currently an official international standard; my impression on hearing the term is that it means the illuminant is explicitly specified, as compared to e.g. a generic unspecified "compact fluorescent bulb" or "cloudy daylight", or a specific product like "Phillips lamp 5A19/LED/927/FR/P/E26/ND/T20 6/1FB". The current article (and its title) seems fine to me. If you want to add some clarifying text explaining the history of standardization / deprecation, that would be fine. –jacobolus (t) 02:36, 22 October 2021 (UTC)
 * Hi I'm with you regarding C, though my point is not about if a former standard should still be called standard. My point was simply relying on the CIE statement (in Colorimetry 2004 and 2007) that "only A and D65 are to be called 'standard' illuminants"  and all the others were to be referred to as only "illuminants". It seemed to me then that the article is better termed CIE Illuminants as being more descriptive. I've just been trying to line up some Wikipedia color things with actual standards... Myndex (talk) 04:09, 24 October 2021 (UTC)
 * Wikipedia should try to follow whatever prevailing practice is, rather than what the CIE recommends per se. If you want to reorganize the article to emphasize illuminant A and the D series, with illuminants B/C relegated to a later section talking about the history, past adoption in other contexts, and deprecation, that would probably be fine. I don’t think the article needs to be retitled though. There are plenty of books (including recent ones) referring to e.g. “standard illuminant C”. If you want to just call these all “illuminant A”, “illuminant D50”, “illuminant D65”, “illuminant C”, etc. in the article that also seems fine. –jacobolus (t) 04:56, 24 October 2021 (UTC)
 * In one meaning, there needs to be some authority enforcing/recommending a standard, and many parties ratifying and abiding by the standard. However, in a loose context, this could apply to any published illuminant intended for use by others. Otherwise defining what is a 'standard' just runs into gatekeeping issues. You are absolutely right though, that CIE themselves do state:
 * So if we are going whole hog on this being a CIE article, then I agree. However, I think I have a better compromise. I was considering creating a new article illuminant to deviate from the CIE illuminants, but in reading this chapter, it became clear to me that renaming this article simply to Illuminant with a section list of "published" illuminants and a deeper focus on the two CIE "standard" illuminants, would probably be best. Heck, D65 has already got its own article. It may not even be necessary to cover it much more in depth in this article. Curran919 (talk) 13:50, 18 November 2022 (UTC)
 * So if we are going whole hog on this being a CIE article, then I agree. However, I think I have a better compromise. I was considering creating a new article illuminant to deviate from the CIE illuminants, but in reading this chapter, it became clear to me that renaming this article simply to Illuminant with a section list of "published" illuminants and a deeper focus on the two CIE "standard" illuminants, would probably be best. Heck, D65 has already got its own article. It may not even be necessary to cover it much more in depth in this article. Curran919 (talk) 13:50, 18 November 2022 (UTC)

but are easy to characterize mathematically
No, they're quite hard to characterise mathematically, at least compared to the other ones. There's no neat formula, just tables, which need to be interpolated. Whether this interpolation is done and if so how even determines the coefficients you need to use. I'm not saying it cannot be done, but I don't think the average reader will find it easy. — Preceding unsigned comment added by 92.67.227.181 (talk) 00:34, 13 June 2022 (UTC)

Illuminant F2 (cool white fluorescent) I think is inaccurate
The line in the table for this illuminant says:

F2 0.37208  0.37529  0.37925  0.36733  4230

So the color temperature for this is supposedly 4230K. However that's too yellow of a color temperature (5000K is approximately pure white). I've used cool white fluorescent lamps, and they are slightly bluish compared to pure white (I'm guessing about 5500K to 6000K). Also, the x and y chromaticity coordinates given do produce a yellowish color when rendered. So it seems that the chromaticity coordinates are matched properly to the color temperature, but the whole data set is wrong for an F2 illuminant (a cool white fluorescent lamp). Either that, or the table's description of the F2 illuminant is wrong (it may actually represent a variant of warm white fluorescent lamp, contrary to what that table says).

If anybody here can post a reply to clear up these discrepancies, please do so.

Benhut1 (talk) 10:46, 2 October 2022 (UTC)


 * The lower the CCT, the warmer (redder) a light looks. 4230K is about the same color as moonlight, which is "cooler" than your old tungsten but "warmer" than your expectation of a 5000K white. If I recall correctly, in the old days fluorescent manufacturers used to give "warm" (~2800 K incandescent), "cool" (~4000 K moonlight-ish), and "daylight" (5000~6500) options. Artoria2e5 🌉 07:40, 27 January 2024 (UTC)

Merge proposal
I propose merging Illuminant D65 into Standard Illuminant. I think D65 only exists because it has been around since 2006, 2 years before standard illuminant. There is very little information there that is not already in standard illuminant, and the few sentences I'd take over would be mostly applicable to all D-series illuminants anyway. I know that D65 has special status amongst all the other illuminants, but I think that can be highlighted on the general page. I'm actually surprised this hasn't been done yet.Curran919 (talk) 13:32, 8 February 2024 (UTC)