Talk:Standard illuminant

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

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

message: 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)
thread_title:  CCT of Illuminant E 

message: 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)
thread_title: How it got this way

message: 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)
thread_title:  Series D Calculation and Tabulated Values 

message: 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)
thread_title:  but are easy to characterize mathematically 

message: 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)
replies: text: 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)
thread_title:  Illuminant F2 (cool white fluorescent) I think is inaccurate 

message: 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)
thread_title:  Merge proposal