Talk:Planckian locus

message: I have some questions about the approximation equations.
# The referenced page ( http://www.vendian.org/mncharity/dir3/blackbody/UnstableURLs/bbr_color.html ) gives a list of black body sRGB coordinates for various temperatures. There is no information on how the sRGB coordinates were converted to xy coordinates, there is no information as to the fitting procedure used. We need a reference for these fitting coefficients.
## this is somewhat explained at http://www.vendian.org/mncharity/dir3/blackbody/, and there is Perl sources used to compute that, with links to CMFs and spectrum data he used. (on the 2nd note, http://www.vendian.org/mncharity/dir3/blackbody/parameters.html shows 10deg and 2deg CMFs integration curves plotted together, which is kind of obscures the fact they are different coordinates, I wonder if the author even realizes that). 91.124.93.184
# What does the phrase "fitting 1" and "fitting 0.9996" mean?
PAR 13:23, 11 May 2006 (UTC)
replies: text: Those equations are garbage and the person who put them there is not responding. I have removed them. PAR 22:13, 21 August 2006 (UTC)
thread_title:  Approximation - some questions 

message: for the exact calculation of "The Planckian locus in the XYZ color space". Is it really necessary (and why) to integrate from zero to infinity? I would guess it is totally sufficient to integrate in the visible spectrum from 380 to 780 nm. The other wavelengths are not visible and thus shouldn't play a role. And the values of X(lambda), Y(lambda) and Z(lambda) should also be zero for any invisible wavelength.--TeakHoken193.187.211.118 (talk) 12:59, 18 March 2009 (UTC)
replies: text: Of course, when you integrate, you can skip any interval where the integrand is zero.  The XYZ functions are zero wherever light is invisible, so you could make the integral just go over the defined nonzero range of those, if you find a good source for their defined nonzero range.  Dicklyon (talk) 16:52, 18 March 2009 (UTC)
thread_title:  Integration from zero to infinity or in the visible spectrum? 

message: The article uses "SPD" twice, but doesn't explain what that refers to. smurfix (talk) 20:13, 25 April 2012 (UTC)
replies: text: Spectral power distribution. –jacobolus (t) 21:22, 25 April 2012 (UTC)
thread_title:  "SPD" ? 

message: from this article:
'The mathematical procedure for determining the correlated color temperature involves finding the closest point to the light source's white point on the Planckian locus'.   The intention was probably 'the light source's tristimulus value', and not white point.
Similarly on the color temperature article it says 'The color temperature of a light source is the temperature of an ideal black body radiator that radiates light of comparable hue to that of the light source'.
Hue has little to do with it - I imagine the intention was also the tristimulus value.  — Preceding unsigned comment added by 82.81.32.236 (talk) 21:57, 3 July 2012 (UTC)
replies: text: Your changes seem reasonable to me, though I am no expert. Why don’t you make it so, and then see if anyone complains? Vadmium (talk, contribs) 06:00, 5 July 2012 (UTC)
replies: text: Well, the white point of a light source is the tristimulus value of that light source by definition; these are equivalent termini. Hue is indeed something different, but is probably used as an illustrative comparison (the quote does not say "identical" (which it should if the correct terminus "tristimulus value" was used), but rather "comparable"). I’m undecided as to whether that’s a good idea. --Uli Zappe (talk) 04:25, 13 November 2015 (UTC)
thread_title:  CCT calculation 

message: Over the years, there seems to have been constant confusion about whether to add or not add PI to the formula describing Planck’s law. There was a debate about that in 2007 here on this talk page, and as recently as this year User:HumblePiero "corrected" the formula by removing PI from it. So I want to clear up a few points:
# There is not only one correct way to describe Planck’s law, there are several valid variants. The version used in this article is correct with PI as well as without PI. The variant with PI calculates the spectral radiant exitance of the black body, the variant without PI calculates the spectral radiance of the black body. Both describe Planck’s law perfectly well. But note that in any case, the letter I (capital i) is incorrect; this letter would describe the spectral intensity. The correct letters would be L for spectral radiance and M for spectral radiant exitance.
# Even if the formula for spectral radiance is used, PI is usually not omitted but rather balanced by a second PI in the denominator. The reason is that 2 * PI * h * c^2 is the first radiation constant  (c1), which is usually left untouched. (h * c / k is the second radiation constant, so the formula can be expressed more easily using c1 and c2.)
# The funny point is that for the context of this article, PI or no PI doesn’t matter at all, because the whole 2 * h * c^2 (= c1) constant is irrelevant for the calculation and might as well be omitted. While this constant obviously influences the absolute values of XYZ, XYZ is always normalized at the end (to Y = 1, or by converting to xy, as in this article), so the absolute values don’t matter. So to avoid this confusion, it would be best to simply omit 2 * h * c^2 (with or without PI …) from the formula.
Is someone currently maintaining this article? If so, s/he might want to edit it accordingly. If not, I could do it myself, but since English isn’t my mother tongue, I would prefer a native speaker to do this. --Uli Zappe (talk) 06:11, 18 September 2014 (UTC)
replies: text: Since nobody seemed to care, I have updated the article myself. Please correct any English deficiencies I might have introduced. Uli Zappe (talk) 06:29, 12 February 2015 (UTC)
thread_title:  The seemingly endless PI – no-PI debate