In the file espd_cie_standard.inc, the correlated color temperatures of 
illuminants B, C, and F9 are given as 5860 K, 6769 K, and 6150 K, 
respectively, in the comments.  As far as I can determine, those values 
should be 4874 K, 6774 K, and 4150 K.

Being only in the comments, these errors do not affect the operation of 
Lightsys IV.

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El 20/05/16 a las 02:46, Cousin Ricky escribió:
> In the file espd_cie_standard.inc, the correlated color temperatures
> of illuminants B, C, and F9 are given as 5860 K, 6769 K, and 6150 K,
>  respectively, in the comments.  As far as I can determine, those
> values should be 4874 K, 6774 K, and 4150 K.
>
> Being only in the comments, these errors do not affect the operation
> of Lightsys IV.

   Yes, that seems to be the case... I've corrected those comments for
future versions (not worthy pushing a new release now just for that).

--
jaime

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Am 5/20/2016 um 2:46 schrieb Cousin Ricky:
> In the file espd_cie_standard.inc, the correlated color temperatures of
> illuminants B, C, and F9 are given as 5860 K, 6769 K, and 6150 K,
> respectively, in the comments.  As far as I can determine, those values
> should be 4874 K, 6774 K, and 4150 K.
>
> Being only in the comments, these errors do not affect the operation of
> Lightsys IV.

Just seen this post and you are right - almost. 6150K seems to be an 
unspotted typo and 5860K is plain wrong.
So, to be sure and in case there is a color scientist reading this, I've 
recalculated the values using the method of A. R. Robertson as described 
in "Color Science: Concepts and Methods, Quantitative Data and Formulae" 
by G. Wyszecki and W. S. Stiles.
The result:
illuminant B: 4871 K
illuminant C: 6774 K

So you are close with B and perfect with C in whatever way you've 
determined it and thanks for spotting the errors.

P.S. @Jaime: in case you are updating lightsys, please use these values 
and change it also within your version of CIE.inc where the values are 
4882K and 6769K - the result of some lazy way I've used at this time to 
calculate it.

-Ive

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Ive <ive### [at] lilysoftorg> wrote:
> So you are close with B and perfect with C in whatever way you've
> determined it and thanks for spotting the errors.

Various sources on the Web, but I haven't got behind any pay walls.

Your old C is very close to the new one, and your new B is close to what I found
for B.  Could this have anything to do with the refinement of the Boltzmann
constant, or would it be strictly methods of calculating the CCT?  (I'm nowhere
near where I want to be in color science.)

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Am 5/23/2016 um 18:57 schrieb Cousin Ricky:
> Ive <ive### [at] lilysoftorg> wrote:
>> So you are close with B and perfect with C in whatever way you've
>> determined it and thanks for spotting the errors.
>
> Various sources on the Web, but I haven't got behind any pay walls.
>
> Your old C is very close to the new one, and your new B is close to what I found
> for B.  Could this have anything to do with the refinement of the Boltzmann
> constant, or would it be strictly methods of calculating the CCT?  (I'm nowhere
> near where I want to be in color science.)
>
>
>
>

I'm pretty sure it is the way you are calculating it. You can do it in a 
lazy way as I usually did while I was working in the field and accuracy 
really didn't matter (which should not be an excuse for making plain 
mistakes) or you can do it in the way of Robertson who calculates the 
closest distance for a given point in the CIE XYZ color space to the 
blackbody radiation curve. But it requires inverse interpolation of the 
Blackbody temperatures and forward interpolation on a data table and 
other nasty algebra stuff. And nobody likes algebra, right? ;)

"Color Science: Concepts and Methods, Quantitative Data and Formulae"
is not behind a paywall, it is one of this old fashioned things where 
pages are still made of paper. And it is "The Bible" of color science.

http://eu.wiley.com/WileyCDA/WileyTitle/productCd-0471399183.html

Anyway I did add a POV-Ray SDL implementation of Robertson's method 
within CIE.inc. The new version can, as usual, be downloaded from my 
spectral render web page - or directly via

www.lilysoft.org/CGI/SR/LS_SpectralRender.zip

Following the tradition of CIE.inc the new macro is called XYZ2K(XYZ),
it takes a CIE XYZ coordinate as parameter and gives the color 
temperature in Kelvin back.
Here is the way it is called to calculate the B and C illuminants:


//*******************************************************************

#include "CIE.inc"

#declare XYZ_B = xyY2xyz(<Illuminant_B[0], Illuminant_B[1], 1>);
#declare XYZ_C = xyY2xyz(<Illuminant_C[0], Illuminant_C[1], 1>);

#declare KB = XYZ2K(XYZ_B);
#declare KC = XYZ2K(XYZ_C);

#warning concat("Correlated color temperature for illuminant B: 
",str(KB,4,1),"K")
#warning concat("Correlated color temperature for illuminant C: 
",str(KC,4,1),"K")


//*******************************************************************


-Ive

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Ive <ive### [at] lilysoftorg> wrote:
> Am 5/23/2016 um 18:57 schrieb Cousin Ricky:
> > Ive <ive### [at] lilysoftorg> wrote:
> >> So you are close with B and perfect with C in whatever way you've
> >> determined it and thanks for spotting the errors.
> >
> > Various sources on the Web, but I haven't got behind any pay walls.
> >
> > Your old C is very close to the new one, and your new B is close to what I found
> > for B.  Could this have anything to do with the refinement of the Boltzmann
> > constant, or would it be strictly methods of calculating the CCT?  (I'm nowhere
> > near where I want to be in color science.)
>
> I'm pretty sure it is the way you are calculating it.

I didn't calculate anything.  I just got those numbers from various sources on
the Web.

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