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ciespec2cct

The ciespec2cct function derives the Correlated Colour Temperature (CCT) T_{cp} for a given spectral power distribution (SPD) as in CIE 15:2018. Any errors in the data set or in results generated with the Lighting Toolbox are not in the liability of the CIE nor me, see licence.

Usage:

[Tcp,x,y,u,v] = ciespec2cct(lam,spec,method)

Where:

ParameterDescription
TcpReturns the Correlated Colour Temperature: Tcp
x and yAre the CIE 1931 x and y chromaticity coordinates.
u and vAre the CIE 1960 u and v chromaticity coordinates.
lamDefines the wavelengths, vector.
specDefines the spectral power distributoin (SPD), vector or matrix.
method
(optional)
Specifies the determination method:
‘Robertson’: (default) Robertson’s calculation algorithm, formerly the only recommended algorithm by the CIE. This method is fast and quite accurate.
‘exact’: shortest distance method as described in CIE 15:2018, very accurate but comparably slow. Results may vary with different implementation methods.

Both methods return NaN if the colour coordinates lie outside the meaningful interval of \Delta uv < 0.05 from the planckian locus in CIE 1960 chromaticity diagram.

Examples

Derive Correlated Colour Temperature (CCT) of standard illuminant ‘A’:

lam = 380:780;
spec = ciespec(lam,'A');
Tcp = ciespec2cct(lam,spec)

Result:

Tcp = 2856.0

Derive Correlated Colour Temperature (CCT) of standard illuminants ‘D65’ and ‘D50’ and the corresponding chromaticity coordinates:

lam = 380:780;
spec = ciespec(lam,{'D65','D50'});
[Tcp,x,y,u,v] = ciespec2cct(lam,spec)

Result:

Tcp =

   6501
   4999

x =

   0.3127
   0.3458

y =

   0.3291
   0.3586

u =

   0.3127
   0.3458

v =

   0.3291
   0.3586

Reference

CIE 15:2018: Colorimetry, 4th Edition. Commission International de l’Éclairage (CIE), Vienna Austria, 2018, ISBN: 978-3-902842-13-8 , (DOI: 10.25039/TR.015.2018).

A. R. Robertson: Computation of Correlated Color Temperature and Distribution Temperature. In: Journal of the Optical Society of America, vol. 58, no. 11, pp. 1528-1535, 1968, (DOI: 10.1364/JOSA.58.001528).

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