The ciesky function calculates the corresponding luminance distribution for a Tregenza hemisphere with 145 patches according to the CIE procedure described in ISO 15469. The resulting luminance distribution is relative to the zenith patch, but the function allows absolute values for horizontal illuminance E_{\text{h}} or zenith luminance L_{\text{Z}}.

L = ciesky(type,sunaz,sunel,'target',value,'mode',value)


LReturns the luminance distribution of a Tregenza hemisphere, column-wise for multiple sky type input.
typeDefines the CIE sky type 1 – 16. Multiple sky types can be submitted as vector.
sunazIs the sun azimuth angle in ° (0 – 360). The azimuth angle starts in north position and goes clockwise.
sunelIs the sun eleavation angle in ° (0–90).
'target'Specifies the target unit (optional)
’Lz’ for zenith luminance
’Eh’ for horizontal illuminance
target valueAbsolute value of specified target: horizontal illuminance E_{\text{h}} or zenith luminance L_{\text{Z}}
'mode'Enables to specifies the luminance determination mode. (optional)
mode value’center’ for luminance detmerination for the patch center
’mean’ for mean luminance of the 4 patchcorner luminances as suggested by


Relative luminance distribution for CIE clear sky type 12 at sun position \alpha = 160° and \gamma = 30°:

L = ciesky(12,160,30);

See also: plottregenza


Absolute luminance distribution for CIE overcast sky type 1 at sun position \alpha = 210° and \gamma = 40° with a zenith luminance of L_{\text{Z}} = 10000~\text{cd}\,\text{m}^{-2} and Trgenza patch numbers:

L = ciesky(1,210,40,'Lz',10000);
p = 1:145;
plottregenza([p' L],'clr','L in cd m^{-2}')

See also: plottregenza


Absolute luminance distribution for CIE intermediate sky type 7 at sun position \alpha = 180° and \gamma = 20° with a resulting horizontal illuminance of E_{\text{h}} = 50000~\text{lx}:

L = ciesky(7,180,20,'Eh',50000);
plotskydirecto(L,'clr','L in cd m^{-2}')
% Test E_h
Eh = polardataE(L)

See also: plotskydirecto, polardata


Eh = 5.0000e+04

Absolute radiance distribution for given uniform Correlated Colour Temperature (CCT) T_{\text{cp}} = 6500~\text{K} and resulting horizontal illuminance of E_{\text{h}} = 10000~\text{lx}:

% calculate relative luminance sky distribution:
% CIE sky type 5
L = ciesky(5,180,60,'Eh',10000);

% Judd CCT to spectrum calculation for Tcp = 6500 K
[spec,lam] = ciecct2spec(6500);

% repeat CCT spectrum 145 times
spec = repmat(spec,145,1);

% calculate luminance of CCT spectrum
Y = ciespec2Y(lam,spec);

% weight radiance distribution correctly
spec = spec.*L./Y

% test Eh = 10000
Eh = polardataE(ciespec2Y(lam,spec))

See also: ciecct2spec, ciespec2Y, polardataE, specsky


spec =

0.0000 0.0014 0.0028 ...
0.0000 0.0014 0.0028 ...
0.0000 0.0014 0.0028 ...
0.0000 0.0014 0.0028 ...
0.0000 0.0014 0.0028 ...
Eh =


ISO 15469:2004(E)/CIE S 011/E:2003: Spatial Distribution of Daylight - CIE Standard General Sky. Commission Internationale de l'Éclairage (CIE), Vienna Austria, 2004.

Peter Roy Tregenza: Subdivision of the sky hemisphere for luminance measurements. In: Lighting Research and Technology, vol. 19, no. 1, pp. 13-14, 1987, (DOI: 10.1177/096032718701900103).

Leave a comment

* I accept the use of cookies as well as the terms in the privacy policy. I accept that data provided by me is processed and saved. I know that comments are saved and published after review.