frudawski

ciesky

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)

Where:

Examples

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

L = ciesky(12,160,30);
plottregenza(L)

Result:

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}')

Result:

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)

Result:

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);

spec = spec.*L./Y

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

Result:

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 =
1.0000e+04

References

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).