Create daylight illuminants

First, we use the daylight function to create illuminants with a range of correlated color temperatures

Second, we use the CIE daylight basis functions to create examples of daylight spectra.

See also: ieLuminanceFromPhotons, ieLuminanceFromEnergy, daylight

Create daylight spectra with different correlated color temperatures
Calculate the luminance of these SPDs
Plot the spectral power distributions (photons)
Now perform the same calculation in energy units
The CIE defined a set of daylight basis functions
Three examples of daylights built from these basis functions

ieInit;

Create daylight spectra with different correlated color temperatures

wave = 400:770;                % Wavelength in nanometers
cct = 4000:1000:10000;         % Correlated color temperature
spd = daylight(wave,cct,'photons');

Index in position 1 exceeds array bounds. Index must not exceed 31.

Error in s_sceneDaylight (line 21)
spd = daylight(wave,cct,'photons');

Calculate the luminance of these SPDs

lum = ieLuminanceFromPhotons(spd',wave(:));

% Scale the luminance to 100 cd/m^2
spd = spd*diag(100./lum);

Plot the spectral power distributions (photons)

ieNewGraphWin;
plot(wave,spd);
grid on; xlabel('Wavelength'); ylabel('Photons (q/sr/m^2/s)');

Now perform the same calculation in energy units

spd = daylight(wave,cct,'energy');

% Calculate the luminance of these SPDs
lum = ieLuminanceFromEnergy(spd',wave(:));

% Scale them to 100 cd/m2
spd = spd*diag(100./lum);

ieNewGraphWin;
plot(wave,spd);
grid on; xlabel('Wavelength'); ylabel('Energy (watts/sr/m^2/s)');

The CIE defined a set of daylight basis functions

dayBasis = ieReadSpectra('cieDaylightBasis',wave);

% Daylight spectral power distributions are weighted sums of
% these basis functions.
ieNewGraphWin;
p = plot(wave,dayBasis,'k-');
set(p,'linewidth',2);
xlabel('Wavelength'); ylabel('Energy (relative)'); grid on

Three examples of daylights built from these basis functions

% The mean, and +/1 the first coefficient.
wgts = [1 0 0 ; 1, 1, 0; 1 -1 0]';
ieNewGraphWin;
plot(wave,dayBasis*wgts)
grid on; xlabel('Wavelength'); ylabel('Energy (relative)');