# 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.

Copyright ImagEval Consultants, LLC, 2010.

## Contents

```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');
```

## 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)

```vcNewGraphWin;
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);

vcNewGraphWin;
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.
vcNewGraphWin;
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]';
vcNewGraphWin;
plot(wave,dayBasis*wgts)
grid on; xlabel('Wavelength'); ylabel('Energy (relative)');
``` 