of the assumptions made are not completely fulfilled. For example, in Fig. 4b) it can be seen, that the sample may not be treated as a point source. Nevertheless, accepting this factor two, the profiles of the measurements are highly comparable. With this information the expected beam shape on a screen can be calculated from the spectro-goniometer data or even from simulation data, which opens further possibilities for sample optimization. The first step to be done is to transform the spectra. In Fig. 11, this is shown for the experimental data. Of course, this transformation leads to an enhancement of low-angle parts, shifting the maximum to a lower angle. Subsequently, the CIE-XYZ coordinates are calculated for each angle, using the CIE2006 colour-matching functions. 3 Figure 10 | Brightness profiles under different conditions. The black lines show the brightness distribution on the screen. The abrupt drop around -60 ◦ in side emission is caused by the shadow of the sample holder. Red lines with white dots show the irradiance measured at the spectro-goniometer. Applying a transformation factor cos $^{2}$( θ ) on the latter, both measurements coincide as shown in red lines with solid dots. Figure 11 | Spectral transformation. Applying the azimuthal transformation on the spectral radiant intensity, the contrast between 0 ◦ and maximum emission gets reduced. 6 Viewing angle [°] Forward Side Norm. brightness / irradiance Viewing angle [°] Norm. brightness / irradiance − 0.2 0 0.2 0.4 0.6 0.8 1 1.2 − 80 − 60 − 40 − 20 0 20 40 60 80 − 0.2 0 0.2 0.4 0.6 0.8 1 1.2 − 80 − 60 − 40 − 20 0 20 40 60 80 0 10 20 30 40 50 60 70 80 Angle [°] 500 600 550 650 700 750 Wavelength [nm] 0 0.2 0.4 0.6 0.8 1 0 10 20 30 40 50 60 70 80 Angle [°] cos²( ) Norm. SRI