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<img src='content_image/311790.jpg'>

If the screen is at a distance R ′ ̸ = R from the OLED, equation (2) contains an additional factor ( R $^{′}$/ R ) $^{2}$. However, by normalizing the spectra, this factor cancels again. It is worth mentioning that the surface element in spherical coordinates is not of constant size, but dependent on the azimuthal angle θ . Yet, the spectrometer comprises a constant aperture. This situation can be modelled by cylindrical coordinates. In this case the transformation factor becomes 1 / cos $^{2}$θ . However, projecting the respective surface element on a two dimensional plane does not give a filled surface. Hence, the true transformation should lie between those two models. This transformation points out the importance that the integrated radiant intensity for sideward emission has to be strongly enhanced (here, a factor 2.7 to normal emission, cf. Fig. 1d). Otherwise a hollow image, as shown in Fig. 1c for the sideward emission, cannot be realized. 

