Figure 5 | Adding secondary optical elements to active beam-shaping OLEDs. a) The normalized brightness distribution along the evaluation line for forward (left) and sideward (right) emission are shown with and without additional optical elements placed on top of the OLED. The images on the projection screen obtained with a half sphere b) and prism c), respectively. Using the above transformation, the beam shape can be predicted if the spectral information is provided either by simulation or the goniometer measurement, which is of great importance for further optimization. Using CIE2006 colour matching func- tions and a subsequent linear transformation to RGB-colour space, a displayable picture of the beam’s shape is achieved. 33, 34 In Fig. 4c a calculated image is compared to a photograph. Both the brightness distribution and the colour are well repro- duced. To prove the reliable reproduction of colours, OLEDs were build that emit green in the centre of the spot and red to the sides (cf. Fig. 4d). The brightness-colour distribution is still well reproduced. Further information on this transformation is given in the Supplementary Information (cf. Fig. S5 and S6). There remains an influence on the shape of the beam that has not yet been discussed. In the considerations above, the OLED has been treated as a point source. This gives rise to question the limits in which this assumption is right. There are two general ways to investigate this behaviour: either the size of the OLED or its distance to the screen must be varied. In the following discussion, the ratio of the size of the pixel l$_{dia}$ and the distance d$_{scr}$ will be analysed, wherein the size denotes the length of the diagonal of the square pixel. This ratio will be referred to as the relative size S$_{rel}$ = l$_{dia}$ / d$_{scr}$ . For large values of S$_{rel}$ , rays emitted under various angles at different points of the source will hit the screen on the same spot, blurring the contrast. Experiments are carried out with beam-shaping OLEDs of l$_{dia}$ = 28 mm pixel size. Using shadow-masks, the pixel size could be varied stepwise at a constant distance to the screen of 105 mm. As expected, the resulting contrast increases with decreasing relative size, as shown in black in Fig. 4b. More surprising is the result for a constant pixel size of l$_{dia}$ = 24 mm. For relative sizes larger than 0.3 the values add nicely to the ones in black, but around 0.3 the curve is 8 Normalized brightness Angle [°] -80 -40 0 40 80 0 1 1 Normalized brightness Angle [°] -80 -40 0 40 80 0 a b c Referen ce Half-sph ere Prism x x y Half-sphere Prism y