Figure 1 | Working scheme of active beam-shaping OLEDs. a) Two stacked OLED units, electrically connected for AC operation. b) Experimental setup for analysis of the brightness distribution on a planar, two-dimensional surface. The OLED and the screen have to be parallel to each other. The evaluation of the brightness is done in the vertical direction as indicated by the dotted line. c) Using PWM, different AC-signals can be applied to the device resulting in either a ring shaped beam (left), broad homogeneous illumination (centre) or a focused spot (right). d) Respective irradiance as a function of the viewing angle for the conditions shown in c), measured using a spectro-goniometer. diffractive gratings to achieve a very directional emission, 8 or by reducing the size of OLED pixels such that, when combined with microlens arrays, their output resembles that of a point source. 9 What all of the above concepts have in common is the fact that only one final light distribution is realized, which is defined by the optical interplay between light source and secondary optical elements. To circumvent this limitation, mechanically tuneable elements are necessary and result in a setup 2 OLED Evaluation line S cree n Sample holder Glass Electrode 1 OLED 1 OLED 2 Electrode 2 Electrode 3 ~ V a b Sideward emission Customized waveform Forward emission c 1.0 2.0 3.0 0° 30° 60° 30° 60° 0.2 0.6 1.0 Lambertian 0° 30° 60° 30° 60° d t V PWM Lambertian 0.2 0.6 1.0 Lambertian 0° 30° 60° 30° 60° ITO ( ) transparent ( ) opaque ( )