The emission pattern of organic light-emitting diodes (OLEDs) is usually close to Lambertian. This paper explores the
factors controlling the angular dependence of the emission from OLEDs. In particular it considers the question of how
far from Lambertian can the emission of an OLED be? We have examined how wavelength-scale microstructure can
modify the pattern of light emission from OLEDs. We demonstrate OLEDs in which emission is strongly directed
towards, or away from, the forward direction. We consider the relative importance of scattering of waveguide modes,
surface plasmons and microcavity effects in the strongly modified emission patterns which we observe.