Photonic crystals (PhCs) have attracted much attention during the last decade as a solution to overcome the low extraction efficiency of as-grown light-emitting diodes (LEDs). In this review we describe the underlying physics and summarize recent results obtained with PhC LEDs. Here, the main focus is on diffracting PhC. In order to quantify the benefit from the incorporation of PhCs for diffracting light a comparison by simulations between a PhC LED and a standard state-of-the-art LED is carried out. Finally, the impact of the PhC on the LEDs emission characteristics will be discussed with respect to étendue-limited applications.