Abstract: We present a new method for procedurally generating window lighting and building interior effects for real-time rendering of city scenes. Our method can selectively light a random subset of windows on the building with varying color and brightness. This window light can be combined with cube maps of representative building interior (i.e. interior maps) to generate rich details at different scales in large-scale city rendering. Our method relies solely on window transparency cutout (alpha) layer and a simple texture parameterization scheme in the building models and requires no additional information to be stored per building. The algorithm can be implemented completely in a fragment shader function, which makes it suitable for integration into existing render engines. The percentage of window lighting can be adjusted smoothly using a single parameter. We demonstrate our method using a large-scale 3D city data set, running with interactive frame rates on both PC and mobile platforms.