This paper presents a framework for 3D knowledge-based sketching tools for lighting design and two software prototypes built to illustrate sketch-based interaction with intelligent systems in 3-D domains. Spot supports direct sunlight simulation and visualization in a selected time period and Light Pen supports placement of electric lighting designs to light an intended area in space. In both examples, a 3-D sketching front-end is coupled with a back-end knowledge-based system. This enables a designer to pose a problem by drawing onto a 3-D model to which the knowledge-based system offers a solution – in one case by providing quantitative data analysis; in the other by modifying the 3-D model. Spot and Light Pen's specific domain of architectural lighting design exemplifies a more general class of 3-D interaction with intelligent systems.