Designing spaces that are able to balance illumination, glare and solar gains over a year is a real challenge, yet a problem faced every day by building designers. To assist them, a full year, climate-based daylighting simulation method, called Lightsolve, was developed, providing guided search based on the variation of daylight performance over the year by combining temporal performance visualization with spatial renderings. This paper focuses on the user’s perspective for Lightsolve. After a summary of its foundational concepts, it discusses the results of several pilot and more formal user studies conducted in educational contexts. As a core element of the paper, the method and results of an original, design-oriented user study on Lightsolve’s expert system are discussed. It was conducted to determine how well its decision-making algorithm would work when independent human interactions were included. It demonstrated that the expert system is generally successful as a performance-driven design tool respectful of the non-deterministic nature of the design process itself, and as a method for educating designers to improve daylighting performance.