Daylighting has always been an integral component of The Weidt Group’s energy and sustainable design assistance, which it has been providing to architects and engineers for nearly three decades. Our holistic design approach involves optimizing both daylighting and energy performance to achieve sustainable goals. Our tools of daylighting and sun penetration analysis have evolved over time- from physical models to present day computer simulations. Some of the programs we have used are Lumen Micro, Lumen Designer, Lightscape, DOE-2, custom-made spreadsheet calculations and Radiance. The addition of Radiance to our palette of available tools has enabled us to do more detailed and accurate daylighting analyses. Our daylighting analyses vary according to the projects’ design goals. While a swimming pool project might require high quality renderings to analyze glare and reflections, other projects like offices and educational facilities might require illuminance analysis on the work-plane to optimize window design. Radiance is also used for solving glare problems in existing buildings. Our custom spreadsheet tools are used more effectively for sun-penetration analysis and during design charrettes, where time is critical. A majority of the work at The Weidt Group is focused on whole building energy analysis using the hourly energy simulation program DOE-2. Similar to DOE-2 modeling, we have developed a custom spreadsheet-based interface for Radiance simulations as well. The interface is used for running parametric options in Radiance. We have also developed similar spreadsheet-based tools for analyzing sun-penetration and daylight factor for simple geometries. Our continuing research helps us constantly update these tools with new features. As we continue to explore daylighting in architecture, Radiance not only offers us cutting edge tools to expand the realms of simulation, but helps us achieve our sustainability goals.