Abstract: We present a study of a tangible user interface (TUI) for architectural design and daylighting analysis. This tool provides an intuitive way for architects and future building occupants to quickly construct physical models and then view a simulation of daylighting in the model at interactive rates. We conducted a user study of both formally-trained architects and non-architects in a set of analysis and design exercises. This study investigates the effectiveness of this interface as an educational tool, the precision and accuracy of the constructed physical models, and the overall effectiveness of the tangible interface. The four part study investigates users' intuitions about daylighting and their interaction with the tool for analysis of an existing space, for proposing renovations to the space, and for designing a totally new space with the same architectural program that better addresses the occupants' needs. These exercises revealed misconceptions in many of the participants' intuitions about day-lighting and overall the participants expressed interest in this simulation tool for daylighting analysis in architectural design.

Architectural daylighting design is the use of windows and reflective surfaces to make effective use of natural light from the sun and sky within a physical environment. Increased use of daylighting can reduce the need for supplemental electric lighting during the day, decreasing operating costs and reducing the consumption of non-renewable resources.

The daylighting analysis system simulates the complex inter-reflection of natural light within a scene and uses a set of six standard office projectors surrounding the table to "paint" the physical primitives with the simulation results. Designing in the tabletop system is done by sketching with physical wall primitives to create a closed space with window primitives that are placed over the top edge of the walls. A calibrated overhead camera captures the arrangement of these elements and the geometry is converted into a closed triangle mesh. Radiosity, a patch-based lighting method, is used to simulate light propagation within the space and the rendering system displays the simulated natural lighting on the physical model using six projectors positioned in a circle above the table.