Rosenfeld founded a group that became the lab's Center for Building Science. Research on the miniaturization of electronic ballasts in fluorescent lamps led to the development of the first compact fluorescent lamps. The center also developed low-emissivity windows as well as computer programs for the energy analysis and design of buildings.

Though electricity demand nationwide has risen sharply in recent years, California's per capita electricity use has remained relatively flat since 1973 because of the state's strict energy-efficiency regulations. Known as the "Rosenfeld Effect," it has saved California billions of dollars annually in energy costs.