In October’s article, we referred to newer fluorescent lighting technologies that make it relatively easy to comply with ANSI/ASHRAE/IESNA Standard 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings. In general, there are three areas that we look at for energy-efficient lighting — lighting system efficiency, lighting design, and lighting controls. Since so much of lighting energy efficiency is based on the lighting power density (LPD), or W/ft², we’ll start by looking at how lighting system efficiencies reduce the LPD in buildings. Future issues will explore improved lighting design and controls.