1) The document discusses the importance of considering both luminaire efficiency and application efficiency when designing lighting. While saving energy is important, overemphasizing luminaire efficiency alone can result in glare or gloomy spaces.
2) Application efficiency is determined by factors like adequate light levels, uniform illumination, visual comfort, and accurate color rendition. It employs metrics like footcandles, luminaire spacing, and candela measurements.
3) The most appropriate efficiency metric is lighting power density, which establishes an energy budget based on watts per square foot and allows achieving design goals with lower energy use. Considering both luminaire and application efficiency leads to well-lit spaces that satisfy needs and minimize consumption.