Luminaire vs. Fixture: What's the difference?Michael A. Heinsdorf, P.E., LEED APMasterSpec Engineering Specification WriterOn the drawings, it is referred to as the "Lighting Fixture Schedule." The Illuminating Engineers Society (IES) uses luminaire. Congress uses fixture. And it's not uncommon to hear someone use lamp when pointing out a source of light. Which term is correct when referencing a lighting unit?