The Illuminating Engineering Society’s Recommended Practice 16 Nomenclature and Definitions for Illuminating Engineering (aka RP-16) has long been one of the two reference sources for the definition of lighting related words and phrases – the other being the CIE International Lighting Vocabulary (ILV).
As part of the IES converting all of their publications to an online library format, some publications have been given a new designation. RP-16 is now Lighting Science 1 (LS-1) and is at this link. Bookmark it now!