IEC PAS 63421:2022(E) This Book 18 defines a standardized interface between a LED Luminaire and a sensing/communication module (Luminaire Extension Module, LEX-M) that can be attached to the Luminaire. The interface is intended to be used in outdoor applications with high IP rating. The LEX-M may provide for example sensory inputs to the Luminaire or communication between the Luminaire and a network. This Book 1 defines the common concepts that underlie the Zhaga interface specifications. In addition, this Book 1 specifies general requirements for Zhaga compliant components of LED Luminaires.