Light Monitoring System for the Lead Tungstate Calorimeter in Hall D at Jefferson Lab

A new electromagnetic calorimeter composed of 1596 lead tungstate (PbWO${}_4$) scintillating crystals has been constructed for the GlueX detector in Hall D at Jefferson Lab. The calorimeter is equipped with a light monitoring system that uses light-emitting diodes. The light monitoring system was fabricated, installed, and integrated into the GlueX trigger system. It was successfully operated during detector commissioning and data collection. The paper describes the design, installation, and performance of the light monitoring system.