Scope and starting point
Start with the symptom, history and safe isolation, not live rewiring. Record whether the failure changes with temperature, dimming, supply variation or a replacement load. Mains equipment and UV sources require qualified handling. Preserve failed samples; changing several variables at once destroys useful evidence.
Selection notes
Use heat dissipation, not optical output, in the thermal budget. Include junction-to-case, interface and sink-to-ambient paths. Heat-sink resistance depends on orientation, airflow and test conditions; do not transfer one catalog number to an enclosed assembly without validation.
Keep a reproducible record
Save the complete part number, source revision, operating point and the reason for each decision. Keep calculated examples separate from observed results. A measurement report needs its sample identifier, instrument and calibration details, stabilization, ambient conditions, raw record and uncertainty statement. Do not replace a missing value with zero or a typical value with a guaranteed limit.