LM-80 / TM-21

LM-80 is the IES method for measuring lumen maintenance of LED packages: chips are operated at controlled case temperatures and drive currents for at least 6,000 hours while output is tracked. TM-21 is the companion calculation that extrapolates those measurements into lifetime projections — producing the L70/L80/L90 figures quoted on datasheets, capped at six times the tested duration. Together they replace guesswork with a defined engineering chain: chip data (LM-80) plus the fixture’s real in-situ temperature yields a defensible L70 claim. When a supplier quotes 50,000-hour life, the follow-up question is whether LM-80/TM-21 documentation at a realistic operating temperature stands behind it.