This document recommends a method for projecting the lumen maintenance of LED light sources from the data obtained by the procedures found in IES document LM-80-08 Approved Method for Measuring Lumen Maintenance of LED Light Sources.

LED light sources provide a very long usable life but light output gradually depreciates over time. TM-21-11 provides the method for determining when the “useful lifetime” of an LED is reached, a point when the light emitted from an LED depreciates to a level where it is no longer considered adequate for a specific application. Lumen maintenance of LEDs can vary from manufacturer to manufacturer and between different LED package types produced by a single manufacturer.

CONTENTS
Introduction
Scope
Normative References
Definitions
Test Data and Sample Size
Lumen Maintenance Life Projection
Temperature Data Interpolation
Report
Annex A Rationale for the Recommended Data Extrapolation
Annex B Sample Size Selection for Data Extrapolation
Annex C Least Squares Formula
Annex D Limit for Duration of Prediction
Annex E Data Test Set for Validation of Calculation – Examples
Annex F Consideration of Manufacturer’s Prediction Model
Annex G Analysis of Mathematical Modeling as a Method of Projecting Lumen Maintenance Life
Informative References

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