Test reports arrive with LM-79, LM-80 and TM-21 often bundled together, but the three describe different things. Read as one document, they get confusing.
LM-79 measures the luminaire: luminous flux, efficacy, CCT, CRI, chromaticity, light distribution. It runs on an integrating sphere or goniophotometer, takes one measurement, and needs no long ageing. From an LM-79 you learn how bright and what colour the fixture is at the factory gate.
LM-80 measures the LED package's lumen maintenance. A batch of packages runs in a temperature chamber at a specified case temperature for 6,000 hours or more, with output logged at intervals. The report states the case temperature, commonly 55°C and 85°C.
TM-21 is not a test. It extrapolates from LM-80 data, and the standard allows extrapolation to at most six times the test duration. A 6,000-hour LM-80 therefore supports 36,000 hours. Products claiming 50,000 hours on a 6,000-hour LM-80 have exceeded the maths.
This is where the three most often break: the LM-80 case temperature does not match how your fixture actually runs.
Concretely, the report was run at 55°C, and your luminaire has ordinary thermal design with the die sitting at 95°C. Degradation rises exponentially with temperature, so 55°C data does not transfer to 95°C. Judging that requires a fourth document: ISTMT, the in-situ temperature measurement test, which records solder-point temperatures of the LED and driver in the assembled fixture.
So the complete chain is: LM-79 for out-of-box performance, ISTMT for real operating temperature, LM-80 for maintenance at that temperature, TM-21 to extrapolate to a lifetime claim. With all four aligned, a lifetime figure stands up.
One more detail: an LM-80 report must name the die and the packaging house it tested. A report that does not match the materials in the product is the most common substitution.
The purchasing routine is short. Read the model and case temperature on the cover, then look for the ISTMT. If one is missing, ask. A factory that cannot state the case temperature is usually handing over someone else's report.