The output of two lamps made based on the same LED device may differ significantly after five years. The difference is almost never in the chip itself, but in the rate at which heat is expelled from the chip-which is determined by the shell structure, not the heading number on the parameter sheet.

As the junction temperature increases, the output decreases, and the effective life also decreases. The industry uses the term "light flux maintenance rate" to express this: a value like L70 represents the point at which the output has decayed to 70% of the initial value. No one can wait 50,000 hours to measure it, so this number is derived. LM-80 is a standard method for running LED devices at a specified shell temperature (usually three temperature points, typically 55, 85, and 105 °C) and recording thousands of hours of output;TM-21 specifies how to extrapolate these measured values over a longer period of time, how far the extrapolation can go, and how confidence can decrease after exceeding them.

With this background, let's look at the longevity statement. The phrase "50,000 hours L70" is only meaningful when given together with the shell temperature on which it is based, because the same device can easily exceed this number at 55 °C, but may not reach it at 105 °C. Please request the LM-80 report and TM-21 extrapolation results, and compare the test temperature with the actual ambient temperature of the lamp.

Heat leaves the device along a fixed path-chip, solder, thermal pads, substrates, thermally conductive interface materials, heat sinks, air-and every junction along the chain can be a bottleneck. The most common problem on site is not that the LEDs fail, but that the radiators in workshops with fiber or flour in the air are stuck with dust; this is both a maintenance issue and a design issue.