In the lighting industry, probably no number is cited more or understood less than "50,000 hours". It's neither a warranty commitment nor an expiration date, but an estimate-figuring out what's behind it will change the way you select models.

Here's how the chain works: LM-80 is a test standard that runs a batch of LED packages at controlled temperatures for a specified period of time and measures light output at intervals;TM-21 extrapolates from these measurements to a longer life method. The results are expressed in L70 or L90-the point at which the light output is expected to drop to 70% or 90% of the initial value, and the corresponding ambient temperature is usually noted.

There are three places where purchasers can easily step on. First, temperature is critical: estimates at a shell temperature of 55°C are not the same promise as estimates at 85°C, and outdoor equipment is often hotter than in the laboratory. Second, this number describes the LED package, not the finished lamp-it is usually driver durability, thermal design and sealing performance that determine when a lamp is replaced. Third, L90 is a stricter requirement than L70, and the numbers given are generally shorter.

When comparing specifications, please make similar comparisons: same standard, same temperature, and same threshold. If a number completely lacks these prerequisites, treat it as marketing words rather than engineering data.