It’s common knowledge that the incandescent bulb does not last as long as the CFL bulb, which in turn, does not last as long as the LED bulb. But did you know that LED lifetime is judged by a different set of criteria to what we are accustomed?

Incandescent and CFL bulb manufacturers base bulb lifetime on the death (failure) of the bulb. Incandescent bulbs fail after 1000 hours of use while CFLs fail around 20,000* hours of use.

LED lamps don’t burn out in the same fashion as other technologies. Instead, they fade out over time. As such, the LED lighting industry chose to find more appropriate criteria in which to measure LED lifetimes. After much analysis, lighting engineers concluded that only when an LED bulb emits around 70% of its original brightness do people start noticing a difference in light output. Accordingly, LED manufacturers base bulb lifetime on the period in which the bulb fades to 70% of its original brightness, which is usually between 40,000-50,000 hours.

Why is this distinction among different lighting technologies important?  When calculating your return on investment—which we highly recommend prior to switching lighting technologies (see our Leapfrog Lighting Savings Calculator)—bulb lifetime is a necessary input. You need to have accurate figures. You also need to take into account the application/location of the bulbs you want to replace.

For example, if replacing your porch light, on a hanging fixture, which is exposed to colder temperatures, you should use a much lower lifetime if installing a CFL (A CFL’s power supply heats up when installed upside down). Or if replacing your dimmable dining room light, you should use a much higher lifetime if installing an LED—which can be scaled back to ~10% of its full output.

And remember, once an LED’s lifetime is reached you won’t be sitting in the dark, on an extremely time-sensitive mission to locate a replacement bulb. You’ll still have 70% of the light—and lots of time—to find a suitable, well-investigated, replacement.

“That bulb died fast!”

Have you ever had a bulb fail much sooner than expected? Tell us your story in the comments below.

*It is important to note that unlike LEDs, CFL bulbs are highly affected by environmental conditions (such as cold temperatures) and on/off power cycling. For the latter, it has been determined that turning off a CFL bulb powered on for less than 15 minutes significantly affects the lifetime of the bulb. As such, CFL bulbs installed in bathrooms or hallways—or any other space that is occupied for less than 15 minutes—will always fall short of the manufacturer’s stated claim. For a more complete comparison of CFLs and LEDs, see 5 reasons why LED lamps are better than CFLs.

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