Lumen Depreciation

As LED technology continues to evolve, so too grows the efficiency and lifespans of LED lamps. Because LEDs have such long lives (estimated at 35,000 to 100,000 hours), it’s rather challenging to measure precisely how long they really do last — few groups have the patience or resources to measure an LED in various environments for 5 or more years. However, the National Institute of Standards and Technology (NIST) is currently working on such a project.

Without a predictable failure point, manufacturers decided to define LED life as the amount of time it takes for the light to fade to a certain percentage of its original strength. “Lumen depreciation is widely understood in the lighting community and is not unique to LEDs. But it doesn’t come into play when you have a light source that only lasts hundreds or thousands of hours, as with incandescents. On average, incandescents fail before the eye notices a difference in their output,” says Philips Marketing Communications Director Steve Landau.

People in an average office setting can’t tell there is a change in illumination until a lamp has dropped 30% in output. So it is not objectionable to wait until the LED is at 70% of its original spec before you replace the lamp.

This designation is represented by the letter ‘L’ followed by a set of numbers such as:

L70 = time to 70% of original light output. There are other ratings, but this is the most common rating and is universally accepted as the standard to measuring LED life.

For colored accent and exterior lighting, the lumen acceptable lumen drop-off threshold is often considered to be 50%.

Still, even these numbers are highly variable depending on how and where the LED was operated. Things that may influence the LED’s life are line current, ambient temperature, the type of luminaire and the quality of the material used. These differences make defining a LED’s service life even more challenging, since the lamp’s environment can drastically influence its lifespan.

Simply, we can’t determine the service life of an LED without considering its housing and application. This is the major reason why the NIST is conducting their LED study. They are monitoring LEDs in various scenarios with the goal of uncovering a reliable method of projecting how long LEDs will last.

HOW LONG is 100,000 HOURS?

bulbsWhether you believe 100,000 hours is realistic or not, I’ve included a chart to make understanding the life of a 100,000 hour rated bulb easier.

Hours of Operation:  100,000 hours is:
24 hours a day                11.4 years
18 hours per day             14.8 years
12 hours per day             22.8 years
8 hours per day               34.2 years


Although the lighting industry is still learning about the efficiency of LEDs, what we currently know holds real promise for major energy savings in the future. And while the LED bulb you pick off the store shelf may not entirely live up to its 100,000 hour rating, it will certainly outperform most traditional bulbs.

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