How long do LED lights last?

You may have become drawn to LED strip lights because of their long lifetime claims. But how long do they actually last? How is lifetime defined?

LED lifetime and the 70% rule (L70)

Unlike incandescent bulbs which burn out and fluorescent lamps which begin to flicker, LEDs behave differently in that over time, they slowly and gradually lose their light output. Therefore, barring any "catastrophic" failures caused by things like power surges or mechanical damage, you can expect the LEDs on your LED strips to be usable until they are considered too dim for use.

But how dim is "too dim for use"? The industry has somewhat arbitrarily decided that 30% light loss, or 70% of light remaining, should be that line in the sand. This is commonly called the L70 metric, and is defined as the number of hours it would take for an LED to diminish to only 70% of the original light output.

How is L70 calculated?

There are many factors that influence LED longevity such as materials selection, durability & quality. The general rule, however, is that higher temperatures and higher drive currents both lead to faster light output decline.

Because materials selection can vary widely among LED types and manufacturers, a test methodology called LM-80 was developed to dictate the primary standard for light longevity tests. LM-80 prescribes testing of sample specimens at predetermined temperatures and drive currents, with changes in light output measured in 1000 hour intervals, up to 10,000 hours.

The difficulty with LED longevity testing is that it takes a long time. Even if the LEDs are illuminated 24/7, a 10,000 hour test requires 14 months or so. Testing a product to the full 50,000 hour claim would, in turn, require nearly 6 years of continuous testing.

As a result, an extrapolation algorithm called TM-21 was developed. The algorithm takes in the performance of the LM80 samples over the first several thousand hours and spits out an estimated lifetime number. This is the number that is typically reported on specification sheets and warranties.