Measuring the Life of LEDs

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Measuring the Life of LEDs

Due to the long life of light emitting diodes (LEDs), there have been many questions regarding how their life is measured when compared to other types of lamps. Typically, the average LED lasts an estimated 35, 000 to 100,000 hours. LED technology is relatively new and because of this, there have been few studies which measure their lifespan in various environments. In order to properly measure the life of an LED, a lot of patience and resources are needed to do this for at least five years.

Conventional Bulb Life

We must first understand how the life of a conventional bulb is measured in order to understand how the life of an LED is measured. The term used to measure lamp life is called Average Rated Life (ARL). This refers to the length of time in which 50% of lamps in a particular test batch to fail. For example, if 200 incandescent bulbs are tested and 100 bulbs die after 900 hours, that type of bulb has an ARL of 900 hours.

Conventional lamps, such as incandescent and fluorescents, have been in use for a long time and therefore the reasons for their failure are highly predictable. With LEDs, failure does not mean the same thing. They do not have a consistent type of failure and they don’t burn out but simply become dim.

LED Bulb Life

Since there is not a predictable failure point, manufacturers decided to define the life of LEDs as the amount of time that it takes for the light to dim to a certain percentage of its original strength (also known as Lumen Depreciation). It was decided that the terms L70 and L50 would be used to signify the length of time at which a given type of LED would reach 70% and 50% of its light output, respectively.

However, the life of an LED can still vary depending on the environment in which it was used. How and where an LED is used can have a major effect on its life, as well as the housing and materials used in its design. LED performance is also temperature dependent. Over-driving an LED in high ambient temperatures may result in overheating the LED package, eventually leading to device failure. An adequate heat sink is needed to maintain long life. This is especially important in automotive, medical, and military uses where devices must operate over a wide range of temperatures, which require low failure rates. For lower temperatures, its light output rises, usually leveling off at -30° C.

Summary

Despite some uncertainties and given the right conditions, LEDs have the potential to far out last conventional lamps.

One thing that can be done to get the maximum life from LEDs is to buy products that use high quality LED chips and a quality heat sink that properly dissipates heat away from the LED. This may cost more but it will increase service life.

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