Understanding LED component and system lifetime

LED components

LEDs are not likely to fail and burn out like traditional light sources. LEDs gradually decrease over time until they no longer produce useful light. End of life for an LED is the first time the fixture requires maintenance, which would likely be due to a noticeable decrease in light output or a driver failure, resulting in a lack of light output. Understanding L70 and LM-80 can help you evaluate LED fixtures.

Projecting LED life

L70 Rating

By industry standards, an LED light source is considered end of life when it loses 30% of its light, or what is known as the L70 rating. The L70 rating is calculated with data provided by an LED component manufacturer’s LM-80 report and extrapolated using an industry accepted TM-21 calculator.

LM-80 standard

LM-80 refers to a method for measuring the lumen depreciation of solid‐state light sources, such as LED packages, modules, and arrays. When an LED is manufactured, it must be entered into a series of tests at 3,000, 6,000, and 10,000 hours to measure performance at multiple temperatures and amperages.

After LM-80 testing is complete, the luminaire manufacturer can use it to generate a TM-21 report, which provides LED life projections in a luminaire. The TM-21 report uses statistical analysis and LED performance info, defined by the LM-80.

After the LED has been selected for the light fixture, its performance is measured to validate light output, LED junction temperature, and case temperature. The LM-80 data is used with this additional data to define the L70 rating of the LED.

Fixture lifetime

A common misconception when considering fixture life is only accounting for the L70 rating. More often than not, the point of failure is the driver. Driver life is estimated using MTBF or accelerated thermal test data at elevated ambient temperatures which are then extrapolated using Bellcore or Milspec standards.

Fixture lifetime must take into account the lifetimes of both the LEDs and the driver. System construction, along with ambient temperature, figure heavily into fixture lifetime.

Projecting fixture/system life

Rated Life

Defined as the maintenance-free life of an LED fixture under worst-case operating conditions (fixture is always on, with a constant temperature environment typically at 55ºC).

Economic life

The period of operation before fixture failure.

The biggest variable between rated and economic life is temperature, with rated life at a worst-case temperature, versus economic life where temperature will vary according to the actual installation.

The economic life of LED luminaires can be substantial. For example, at an ambient temperature of 40ºC, the economic life of a Crouse-Hinds series LED fixture could be as long as 100,000 hours. At 25ºC, the economic life would increase to 170,000 hours.

Economic life is an important concept when defining the total cost of ownership of an LED light luminaire. The figure below illustrates the relationship between economic and rated life.

This LED Lighting Design and Specification Guide details key factors to consider when selecting a manufacturer for industrial lighting, and demonstrates how Eaton’s Crouse-Hinds series LED solutions are built to withstand the toughest conditions, deliver maximum lighting performance and safety, and reduce expensive maintenance costs.

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