Life, Lumen Maintenance and Reliability

Light emitting diodes (LEDs) are solid state devices offering many advantages over conventional lighting sources. A primary advantage is that LEDs typically do not fail suddenly or burnout, but gradually degrade. Unlike LEDs, conventional lighting sources commonly fail catastrophically.

Predicted Life
A primary metric for judging useful life of conventional lighting sources is lamp lifetime commonly expressed as the time to failure or burnout. Life of conventional lighting sources is based on the time it takes for 50% of lamps to fail. LEDs, being semiconductors, express their failure rate using 'mean time to failure' (MTTF), a well-defined statistical term commonly used in the semiconductor industry. LED manufacturers typically predict high brightness LED MTTF to be on the order of 100,000 hours, provided LEDs are properly packaged and used in accordance with manufacturers' recommendations. These predictions apply to catastrophic failures where the device is rendered completely inoperable.

Lamina light engines are built using proprietary packaging technology which ensures an excellent thermal path from the LED junction to the outside of the light engine (where an application specific heat sink takes over). Lamina's packaging also provides an excellent thermal coefficient of expansion (TCE) match to the LED. This ensures that the bond between the LED and the package is not subject to undue stress as the entire assembly expands and contracts with heating and cooling. By minimizing both the LED junction temperature and the mechanical stress on the device, Lamina's packaging system provides the best operating environment available in the industry for ultra-high brightness LEDs.

Average Lumen Maintenance
Conventional lighting sources and LEDs both experience lumen depreciation (loss of lumens) over time even when operated within specified conditions. Therefore, when considering the useful life of very long life products such as LEDs, lumen depreciation must also be taken into account. Lumen depreciation is typically expressed as lumen maintenance – the percentage of initial lumens remaining after a specified period of time.

Lumen maintenance of LED light sources is dependent on many factors including ambient temperature and humidity, the method of electrical control, drive current, and effective thermal management. High LED junction temperatures accelerate degradation in lumen maintenance and result in a temporary reduction in luminous flux.

For more information on the relationship between luminous flux versus LED die junction temperature, please review Lamina Application Note 01 entitled Life, Lumen Maintenance and Reliability. Here you can read more about Lamina's unique packaging technology which provides exceptional thermal management, a critical factor in optimizing lumen maintenance and luminous flux with high density LED arrays