Without successful thermal management, LEDs’ light output, color and efficacy can quickly degrade.
In my previous column, I said today’s high-power (HP) and high-brightness (HB) LEDs are more difficult to manufacture — and don’t endure as long — as low-power (LP) LEDs, because the advanced group requires higher operating currents, which accelerates lamp aging. Directing an elevated injection current into an LED chip causes relatively higher junction temperature (TJ), and, because heat must be conductively removed from the LED chip’s backside, such an increase requires a sophisticated, thermal-management system.
The complexity of LED lamp thermal management is a major reason why LEDs haven’t yet become mainstream in the illumination industry.
To come into common use, LED-based, regular household lighting and signage applications need consistently higher — and less costly — performance, sans sophisticated systems or end-user adjustment.
Without successful thermal management, LEDs’ light output, color and efficacy quickly degrade. However, LEDs mounted in sophisticated, electronically controlled, interpretive systems (such as those found in electronic displays) degrade at a much slower rate.
We’ve all seen electronic or electrical gadgets’ LED indicator lights last a long time, and this endurance causes the belief that LEDs last almost forever. However, indicator lamps need only a few milliamps to operate, and diminishing light output isn’t a concern.
General-illumination and signage lamps require several hundreds of lumens, from limited-size sources, and also demand certain luminance levels, as well as color quality and uniformity. And, certain high-end applications, such as automotive headlights, need even higher lumen output and luminance; thus, sophisticated, thermal-management systems are needed to ensure longevity with high optical quality.
For example, Osram Sylvania has produced its OSTAR brand, LED headlights for Audi’s $75,000 A8 sedan. Osram says the headlights have a minimum life of 7,000 hours. While this lifespan seems adequate for this application, typically, less-bright LED lifespans are much longer.
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