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LED Expected Lifetime

Last updated 2011-02-08 - Send Feedback
Related: lighting

LEDs don’t fail like conventional bulbs, generally never “burning out”. Rather, their brightness will slowly diminish as their “mileage” increases. The emitted light will become more bluish. The effect depends both on the cumulative runtime and the stress placed on the LEDs, with high operating temperatures being a Very Bad Thing (just as with all electronic components).


The Wilma’s deep cooling fins.

Think of LEDs like a car engine; usage wears out an engine slowly over time, but an engine can also be worn out in a single day on a racetrack when operated under extreme stress. Fortunately, Lupine’s advanced electronics actually contain an internal temperature sensor, and automatically cut light output (and therefore heat) if the lamp becomes too hot. The 2008 Wilma is rated to run at 15 watts continually, though output from 6 watts to 20 watts is possible with extremes of heat and cold respectively, according to Lupine. Later Wilma models run at slightly higher output levels.

According to Lupine, at maximum operating temperature (eg conditions most stressful for the LEDs), light output will diminish by 10% after 1500 hours of burn time, 15% after 2500 hours. Lower operating temperatures should delay the “aging” of the LEDs significantly.

Cyclists should be happy to know that continual air flow is very friendly to the LED lampheads. I have verified this on a nighttime ride at 12°C/54°F, finding that at maximum output and an average speed of 20mph (32kph) the black anodized metal housing of the Wilma remained only slightly warm to the touch. Ditto for the Betty.

Wattage

Lupine has over a decade of experience with LED technology. Experience matters when building a light that will perform well 100% of the time. Careful design and testing are needed; one cannot simply assemble parts.

The 2010 Wilma draws 17 watts. Disassembling the Wilma, it’s plain to see that dissipating 4+ watts from each of the tiny LEDs must create intense localized heat.

It’s all about heat dissipation. First, the Wilma’s all-metal body and deep heat fins allow rapid heat dissipation. Second, its sophisticated electronics, including an internal temperature sensor, allow the Wilma to run the LEDs at optimal and safe (non-damaging) temperatures, dropping the wattage with inadequate cooling.

The smart head management also means that if it’s 30° out, the Lupine lights will be able to run safely at slightly higher output— which they do! But at 100° with no air movement, the lampheads protect the LEDs by reducing power slightly.

According to Lupine (and this is on 2008 LEDs), the LEDs themselves run at peak efficiency at around 25°C/77°F (“junction temperature”), though that is unrealistic for ongoing operation (and the basis for unrealistic claims about lumens per watt by some LED manufacturers). When switched on, the Wilma draws a few extra watts for a fraction of a second until its operating range is reached, then adjusts power draw up to 15 times per second so as to maintain an operating temperature from 25°C to a maximum of 120°C. Beyond 120°C, light output, color temperature and LED lifetime degrade badly, so maintaining operating temperature within bounds is critical.


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