SEMICONDUCTORS
mask or compensate for catastrophic failures at the probable rate specified by the LEDmanufacturer.
LED reliability Operating temperature and drive current are the acceleration factors in the lumen degradation of an LED; part of the luminaire customer’s challenge is to select drive current values and cooling mechanisms so as to optimize the systemfor cost, size and performance over time and operating conditions.
But external factors can also cause early failure, including thermal,
electrical ormechanical overstress, aswell as chemical contamination. The luminaire customer can take steps to eliminate, reduce or mitigate these effects.
Systemreliability Creating a reliable SSL luminaire involves more than careful LED selection and a suitable light engine design: it requires equal attention to other components in the system.
The secondary optic should not be
neglected in SSL systemlifetime assessment, in particular because of its potential to affect the intensity and chromaticity of luminaire’s light output over time.Manufacturers have no alternative but to run lifetime tests and explore alternativematerials.
Themarket offers a range of LED
drivers at awide range of prices. The difference between the best and the worst drivers is verymarked indeed, and thiswill be reflected in the average lifetime each product offers. Unfortunately, even themost reputable manufacturers sometimes neglect to provide reliability data; this presents a considerable difficulty to the luminaire designer.
Where to find help The lifetime of LED-based luminaires is governed by numerous factors such as LED lumenmaintenance and catastrophic failure rates; secondary optic stability over time and operating conditions; and LED driver reliability. An SSL system’s reliability is only as good as the reliability of its weakest component, therefore the luminaire designer and buyermust take a system- wide view of the problem, rigorously selecting components and applying strict design rules.
Component suppliers should be expected to provide relevant reliability
data and, for LEDs, additional standards are needed to enable an accurate and confident prediction of a LED light engine’s economic life.
Solid-state lighting can certainly achieve long termreliable
operation; for the good of thewhole industry, luminaire manufacturers and their supply chainmust deliver on this promise.
FrançoisMirand is technicalmanager, EMEA, for Pointe Claire, Quebec-based Future Lighting Solutions
www.futurelightingsolutions.com
Are counterfeit components hiding in plain sight?
September 2010 | 17
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