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Effect of Rise in Ambient Temperature on Based LED Lamp's Longevity

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Cost Justification for LED Lamps

Since LEDs are current driven, each degree the ambient temperature rises it affects the Based LED's (including its components) operating temperature. In order to maintain the projected longevity (100,000 hours) of the Based LED, the Based LED and its components should be redesigned to operate within the nominal desired operating temperature range of 35°C - 45°C. 

 This can be accomplished by derating the operating current (mA) of the Based LED by 0.3 mA per each degree rise in ambient temperature above nominal (25°C). For example: When the ambient temperature is specified around 25°C but rises to 55°C, the Based LED experiences an increase of 30°C in its operating temperature. As a result the LED's operating current range should be reduced by 10 mA (70°C - 40°C x 0.3) to compensate for the rise in ambient temperature and to maintain the expected longevity of the Based LED. Similarly, if the operating current of the Based LED lamp is not derated to compensate for the rise in ambient temperature, the Based LED at an ambient temperature of 55°C/operating temperature 70°C is actually operating at a current 10 mA higher than it was designed to accommodate. (The maximum current for most LEDs is 20 mA.) This reduces the Based LED's expected longevity.  (see Figure P)

Conclusion

Operating the Based LED lamps at a higher operating temperature than for which it was designed adversely affects the longevity of the LED lamp. However, without extensive life-cycle testing on the Based LED lamp, it is impossible to determine the precise number of hours by which the Based LED lamp's longevity will be reduced.


Figure P

 
 
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