LEDs and Solid State Devices: Lifespan Explained

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Discussion Overview

The discussion focuses on the lifespan of LEDs and other light-emitting solid-state devices, exploring the factors that contribute to their longevity and the relationship between energy efficiency and lifespan.

Discussion Character

  • Technical explanation, Conceptual clarification

Main Points Raised

  • One participant inquires about the reasons behind the definite lifespan of LEDs and solid-state devices.
  • Another participant explains that elevated temperatures can lead to changes such as dopant migration, merging of crystalline defects, charging of insulating layers, and diffusion of contact metals into the semiconductor.
  • A subsequent participant suggests that higher energy efficiency could correlate with longer device lifespans.
  • In response, it is noted that as LED efficacy approaches 300 Lumens/Watt, heat generation decreases significantly, leading to longer lifespans despite potential degradation from phosphor and encapsulant under high luminous flux.
  • It is mentioned that peak efficacies of laboratory devices are nearing 200 Lumens/Watt.

Areas of Agreement / Disagreement

Participants appear to agree on the relationship between energy efficiency and lifespan, but the discussion does not reach a consensus on the specifics of how these factors interact or the implications of current efficacy levels.

Contextual Notes

The discussion does not clarify the assumptions regarding the definitions of energy efficiency or the specific conditions under which lifespan is measured.

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Why do LEDs and other light emitting solid state devices have a definite lifespan?
 
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Because at elevated temperatures they change. Dopants migrate, crystalline defects merge, insulating layers become charged (under the influence of ionizing radiation), contact metals diffuse on and into the semiconductor.
 
thank you very much. that would mean that higher energy efficiency of a device would mean not only more energy efficiency in and of itself, but higher total lifetime, correct?
 
Indeed. When the LED efficacy in Lumens/Watt starts to approach 300, the heat generation falls rapidly. All the energy is coming out as light. At that point you only have phosphor and encapsulant degradation due to high luminous flux. It will still degrade but the life could be measured in the many decades, not years, of continuous operation.

Peak efficacies of lab devices today are approaching 200 Lumens/Watt.
 

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