Reliability Assessment of Light-Emitting Diodes

The reliability assessment of light-emitting diodes (LEDs) underpins the widespread adoption of solid-state lighting across domestic, commercial and industrial sectors. Key performance metrics include lumen maintenance, colour stability and electrical integrity over time. Degradation arises from a combination of thermal, electrical, mechanical and environmental stresses, leading to gradual lumen depreciation, shifts in spectral output and eventual device failure. Standardisation efforts such as LM-80 and TM-21 provide guidelines for accelerated testing and extrapolation of lumen maintenance, yet these methods often rely on deterministic regression and neglect stochastic variation. Recent advances embrace multi-physics modelling to capture thermal-mechanical interactions, statistical degradation processes to characterise unit-to-unit variability and in-situ prognostic techniques for real-time health monitoring. By integrating accelerated degradation tests with physics-based and data-driven models, researchers aim to improve life prediction accuracy, reduce test durations and guide the design of more robust materials and package architectures. Reliable lifetime estimation is vital not only for manufacturers to optimise cost and performance but also for urban planners, safety-critical applications and sustainability mandates worldwide.

Research from Nature Portfolio

Recent studies have elucidated the combined influence of humidity, temperature and electrical load on outdoor LED reliability. One foundational investigation introduced a moisture–electrical–temperature (MET) accelerated test to compare blue chips with and without phosphor converters. Using high-resolution acoustic microscopy, researchers observed delamination at material interfaces and demonstrated that thermal expansion mismatches and heat generated by phosphor layers govern distinct degradation pathways under powered and unpowered conditions. This work has established a comprehensive framework for assessing real-world outdoor performance and guiding the selection of encapsulant materials for improved long-term stability.

Reliability Assessment of Light-Emitting Diodes publication trend

The graph below shows the total number of articles in reliability assessment of light-emitting diodes across all publications each year (not limited to Nature Index journals).

Technical terms

Lumen maintenance: The percentage of initial light output retained by an LED over time, often used to quantify degradation.

Colour shift: The gradual change in chromaticity coordinates of an LED, affecting perceived colour quality.

Accelerated degradation testing (ADT): Experimental protocols that apply elevated stress levels (e.g. temperature, current, humidity) to induce failure modes more rapidly than under normal use.

Gamma process model: A stochastic framework describing cumulative degradation as a random process with gamma-distributed increments, enabling probabilistic life-time predictions.

Moisture–electrical–temperature (MET) test: A combined-stress methodology evaluating the effect of humidity, current and heat on LED package integrity and performance.

References

1. Overview of high-power LED life prediction algorithms. Frontiers in Sustainable Energy Policy (2024).
2. Degradation Physics of High Power LEDs in Outdoor Environment and the Role of Phosphor in the degradation process. Scientific Reports (2016).
3. Lumen Degradation Lifetime Prediction for High-Power White LEDs Based on the Gamma Process Model. IEEE Photonics Journal (2019).
4. An Alternative Lifetime Model for White Light Emitting Diodes under Thermal–Electrical Stresses. Materials (2018).
5. Prognostics and Health Monitoring of High Power LED. Micromachines (2012).