The advancements in solid-state lighting have been remarkable in recent decades, particularly with light-emitting diodes (LEDs). Manufacturers tout these LEDs for their long lifespan, often advertised as 50,000 hours or beyond. However, the validity of these claims and their actual reliability warrant exploration. This piece aims to tell you everything you need to know about LED luminaire reliability.
What Is LED Luminaire Reliability?
LED luminaire reliability refers to the capacity of an LED lighting fixture to function reliably and as anticipated throughout its designated service life.
How to Evaluate LED Luminaire Reliability?
It is determined by the moment when a certain proportion of lights fail completely. In contrast, well-designed LEDs seldom experience complete failure; rather, they gradually decline in output, a phenomenon known as light level maintenance.
The Illuminating Engineering Society of North America (IESNA) established the industry-standard LM-80 test to quantify this maintenance. The test is conducted by some facilities certified by the National Voluntary Laboratory Accreditation Program (NVLAP).
During LM-80 testing, LED output at various temperatures and currents is recorded over no less than 1,000-hour intervals for a minimum of 6,000 hours (though 10,000 hours are recommended). The graph below illustrates a typical LM-80 testing result.
How do LED manufacturers claim their LED lighting has a lifespan of 50,000 hours since the test time is quite limited? This is where TM-21 comes into play. TM-21 extrapolates LM-80 data by applying curve fitting to the last 5,000 hours of data, extending the light level maintenance projection up to 6 times the LM-80 duration. See the example below.
This projection is linked to a specific intensity reduction, typically defined as L70 or L50. L70 represents a 70% intensity preservation (30% reduction), and L50 denotes 50% intensity. Take a look at the TM-21 projection at the 70% intensity mark and determine the hours to reach that point, we can define the L70 light level maintenance. This value is often cited to support LED lifetime claims.
Nonetheless, having LM-80 data with a TM-21 projection indicating L70 at 50,000 hours doesn’t guarantee a fixture’s operational time. The B-number is crucial—it signifies the percentage of LEDs expected to fail at 50,000 hours. For instance, L70B50 = 50,000 hours states that 50% of LEDs will decline in intensity by 30% or less after 50,000 hours. Another instance, L50B90 = 40,000 hours, suggests that 90% of LEDs will lose 50% or less intensity after 40,000 hours. Yet, remember that light level maintenance only predicts LED lifetime, not the luminaire’s, which can be influenced by various other factors.
What Are the Main Factors that Affect LED Luminaire Reliability?
In contrast to many traditional lighting, LED lighting is electronic assemblies comprising various components. Despite the duration of LEDs themselves, these systems can experience degradation or malfunctions in different parts. The reliability of LED luminaires is intricately connected to the performance of these constituent elements and their responses to environmental or operational pressures.
LED Driver (Power Supply)
One of the notable challenges associated with solid-state lighting pertains to the complications stemming from the driver used to power LED lights. The driver circuit is responsible for effectively managing the load and supplying the necessary low voltage power to illuminate the LEDs, generating light as a result. Consequently, the design of this driver circuit plays a key role in determining the performance of LED lights. Crucial aspects like lifespan, efficiency, power factor, harmonic distortions, dimming, and flickering crucially hinge on the configuration and electrical capabilities of the LED driver circuit.
Numerous reliability concerns stem from stresses on components, driven by factors such as abnormal environmental conditions and variations in electrical operating parameters due to surges and spikes. An LED driver typically employs a complex AC to DC circuit that encompasses components like triodes, transformers, capacitors, rectifiers, and transistors. Components like triodes, transformers, and electrolytic capacitors are particularly susceptible to temperature fluctuations. As temperatures increase, their efficiency, lifespan, and reliability experience significant declines.
Effective thermal management is critical for LED lighting systems, especially those with high power outputs. In scenarios where LEDs function within confined spaces and high temperatures, the heat they generate can result in overheating and premature luminaire failure. Overheating doesn’t merely impact the LED package; it can also trigger failures in components within an integrated driver, leading to system malfunctions or shutdowns.
The material choice for a heat sink substantially influences its heat dissipation ability. This is due to thermal conductivity directly affecting heat dissipation efficiency. While copper boasts the highest thermal conductivity, its cost is daunting. As a result, aluminum has become the prevalent option owing to its reasonable cost and high thermal conductivity. Nevertheless, aluminum heat sinks necessitate additional components like PC boards and internal fans, which can impede heat dissipation and curtail LED light longevity.
With the development of LED technology, COB LEDs come into the market. They generate more heat and demand efficient heat dissipation methods to maintain LED performance and lifespan.
In conclusion, enhancing heat dissipation is imperative. Contrary to recent claims suggesting that improved LED efficiency renders heat dissipation inconsequential, this notion is misguided. Despite advancements, LED lights operate at only around 50% total energy efficiency, with a substantial portion of energy still converting into heat.
The functionality of an LED light relies on various interconnected elements. Instances like compromised housing integrity, which might allow moisture penetration, debris accumulation, structural breakdown, and so on, can lead to failures. For instance, the efficiency of thermal management components could diminish with dirt and debris buildup. In outdoor settings, inferior gaskets and sealing materials might deteriorate prematurely due to compatibility problems or subpar quality. This deterioration can pave the way for moisture infiltration, eventually causing damage to the lighting system.
LED Light Sources
Today, the LED package is undeniably a remarkably dependable element and is unlikely to be the primary cause of system breakdown. When coupled with a well-designed driving circuit, effective thermal management, and an efficient system layout, LEDs seldom experience severe or parameter-based failures. The primary issues linked to the gradual failure of LED packages are lumen reduction and color shift. Nevertheless, these gradual declines are predictable and are already factored into the design of luminaire systems.
There is a lot more to grasp about LED luminaire reliability than just the straightforward assertion of a 50,000-hour lifespan. Therefore, if you are in the market for an LED light, it’s crucial to request the LM-80 / TM-21 test report and ensure the reliability of LEDs. And then check the reliability of the components in the lighting. After all, they significantly affect your LED luminaire reliability.
At MokoLight, we boast a robust team of engineers, with 50 dedicated to design and 20 focused on production. Additionally, we own our factory, covering an expansive area of 12,400 square meters. LEDs we produce come in a 3-year warranty and are certified by ISO9001, ISO14001, ISO13485, ROHS, BSCI, and UL. Any questions about LED lights? Talk to our experts.