Everything you need to know about LED light decay
بواسطة Amy Topsun lighting
February 17th, 2025
25 مشاهدات
What is LED light decay?
LED light decay, also known as lumen depreciation, is a characteristic of LED (Light-Emitting Diode) lighting in which the luminous output of the LED gradually decreases over time. This decrease in light output occurs as LEDs age and is influenced by various factors. Understanding LED light decay is crucial for predicting the lifespan and maintaining the performance of LED lighting systems.
LED light decay is typically measured using the Lumen Maintenance curve, which indicates the percentage of initial light output (lumens) that the LED will maintain over time.
Common metrics that describe LED light decay include L70 and L50, which represent the time it takes for the LED to reach 70% and 50% of its initial light output, respectively.
Why do LED lights have light decay?
1. Intrinsic defects of semiconductor materials
a. Non-radiative recombination
When electrons and holes recombine at the PN junction of the LED chip, not all energy is converted into light (photons). Part of the energy is released as heat energy through lattice vibrations (phonons).
Impurities or crystal defects in the material will form "traps," increasing the proportion of non-radiative recombination, reducing luminous efficiency, and generating additional heat.
b. Defect diffusion and aging
Under long-term high temperatures, atomic diffusion in semiconductor materials intensifies, and defect density increases, further hindering carrier recombination and luminescence.
For example, dislocation defects in GaN-based LEDs accelerate light decay.
2. Increased junction temperature due to insufficient heat dissipation
a. Heat accumulation effect
When the LED works, about 70-80% of the electrical energy is converted into heat energy. The chip junction temperature (Tj) will increase significantly if the heat dissipation is poor.
Relationship between junction temperature and light decay: For every 10°C increase in junction temperature, the LED life may be shortened by more than half (Arrhenius law).
b. Effect of high temperature on materials
Phosphor decay: High temperature causes the crystal structure of phosphor to be destroyed and the light conversion efficiency to decrease (such as YAG phosphor accelerated failure above 150°C).
Aging of packaging materials: Silicone or epoxy resin yellows and cracks at high temperatures, and the light transmittance decreases (for example, the light transmittance of silicone may decrease by 30% at 200°C).
3. Driving current and electrical stress
a. Current overload
Exceeding the rated current (such as 20mA for low-power LEDs) will lead to excessive carrier density, reduced recombination efficiency, and more Joule heat.
Experiments show that if the driving current exceeds the rated value by 50%, the light decay rate may be accelerated by 3 times.
b. Pulse current shock
Current spikes caused by frequent switching or voltage fluctuations will accelerate electrode metal migration, resulting in local short circuits or increased contact resistance.
4. Limitations of packaging technology
a. Thermal resistance design defects
The thermal resistance (Rth) at the package level directly affects heat transfer efficiency from the chip to the heat sink. The thermal resistance of inferior packages may be as high as 20°C/W, while that of high-quality packages can be less than 5°C/W.
For example, using a copper substrate instead of an aluminum substrate can reduce thermal resistance by more than 30%.
b. Insufficient airtightness
Poor package sealing can lead to moisture intrusion, accelerating electrode oxidation (such as blackening silver electrodes due to desulfurization), and material corrosion.
5. Environment and use conditions
a. High-temperature environment
When the external ambient temperature exceeds 40°C, the efficiency of the heat dissipation system decreases, and the junction temperature may exceed the safety threshold (such as 125°C).
b. Ultraviolet and chemical corrosion
Outdoor LEDs are exposed to ultraviolet rays for a long time, and the packaging materials are prone to brittleness; acid and alkali gases in industrial environments may corrode optical components.
The impact of light decay on LED lamps
1. Decreased lighting effect
Light decay reduces brightness, which may affect visual health (such as increasing the risk of myopia).
2. Shortened lifespan
After light decay, higher power is required to maintain brightness, which increases heat generation and further shortens the lamp's lifespan.
3. Increased energy consumption
Users may compensate for brightness by increasing the number of lamps or power, increasing energy consumption.
4. Environmental protection and economic costs
Frequent lamp replacement increases waste and resource consumption. The maintenance factor (MF) design must compensate for light decay in advance, indirectly increasing initial investment.
How to slow down light decay?
1. Choose high-quality products: prioritize LED lamps with good heat dissipation performance and stable chips.
2. Control working conditions: Avoid overloading and ensure that the driving current is within the rated range.
3. Optimize heat dissipation design: install heat sinks, maintain ventilation environment, and reduce chip temperature.
4. Regular maintenance: clean dust on the surface of lamps and check circuit aging.
Conclusion
LED lamps' normal light decay range is closely related to their quality, heat dissipation, and usage conditions. Reasonable selection and maintenance can significantly extend the service life. If the light decay exceeds 30%, it should be replaced in time to ensure the lighting effect and economic benefits.
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