How to define and measure the lifespan of indoor LED lighting

Unlike traditional light sources, LED lighting no longer simply ends when the bulb goes out. Over time, LEDs experience gradual luminous flux decay, meaning a decrease in brightness. Lumen maintenance is commonly used internationally to define lifespan. When the luminous flux drops to a certain percentage of the rated initial value, the lifespan is considered to have ended. The most common lifetime definition is L70, which is the time at which the LED's luminous flux decays to 70% of its initial value. For example, an LED lamp with a "50,000-hour L70" rating means that under normal operating conditions, the lamp will maintain brightness above 70% after 50,000 hours.

Differences between L70, L80, and L90
In practical applications, in addition to L70, L80 and L90 lifetime indicators are also commonly used. L80 indicates the lifetime at which the luminous flux is maintained at 80%, while L90 indicates the lifetime at which the luminous flux is maintained at 90%. L70 is suitable for general office, commercial, and residential lighting. L80 is more commonly used in locations requiring high brightness stability, such as retail displays. L90 is commonly used in applications requiring extremely high light quality, such as museums, art galleries, and medical lighting. Different lifespan definitions provide users with a more intuitive understanding of lamp performance in specific environments.

Factors Affecting LED Lifespan
LED lifespan is not a fixed value but is affected by a variety of factors:

Thermal Management: Excessive temperatures accelerate lumen degradation and reduce lifespan. Excellent heat dissipation design is critical.

Power Supply: The stability of the power supply directly determines whether the LED can continue to operate efficiently. Power failure often precedes light source degradation.

Operating Environment: Humidity, dust, and air circulation can all affect lifespan.

Electrical Conditions: Voltage fluctuations and inrush currents can shorten LED lifespan.

Lifespan Testing Standards
The International Commission on Illuminating Engineering (IES) has established several standards for evaluating and predicting LED lifespan.

LM-80: A lumen maintenance test for LED light sources, specifying lumen flux measurements for at least 6,000 hours at a specific temperature and current. TM-21: Based on LM-80 test data, mathematical extrapolation is performed to predict lumen maintenance over longer periods of time, thereby deriving lifetime values such as L70, L80, and L90.
LM-79: Primarily used to test overall lamp performance, including luminous efficacy, luminous flux, and light distribution characteristics. While it does not directly define lifetime, it is closely related to lifetime assessment.

LED Lamp Lifetime and System Lifetime
It is important to note that while the LED chip itself may have a theoretical lifespan exceeding 100,000 hours, the overall lamp lifespan is often limited by the driver, cooling system, and optical materials. Many products, despite excellent LED light source performance, experience shortened lifetimes due to driver failure or lens aging. Therefore, the industry places greater emphasis on system lifespan, which measures the duration of stable operation of the entire lamp in actual applications.

Lifetime Verification Methods
Under laboratory conditions, manufacturers record luminous flux changes through long-term lighting tests. LM-80 testing is typically conducted at different junction temperatures, such as 55°C, 85°C, and even 105°C, to simulate the thermal environment found in real-world applications. Extrapolating the resulting data using the TM-21 algorithm can yield a lifespan prediction of 50,000 hours or even longer. In actual engineering projects, accelerated aging tests and environmental stress tests are also conducted to verify the durability of the lamps under extreme conditions.

The Relationship Between LED Lifespan and Warranty Period
Although many manufacturers advertise LED lamp lifespans of 50,000 to 100,000 hours, product warranties typically provide a three- to five-year warranty. This is because lifespan test results are based on laboratory predictions, and the complexity of real-world operating environments can lead to discrepancies. Therefore, when selecting a product, users should consider whether the manufacturer provides reliable lifespan data based on LM-80 and TM-21, and consider the manufacturer's actual warranty policy.

The Significance of Lifespan in Application Scenarios

In commercial lighting, lifespan directly determines maintenance costs. For example, if a large LED panel light in a shopping mall or office building fails to meet its lifespan requirements, replacement and maintenance costs will increase. For demanding environments like museums and medical facilities, an L90 lifespan specification provides better light quality stability. For home applications, an L70 specification is sufficient for years of use.