LED Lifetime – Understanding What It Means


20 January 2015

LED technology is known for its high efficiency and extraordinary long lifetime of over 50,000 hours. But given that people are choosing LED luminaires because of their long product life, how can we  distinguish between LED luminaries and identify reputable manufacturers?

Traditional light sources typically quote lifetime as the point at which most sample of lights (over 50%) will have failed. That is catastrophic failure.

LEDs are different. Due to the material properties of LED, they rarely fail completely; rather their light output slowly decreases over time in a process known as lumen depreciation. In this case, we introduce a measure of the LED degradation and Raytec rate our lights to L70/B50 to better represent the operating lifetime of LED.

L70 (the L is shorthand for lumen depreciation) means the point at which an individual LEDs light output has decreased to 70% of its initial output. B50 indicates the sample size, in this case 50%.

So a rating of L70 /B50 greater than 50,000 hours means that 50% of the LEDs in a product will fall to 70% of their initial power after a period of 50,000 hours. The overall lumen output of the luminaire will still exceed 70%.
70% is significant because it is based on research into human perception. The human eye does generally not detect a decrease in light until the decrease exceeds 30%.

So, what is the difference between a good quality luminaire and a poor quality luminaire?

A poor quality luminaire’s end of life is when it stops working.

A good quality luminaire reaches end of life before you have even noticed.

Many factors influence LED luminaire lifetime. The most important factor is the method and efficiency of heat dissipation. A cooler running environment not only extends the lifetime of an LED but also makes it more efficient and brighter. Other factors include the quality of the LED, mechanical build, drive current and module. Poor quality LED products, though they cost less to buy, will create much higher costs over their lifetime.

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