LED Lifetime- What does it mean?
The replacement of traditional light sources in favour of LED lighting has resulted in huge improvements in function, cost-efficiency and performance. LED lighting is fast replacing traditional light sources. The scale of increase in global LED use in recent years has been demonstrated within this IEA report, with LED’s rising from a 2% market share in 2012 to nearly half of global lighting sales in 2019.
One of the key benefits often cited in favour of switching to LED lighting is their long lifetimes.
But what does a ‘long lifetime’ actually mean and why is LED technology so favourable?
Firstly, let’s look at our main alternative light sources to LED’s, fluorescent and metal halide. Whilst these light sources do fade over time, much like with LED’s, they also ‘burn out’ after a certain period i.e. they stop working completely. Lamp life for these luminaires is therefore measured relatively easily, by the time it takes for 50% of a large group of lamps to fail, referred to as Average Rated Life (ARL).
Unlike other light sources such as fluorescent or incandescent lights, LED’s don’t tend to fail completely. Instead, their light output degrades gradually over time.
Because of this, it is commonly misinterpreted that an LED’s ‘lifetime’ for instance ‘up to 50,000 hours means that that luminaire will stop working altogether once this point has passed. What this actually means is that over the duration of time the light will begin to fade and by 50,000 hours the lumen output will have depreciated by 30% compared to what it was originally.
How is LED life expectancy measured?
Determining LED performance has become much more complex compared with that of traditional light sources.
The difference in luminaire deterioration in comparison to metal halide or incandescent light sources means that LED’s must follow a different method for measuring luminaire life expectancy, as the longevity of LED light makes it impossible to measure the whole-life performance of LED’s. This measurement is called lumen maintenance.
The lifetime of an LED fitting is typically measured by the time in which it takes for its light output to reach 70% of its original output, i.e. when the lumen output has depreciated by 30% compared to what it was originally, with possibly some LEDs giving out no light. This is because it’s commonly acknowledged that the human eye is only sensitive to lumen depreciation of 30% or more. This is referred to as L70, the time at which half the LED’s have fallen below “B50”.
Lumen maintenance involves taking a brand-new light and measuring the light output (lumens) and comparing this with its light output after a certain period of time. This data is then extrapolated beyond the time of testing following set standards.
Current standards for LED lifetimes
The differences in performance characteristics of LED’s compared to traditional light sources has led to the development of standardized tests specifically for LED luminaires. These improved metrics for quality control and improved testing procedures have proven essential in ensuring both energy performance and quality.
The IEC 62722-2-1 is the new international performance specification for LED modules. This publication sets out requirements on how the LED luminaire lifetime should be stated, the test method and the minimum time required for testing LED lifetimes. The minimum testing time is 6,000 hours with a luminous flux recorded every 1,000 hours. These values are then extrapolated using a method stated in IES TM21.
How long do LED lamps and fixtures actually last?
The lighting industry has standardized the lifetime of an LED fixture at L70 = minimum 50000 hours.
The lifespan of LED bulbs does however depend on several key factors and LED luminaire lifetime tends to vary from 10,000 up to 50,000 hours.
What applications might the L70 default failure level differ?
The L70 (70%) minimum threshold used to define a “standard” lifetime does not fit every situation. For instance, in some safety situations, depreciation of this level may be unacceptable.
Conversely, within some situations, usually within cost-sensitive, non-critical cases, higher levels of depreciation are allowed. For instance, another common industry benchmark is L50, referring to when a lumen output has depreciated by 50% compared to what it was originally.
What factors affect LED lifespan?
Several factors influence the useful LED lifetime, or ‘lumen maintenance’ time. These variables include the operating cycle, the ambient temperature, material defects, electrical overstress etc.
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