Understanding why lumen depreciation is a more effective measure of the useful life of LEDs in real-world usage
This leads to amazing energy savings over the long life of their use. However, even high quality LED lights will experience a reduction in brightness output levels) over a long period of time (over 50,000 of use).
Therefore lumen depreciation provides a more practical and effective way of measuring the useful life of an LED light – which is the point till which its light generation allows it to remain effective in real world usage scenarios.
Widely accepted international standards – recommended by the Illuminating Engineering Society (IES) – calculates the life of an LED as the point when the LED reaches 30 percent lumen depreciation. This means that the brightness falls by 30% to around 70% of its original levels.
Lumen maintenance curves for traditional lighting vs LEDs (Source: http://www.digikey.com/en/articles/techzone/2013/dec/standardized-testing-for-leds-extends-to-lighting-fixtures)