7/27/2023 0 Comments Half life source differencesUsing this definition of failure criteria, the statistical measure can be combined with the defined durability measure. In other words, for a given period of time, if an LED produces insufficient light or no light, the LED is considered at failure. For example, failure might be defined as when the light output of an LED reaches 70% or lower of the initial light output (including if the LED’s light output is zero). As a consequence, a smaller sample size will lead to shorter projected life in order to increase the statistical certainty.įor LED light sources, one can define failure as when the LED can no longer produce a certain percentage of the initial light-output value. However, when LM-80 test data is utilized to make lumen-maintenance projections (per TM-21), the sample size will affect the uncertainty of the projection. When testing L p life, there is no sample size requirement. When testing for B p life, a large statistically-meaningful sample size is required. While B p life is a statistical measure, L p life is a defined durability measure. If an LED has L 50 of 30,000 hours, its lumen output decays faster than one with L 70 of 30,000 hours. In other words, L 70 of 30,000 hours means that the tested LEDs produce 70% of the initial light output at 30,000 hours. Rated lumen-maintenance life is measured in hours with associated percentage of light output, noted as L p. If a product has a B 10 rated life of 1,000 hours, this means that only 10% of tested products failed within 1,000 hours, so the product should last much longer than a product with a B 50 rated life of 1,000 hours.įor LED light sources, LM-80 defines lumen-maintenance life as “the elapsed operating time at which the specified percentage of the lumen depreciation or lumen maintenance is reached, expressed in hours.” Different from rated life, the rated lumen-maintenance life is defined as “the elapsed operating time over which an LED light source will maintain the percentage (p) of its initial light output.” B 50 is also known as the products’ rated average life. The statistical measure for the rated life is designated Bp and is measured in hours, where p is a percentage.įor example, a B 50 rated life of 1,000 hours means that 50% of the tested products have lasted 1,000 hours without failure. This is commonly a statistically-determined estimate of median operational life.” The rated life in hours of an LED lamp or light source, specified by the manufacturer, applies under certain operational conditions and for defined failure criteria. The rated life of a lamp or light source is defined, per ANSI/IES RP-16, as “the life value assigned to a particular type lamp. Rated life is an essential reliability property for LED integrators that design LED luminaires, providing luminaire users with warranty and usage information However, there is still one measure that is missing: the rated life for LED light sources. The new TM-21 method is then applied to the collected measurement data to make lumen-maintenance projections, including in-situ temperature calculations. First, the LED light sources must be tested per LM-80. With the completion of the IES test method TM-21-11 (see page 9), the SSL industry now has a standard method of obtaining long-term lumen-maintenance information for LED light sources.
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