Sounds straightforward, but let’s break down some of those terms.
The rated life of an LED luminaire is measured in hours and translates into how long the user can expect that fixture to reliably produce light.
In light bulbs, Average Rated Life (ARL) is measured by how long it takes for half the light bulbs in a test batch to fail. A bulb with an ARL of 1,000 hours means in a test of 100 bulbs, 50 died when the test time reached 1000 hours. Most LEDs have an ARL of 50,000 hours. (BTW, Litetronics LEDs have an ARL of 100,000 hours.)
Light output is the luminous flux (measured in lumens) emitted by a lamp or luminaire. If the light output at installation is 100%, then the output is usually said to be significantly diminished when there is a 30% decrease in output for general lighting, and 50% decrease for decorative lighting. That’s referred to as the LEDs useful life.
The manufacturer will define the conditions that correspond to normal use, but in general, ARL tests are conducted in conditions that one would reasonably expect in customer applications. A bulb used in an area that is unusually hot or cold, exposed to wet or hazardous materials, or near vibrating machinery or any other “abnormal” situation, may not reach the ARL.
How the LED light is used has an impact, too. Turning a bulb on and off frequently will reduce the ARL, for example. Now, LED bulbs are less affected by on/off cycles than older fixtures like fluorescents, compact fluorescent and HID bulbs, but in general, you can expect the ARL for a bulb that is turned on and off once a day to be much longer than one that is cycled many times a day.
