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What does Average Rated Life for a light bulb mean?

Lighting Basics

In the light bulb industry, the Average Rated Life (ARL) is how long it takes for half the light bulbs in a test batch to fail. It’s also been called a half-life. For example if 100 bulbs are tested and have an ARL of 1000 hours, 50 of the bulbs had died when the test time reached 1000 hours. Some bulbs may have failed within 50 hours, some within 450 hours, some within 700 hours, etc. but half were dead within 1000 hours.

Turning a bulb on and off, on and off, on and off reduces the ARL. Incandescent, halogen, and LED bulbs are less affected by on/off cycles than Fluorescent, Compact Fluorescent, and HID bulbs. In general, the ARL for a bulb that turns on and off once a day will be much longer than a bulb that turns on and off many times a day.

Keep in mind that ARL tests are run at conditions that can reasonably be expected in typical applications. If a bulb is used in an area that is hot (above an oven or in the ceiling), cold (in a freezer or outdoors in winter), wet (exposed to rain or near a sprinkler), or vibrating (near machinery or slamming door)-any “abnormal” situation-the ARL will most likely not be reached. Think about it like a marathon runner. If it’s too hot, too cold, too wet, or too windy the runner won’t run as fast or as far.

Typical Average Rated Life for Various Types of Bulbs

Incandescent 750-2,000 hours
Fluorescent 24,000-36,000 hours
HID 10,000-24,000 hours
Compact Fluorescent
Plug-in 10,000-20,000 hours
Screw-based 8,000-10,000 hours
Halogen 2,000-4,000 hours
LED 40,000-50,000 hours

 
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