Average Rated Life


Definition of Average Rated Life

Average rated life (ARL) refers to how long it takes for 50% of the light bulbs in a test batch to fail. This lifespan is usually quoted as B50 for most bulbs.

For example, the typical average rated life for fluorescent bulbs ranges between 24,000–36,000 hours. Meaning that, if 100 bulbs were tested, 50 of them failed during this time window hour.

The lifespan of bulbs varies depending on the type and technology of the bulb. This is partly because each bulb behaves differently as it approaches its end.

Incandescent bulbs, for instance, will fail abruptly when the filament breaks and they stop emitting light.

Conversely, LEDs tend to dim gradually, and can technically continue to produce light for decades. Therefore, the ARL of LEDs is based on the percentage of lumens lost in the testing period in order to accommodate their longevity.

The ARL of LEDs may be expressed as L70, L80 or L90.

Simply put, these ARL ratings have the following significance after 50,000 hours of use:

  • L90/B10 rating: 90 percent of LED lamps retained 90% of their lumen and only 10% of lamps failed.
  • L80/B10 rating: 80 percent of LED lamps retained 80% of their lumen with only a 10% failure rate.
  • L70/B50 rating: 50 percent of LED lamps retained 70% of their lumen while the other half failed.

These ARL ratings tell us how long and how well an LED lamp will perform, with L90 being the best, as shown in the graph below.

ARL ratings graph

Fun Fact: The longest burning incandescent light has been on almost continuously since 1901—a whopping 1,000,000 hours and above. Unfortunately, the carbon filament bulb is extremely dim, only giving off about 4 watts of light.

In the table below is a compilation of the typical average rated life of various types of bulbs.

Type Of Bulb Average Rated Life In Hours
LED 40,000–50,000
Fluorescent 24,000–36,000
HID 10,000–24,000
Compact fluorescent plug-in 10,000–20,000
Compact fluorescent - screw-based 8,000–10,000
Halogen 2,000–4,000
Incandescent 750–2,000

ARL is simply a guiding metric for light bulb manufacturers to forecast how long light bulbs will last. Many bulbs fail long before they reach the expected half-life, which correlates to the conditions of their usage.

What are some of the factors that shorten a bulb’s lifespan?

  • Extreme heat conditions, for example, in an oven, freezer, or outside in winter
  • Exposure to moisture from rain, or sprinklers
  • Voltage spikes, which fry the circuitry
  • Frequent turning on and off
  • Mechanical shock and vibration, for example, from slamming doors or loud machinery
  • Operating voltage — a 5 percent increase in voltage may halve a lamp’s life while a 5 percent decrease can potentially double it

Example of Average Rated Life in a Sentence

"The FTC labeling rule requires the average rated life of a bulb to be displayed on its packaging in years, according to the hours divided by 365 and expressed by rounding to the nearest tenth of a year."

Synonyms: half life, B50

Related Terms for Average Rated Life