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Understanding Life Hours, Part 1: How Are Life Hours Determined?

Understanding Life Hours, Part 1: How Are Life Hours Determined?

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Part 1 in a series about life hours and how you can use this spec to inform your purchase and maximize the life of your bulbs. --

The term "life hours" sounds simple but is one of the most misunderstood of all lighting terms. A life hour rating isn't a warranty or guarantee of a light bulb's life, so the life hour rating you see on a bulb's packaging isn't necessarily how long the bulb will last in your fixture.

A manufacturer's projection of life hours has to take into account many variants including the calibration of manufacturing equipment, temperature fluctuations, and material quality, to name just a few. By using a big enough test sample, manufacturers hope to account for any manufacturing inconsistencies, making their rating as accurate as possible.

Manufacturers determine life hours for filament lamps, fluorescent tubes, HID lamps, and LED bulbs all in slightly different ways. Here's the rundown:

Filament Lamps (Incandescent and Halogen)

  • Manufacturers test a group of sample lamps by burning them continuously.
  • The point at which 50% of the lamps fail is the life hour rating.

Fluorescent Lamps (Linear, U-Bend, Plug-In)

  • Manufacturers test a group of sample lamps by burning them for 3-hour intervals.
  • The point at which 50% of the lamps fail is the life hour rating.

HID Lamps (Metal Halide, HPS, Mercury Vapor)

  • Manufacturers test a group of sample lamps by burning them for 10-hour intervals.
  • The point at which the lamps meet 40% of their original lumen output is the life hour rating.

LED Lamps

  • Manufacturers test a group of sample lamps by burning them continuously. Like HID lamps, LEDs aren't allowed to burn out.
  • The point at which the lamps meet 70% of their original lumen output is the life hour rating.

In the next part of this series, we'll show how you can use this information to inform your light bulb purchase.

Understanding Life Hours, Part 2: Life Hours vs. Warranties

Understanding Life Hours, Part 2: Life Hours vs. Warranties

The Light Bulb Ban: A Simple Explanation

The Light Bulb Ban: A Simple Explanation