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

Light Bulb Package

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.

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Benjamin is a writer for 1000Bulbs.com.

  • David Smith

    I have in my hand an LED lamp from Ecosmart in BR30 form factor. The box says “Lasts 23 Years”. Based on this article, this rating was achieved by testing a series of LED lamps to determine the pint at which the lamp output fell to 70% of rated illumination. I have a hard time believing that Ecosmart built a batch of these 23 years ago and has now measured the “life” of the lamp at 23 years. How can manufacturers make these claims that are patently impossible, given the testing criteria you outline?

    • Benjamin

      Excellent point, David. You’re right, Ecosmart didn’t literally watch the test bulbs for 23 years. Essentially what they do is create simulations from which they make predictions of the LED’s life.

      For more detail on LED life hours, you might read up on the specifics of L-70 testing. This document from Cree is a pretty good place to start: http://blog.1000bulbs.com/wp-content/uploads/2012/01/cree-xre-lumen-maintenance.pdf

  • http://www.adamlhumphreys.com/ Adam Humphreys

    This is very helpful! I always had a general idea how hours were determined, but this takes out speculations. I hope you plan to cover the pros/cons of 120V vs. 130V incandescent bulbs and the difference it can make. Looking forward to the next article.

    • Benjamin

      Thanks! We’re glad to hear this was helpful. We’ll be publishing the final part of this series next week. We’ll make sure to address 130V life hours in that post.

  • Ed Jocz

    I think the light industry is just a mess and of half way done job. Always said CFL bulbs last, wrong statement. Just keep replaceing CFL’s that don’t even last a year. Such a wrong statment. CFL’s will not work with wall motion sensor switches, catch on fire, contain mercury and take forever to come up to brightness.

    LED’s just too bright, cost to much, so bright just irritating to no end.

    Halogen bulb are staying but no one can tell me what the difference is between a 60 watt incandescent and 60 watt halogen, same amount to brightness and heat? So what is the saving, NONE.

    I been in our home 16 years and only replaced one incandescent bulbs, but three CLF’s. The last one lasted 15 seconds at a cost of $10.00.

    I use a motions sensors, I walk in the closet, light comes grab a shirt, walk out and the light turns off in 15 seconds, something CFL’s can not do.. So what is the issue, it saves and works. CFL’s can do that, same with LED’s, will not work with motion sensors. Takes 2-3 mins for the CFL to get up to brightness.

    I would purchase bulbs from you, but won’t buy the CFL’s or LED’s. Forty dollars for one LED 60 watt. You got to be kidding and not only bright, just makes things look bad.

    Sad thing we don’t even make the bulbs… Hello China!

    • Benjamin

      Those are some excellent points you raise, Ed.

      In the last part of this series, we’ll discuss how to extend life hours of your bulbs. One point we’ll address there is fluorescent (and CFL) life. A preview: Fluorescent bulbs are not intended to be switched on and off repeatedly. For that reason, they’re not a good option for closets, hallways, etc., but they do work great if they replace bulbs that stay on for long periods of time. They should never be used with occupancy sensors because occupancy sensors, by nature, keep lights turned on for only short intervals.

      As for halogens, I’m afraid you received some misinformation there. If you want to replace a 60 watt incandescent, you’ll only need a 40 to 50 watt halogen to produce the same amount of lumens. Here’s a good example on our site: http://www.1000bulbs.com/product/59024/Q-115042.html

      Finally, you’re right about LED prices. They are high, but they’re coming down very quickly. This bulb from Kobi costs just over $20, while similar bulbs would have cost twice that just a couple years ago: http://www.1000bulbs.com/product/64895/LED-13A1927IND.html

  • Stephen Perkowski

    All lies and deceptions, except old incandescent ratings which were pretty accurate. Testing a bulb without turning it on and off at least once a day is preposterous. Spiral CFL’s blow out at the rate of Incandescents where I switch on and off frequently (or at least the do in my home). LED’s are light emitting DIODES, and diodes do BLOW open. Example, when your power supply goes on your computer, its the rectifier, or bank of diodes, where one or more blow open. I have just gone through my 5th season of using 1 watt C7 LED’s, use about 25,000 of them, and have an approximate failure rate of 0.5% per year, so about 125 to throw out per season! Failure means at least one of the three LED’s in the C7 bulb blew open. Note that I have many Phillips brand LED 8w (40w equivalent), 12w (60 watt eqivalent), and 9w flood lamps (45w eqivalent). Some are over a year old, many in places where switched on and off frequently. I have zero failures to date.

    • Benjamin

      As stated in several of the comments above, you’re exactly right: Frequent on/off cycles of CFLs, or any fluorescent bulb for that matter, will cause premature failure. Next week’s post will explain that in more detail.

      We’re glad to hear you’ve had such good experiences with LED. Are those 25,000 C7 bulbs all for your own home, or are you a contractor?

  • Maynard Franklin

    In our household we have many different lighting requirements.

    I recently replaced 6 PAR 60W bulbs with CFL PAR’s in our kitchen. They take about 90 seconds to attain full brilliance. In the kitchen that’s no big deal, but in an area where you want full light instantly, it’s unacceptable. Kitchen lights are turned on for a duration, whereas hall lights need instant illumination. I am continuing to use incandescants in the hall lighting, and where dimming is required.

  • Joshua Rice

    Hi, I have some thoughts. As we know Thomas Edison, what the world did he gave out a “candle power” instead of “lumens”? When Thomas taught the customer looking or shopping for a simple wattage of the light bulb. Yearly later, lumens statement came out on every light bulb package. I selected lumens very well, it like tell you how much brightness the bulb contain. What the wattage comes from? Heat and energy usage, am I correct? Considering myself, when comparing to lumens and life of the bulb (also the voltage). I have been purchased 130 volts bulb shown a different taste of standard 120 volts bulb because of lower lumens, longer life, and little less energy usage. Looking at the picture and says why lumens are quite so low at 130 volts bulb, does meant manufacturers final initialized to put in test how much light output at beginning of life to before ends of life as near? So, what do you think?

    I love the name of website. Great services, unbeatable prices, and easy orders online. Thank you!

    • Benjamin

      Thanks, Joshua. If I understand our question correctly, you’re asking why lumens (light output) is lower on a 130V bulb than on a similar 120V bulb.

      A 130V bulb has a thicker, more sturdy filament meant to withstand a hypothetical input voltage of 130V. Most homes, however, provide an input voltage of only 120V. When the lower voltage meets the increased resistance of the 130V rated filament, it is unable to produce the full design lumen output of the bulb.

      But there is also a trade-off here. Even though it produces less lumens, it also uses fewer watts and lasts longer, making it a better value in most cases.

  • Dennis Murray

    I love this. It’s good to get information but also feedback from individuals that are experiencing different issues with the product. Very informative.

  • Larry Adelmund

    Is it possible to install a T8 in place of a T12?

    • Benjamin

      With modifications, yes. You would most likely have to change out the ballast.

  • Pingback: Light Bulbs: How many hours will a Filament bulb last? - Quora()

  • Ashley Hunter

    For which type of bulb? LEDs are less effected by on/off cycyles than other bulbs. They are instead tested for light output over a period of time. Our more recent article “How Long Will Your Light Bulbs Last?” may give you some more insight.

    Link: http://blog.1000bulbs.com/how-long-will-your-light-bulbs-last/