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Thread: Totally OT, LED lighting question

  1. #1

    Question Totally OT, LED lighting question

    I recently replaced my Kitchen ceiling florescent fixture with a 18"X48" LED fixture, it uses an LED strip that appears non-replaceable. While the unit is
    rated for 30,000-50,000 hours I am skeptical. My question therefore is, what has the greater effect on LED burnout, cycles or burn time?

    Any solid state electronics engineers care to authoritatively answer that?

    Thanks!
    -bruce

  2. #2
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    I have done electrical work for awhile and recently we have been installing a lot of leds . I think the only failure was from a lightning surge I seen. I think long term vibration would cause problems. And why I say that is have you seen cars with leds and one or two be out with the rest doing fine.

  3. #3
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    Quote Originally Posted by Bruce Schoenleber View Post
    I recently replaced my Kitchen ceiling florescent fixture with a 18"X48" LED fixture, it uses an LED strip that appears non-replaceable. While the unit is
    rated for 30,000-50,000 hours I am skeptical. My question therefore is, what has the greater effect on LED burnout, cycles or burn time?

    Any solid state electronics engineers care to authoritatively answer that?

    Thanks!
    -bruce
    In my experience and research the life may related to the heat. Those with poor heat sinks might go quicker. Those with low quality circuitry might also go quicker even though the LED emitters are still fine, same as CFLs. The life ratings on all the fixtures are calculated estimates, not tested times.

    My on anecdotal "evidence" is with some I left on all the time. These were porch light fixtures and they did get warm. Both started flickering and failed within four years.

    Save the receipt. My new policy is to not buy fixtures with non-replaceable elements.

    JKJ, not a solid state engineer or liquid or gaseous state engineer

  4. #4
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    I have had Led lights already for a couple of years in use in our house, and have a few that stopped working after a relatively short time, it was not the LEDs but the electronic part within that malfunctioned, heat seems to the biggest problem with that, as it was the lights that had no airflow, closed to the top fixtures that were the ones that I had to replace.

    My son here build his new house, and it is totally “off grid” he installed LEDs when building his house, they are outside as well as in every room, this going to be about 5 years now, and he had only one LED light stop working, it was very soon after it was installed, he did get a replacement for it, he also bought several spares, (for just in case).

    These lights are all so called pot lights and have lots of ventilation above the ceiling they sit in.


    Have fun and take care

  5. #5
    Talked with an EE friend of mine. His claim is LEDs are uneffected by cycling, unlike florescents. That is the answer I am going with.
    Hoping that I will be within the mean of the MTBF

    Thanks for the replies.

  6. #6
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    Quote Originally Posted by Bruce Schoenleber View Post
    Talked with an EE friend of mine. His claim is LEDs are uneffected by cycling, unlike florescents.
    That makes sense when you consider that LEDs are often turned on and off many times a second to control the color, temperature, apparent brightness, or even to create a strobe, usually through pulse width modulation. But maybe ask him if he is referring to the LED emitter itself or the whole package including the driving electronics. My understanding is the LED itself is not affected but cycling the fixture/bulb may be affected since that will cycle the electronics that drive the LED. A "great" way to blow a circuit is with multiple heating/cooling cycles - components can break from the thermal expansion itself, and worse, the current surge in poorly designed circuits.

    One possibly interesting tidbit about how heat can affect the life of the LED emitter: a discrete LED (the emitter itself) will only withstand a few milliamps of current before it gets too hot and "pops". Much of the circuitry in a fixture is to control this current. Maybe 30 years ago a friend and I experimented with supercooling a single red LED by immersing it in a dewar of liquid nitrogen (minus 321 deg F) and seeing how much current it would take. We set the dewar on my kitchen floor and cranked up the current driving an LED dunked in the liquid. We never could blow it out but it got so bright it made a blindingly bright circle of light on the ceiling 8' above. It was so bright I suspect looking directly at the LED would have caused eye damage. (and a safety warning: use extreme caution when playing with liquid nitrogen!)

    For those of us who have been "playing" with electronics for decades the advance in LED technology is astounding, not only in color and brightness but in the cost of both the emitters and the driving electronics (and integrated modules). It will be fun to watch what the next few years will bring.

    JKJ

  7. #7
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    I've had LED fixtures in the ceiling of my shop now for 2 years. They run all day most days. they are the 2 light 4 foot fixtures from Costco. I have had on bulb fail. The bulb on the other side works fine. It's the electronics because I swapped the leads on the bulbs and both bulbs will work when connected to the good side. In the kitchen we have 10 individual lights and they were burning out constantly. These were incandescents. I put LED's in their place and they are still running and that was about 2 years ago.

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    When we remodeled our kitchen 4 years ago, I started buying and replacing light bulbs with LEDs. I have had a couple expensive 3-way leds (used in reading lamps) fail. I have had a couple regular leds fail. But gradually as my incandescent bulbs fail, I am going to all leds. The combination of new windows, and going to leds has reduced our electrical use according to our service provider by 17-18%.
    Ken

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    Even though the life in hours of these LED's is huge if you look at the warranty on the box it no where matches this value. I too remodeled our kitchen a few years ago and replaced the can lights with expensive Sylvania LED's and after about 1-1/2 years they started to fail about one a week. Sylvania replaced them but the replacements didn't even look like the original. Was lucky that I bought these at Menards in that I brought all the bulbs back and they gave a full refund since I had the receipt and one of the boxes.

  10. #10
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    I'm an EE and my company produced IC's for these bulbs for a while. Any early failures would be due to the control circuitry and not the actual LED. The intrinsic reliability of a single LED should be on the order of 100's of years.

  11. #11
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    I just hung two of those "permanent" LED fixtures in our kitchen. I'm not really worried as the chance is they will out-live me, I suspect.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  12. #12
    As others have said, it's the drive electronics (which convert 120VAC to a tightly-regulated DC current) that will likely fail before the LEDs, themselves.

    That said, while they make appear to be non-replaceable, it's almost certain that the light fixture manufacturer is just buying the entire LED/driver module from someone else, and you can likely find the entire module as a replacement. I had a lightning strike damage a ceiling fan with an LED fixture, and found the entire LED/driver circuit board for a few dollars on Digikey.

  13. #13
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    Quote Originally Posted by Ken Fitzgerald View Post
    When we remodeled our kitchen 4 years ago, I started buying and replacing light bulbs with LEDs. I have had a couple expensive 3-way leds (used in reading lamps) fail. I have had a couple regular leds fail. But gradually as my incandescent bulbs fail, I am going to all leds. The combination of new windows, and going to leds has reduced our electrical use according to our service provider by 17-18%.
    SWMBO has a fondness for 3 way bulbs, it was the only practical way to vary light intensity of a fixture until fairly recently. I'm trying to replace 3 way fixtures with dimmers that replace the switch/lamp holder like this.

    https://www.amazon.com/Leviton-6151-...+dimmer+socket.

    I initially bought a different guts-only fixture but it had a short functional life. The Leviton has been good to date. We're running dimmable LED bulbs, the only problem is that the LED bulbs will run at a lower light output than they will start at so turn the knob until the light comes on then reduce the brightness if desired.

  14. #14
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    Dimming LEDs

    Quote Originally Posted by Curt Harms View Post
    ...We're running dimmable LED bulbs, the only problem is that the LED bulbs will run at a lower light output than they will start at so turn the knob until the light comes on then reduce the brightness if desired.
    I understand that may depend on the electronics in the bulb. Have you tried with others? Apparently the electronics in the bulb itself must sense the output from the dimmer and reinterpret it to drive the LED appropriately, with either current reduction or pulse width modulation. It seems that some dimmers and some bulbs don't communicate or work together well.

    A search found several tips. Perhaps this one is useful: http://luxreview.com/article/2016/02...-dim-led-lamps

    JKJ

  15. #15
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    Hello Bruce,

    Where I worked we had equipment that had LEDs for a light source. They were powered by a 2400 Hz square wave. So they were turned on to full luminescence and full darkness 2,400 times each second. We had 14 of these and they ran 365.25 (add the leap year, ya know) days a year. After 10 years we had zero failures of the LEDs. Of course you could say it was a cheat, the LEDs had a 50% duty cycle so they actually had been on for only 5 years!

    It's safe to say a LED can be turned on and off without any problem. The problems with the lights have been pretty much covered. Heat will kill the LED and the supporting electronics can fizzle out. The screw in LEDs I've bought that died still had working LEDs. Did I take them apart? 'Course I did. I've never seen a LED that needed 25 volts for the forward junction to conduct. But then I haven't paid much attention to the illumination LED market.

    If the LEDs don't have a problem with heat dissipation they won't normally just go out. The rated life is reached when the LED dims to about 50% of it's initial output. The small signal LEDs I've seen get too dim to be useful after about 12-15 years continuous use IME. It's a long time.

    -Tom

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