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  • Author Author: ralphjy
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Filament LED Failure Conundrum

ralphjy

I recently started having problems with an LED bulb "burning out".  I've used LED filament lights for a few years.  I have noticed that they don't seem to have the lifespan of the more prevalent individual chip on substrate lights that I normally use.  If the chip on substrate LEDs fail early it is usually due to the LEDS having a poor bond to the heatsink which causes thermal induced failure (once I had a component fail in the current source).  These filament bulbs normally seem only to last 2-3 years @ ~4000hrs/year.  I use them in my outdoor garage lamps to get the old style "filament" appearance.

 

One of my older filament bulbs started to get dim, so I replaced it with a new one.  After about a week I noticed that the new bulb was also dim.  I verified that the bulb itself was bad and replaced it with another new one - only to have it also fail after a few days.

 

This bulb is on a circuit with with 4 other bulbs (3 lamps on the garage and 2 on my entry).  All of the other bulbs are doing fine.

image

 

In old incandescent bulbs this would usually indicate an intermittent socket contact causing the filament to burn out..

 

 

These are the bulbs that I'm using:

 

Vintage Dimmable Edison LED Light Bulbs 100W Equivalent, E26 Base ST64/ST21 8W LED Filament Bulbs, 2700K Warm White, 1200Lumens, Antique Clear Glass Light Bulbs.

image

 

 

I took a quick look on wikipedia: https://en.wikipedia.org/wiki/LED_filament .

image

 

Some excerpts of interest:

"The LED filament consists of multiple series-connected LEDs on a transparent substrate, referred to as chip-on-glass (COG). These transparent substrates are made of glass or sapphire materials. This transparency allows the emitted light to disperse evenly and uniformly without any interference. An even coating of yellow phosphor in a silicone resin binder material converts the blue light generated by the LEDs into light approximating white light of the desired colour temperature—typically 2700 K to match the warm white of an incandescent bulb."

 

"The lifespan of LED emitters is reduced by high operating temperatures. LED filament bulbs have many smaller, lower-power LED chips than other types, avoiding the need for a heatsink, but they must still pay attention to thermal management; multiple heat-dissipation paths are needed for reliable operation. The lamp may contain a high-thermal-conductivity gas (helium) blend to better conduct heat from the LED filament to the glass bulb."

 

"The life expectancy of the LED chips correlates to the junction temperature (Tj); light output falls faster with time at higher junction temperatures. Achieving a 30,000 hour life expectancy while maintaining 90% luminous flux requires the junction temperature to be maintained below 85 °C.  Also worth noting is that LED filaments can burn out quickly if the controlled gas fill is ever lost for any reason."

 

But nothing that suggests that this is a typical early failure mode.  I doubt that it is caused by bad filaments since they all went dim at the same time.  More likely caused by the electronics in the socket base.

 

Anyone else experience this type of repeated failure where only a single bulb in a parallel circuit is going bad?  I guess I'll have to deconstruct the bulb to determine what actually failed.  I noticed that this is a "dimmable" bulb.  At least now I have a couple of bad ones to play with image.

Parents

  • The problem may just be bad quality with newer products, but could also be thermally-induced. Enclosed fixtures and high temperatures may cause certain drivers to "fold-back" resulting in dimmer output after the globe has been running for a while, but is reversible. Permanent dimming can occur if the LEDs have been overdriven and overheated, although sometimes you might encounter issues with heat destroying the electrolytic capacitor in the driver causing it to "dim" through increased flickering.

    It is quite perplexing, but we do know that manufacturers sometimes are overzealous with the number of lifetime hours. An estimate of 15,000 is usually reasonable but not all globes will get there for a number of reasons ...

    - Gough

Comment

  • The problem may just be bad quality with newer products, but could also be thermally-induced. Enclosed fixtures and high temperatures may cause certain drivers to "fold-back" resulting in dimmer output after the globe has been running for a while, but is reversible. Permanent dimming can occur if the LEDs have been overdriven and overheated, although sometimes you might encounter issues with heat destroying the electrolytic capacitor in the driver causing it to "dim" through increased flickering.

    It is quite perplexing, but we do know that manufacturers sometimes are overzealous with the number of lifetime hours. An estimate of 15,000 is usually reasonable but not all globes will get there for a number of reasons ...

    - Gough

Children
  • in reply to Gough Lui

    This is an interesting failure mode.  I was contemplating the best way to cut the glass globe from the socket and realized that I should take a picture of the dim filament (to show the individual LED elements).  When I turned the bulb on - it had recovered.  Of course, I put it back out and it failed again after a few hours.

    I tried the second bad bulb and it is still bad.  I'll need to check the first bulb to see if it will recover again - just need to get the ladder out Unamused.

    So, probably is something thermal - I won't know until I cut one open to look at it.