Electronics > Repair

Why/how do these LED lamps fail so fast?

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cosmicray:
From the wordpress document ...


--- Quote ---The PCB is glued to an aluminium heatsink
--- End quote ---

That is a sign that the LEDs are being run out towards the datasheet limits. Normal practice is that 50% of the power is being dissapated as heat, but a Cree Thermal Management document says to plan for as much as 70% heat. The heat is what destroys the LEDs. Get rid of that heat, and they will last a very long time.

jmelson:

--- Quote from: cosmicray on November 23, 2024, 06:27:53 pm ---From the wordpress document ...


--- Quote ---The PCB is glued to an aluminium heatsink
--- End quote ---

That is a sign that the LEDs are being run out towards the datasheet limits. Normal practice is that 50% of the power is being dissapated as heat, but a Cree Thermal Management document says to plan for as much as 70% heat. The heat is what destroys the LEDs. Get rid of that heat, and they will last a very long time.

--- End quote ---
Yup, I built my own fluorescent tube retrofits with a commercial constant current supply, see :
http://pico-systems.com/Lighting.html
I did this about 11 years ago.  I made a very conservative thermal design, with PC board as the thermal sink, and they have lasted quite well.  Possibly there is a tiny bit of brightness loss over this time, but I am REALLY happy with the results and longevity.  I am running 20 1W LEDs in series, at just about the 1 W level each, total power draw from the mains is a measured 21 W.
Jon

Pid:

--- Quote from: David Hess on September 21, 2023, 01:56:01 pm ---
--- Quote from: T3sl4co1l on September 21, 2023, 03:08:05 am ---Anyway, regarding LEDs: they are extremely long lived, in and of themselves, when ratings are respected.

The phosphor is actually the higher wear element, as it tends to fade over time.  The power density on it is quite impressive, for just a powdered mixture of ceramics that have this one magical property (fluorescence).  The blue LED chip itself also declines, but slower.

But that's just the LEDs themselves.

What's powering them, is another matter.

Lifetime can always be lower, and when it is economical to do so, it absolutely will be done.  Electrolytic capacitors are the most obvious and worst offender, with 2khr 85°C parts being common picks.  Put that in a stuffy lamp fixture and it might last mere months!
--- End quote ---

Exactly, the "50,000 hour operating life" specification is a fantasy based on the operating life of the LEDs to reach 50% brightness and has nothing to do with operating life and reliability of the LEDs and ballast.

When California passed their LED bulb mandate, they based the economics on that 50,000 hour operating life saying that LED bulbs would actually cost less over the long term.  (1)  After a few years, they admitted in a report that that operating life was grossly exaggerated (I knew that) and that the economics were so bad that incandescent bulbs were better; the extra cost of the LED bulbs was greater than the extra cost of the power for an incandescent bulb.  (2) Unfortunately, but not surprisingly, California has since censored that report and removed access to it, because fuck you citizens.

A reliable electronic ballast needs to not use operating life limited parts like aluminum electrolytic capacitors, be significantly derated, and include protection circuits which themselves will not fail.  Because of operating temperature, it probably also needs to use hybrid construction.

(1) I do not believe that politicians are stupid enough to fall for this.  They did it deliberately for purposes of rent seeking, so fuck them.

(2) I have had the same experience with government mandated electronically commuted motors which replace less efficient shaded pole motors.  Their operating life is short and replacement cost is high so their total cost of ownership is higher despite the power saved.

--- End quote ---

My understanding is that LEDs are rated by average rated life the same metric used for incandescent lamps.

cosmicray:

--- Quote from: Pid on November 24, 2024, 08:48:03 am ---
--- Quote from: David Hess on September 21, 2023, 01:56:01 pm ---
--- Quote from: T3sl4co1l on September 21, 2023, 03:08:05 am ---Anyway, regarding LEDs: they are extremely long lived, in and of themselves, when ratings are respected.

The phosphor is actually the higher wear element, as it tends to fade over time.  The power density on it is quite impressive, for just a powdered mixture of ceramics that have this one magical property (fluorescence).  The blue LED chip itself also declines, but slower.

But that's just the LEDs themselves.

What's powering them, is another matter.

Lifetime can always be lower, and when it is economical to do so, it absolutely will be done.  Electrolytic capacitors are the most obvious and worst offender, with 2khr 85°C parts being common picks.  Put that in a stuffy lamp fixture and it might last mere months!
--- End quote ---

Exactly, the "50,000 hour operating life" specification is a fantasy based on the operating life of the LEDs to reach 50% brightness and has nothing to do with operating life and reliability of the LEDs and ballast.

When California passed their LED bulb mandate, they based the economics on that 50,000 hour operating life saying that LED bulbs would actually cost less over the long term.  (1)  After a few years, they admitted in a report that that operating life was grossly exaggerated (I knew that) and that the economics were so bad that incandescent bulbs were better; the extra cost of the LED bulbs was greater than the extra cost of the power for an incandescent bulb.  (2) Unfortunately, but not surprisingly, California has since censored that report and removed access to it, because fuck you citizens.

A reliable electronic ballast needs to not use operating life limited parts like aluminum electrolytic capacitors, be significantly derated, and include protection circuits which themselves will not fail.  Because of operating temperature, it probably also needs to use hybrid construction.

(1) I do not believe that politicians are stupid enough to fall for this.  They did it deliberately for purposes of rent seeking, so fuck them.

(2) I have had the same experience with government mandated electronically commuted motors which replace less efficient shaded pole motors.  Their operating life is short and replacement cost is high so their total cost of ownership is higher despite the power saved.

--- End quote ---

My understanding is that LEDs are rated by average rated life the same metric used for incandescent lamps.

--- End quote ---
The finished consumer device (a light bulb) may well be rated like that, some of this discussion is about the component parts (i.e. the LED chip). Those tend to have a much longer life span, when not pushed to the electrical maximum ratings.

David Hess:

--- Quote from: Pid on November 24, 2024, 08:48:03 am ---My understanding is that LEDs are rated by average rated life the same metric used for incandescent lamps.
--- End quote ---

No, the operating life of the LED bulbs was rated to be the operating life of the LEDs which is based on how long it takes for the LEDs to reach 50% brightness, so 50,000 hours or whatever.  This is irrelevant because LED bulbs fail in other ways, long before that number is reached.  Incandescent bulbs are rated by mean time to failure and designed so they say for a 1000 hour life.

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