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Old 4th February 2012, 10:28 AM   #101
SY is offline SY  United States
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* if an LED light source is treated well (good circuit design, no power surges etc) and it is simply used as intended, what finally causes it to fail? Do the materials it uses breakdown due to age, electrical causes or both?
The electronics in the driver are far and away the most likely failure mode. The LEDs themselves have an insanely long lifetime if they are kept cool.

The materials used in the LED itself are generally indium, gallium, and nitrogen. The phosphor is yttrium, aluminum, and oxygen, usually with a trace amount of cerium. The quantities of the rare earths used are tiny.
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Old 4th February 2012, 10:37 AM   #102
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Just wanted to assure myself you were speaking of dopants and ran across this tidbit I didn't know - "Many commercial LEDs, especially GaN/InGaN, also use sapphire substrate." Might require further investigation.
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Old 6th February 2012, 02:01 AM   #103
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Quote:
Originally Posted by SY View Post
The electronics in the driver are far and away the most likely failure mode. The LEDs themselves have an insanely long lifetime if they are kept cool.

The materials used in the LED itself are generally indium, gallium, and nitrogen. The phosphor is yttrium, aluminum, and oxygen, usually with a trace amount of cerium. The quantities of the rare earths used are tiny.
Thanks! (now all those movies like Planet of the Apes and shows like Stargate SG-1 with their respective technologies that seem to last for thousands of years are a little more believable ).
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Old 7th February 2012, 04:33 PM   #104
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Quote:
Originally Posted by River757 View Post
Couple questions:

* if an LED light source is treated well (good circuit design, no power surges etc) and it is simply used as intended, what finally causes it to fail? Do the materials it uses breakdown due to age, electrical causes or both?
Whith products sold to consumers, I would think the driver electronics would be likely the first part to fail, especially if there are electrolytic caps in it. But only time will tell for sure.

I maintain the lighting in the lobby and stairwell of our apartment building, and I mainly use consumer grade CFLs. At one point in time I used both the Philips Genie and an identically looking and specced version sold under a private label (but with a Philips Lighting factory symbol on the socket).
In all Genies the ballast outlived the lamp. With the seemingly identical private label, however, it was the other way around.
I opened several of both and found that the Genie had a slightly different ballast with higher grade caps than the private label. In all of the private labels the smoothing cap had blown.

The answer to your question will probably depend on the quality of the components used in the LED driver. I'd definitely stick with reputable brands.

With professional equipment, I'd expect the driver stage to have been designed with as long as possible lifespan in mind.
As an example I take the Philips GentleSpace LED high-bay lighting http://download.p4c.philips.com/l4bt...37_ffs_eng.pdf .
The specified lifetime is unbelievable (75,000 hours at 70% lumen maintenance). They also specify total luminaire failure rate and driver failure rate.

Last edited by jitter; 7th February 2012 at 04:39 PM.
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Old 7th February 2012, 04:39 PM   #105
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In all electronics there is a reservoir electrolythic capacitor associated with the DC part. The capacitor is the one that does not like to be hot. And limits the life of the LED/CFL bulbs.
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Old 7th February 2012, 04:49 PM   #106
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Originally Posted by sofaspud View Post
Just wanted to assure myself you were speaking of dopants and ran across this tidbit I didn't know - "Many commercial LEDs, especially GaN/InGaN, also use sapphire substrate." Might require further investigation.
Yes the sapphire substrate is used as a mirror. People think that LEDs are by nature directional, this is true for the light emitted from the completed unit, but the actual emitting device isn't. From what I understand the sapphire substrate is used as a mirror to make sure that most of the light is reflected back in the direction it is wanted. The sapphire part of the construction is apparently one thing that sets a reasonably high price for LEDs. I do know that some manufactures are researching the use of different materials for this job, as a way of reducing price, but as far as I know most LEDs still use sapphire.

Quote:
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In all electronics there is a reservoir electrolythic capacitor associated with the DC part. The capacitor is the one that does not like to be hot. And limits the life of the LED/CFL bulbs.
This isn't necessarily true. Most of the low voltage LED drivers don't need anything else then a few small ceramics. So in theory any low voltage halogen replacement would never need see an electrolytic cap. Of course the SMPS that steps down the mains voltage probably does have lytics in side but then this can be hidden somewhere out of sight, can be reasonably bulky and can be kept cool. I think the biggest bane of LED lighting is trying to come up with retrofit bulb designs.
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Old 7th February 2012, 05:35 PM   #107
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I think the biggest bane of LED lighting is trying to come up with retrofit bulb designs.
I totally agree. Lately I've noticed some wonderful examples of how well LEDs can perform in made-for-LED luminaires in industrial and commercial applications.
But the ugly retrofit LED bulbs intended as a replacement for incandescent lamps? That's not the future of LED lighting, at best it's an intermediate that IMHO should disappear in the next decade and take the old sockets (e.g. E14/E27) with them.
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Old 7th February 2012, 05:48 PM   #108
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I recently removed under-cabinet lights in my kitchen and fixed instead LED rope there under cabinets. Now it is more reliable and the light is smooth and well diffused.

Speaking of LED bulbs, it is pure business approach, to sell more of goods for existing sockets. And some goods are bad, for example a bulb I bought one month ago has a cap that leaks electrolyte.
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Last edited by Wavebourn; 7th February 2012 at 05:52 PM.
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Old 7th February 2012, 07:59 PM   #109
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Well I think the biggest problem is the mindset that everyone has attached to lighting in general. This is at least true in the sense of a lot of decorative lighting, where traditionally one buys the lamp body/shade etc to suit their decor and then you fit the bulb and replace it as it breaks.

The trouble with that is that most people already have loads of lamp bodies and as a result the industry tries and makes replacement bulbs. What one needs are entire replacement lamp bodies for complete replacement designs where the body can act as a heatsink. This vastly increases the available surface area for cooling the LEDs and allows an efficient driver to be used in the base of the lamp. Efficient mainly because the size constraints created by needing a tiny LED driver in a replacement bulb drive down component sizes but as a result reduce overall efficiency, they also run hot which reduces efficiency even further, both in terms of the driver and the LEDs themselves. Having a larger cool space means you can use lytics without too many concerns for reliability if decent quality parts are used.

Of course the lamp base design would have to emit light over the surface area of a sphere, but they could be designed with a normal shade fitting built in so one at least can have some extra choice over the decor. They would also be quite expensive, but brightness shouldn't be an issue as the extra heatsink area provided by the base unit would allow the light output to be scaled up so that it easily competes with or outperforms the light output of a standard 60 watt incandescent.
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Old 7th February 2012, 08:40 PM   #110
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Over the last month, I've bought a few different LED globes, The Osram bulbs, though expensive, have much better light than CFL, the cheaper Chinese ones very bright white, interesting to see if they last the distance...

An interesting problem with a 4.5W Osram bulb in a downlight fitting - it would flash, with the power turned OFF - apparently the capacitance between live & neutral is enough to charge the starter circuit to the point where it will discharge. Swapping the bulb with a different model fixed the problem, but apparently a high value snubber resistor will also fix it.
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