LEDs and Temperature

Just reading of LED needing to be kept cool and I was wondering why. Is it because standard components are used which will fail, or is there some electrical principle that will always cause failure at a particular temperature? Could some re-design make them happier at higher temperatures?

Reply to
DerbyBorn
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All semiconductors need to be kept relatively cool. A max of about 200C comes to mind from years ago.

Reply to
Bob Minchin

I think its a problem of removing the heat fast enough. Most semiconductors become problematic if they get too hot. Brian

Reply to
Brian Gaff

Germanium was very bad indeed, you could not get that semiconductor very hot before thermal runaway happened. I don't know the figures for Galium arsanide and the other materials used in LEDs. Brian

Reply to
Brian Gaff

Diffusion kills semiconductors when they get too warm and it also cooks the phosphor used in white LEDs. Some show obvious signs of scorching after a length of time in service. There are images online somewhere.

Efficiency also suffers when they get warm as more leakage current flows through a hot semiconductor junction without making light.

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Although I think their curves are a bit out of date (ie pessimistic).

You can design semiconductor devices to survive at higher temperatures but in domestic lighting applications the weakest link is usually the capacitors in their power supply rather than the actual LED itself.

For white LEDs the phosphor tight up against the emitting blue LED die is a weak point in that it is operated close to its limit and suffers photon damage losing output in the longer term even if it doesn't char.

Reply to
Martin Brown

200C storage. Genereally 180C operating junction temps.

But lifetime is a lot less at that sort of temp.

Dopant actually migrates through the semiconducting barriers as they age, and heat speeds it up.

Reply to
The Natural Philosopher

Another problem with many LED lamps is the electronic drivers don't like heat much either. So if your lamp base has an electrolytic cap in it (as many do) its not going to last long at over 100 degrees.

Reply to
John Rumm

Capacitors too have a shorter life with heat. And SWPS rely on fairly high stressed caps.

Reply to
Dave Plowman (News)

I have some kitchen downlights (Halers) where the driver assembly is separate from the lamp unit. They have a 7 year warranty - I guess this is the way to go. Imagine the electronics in a "ceiling rose) and the lamp on a pendant. I guess that would work. However, makers have felt pressure to make everything fit a conventional lamp envelope.

Reply to
DerbyBorn

Yes, we're in a transition phase at the moment. The problems are really with LED lamps which have to retrofit an existing, often unsuitable, luminaire. The purpose made LED lights should be much better in this respect, and with the greatly improved lifetime, replacing a whole unit rather than just a lamp shouldn't cost more in the long run.

Cheers

Reply to
Syd Rumpo

same thing happened with PC PSUs a while back someone had one the other day and I brought some capacitors rated at 130C 2000hrs I think, you can get 105C and the normal range are mostly 85C. This is why a lot of LED lamps donl;t last the 50K hours stated, if you read the full specs some are only rates at 50K if you use them for less than x hours at a time.

Of course there are some 'ankers on her that will say I'm wrong. So before tehy embarress themselfs lijke a high wranking academci telling me there no such thing as the factories and workplaces act.....

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Go to the specs tab on the 3.6 Watt GU10 LED Spotlight - 35W Replacement hover the mouse over the average life hrs the green.

For dave plowman who has trouble reading it says. "When the bulb is on for 4 hours a day".

and this is another reason I dim LEDs it's not brightnes or to save money on electricity costs.

Reply to
whisky-dave

True. And the same applied to CFL. Making any energy saving type which needs a power supply of some sort with the PS built in is invariably a compromise. I'm rather surprised new standard lighting wiring for LEDs - perhaps with a central power supply or two - hasn't been devised.

Reply to
Dave Plowman (News)

It has, they are 12V usually.

For some reason people fit 240V ones instead.

Reply to
dennis

I'd have thought those academics able to afford teeth?

Reply to
Dave Plowman (News)

I've not seen much of a range of 12v LEDs - apart from MR16 and those made for cars. Can you give a link to a site that sells them? But a 12v LED would also include a power supply of some sort.

They're likely to want something looking like they're accustomed to see.

Reply to
Dave Plowman (News)

Maybe they just like sucking ;-P

Reply to
whisky-dave

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Reply to
73hg

Yup indeed. I retired a GU10 spot the other day that was still working LED wise, but was flickering because the cap in its base had lost so much capacitance.

It actually says: "Manufacturers will give lifetime claims in multiples of 1000 hours. One thousand hours is equivalent to about 6-months use when the bulb is on for 4 hours per day. A traditional halogen spotlight bulb is expected to last about one year (2000 hours) where as an LED will last between 30,000 and 50,000 hours - that?s between 15 and 25 years! Switching to LEDs means you may never have to change your light bulbs again.",

which (to me at least) does not seem to imply any maximum duty cycle or period of on time to achieve that lifetime on that particular product. (others may differ obviously)

Reply to
John Rumm

So that's why you keep on having to buy new dimmers?

BTW, have you any data to prove altering the waveform into the LED PS will actually improve the life? My guess is not.

Reply to
Dave Plowman (News)

Heh heh. If the average life of an LED was actually 15 years, why don't they give them a lifetime warrenty? The number of people who could produce a receipt after 15 years would be very very small.

Any claim made to the life of a product should be taken as Trump speak unless backed up with a decent warrenty.

Reply to
Dave Plowman (News)

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