Weskix
Newly Enlightened
I was wondering if LED's slowly dull after hours of use, or do they just quit at the end of their 100,000 hour or 50,000 hour life?
Do LED bubls weaken/lose brightness over time?
- Thread starter Weskix
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Illum
Flashaholic
Welcome to CPF! :wave:
theres a couple of threads open to this topic, LEDs will lose their brightness over time, but that amount of time before a significant drop in output is nearly impossible for any user to attain under normal operating conditions...
try this thread: http://candlepowerforums.com/vb/showthread.php?t=131304
theres a couple of threads open to this topic, LEDs will lose their brightness over time, but that amount of time before a significant drop in output is nearly impossible for any user to attain under normal operating conditions...
try this thread: http://candlepowerforums.com/vb/showthread.php?t=131304
Weskix
Newly Enlightened
Thanks I tried a search, but since the title is a litte different than what i was looking for, it came out a little spotty. Thanks for the welcome
LED lifespan is rated to a percentage of the initial brightness. Most LED lifespan estimates are to 70% of initial brightness. Luxeon LEDs will get slightly brighten over the first few thousand hours. The brightness dropoff is very gradual at first, then steepens near the end of the LEDs life. LEDs don't simply blink off unless there is a major failure due to a power supply problem (such as being severly overdriven or severly overheating).
5mm LEDs are shown to not get anywhere near their rated lifespan, due to a poor thermal path from the LED chip, and the clear epoxy encapsulent yellowing/fogging over time. This is especially true of blue and white LEDs, where the blue light significantly acellerates the degridation.
Luxeon LEDs will actually achieve their rated lifespan if properly heatsinked and driven with a proper current regulator. They have a very good thermal path from the LED chip to a heat sink attachment point, use a silicone encapsulant to ease bond wire stress, and an acrylic dome to prevent yellowing/fogging.
Read this document from lumileds, it shows the effects of heat and drive current on several types of luxeon LEDs, and is using actual test data:
http://www.luxeon.com/pdfs/RD25.pdf
5mm LEDs are shown to not get anywhere near their rated lifespan, due to a poor thermal path from the LED chip, and the clear epoxy encapsulent yellowing/fogging over time. This is especially true of blue and white LEDs, where the blue light significantly acellerates the degridation.
Luxeon LEDs will actually achieve their rated lifespan if properly heatsinked and driven with a proper current regulator. They have a very good thermal path from the LED chip to a heat sink attachment point, use a silicone encapsulant to ease bond wire stress, and an acrylic dome to prevent yellowing/fogging.
Read this document from lumileds, it shows the effects of heat and drive current on several types of luxeon LEDs, and is using actual test data:
http://www.luxeon.com/pdfs/RD25.pdf
JohnK
Flashlight Enthusiast
My Streamlight 4AA7LED was replaced (by SL) because a couple of the LEDs began strobing.
This was the second version, still seriousy overdriven.
The new module was easily three times as bright as the old.
Serious degradation here. I think I ran 3 sets of batteries through the old one, so maybe 12-15 hours of operation.
This was the second version, still seriousy overdriven.
The new module was easily three times as bright as the old.
Serious degradation here. I think I ran 3 sets of batteries through the old one, so maybe 12-15 hours of operation.
NewBie
*Retired*
The small 5mm LEDs degrade really fast, especially if they are overdriven.
Good examples:
https://www.candlepowerforums.com/threads/126857
A actual product that degrades really fast:
https://www.candlepowerforums.com/posts/1583347
There are the LEDs that were designed as higher power parts from the get go, made by Philips (Luxeon), Nichia, SSC, CREE, OSRAM (used to be Siemens), and others. You will notice their construction is quite different, designed to greatly lower the thermal resistances (so you can get the heat out), and using larger die, to handle the power better, as well as using silicone instead of epoxy/acryllic to greatly reduce the effects of yellowing with the high lighting and heat levels. You will notice they also have robust thermal interfaces to allow you to heatsink the parts properly. There are a number of other things, but these are the nuts and bolts.
Each company has a number of application guidelines, which are designed to allow you to properly employ these high power parts, and maintain the performance of the devices over time, and they should be closely followed and understood.
As an example, OSRAM has specific information for dealing with just the thermal requirements:
http://catalog.osram-os.com/media/_en/Graphics/00036578_0.pdf
And the electrical requirements:
http://catalog.osram-os.com/media/_en/Graphics/00015957_0.pdf
Other things available are stuff such as reliability information (check out the g forces these can take):
http://www.cree.com/products/pdf/XLamp_Reliability.PDF
CREE has their thermal guidelines also:
http://www.cree.com/products/pdf/XLampThermalManagement.pdf
Philips has their guidelines as well, for their Luxeon devices:
Electrical:
http://www.lumileds.com/pdfs/AB11.PDF
Lifetime:
http://www.lumileds.com/pdfs/AB07.PDF
Thermal:
http://www.lumileds.com/pdfs/AB05.pdf
Seoul Semiconductor Corporation:
Reliability:
http://www.essc.co.kr/_HOMEPAGE/home_kor/product/spec/Reliability.pdf
Thermal Management:
http://www.essc.co.kr/_HOMEPAGE/home_kor/product/spec/thermal.pdf
Electrical:
http://www.essc.co.kr/_HOMEPAGE/home_kor/product/spec/electrical.pdf
Electrical failure modes:
http://www.essc.co.kr/_HOMEPAGE/home_kor/product/spec/failuremode.pdf
LED myths:
http://www.lumileds.com/pdfs/10Myths1.PDF
Good examples:
https://www.candlepowerforums.com/threads/126857
A actual product that degrades really fast:
https://www.candlepowerforums.com/posts/1583347
There are the LEDs that were designed as higher power parts from the get go, made by Philips (Luxeon), Nichia, SSC, CREE, OSRAM (used to be Siemens), and others. You will notice their construction is quite different, designed to greatly lower the thermal resistances (so you can get the heat out), and using larger die, to handle the power better, as well as using silicone instead of epoxy/acryllic to greatly reduce the effects of yellowing with the high lighting and heat levels. You will notice they also have robust thermal interfaces to allow you to heatsink the parts properly. There are a number of other things, but these are the nuts and bolts.
Each company has a number of application guidelines, which are designed to allow you to properly employ these high power parts, and maintain the performance of the devices over time, and they should be closely followed and understood.
As an example, OSRAM has specific information for dealing with just the thermal requirements:
http://catalog.osram-os.com/media/_en/Graphics/00036578_0.pdf
And the electrical requirements:
http://catalog.osram-os.com/media/_en/Graphics/00015957_0.pdf
Other things available are stuff such as reliability information (check out the g forces these can take):
http://www.cree.com/products/pdf/XLamp_Reliability.PDF
CREE has their thermal guidelines also:
http://www.cree.com/products/pdf/XLampThermalManagement.pdf
Philips has their guidelines as well, for their Luxeon devices:
Electrical:
http://www.lumileds.com/pdfs/AB11.PDF
Lifetime:
http://www.lumileds.com/pdfs/AB07.PDF
Thermal:
http://www.lumileds.com/pdfs/AB05.pdf
Seoul Semiconductor Corporation:
Reliability:
http://www.essc.co.kr/_HOMEPAGE/home_kor/product/spec/Reliability.pdf
Thermal Management:
http://www.essc.co.kr/_HOMEPAGE/home_kor/product/spec/thermal.pdf
Electrical:
http://www.essc.co.kr/_HOMEPAGE/home_kor/product/spec/electrical.pdf
Electrical failure modes:
http://www.essc.co.kr/_HOMEPAGE/home_kor/product/spec/failuremode.pdf
LED myths:
http://www.lumileds.com/pdfs/10Myths1.PDF
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