# Durability of 110V LED bulbs?



## dirckj (Aug 9, 2007)

I love these new bulbs; best that I have bought are the 3x1W CREE XR-E 240 lumen standard Edison base type. Really, we are _above_ CFL efficiency now. And, CFLs dim to 80% of original brightness in 2000 hours, as I understand it.

So the question is, does anyone have information on the brightness dropoff over time of the new LED 110V bulbs? I have some older versions that have terrible durability (less than hundreds of hours to brightness half life), but my use of the new bulbs with the CREE XR-E leads me so far to think that these will in fact be quite durable. Anyone know?


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## brickbat (Aug 9, 2007)

I don't think it's possible to answer this accurately. It depends on two main factors. First, what LED is being used? Some, Like the CREE and others have decent longevity and the manufacturer's claims are probably credible. Some LEDs come without the pedigree, and the manufacturer's claims about lifetime might be, umm, let's say optimistic.

The other factor is the die temperature at which the LED is operating. Semiconductor lifetimes depend on temperature, and if the lamp manufacturer is overdriving the LED, or has the undersized heatsink system, the LED won't meet the specified lifetime.

I suppose another factor needs to be considered, too. And that is the susceptability to power line surges and transients. Any lamp can die an untimely death if subjected to a massive spike...

So, if you have a lamp in hand that you know is using CREE LEDs, and wonder about its longevity, I'd meassure the LED temperature, calculate the die temperature, and look at the data sheet for the LED to see if its being operated within the published specs. That's the engineer's way. The other way is to post a question here, get a lot of anicdotes, and take a guess you're comfortable with...


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## Kinnza (Aug 10, 2007)

Fully agree with what *brickbat *said.

The only accurate way is measuring temp and calculating LED's junction temps.

But if the bulb is running the LEDs at 350mA (for about 1w each) and the design decent, those LEDs should reach 50Kh of use before reaching 70% of initial output. Minimun 35Kh.

If the LEDs run harder, then accurate measurement would be required to do any stimation.


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## dirckj (Aug 13, 2007)

Now I are enguneer (mechanical), but I don't know how to go about measuring these critical temperatures, much less do a calculation of the junction temperature. I can say that it appears that the new designs that I have bought are far better than the early ones, simply because the early designs have horrid durability. Of course, I am hoping that the newer models will realize the longevity that you suggest may be possible. Time will tell. (But slowly, since I only these lights a max of 5 hours/day, or tops ~2k hours/year, meaning I will need to wait 25 years to know.) (And yeah, others will do 24/7 testing on equivalent bulbs so I will know before then, and some engineers will also Arrhenius evaluations, so maybe I won't have to gaze w/ glazed eyes until I'm well over 70.) 

On the other hand, I are enguneer and fascinated with these things, and I like the bluish color, so maybe you will find me gazing dazedly on...


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## James Jackson (Aug 13, 2007)

Well, I have a couple of the newer Acriche 120VAC LEDs from Seoul Semi.

They come mounted to a thermal board, and you need to wire wires to the SMT pads, and add a heatsink.

The ones that I got are rated at 150 lumens and 4.0 watts.

I added a salvaged heatsink from a pc IC, and two 10-degree lenses - and wired it to an Edison base socket.

I plugged this in to the light socket, and lit it up. It's bright!

I measured the power at about 3.0 watts. Not bad.

The light - I measured at about 150 lux - at 1 meter - which jives with their spec.

I also measured the temp with an InfraRed thermometer - and it gets to about 80-degrees C. 

I think it'll be working for a while - unless it 'pops' from a powerline surge.

I like it a LOT!!!

Regards,

James


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