Quetion/concern regarding LEDs

wraith1701 · Post by **wraith1701** » Fri Nov 09, 2007 1:51 pm

Hi gang.

This might be a stupid question, but don't LEDs burn out? I've frequently seen burned out bulbs on Christmas tree lights, and I'd hate to go through the trouble of building a lighted kit, only to have the bulbs go out on me. It would suck to have to tear the thing apart, re-install new LEDs, and try to re-build it.

Has anyone out there run into this problem?

Kylwell · Post by **Kylwell** » Fri Nov 09, 2007 2:51 pm

Yes LED will burn out but unless you're planning on running the light on the model continously you may never see them go.

macfrank · Post by **macfrank** » Fri Nov 09, 2007 3:04 pm

Kylwell wrote:Yes LED will burn out but unless you're planning on running the light on the model continously you may never see them go.

An LED correctly biased so that it's running within specs can run continuously for years, if not decades before it burns out.

USS Atlantis · Post by **USS Atlantis** » Fri Nov 09, 2007 3:49 pm

macfrank wrote:
Kylwell wrote:Yes LED will burn out but unless you're planning on running the light on the model continously you may never see them go.
An LED correctly biased so that it's running within specs can run continuously for years, if not decades before it burns out.

Searching around, I found that the generally accepted life-span of LED's is 50,000 hrs for White/Blue/Green and 100,000 hours for Red/Yellow

So, divide that into a year (8766 hours) you get 5.7-11.4 years continuous use. That's if you leave it on 24/7/365.

Have it on only 3-4 hours a day? 35-80 years

Also, that's it's nominal life at normal output. Using larger Resistors to drop it back to a lesser current will add years to that. - Take a 2750mcd Red resistor; nominal is 2.2v@20ma - using a larger resistor you can drop that to 1000mcd which is 2.2v@7.27ma . Still bright enough to light a model, but running at 36% the current should more than double the lifespan.

Atlantis

en'til Zog · Post by **en'til Zog** » Fri Nov 09, 2007 10:29 pm

Sitting here, looking at my computer, I can see three LED gadgets that have been plugged in and running continuously for over a third of a century each (except when I was actually moving my habitation).

One is a clock - one segment of each digit has been on 90% of the time and isn't noticeably dimmer than any other segments.

One is a cast pyramid of clear/red plastic with 10 of the first LEDs to become commercially available - blinking away since the very early 70's or late 60's. Hard to replace a LED that's been cast into a solid block of plastic.

The third is a 16 LED "Cylon Scanner" built in the early 70's - still glowing strong.

Also, I think the estimated life of the LEDs isn't to extinction or "burning out" but to the point that the LED is putting out half the light that it started with - the half life of the LED so to speak.

So, just run your LEDs a bit 'cooler' than the specs say and you shouldn't have much noticeable degradation. Say until maybe around 2060 or so!

Madman Lighting · Post by **Madman Lighting** » Sat Nov 10, 2007 3:59 pm

Ditto on all those thoughts of long-lived LEDs.

Atlantis is right, LEDs last from 5 to 11 years of constant on-time. I've had my DS-9 on most of the time for the last several years and its still just as brilliant as ever. That why I use ONLY LEDs for all my light up projects, they last practically forever.

-John C.

Mr. Engineer · Post by **Mr. Engineer** » Tue Dec 11, 2007 5:20 am

LEDs are current sensitive devices and as long as you feed it the right amount of current using the correct resistor values, they would last for a long time.

The only time it "died" in my hands were when I accidentally gave it the wrong voltage/current, static shock (some version LEDs are sensitive to this) or ran without heatsinks (for Luxeons)

en'til Zog · Post by **en'til Zog** » Tue Dec 11, 2007 11:10 am

And Welcome, Mr. Engineer, to our group!

Luxeons and other 1,2,3 or 5 watt LEDs are so neat to work with, aren't they! As long as you keep 'em sorta cool with heat sinks as you said.

Model ON!

Mr. Engineer · Post by **Mr. Engineer** » Tue Dec 11, 2007 9:14 pm

Thanks.

There is a solution to driving Luxeons to keep them cool. I am used to direct drive (i.e. Batteries and resistor) that I forgot about PWM and also those Boost/Buck drivers which I am not so familiar about.

These will keep the Luxeon bright and cool (and do not kill your batteries like when I did my own lightsaber)

My Lightsaber
http://www.chowfookcheong.com/Lightsaber/Lightsaber.htm

jwrjr · Post by **jwrjr** » Tue Dec 11, 2007 11:28 pm

Once you get the hang of pulse width modulating leds, you can do amazing things with them. But as lonf as you are careful about not exceeding the current limits on them, you don't have to worry about them failing. If they survive the first hour or 2, they will last a long time.

robiwon · Post by **robiwon** » Wed Dec 12, 2007 5:51 pm

Welcome Mr Engineer and fellow lightsaber builder! As much as I love Luxeons the way to go in the future for model lighting will be the new Rebel LED. I have been playing around with a few for a while and they are awesome.
Oh, here are a few pics of my Lightsaber that I built, it uses a 5w Luxeon.
http://img.photobucket.com/albums/v606/ ... G_1742.jpg
http://img.photobucket.com/albums/v606/ ... G_1745.jpg
http://img.photobucket.com/albums/v606/ ... G_0473.jpg

Mr. Engineer · Post by **Mr. Engineer** » Wed Dec 12, 2007 8:54 pm

That is so sweet!

Anyway, as much as I try, PWM is way out of my league here as I am hopeless in PIC programming. So much so, I am using another software to do all this for me. But if the PIC does not have PWM, the software cannot do this (I think) but using pure assembly language it is possible.

I should have stayed awake when they do assembly in my lectures

jwrjr · Post by **jwrjr** » Wed Dec 12, 2007 11:10 pm

For all of the PICs I do the PWMs in software. Some do come with this in hardware, but usually only one, and it is meant for motor control.