Do 5mm LEDs burn out quickly?

[LEDrock]

After reading another post here http://www.candlepowerforums.com/vb/showthread.php?t=201171

I am starting to wonder about a few of my lights and whether or not they were worth getting. Do 5mm LEDs only have a lifespan of about 6 hours of use? I always thought that lower powered LEDs would last longer than the higher powered ones, because they aren't being forced to do as much. I have a couple of minimag AAs with the nite-ize module from Walmart and like that they have been reviewed to be able to last about 11 hours on a set of alkalines. I assume these modules use 5mm LEDs. Correct me if I'm wrong about that. But should I only expect about 6 hours of total life from these things???

 

[Jarl]

There is no heatsinking on a 5mm LED. If you run it hard, then you can make it burn out within 6 hours (same as with any other insufficiently heatsinked LED). If you run them at spec, you'll see at least several hundred hours. Nite-ize, etc, run them at low power, within spec, and as such you'll get a long life. DX lights making ~40 lumens off one 5mm won't last long at all. Generally speaking, if it's more than 10 lumens/5mm LED it's being overdriven.

 

[LEDrock]

There is no heatsinking on a 5mm LED. If you run it hard, then you can make it burn out within 6 hours (same as with any other insufficiently heatsinked LED). If you run them at spec, you'll see at least several hundred hours. Nite-ize, etc, run them at low power, within spec, and as such you'll get a long life. DX lights making ~40 lumens off one 5mm won't last long at all. Generally speaking, if it's more than 10 lumens/5mm LED it's being overdriven.

Thanks! I think I understand now. So my MM nite-ize should last quite awhile and make a good long-term power outage light.
One thing though---I always thought heat sinking was a function of the flashlight's design and not of the emitter itself. Is that wrong though?

 

[TigerhawkT3]

It's wrong with 5mm LEDs. They're basically wrapped in plastic, which insulates them. The only way to heatsink a 5mm is to heatsink the legs, and that isn't often done.

http://www.molalla.net/~leeper/5mmdeg.htm

 

[Lynx_Arc]

If you can replace them easily enough they are now disposable compared to a few years ago. I used to struggle to get enough LEDs for projects not having to pay $1 each for them now I find junk lights and stuff with them in them for cheap. You can get them for 5 to 10 cents each if you don't want the super duper 50kmcp ones. Compare to a high power LED at $3-$10... which IMO is far from disposable since bulbs are 50 cents to $1 each.

 

[parnass]

After reading another post here http://www.candlepowerforums.com/vb/showthread.php?t=201171

I am starting to wonder about a few of my lights and whether or not they were worth getting. Do 5mm LEDs only have a lifespan of about 6 hours of use? ...

The original poster was asking about 5mm LEDs he used in night lights. Most of the LED night lights I installed were dead within one year. But, they were powered on for many more hours each night than most flashlights.

 

[Lynx_Arc]

I have walgreens night lights (screw in base bulb replacement) and they seem to last about 6 months before dimming too much. Last one I threw away I think this time I will replace the LEDs instead with perhaps 6 leds as there is 3 in them.

 

[carrot]

Cheap 5mm's have a fairly short life span. Also, overdriven 5mm's have a short life span.

Good 5mm's (CS, DS, GS, etc), driven within spec, will last awhile... they are spec'd to last longer than power LED's (Rebel, XR-E, P4). Good 5mm's overdriven will still last awhile, but will fade over time (Arc-AAA).

 

[evenchaos]

All those leds that quickly die must be overdriven too much. 5mm leds last forever (at least 30k+ hours) if you don't exceed the recommended current (don't even look at the max current rating). Then again this is CPF, so what am I saying

 

[EngrPaul]

I spent some time modding Luxeon flashlights to Seoul. This left me with many Luxeon 1W/3W emitters.

When my nitelites dimmed out to faint purple, I opened them up and found 3 LEDs wired in series.

I unsoldered these, and replaced them with 1 luxeon emitter and a voltage dropping resistor. No heat-sinking, just sitting above the board on the excess leads I cut off of the resistor.

It's been a year of usage, and they are still white and bright.

 

[Illum]

Cheap 5mm's have a fairly short life span. Also, overdriven 5mm's have a short life span.

Good 5mm's (CS, DS, GS, etc), driven within spec, will last awhile... they are spec'd to last longer than power LED's (Rebel, XR-E, P4). Good 5mm's overdriven will still last awhile, but will fade over time (Arc-AAA).

took the LED from a cheapie fauxton from lighthound, added a resistor to keep it around 20ma and set a couple outside connected to spent lithium cells. From the performance I've seen cheap LEDs lasts pretty long for their size, better tint too

the trick is to keep them out of direct sunlight, if your soldering them thru-hole or floating, keep as much leg room as possible, DO NOT TRIM THEM, add a resistor of appropriate size to drive them under 20ma, if thats too dim add another LED.

If you've soldered whole clusters together and trimmed all the legs flush go to allelectronics.com, buy a cheap painted heatsink [paint = insulator] that can satisfy the dimensions of your perf board, coat the bottom of your LED cluster with Arctic Alumina and epoxy it on top of the heatsink.

 

[JWP_EE]

Most 5mm LEDs will last from 2000 to 10000 hours when driven at rated current and properly heat sinked. The problem with 5mm LEDs is the thermal resistance from the heat sink point (the leg right at the bottom of the LED) to the junction is about 300 deg C/W.

A CREE LED has a thermal resistance of 8 deg C/W from junction to heat sink point. If a flashlight has a good thermal design and uses a power LED then 50,000 hours life is reasonable. If the light has a low setting of say 10 to 20 lumens, then the LED life at that output level is in excess of 500,000 hours!

 

[Mr Happy]

One thing perhaps to mention with LEDs in night lights is to be careful when driving them direct from the mains. A badly designed circuit could subject the LED to excessive transients or peak currents in operation that would shorten the life of the emitter, even though the average current seems to be within design limits.

This web page gives some good instruction on how to design successful circuits for mains powered LED applications: http://www.marcspages.co.uk/tech/6103.htm

 

[Jarl]

Nice link, thanks

 

[hopkins]

Yes. Good link Mr Happy. I've got all the parts here in front of me and want to
make a 5mm nite light but am hesitant...

I used to work for a guy who told many stories about coworkers being electrocuted on the job. (in the UK) He had a storytelling style that left me with a primal horror of dying by AC current.

 

[Mr Happy]

Here's another link with further variations on the same idea, and some hints about safety: http://bigclive.com/fibre.htm

The main things are to keep the conductors carrying mains voltage well separated, make sure everything is well insulated in a plastic enclosure, and consider putting a fuse on the mains input. (Note that in the UK all mains plugs have a fuse in them so you don't often see a separate fuse shown in circuits like these. But in the US it wouldn't hurt to put a fuse inside the enclosure.)

 

[HKJ]

And here is a link to a program that can calculate some led driver circuits:
http://www.miscel.dk/MiscEl/miscelLeds.html