LED Light Bulb Failure

[peter scott]

It is disappointing when a lamp quoted as having thousands of hours of life fails after less than 100 hours. I thought I'd take a look inside to see what had actually failed.

The lamp in question had the conventional light bulb shape and has 9 LEDs in series mounted on a PCB supported by an alloy disc that sits between the hemispherical translucent dome and the tapering body. The power supply takes the mains to a bridge rectifier that powers a switching transistor driving a transformer and diode rectifier.

There is a 3mH inductor in the negative supply from the bridge that it not well soldered but I don't think it has an intermittent connection.

The actual failure appears to be burn-out of one of the LEDs.

   
   
   

Peter

[Keithstv]

I've had several LED lamps fail, one had a dodgy connection between the base and the lead to the PSU but two of the others had failures of the PSU. In all cases the LED element was OK.  The first one had a claimed life of 30,000 hours but it's replacement, replaced under warranty, stated 25,000 hours. Now I can just about  believe the lifetime figure for the LED element but the PSU will never last the stated time.

The LED elements in my failed lamps were arranged in a series parallel arrangement and appeared to run off 12V. I applied 10V to them and it was extremely bright.

Keith

[BusyBee]

I have had a couple of lamps fail, with intermittant failure - flashing of the LED's. I didn't take them apart, although I think I still have one of them somewhere. I wonder if the failures are more comon in higher wattage types as the electronics, in general, seems to be fairly hard pushed. I prefer to use 100W equivalent or similar, which may be towards the limits.

Tracy

[ppppenguin]

So far so good for me on LEDs. Now using them almost everywhere in the house.

One exception. A few years ago I fitted some fairly expensive (c£30 each) LED downlights in the kitchen. About £30 each back then. Really good in all respects: brightness, distribution of light, dimmable, colour rendering. the driver is in a little box outside the main unit. Way better than anything else on the market at the time. Then within a couple of years they started failing. I'd got them from TLC who freely admitted there had been a bad batch of drivers. They replaced all of them without quibble, whether they had failed or not. The only nuisance was re-installing the new ones and pulling out the old ones.

Now rather cheaper:
https://www.tlc-direct.co.uk/Products/LTFRD12WW.html

Also lots of other good ones around for the same or less money. Some are more efficient too. Mine use 12W to give more light than a 50W 12V halogen but you can probably do it with 8W or so now. I've used some of these recently. Excellent light. Don't know about reliability yet. https://www.toolstation.com/shop/Lightin...ght/p29731

At the low end of the market, if you've got fittings that use GU10 halogens then Poundland and Ikea will provide you with decent LED repalcements for very little money. Not quite as much light as a good halogen (does such a thing exist? they have very short lives) but very acceptable.

For replacing 100W GLS lamps I've mostly used the Diall range from B&Q. Cheaper than most and a nice light. 1521 lumens so brighter than 100W GLS in theory and at least eqaul in practice.

[Murphyv310]

Hi.
We have been 100% Led for some time. The older ones have been replaced with up to date and more efficient ones. I've had around three GU10 types fail and it is always the PSU that fails.
I also feed 12v from my excess solar capacity from the shed which feeds occasional lights in the living room and lighting above the worktops in the kitchen. Great when we had a short power cut a few weeks back. The 12v lamps still give good light with the losses that are inevitable on 12 metres of cable. 11 volts with them all on, so around 1.25v loss at night.

[Nick]

The LED elements in my failed lamps were arranged in a series parallel arrangement and appeared to run off 12V. I applied 10V to them and it was extremely bright.

Small and obvious point - LEDs are current, not voltage devices - once there is enough PD across then to conduct, they need current limiting - connecting a bunch of LEDs across a 12V supply (assuming there's only a few of them) will cause them to burn very brightly indeed, but not for long...

[ppppenguin]

A lot of common LED strips etc run off a 12V supply. They simply use resistors to control the current which isn't efficient and probably none too accurate either.

[Murphyv310]

Hi.
I've had virtually all lighting in my shed fed from solar and high capacity 12v leisure batteries for 5 years. I use LED strips, MR16 and some LED small panels all that are 12volt. No failures as yet bar one strip that went O/C as the flexible strip split. On the couple of occasions that battery volts dipped, light output dropped a little but of course so did current consumption.

[Old Sparky]

I recently replaced a halogen bulb in a wandering lead lamp with a(n)LED one. Almost every time I switch it on since so doing, it flickers rapidly for maybe a minute before stabilizing, which it never did with the halogen bulb. Haven't investigated the in-line switch, wiring, or socket, but, AFAIK, all are O.K.

[ppppenguin]

Check the bulb in another fitting. They should start instantly and cleanly. If it doesn't, it's faulty.