When is 25k hours not 25k hours?

There are two failure modes:

2) PSU output stops working. The SMPS in the base of the bulb uses an electrolytic capacitor. It lasts 2000 hours at 105C, it lasts 60000 hours at shirt sleeve conditions. Overheating the PSU is not part of the reliability specification. There is an assumption you did not "cook the product on purpose".

Thus, the GU10 bulb maker assumes you placed the bulb in ordinary room air, where convection keeps the bulb at some ridiculously low temperature. That solves the [2] problem.

Then we write the number from [1] "on the tin", as the reliability number.

A "flickering failure" is not an expected failure mode. It might mean the PSU is cooked.

Here is a bulb take-apart.

The black can with the two wire legs, is the electrolytic capacitor.

Paul

Did you remove enough of the joist to make it fit? Was there much left?

Bought 15 similar ones 6 years ago for the kitchen. Got them from eBay - pretty much the cheapest that i could find.

Not a single one has been replaced yet...

In message snipped-for-privacy@brightview.co.uk>, at

That's right - theyare easily replaced.

Being in the ceiling of an extension they are very well insulated to the side and above.

In message <s08fvq$1lu$ snipped-for-privacy@dont-email.me, at 12:17:05 on Sat, 13 Feb

I contacted them when three had blown (that was about a month ago), and they sent me only two. (But I had a box of very similar LEDS anyway). Since then one more has gone. I'll be reminding them about the short-shipment when I next contact them.

I didn't [directly] buy (or even specify) anything. The builder's subcontractor did.

In message <s08no6$16q7$ snipped-for-privacy@gioia.aioe.org>, at 14:29:18 on Sat, 13 Feb

When I changed the 4th one the other day, the main part was OK but the base stub was almost too hot to hold.

I'll do that (although it's more like mechanical engineering ;-)

I'll take a look at a fitting later, and report back.

In message <s092h0$1rqa$ snipped-for-privacy@gioia.aioe.org>, at 12:33:21 on Sat, 13 Feb

What happens is the light starts by blinking off just long enough to be noticeable as a flicker about once even ten seconds. After about a week the rate increases until it's flickering constantly. One of them then went into "steady, but only 10% light output" mode.

And fire-rated (which tends to mean reduced ventilation)?

This is obviously a branch of maths I'm not aware of? Brian

Where is this day which is over 24 hours long though?

Half the issue is often the heat, but I'd have thought in a normal installation they would be designed to have an acceptable life under such conditions, otherwise where do you draw the line? Brian

So, how hot do they get? Does seem to me that they have not been designed with a typical use condition in the first place. What actually fails, I wonder. Do they have a psu or is it strictly diodes and some kind of over voltage protection with them all in series? Brian

Do these devices run on transformers or are they mains with internal psus. I'm out of touch since the halogen days. I think I'd be having a look inside one to see how it works. Brian

In message <s0ap83$fk3$ snipped-for-privacy@dont-email.me, at 09:07:14 on Sun, 14 Feb

The latter.

I have seen quite a few LED street lamps in the flickering mode and they are probably no older than two years. I can't see why they should be so unreliable after all the engineers have complete control of the thermal environment and heatsinking. However, they do seem to fail quite often.

By comparison most of my domestic LED bulbs even the ones in old spotlight fittings seem to survive remarkably well. Airflow is everything.

The fitting that kills LED bulbs most effectively is a hangs down from the ceiling full globe type diffuser with no way out for the warm air.

But purchasing departments tend to over-ride such issues.

That's the problem, in reality they were not designed for LED lamps.

So GU10 LED lamps are a retrofit option, but many existing lamp holders were not designed to facilitate adequate cooling of the lamps.

Usually the capacitors in the PSUs fail at high temperatures.

I have used some of those...

Because they were good fit for the application, and provided a lighting pattern that was not easy to achieve via other means.

The enclosure was designed for the lamp which it contains, and the method of installation (flush fitting in an insulated ceiling), so there is no reason to expect premature failure from them.

Both these things are true, but miss the vital point that if the equilibrium temperature is too hot for the LED lamp then it will fail prematurely.

This is a common problem with GU10 filament lamps anyway. They are also very vibration sensitive. Their life (and light quality) compared to 12V GZ10 fittings is very poor.

Indeed - even a LED GU10 experiencing a short life of 4K hours will still last longer than the best GZ10 halogens.

However, stick a LED GU10 in a fitting where it can't cool properly then you won't achieve the anticipated 15k to 25k hour life times - even if it's still better than the mains halogen.

LED lamp reliability across the board has improved with time. The early ones gave poor quality light and tended to not last that long (although arguably still met the requirement of low power consumption).

Or perhaps not all of them read the instructions and observed the requirement to fold back any insulation 2" clear of the lamp, and also allow 2" free space above the lamp etc. :-)

It will likely be a bit hotter - so running very close to, or over the maximum temperature for many budget capacitors.