LED spot lights

[L Austin France]

I've got about 8 LED spot lights varying from 30 -100w & some don't last very long.
They're about a 50/50 split between outside lights sat in free air under soffits etc & inside lights at high level under flatish barn 'crinkly tin' roof.
The barn lights, which are the short lived ones, are only used intermittently whereas the outside ones can be on for hours in the winter & have rarely been replaced & only then after years of service.
The common denominator seems to be temperature as the barn roof gets very hot in the summer but the lights have heat sink cases so I'm not sure.
Any ideas why these things don't last?

[RobertArthur]

I'm afraid the MTBF (Mean Time Before Failures) has to cope with the same restraints and rules of thumb wisdom as we experienced in the late sixties and seventies: from valves to transistors and integrated circuits etc. Every 10 degrees temperature rise (ambient temperature and generated heat) and there it goes down from 100% promise - ambient 20 degrees C - to 50%. It has become a sin in modern consumer electronics to use the concepts "safety margins" and even worse "overdimensioning". The hotter they get, the less they will be able to survive short overvoltages. Even a very short "spike" can bring them to their knees. This is another tricky design problem, yes it can be done, but at what cost... The leds themselves are still okay, but the little integrated powersupply, from 230 V AC to a constant DC voltage or current, has given up the will to live. Yes, leds guaranteed for more than 20,000 hours, but please there is another element in the equation, missing.....

[L Austin France]

Yes, leds guaranteed for more than 20,000 hours, but please there is another element in the equation, missing.....

Are you going to keep it a secret?

[suein56]

LEDs in our house prefer being on for a long time rather than switched on and off repeatedly.
We used one 40w equivalent bulb for just shy of 3 years every night as a 'see your way downstairs' bulb between approx 11pm and 7:30/8am. Ones that are switched on/off more often last about half that time.

[RobertArthur]

I'm not an experienced member of the Secret Service, difficult for me to hide what is out there in the public domain.

[L Austin France]

@suein 56.
We've lots of LED Bulbs which I don't think I've ever changed in the yonks they've been in use.
Our downstairs windowless loo has one which gets switched on/off every time someone wants a wazz so quite often during the day.
@RobertArthur
Yeah I do know about LED bulbs (see above) but I've a feeling that in my barn they'd be like Glow Worms in a jam jar 4-5 m up in the air.

[exile]

You can get LED arrays as opposed to a single bulb. Not necessarily that big although some can get a bit bigger than a spot. <we had one outside at 140W - real Watts not equivalent - until a storm destroyed the PIR.

[Hotrodder]

LEDs in our house prefer being on for a long time rather than switched on and off repeatedly.
We used one 40w equivalent bulb for just shy of 3 years every night as a 'see your way downstairs' bulb between approx 11pm and 7:30/8am. Ones that are switched on/off more often last about half that time.

Interesting point. It was commonly understood back in the days of filament bulbs that the ones that were left burning continuously lasted the longest and ones that were used only intermittently failed in a fraction of the time. The reason was said to be............the tungsten filament repeatedly heating and cooling caused it to fracture and break. Standard bulbs had a life expectancy of 500+ hours (in constant use) but you could pay more for a 1000 hour one that contained a thicker (more resilient) filament.
I was told by a customer who worked for a lamp manufacturer they could pretty much guarantee the lifespan but only under steady controlled conditions. LED units don't just glow when you stick any old voltage on them so they come with circuitry that adds more complication. This circuitry can be chosen to last much longer but we are not prepared to pay the price.

[L Austin France]

LEDs in our house prefer being on for a long time rather than switched on and off repeatedly.
We used one 40w equivalent bulb for just shy of 3 years every night as a 'see your way downstairs' bulb between approx 11pm and 7:30/8am. Ones that are switched on/off more often last about half that time.

Interesting point. It was commonly understood back in the days of filament bulbs that the ones that were left burning continuously lasted the longest and ones that were used only intermittently failed in a fraction of the time. The reason was said to be............the tungsten filament repeatedly heating and cooling caused it to fracture and break. Standard bulbs had a life expectancy of 500+ hours (in constant use) but you could pay more for a 1000 hour one that contained a thicker (more resilient) filament.
I was told by a customer who worked for a lamp manufacturer they could pretty much guarantee the lifespan but only under steady controlled conditions. LED units don't just glow when you stick any old voltage on them so they come with circuitry that adds more complication. This circuitry can be chosen to last much longer but we are not prepared to pay the price.

A pal of mine used to run a caravan park with bar & restaurant.
The place had dozens of tungsten light bulbs which were always failing.
His trick was to write the replacement date on the bulb &, when appropriate, take a batch of duff'uns back to the merchant who sold 'em for free replacements.
He reckoned he rarely paid for new stock.

[RobertArthur]

Overdue homework. Sometimes assumptions turn out not to be true in practice. In this case, it was not the power supply but the LED array that turned out to be defective. Even with 20 V DC, it was impossible to get it to work, and yes, polarity observed.