'This LED lamp has a life of 50,000 hours’
The world’s longest-burning bulb lives at a fire station in Livermore, California. It has been going almost continuously for over 110 years. Its reward for seeing all this action is a Guinness World Record, its own website (complete with webcam so you can see for yourself) and a continuous stream of lighting aficionados making pilgrimages to celebrate yet another year. Tales of conspiracy are rife in Livermore: surely this proves that we’ve all been robbed for the past century by lighting companies deliberately making lamps fail to make a fast buck.
So how has this freak of the lighting world managed to see itself through two world wars and countless economic disasters? The truth probably lies in its power supply. It is never switched off, and its 60W of power is dimmed to a mere four. Switching kills many types of lamp – that’s why they always fail just as you turn them on. The stress of the start-up is what causes the damage.
It’s also well known that dimming extends the life of most types of lamp. If we extrapolate the Livermore example to a 75,000-hour rated fluorescent tube dimmed to five per cent, it could last for thousands of years. LEDs can be switched millions of times without failing, so a dimmed LED switched on for an hour a day could last for tens of thousands of years, only to be extinguished by the shifting of continents. So why can’t we have these super long-life devices?
Fifty-thousand hours is a figure seen often on LED data sheets and in lighting manufacturers’ catalogues. That’s nearly six years. Now we are starting to see manufacturers giving 10-year warranties – up to about 90,000 operating hours, in theory. At the other end of the scale some LED replacement lamps are rated at just 10,000 hours. So why the difference? After all, many of these products are using the same chips.
The answer is it’s all down to a complex trade- off – you could probably produce a 100-year rated LED bulb, but it might not be very bright and no-one would stump up the cash to buy it. In any application the trade-off between achieving the right amount and quality of light, combined with space and thermal factors, determines the cost of the product and its life.
A streetlight must last for a considerable amount of time, because the capital cost and effort required to install it are significant. LED bulbs are easier to replace, and they’re constantly getting cheaper and better anyway. So do we need expensive 50,000- hour lamps today? Wouldn’t we be better off with a 10,000-hour lamp for a fraction of the price?
Take an example. If you put a 50,000-hour LED bulb in a bathroom which is used for a total of an hour a day, but switched off and on around 10 times a day, the 50,000-hour lamp would last for 57 years. Even if you haven’t moved house or shuffled off this mortal coil by then, I’m sure the room it’s in will have been refurbished once or twice. A 10,000-hour product would do a perfectly respectable 11 years.
LEDs don’t mind being switched, but the drive electronics do, and more and more LED bulbs state the number of switching cycles they’re expected to withstand on the packaging, which can range from 10,000 to 100,000.
Take another look at the bathroom application with 10 switching cycles a day – a unit rated at 10,000 cycles will only last around three years, while one with 100,000 cycles will last 30. The ‘life’, as it turns out, has very little to do with how long the product will actually last.
We need to be clear. Do we need over-engineered LED bulbs likely never to have the opportunity to fail because the building around them has been changed first? Or should we be asking manufacturers to state a reasonable life, and make sure the lamp can be switched on and off enough times during that period?
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