There was a time, not very many months ago, when LEDs were – it seems – immortal. Laboratories were recording life terms measured in centuries (this in a world where many buildings are likely to last less than a hundred years, but its good to know that you can bequeath your lighting to future generations).
The claims have calmed down a bit, with a 50,000 hour life term becoming the norm. For reference, there are 8760 hours in a year, and not much lighting burns 100% of the time, so you can work out what 50,000 hours might mean in practice.
What is not advertised quite s widely is what happens to the light over that period of time. We all experience the ageing of technology, whether it’s a motor car or an electric kettle. Over time, they don’t work as well as they did when first unwrapped. What does this mean for the LED light source?
Old-fashioned filament lamps knew how to die – they went ‘pop’ and that was it. The newer stuff never seems to know when to give up and just go on and on, delivering poorer and poorer performance until they’re reduced to a glimmer. Sounds like a 70s rock band. Maybe this was cause of the figures coming from the labs; the LEDs wouldn’t die.
The commercial response is to determine the end of ‘useful life’. There are two things that we’re concerned with here: the loss of light output and the loss of colour quality over time. Manufacturers will provide different figures depending on the confidence that they have in their product. Xicato, for example, quote a 20% fall-off in light output over 50,000 hours and NO fall-off in colour constancy. That’s quite a claim to be able to make.