With a 100,000 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 100,000 hours might mean in practice.
What is not advertised 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.
The light output of an LED module decreases over the lifetime, this is characterized with the L value.
LED modules LED linear / area L80 means that the LED module will give 80 % of its initial luminous flux. This value is always related to the number of operation hours and therefore defines the lifetime of an LED module.
As the L value is a statistical value and the lumen maintenance may vary over the delivered LED modules. The F value defines the amount of modules which are below the specific L value, e.g. L80F10 means 10 % of the LED modules are below 80 % of the initial luminous flux, respectively 90 % will be above 80 % of the initial value.
In a similar way to the fluorescent tube, the ‘root colour’ of an LED is BLUE. The WHITE light comes from a process of phosphor coating, which acts on the BLUE light and transmits a WHITE light, the tone of the light being based on the make-up of the phosphor coating.
The real issue for LED developers and luminaire manufacturers is to ensure colour constancy in the WHITE light from the many millions of LEDs that are produced in the world. A method of measurement had to be agreed, and that method has become known as the MacAdam Ellipse Tolerance. The MacAdam Ellipse Tolerance method is a way of describing how efficient the LED source is, and the lower the number, the better the LED colour performance.
But is it a good WHITE light? And what does a good WHITE light mean anyway? Our idea of a good WHITE light is based on nature, Daylight, it’s what we see out of the window. Those ‘natural’ WHITES have been measured and have been plotted onto colour diagrams, so whenever a new WHITE light comes along we can check it against the reference colours. The accuracy between the two is known as the Colour Rendering Index., where an Index value of 1.0 is perfect – and anything less than 0.8 isn’t worth considering. LED products offering +0.8 are absolutely fine for general usage.
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