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Understanding LED luminaire lifetime and reliability

LED luminaires are getting cheaper but they’re not cheap so a long life is required, hence the 5 year guarantee.

I last wrote about LM80 TM21 and the life of the LED and what it means in terms of the life of a luminaire.  Whilst the LED life is important there are other factors which need consideration.  The LED is probably the most reliable part.

A luminaire requires 2 parts, besides the LED; a housing and a power supply (driver).  Both of which will affect the overall expected life from the luminaire.

The driver, even more than the LED, doesn’t like heat.  The average for premature failure of a driver is around 5/1000, (0.005%), within 5 years, meaning you can reasonably expect several of your fittings to go wrong and need repair or replacement.  That’s assuming the driver is working at a 50 degree C max case temperature.  If the case temperature gets higher the life of the driver goes down.  Reduce the case temperature by 10 degrees C and you will double the life of the driver.

The housing, apart from providing the aesthetics, is required to remove the heat from both the driver and LED, which is why you often see lots of fins on many designs.  The larger the surface area; the greater the degree of cooling.

So, how does that knowledge help?

Allowing that in many corridors the ambient temperature may be 35 degrees C or more it should be appreciated that the temperature inside the luminaire will be considerably hotter, perhaps as much as 15 to 20 degrees hotter.  That makes the temperature inside the fitting – where the driver is – well over 50 degrees and above the maximum case temperature for the driver.  Care should be taken when a luminaire manufacturer quotes an ambient of 40degs – the internal temp could be well in excess of this and well in excess of the driver operating conditions thus reducing the life.  If the internal temperature is 60 degrees C the life of the driver/luminaire may be as little as 2.5 years.

Most lights now come with a 5 year guarantee so if they go wrong they should be replaced but it will still be very disruptive.

Contact us if you’d like to learn about how good design will help reduce premature failures.

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