Richard Hayes shouts through the letterbox to let us know that there’s been a change to the way that Relux calculates Maintenance Factor. We’ve spoken about this before (Getting Maintenance Factor Right) – and here we are again. This is Important Stuff!
Maintenance Factor calculation for LEDs
Since 2019 there has been a standardized method of calculating Maintenance Factors for LEDs. This is detailed in ISO/CIE TS 22012:2019.. Applying this document has become much easier as the new release of Relux Desktop uses this method to derive LED Maintenance Factors.
Correct calculation of Maintenance Factors for LEDs is important. Designers must work to achieve Maintained Task Illuminance so that the values specified in BS EN 12464 and SLL guide are the minimum levels achieved in the space at the end of the Maintenance period, after which the installation should be returned close to initial conditions by cleaning of the environment and the luminaires – and the light sources are replaced to return to their initial output. Generally it is accepted that to be economic an installation should aim to have a Maintenance Factor of above 0.8.
Manufacturers give information regarding life of their LEDs in terms of TM21 extrapolations in the form of statements such as L70: 100,000 hours. But this data on its own does not help with determining the useful life for the LEDs. One thing for sure is that trying to apply a Maintenance period of 100,000 hours to luminaires using the above LED will not result in an economic Maintenance Factor.
For instance, if we assume a clean environment, annual cleaning, with a direct IP5X luminaire pushing the Maintenance interval out to 100,000 hours that will result in an MF = 0.58; hardly surprising when the Lamp Flux depreciation at that time is 30%.
The new tool in ReluxDesktop makes it easy to set an operating time to the end of the maintenance interval that will result in an economic MF.
In this case, setting the operating hours to 25000 yields MF =0.82 which is a useable economic figure, but means the LEDs will have to be replaced after 25000 hours use, or the installation will fall below the specified Maintained Illuminance Em.
Using this new utility designers can start to see the effects of applying different grades of LEDs to installations. They can easily specify total operating hours of the LED to give the required Maintained Task Illuminance at the end of the Maintenance cycle.
It becomes much easier to debunk the often quoted 0.9 or better MFs used for LED installations at extended operating periods. Even if we use a really good quality LED with TM 21 extrapolation data of L90 60,000 in the above installation we can only push this LED to 30,000 hours operation to have MF = 0.84.
To anticipate a question about this process, the tables used to drive this tool in Relux are taken from Annex B of ISO/CIE TS 22012:2019, the derived Luminous Flux Factors for the different Median useful life figures from the TM21 extrapolation apply to nearly all commercially available LEDs as these are the standard curve fitting data LED manufacturers use to derive the life data they quote to manufacturers.
All screen grabs from ReluxDesktop V 2021.1.0.0, available for download from the Relux website, I hope designers will use this new tool to make sense of LED Maintenance Factors.