Like any piece of technology, the performance of a lighting solution eventually begins to decrease over time. Even LED luminaires, which have a far longer lifespan than the likes of high-pressure sodium (HPS) or fluorescent equivalents, do gradually deteriorate. Naturally, most people involved in planning or purchasing a solution will want to know how this will affect their lighting quality in the long term.
This is where the Maintenance Factor comes in. At a basic level, the Maintenance Factor tells you how much light a system will produce at the start of its lifespan, and how that value will decrease over time. As you might expect, this is a technical subject and one that can become very complex very quickly. That’s why, in this post, we’re focusing on the key things that you need to know about the Maintenance Factor.
What exactly is the Maintenance Factor?
At its core, the Maintenance Factor is just a calculation. The result of that calculation tells us how much light – or specifically, lumens – a lighting system will produce at different points of its life. For LEDs specifically, by virtue of their extreme durability, that lifespan is typically measured in the tens of thousands of hours.
A Maintenance Factor calculation is useful, not only because it tells you how lights will perform in the future, but how – and when – you might need to think about making a change to your lighting solution. If you need your lights to provide a constant value of 500 Lux, for instance, the Maintenance Factor can help you understand at what point in their lifespan their average illuminance will fall below that figure.
How is the Maintenance Factor calculated?
The Maintenance Factor isn’t solely about the performance of a luminaire. Instead, it is calculated by multiplying three* interlinking factors. These are the:
- Lamp Lumen Maintenance Factor (LLMF)
In simple terms, the LLMF tells us how the amount of light produced by a luminaire is affected by aging. The design of a luminaire, its ability to dissipate heat, and the quality of the LEDs will all play a role in the LLMF value. The LLMF should be provided by the manufacturer.
- Luminaire Maintenance Factor (LMF)
The LMF is used to see how the amount of light produced by a luminaire is affected by the build-up of dirt. There are several factors at play here, including the cleaning schedule for a luminaire, the amount of dust or dirt that is typical within the environment, and the extent to which a unit is enclosed.
Different environments can have a dramatic impact on the LMF. Lighting installed in an area where there is lots of dirt and grime – a warehouse, or by railway lines, for instance – will tend to have a lower LMF and therefore a worse Maintenance Factor overall.
- Lamp Survival Factor (LSF)
The LSF takes into account the amount of light that would be lost if a luminaire failed and wasn’t immediately replaced. In the case of LED lighting, this value is very often set to ‘1’, and there are two reasons for this. Firstly, LEDs have a very low failure rate as a whole, and secondly, it is generally assumed that a replacement will be installed almost immediately.
* When dealing with interior lighting projects, a fourth factor can come into play. This is the Room Surface Maintenance Factor (RSMF), and relates to the build-up of dirt on surfaces – something that reduces the amount of light that they reflect. We don’t cover that here since the majority of our projects involve external lighting.
When we multiply the LLMF, LMF, and LSF, we get the Maintenance Factor. So, an LLMF of 0.95, a LMF of 0.95, and a LSF of 1 would give us an overall Maintenance Factor of 0.90 (rounded down to two decimal places).
That, of course, leads to another big question…
What does the Maintenance Factor actually mean?
That figure of 0.90 might not tell us much on its own, but it becomes much more useful when we look at it in the context of light levels. That’s because the Maintenance Factor basically tells us how far those levels will fall over the course of a lighting solution’s lifespan.
This is vital because, in the design phase, a company like Midstream can use the Maintenance Factor to plan for that drop-off and pre-emptively counter it. Essentially, we can create a design that delivers more light than is technically needed at the start of a solution’s lifespan – ensuring that levels are still high enough to meet any minimum requirements further down the line.
Take a tennis court as an example. Britain’s Lawn Tennis Association specifies that the play area should have an average illuminance of 500 lux. If we aim to start with 500 lux though, all of the depreciation factors mentioned above mean that the average values would eventually fall below that.
Instead, using the Maintenance Factor of 0.9 mentioned above, we’d aim for an initial illuminance value of around 555 lux. That’s because, when we multiply 555 by 0.9, we end up with 500 – or, the average light level with depreciation taken into account. This is why the Maintenance Factor is so helpful, because it enables us to ensure a minimum standard of performance even when lights begin to age.
Do I need to calculate my own Maintenance Factor?
Generally speaking, no – this should be carried out for you by a manufacturer or installer. You should, however, make sure that whoever is doing those calculations can explain why the different values have been chosen in each of the four underpinning categories.
Moreover, you should check that the lighting design that your manufacturer or installer has created matches up with the Maintenance Factor, and will provide a suitable amount of light across the system’s expected lifespan.
This quick look at the Maintenance Factor in lighting is a greatly simplified explanation of a much larger – and more detailed – topic. You can find more information in our dedicated Maintenance Factor whitepaper, and if you have further questions or need help understanding your own calculations, we’d be happy to assist.
Please get in touch.