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Part L 2013 Impact of change

17th February 2012

Let the bells ring out, pop open the champagne. All hail Leni, the new lighting king… well, maybe not, but Liz Peck says you can’t blame her for being a little excited


The release of the consultation on the 2013 Building Regulations for lighting folk is all about Section Two, Part L.


As a heads up, the document you really need is the Technical Guidance document – and if you like you can skip to page 125 where you will ­find Appendix 2: Lighting.


This outlines the government’s plan for ef­ficient lighting in non-domestic buildings from 2013 and there are changes.


Big changes.


There are now two options: a conventional solution based on luminaire ef­ficacy (with or without controls) and one using Leni (the Lighting Energy Numeric Indicator). These are both good as far as I am concerned.


In previous incarnations of Part L, areas have been described as ‘desk-based’, ‘display’ and, well, ‘everything else’. Other than for desk-based activities, the metric has been lamp lumen ef­ficacy, meaning that it does not matter how inefficient a luminaire is, as long as the lamp is ef­ficient then it complies.


This has gone. We now have luminaire ef­ficacy for everything. This in itself is quite a step and should not be overlooked. Begone ubiquitous ‘black box’ luminaires – now manufacturers must deliver ef­ficient luminaires. Excellent.


Advanced controls strategies

Compounding this progress is a much more advanced set of control strategies. Occupancy and daylight controls are no longer the only deliverable and measured controls.


This is huge. The controls package can now deliver an up to 30 per cent reduction on the original luminaire ef­ficacy. We no longer need to have a situation where inappropriate luminaires get speci­fied because of their ef­ficacy because we can use whichever luminaire we like (within reason) and control it.


I’ve said many times that the most ef­ficient luminaire is one which is off when it’s not needed and the new controls package drives this positively.


Then there is Leni. The lighting industry (myself included) has campaigned to introduce Leni into the Building Regulations. Leni is just a metric, just a measure – the philosophy behind it is the difference.

Leni measures predicted energy in use, not how ef­ficient a luminaire is, but actual, real, predicted energy use, hopefully with a new set of controls. This is all about the system, not just the luminaire.

Leni embraces daylight, occupancy, operating hours and the controls package to predict lighting energy use for the building. It knows, for example that the same building in Scotland will have to use a little more lighting energy than an identikit building in Brighton because the daylight availability differs.


The alternative metric

So, in the proposed Part L of the future, Leni features as an alternative metric. I know from speaking with people over the past year that there are those who champion it and those who think it is too cumbersome.

Admittedly it is the single-most most complicated equation ever written (and I did maths A-level) but for that we can blame the EC for letting two of our cleverest boffins – Lou Bedocs and Peter Raynham – loose together in a room.


The good news is that not only does all lighting calculation software (free to download) already include a Leni calculation, but that there are also a number of equally free to download software calculation programs available so you can put your calculator away, it gets done for us.



The table of targets also seems more complex than we might have wished for, but we are working towards harmonisation with the Simpli­flied Building Energy Model (SBEM) calculation and this will lead us to it. It’s a ­first step in a journey and we should embrace the move made by the Department for Communities and Local Government in introducing Leni as an optional metric.

For the smaller project


I know there are those who will argue that it shouldn’t be necessary for smaller projects, where there isn’t the budget to invest in a specialist lighting designer – that the whole process is too complex and unnecessary – but I am also privy to a statistic (albeit source unknown, sadly) that a project by a specialist lighting designer will typically use 30 per cent less energy than one from a non-lighting expert. So can we really afford not to be using specialists in this area? I would argue not. And not just because it’s my job.


For a long time, I have been outspoken (probably too outspoken for some people) about how poor Part L is in terms of delivering its goal of ‘conservation of fuel and‑power’.


I can honestly say that with the proposed changes I will have to change my tune. These measures – particularly introducing a measure of energy in use – is a huge step forward. They should be embraced by the whole industry. I honestly believe they can lead to change for the better and will at last serve the purpose of Part L – reducing energy use.


The main changes

  1. Two approaches to calculating e­ficiency: conventional solution based on luminaire e­fficacy (with or without controls) and one using Leni (the Lighting Energy Numeric Indicator)
  2. Target luminaire e­ficacy value raised from 55 to 60 lumens per circuit watt
  3. Leni marks a change in philosophy. It measures predicted energy in use, not how e­fficient a luminaire is, but actual, predicted energy use
  4. Occupancy and daylight controls are no longer the only deliverable and measured controls.
  5. Leni embraces daylight, occupancy, operating hours and the controls package to predict lighting energy use for a building.


Ray Malony, Lux Magazine - February 2012


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