Part L Business - old stuff!
This piece relates to the 2006 edition of Building Regulations Part L: Conservation of Fuel and Power. I'm leaving it up as a reference source only. Its still relevant as a commentary, but the compliance figures have all changed.
LIGHTING SPECIFICATION AND PART L: BUILDING REGULATIONS
As we all know, Part L relates to the Conservation of Fuel and Power in building design. It is there to establish energy design criteria for the specification of materials and equipment in new buildings and existing buildings where refurbishment work is undertaken. There are four parts to Part L: Parts 1L.A and 1l.B, relating to dwellings and Parts 2.L.A and 2L.B, which relate to ‘buildings other than dwellings’. The ‘A’ refers to new buildings and the ‘B’ refers to existing buildings.
Unlike the specifiers of building fabrics and the designers of mechanical heating/ventilation systems, the lighting designer is treated fairly kindly in the specification of low energy lighting1.
Looking at the Part L1 Design Standards for interior lighting, a lighting scheme is deemed to comply if all of the fixed luminaires (table lamps don’t count) use lamps that have a luminous efficacy2 better than 40 lamp lumens/circuit Watt. However, the Standards state that ‘reasonable provision’ of low energy lighting would be achieved if the designer ensures that either:
there is one low energy lamp per 25m2 of dwelling space (excluding garages)
or
that one luminaire in four uses a low energy source.
Its worth noting that, in Part L1.B, this requirement only relates to the areas of the building that are affected by building work. Its not a retrospective requirement on existing lighting systems.
For exterior lighting, the Standards only apply to luminaires attached directly to the surface of the building and either:
use lamps with less than a 150W power rating, and fitted with a motion and daylight sensor
or
use luminaires dedicated to a low energy light source.
And that is all, really.
The Design Standards for Part L.2 are a little different, but clearly have the same intention.
First of all, there’s a need to clarify what’s meant by ‘other than dwellings’. That non-description covers a lot of ground, and the Part L2 Standard doesn’t spend a lot of time going into detail.
Lighting efficacy for ‘office areas’, it tells us, include those spaces that involve predominantly desk-based tasks, and include classrooms, seminar rooms and conference rooms – including those in schools. Apart from that piece of fine definition, all the rest is swept up in a single paragraph.
So, dealing with ‘office areas’ first (both new-build – Part L2.A and refurbishments – Part L2.B), the Standard shifts its emphasis onto luminaire efficacy3 whereby the lighting installation should not exceed an average of 45 luminaire lumens per circuit Watt across its entirety. The idea here is to allow some flexibility in design, so that some less efficient sources can be used, provided they are balanced by sufficient low energy sources.
In everything that’s not defined as an ‘office’, the Standard throws out a blanket statement that the requirements are met if the installed lighting has an average lamp efficacy of 50 lamp lumens per circuit Watt. But there is an interesting addition here; unlike Part L.1, this paragraph of the Standard actually defines what is meant by lamp lumens4.
Lighting control
When the Part L Design Standard was first introduced, there was general disappointment that it didn’t exploit the potential benefits of requiring lighting control as well as low energy light sources.
Part L1 has nothing to say about methods of lighting control, and Part L2 simply includes a note stating that lighting control is covered in the BER accounts relating to the impact of controls. But L2.B does provide guidance on what kind of lighting control the Standard has in mind.
* There should be no ‘unnecessary lighting’ of spaces when daylighting levels are adequate or the space is unoccupied.
* Each working area should have local switches, easily accessible by occupants, where ‘local’ is defined as ‘not more than six metres or twice the height of the luminaire above the floor if this is the greater’.
* ‘Dimming’ means electronic dimming that reduces the energy supply, rather than the old- fashioned rheostat dimmer that diverted it via a resistance (though where anyone would find one of those monsters today is a mystery).
The Standard says nothing about programmable lighting control systems which can control output voltages or establish the operating periods of lighting. Which is a pity.
A word about Display Lighting, because this is extraordinarily important.
The Part L2 Design Standards recognise that there are occasions where low energy sources, and in particular fluorescent sources, do not work effectively. Under the heading of ‘Display Lighting’, the Standard offers a relaxation in the efficacy requirements.
However, the definition of ‘display lighting’ goes much farther than what most of us would understand by the term. Display lighting is defined as ‘lighting intended to highlight displays of exhibits or merchandise, or lighting used in spaces for public leisure and entertainment such as dance halls, auditoria, conference halls, restaurants and cinemas’, which has to be considered as a huge lack of resolve by those drawing up the document.
A lighting scheme in these circumstances need only provide an average of 15 initial lamp lumens/circuit Watt across the installation. Tungsten halogen lamps typically deliver better than 20 lumens/ Watt, whilst traditional tungsten filament lamps (GLS and blown reflector lamps, for instance) deliver only around 10 lumens/Watt.
The Lighting Design approach to the Part L Design Standards.
The simplest way of developing a lighting design that needs the criteria of Part L is to ensure that every luminaire/light source in the specification meets the Standards, especially when looking at non-domestic properties. The problem with this approach is that it can run counter to the stated aims of the CIBSE lighting design Codes of Practice.
For example, the Introduction to CIBSE Lighting Guide 7: Office Lighting states:
‘Even the most dedicated office worker looks up from his or her work from time to time, and when they do they need to see an interestingly lit office space ... ’.
To achieve an ‘interestingly lit office space’ may need more than an installation where every luminaire is 100% compliant with the Part L Design Standards. That is why every performance figure given relates to average efficacy across the installation. Specifiers who choose to ignore the importance of designing a degree of humanity into the built environment do us all a disservice.
Question 1: how are we defining ‘low energy lighting’.
Every electric lamp consumes an amount of electrical energy in delivering its illumination. The performance parameters of Part L determine that, to all intents and purposes, low energy lighting relates to fluorescent sources, high pressure discharge lamps, and some LEDs.
No filament lamps meet the parameters, and neither does any luminaire that can be fitted with a filament lamp – so luminaires have to be dedicated to a low energy light source.
Question 2: but what does ‘luminous efficacy’ mean?
Every lamp delivers a quantifiable amount of light – measured in lumens. Of course, that light also requires a certain amount of electrical energy to deliver it. Dividing the one by the other gives us a comparable figure of light generated per circuit Watt2a.
Question 2.a: but what’s this about ‘circuit Watts’?
Most low energy light sources need some form of electronic circuitry – the control gear. Every piece of control gear uses a small amount of electrical energy just to function, so the important figure here is the combined power figure of Lamp Watts + Control gear Watts = Circuit Watts.
Question 3: what is this ‘luminaire efficacy’?
As soon as you put a lamp into a light fixture, some light is lost within the body of the luminaire. The difference between the amount of light coming from a naked lamp and the light coming from the luminaire housing the lamp is known as the Light Output Ratio, and that defines the luminaire efficacy. Some fixtures can be startlingly inefficient.
Question 4: I thought we’d covered this one?
Yes and no. The troublesome part comes when you realise that the light output from a lamp deteriorates with age. A new lamp is considerably brighter than a lamp that’s been burning for a few thousand hours.
Part L.2 (para 53) calls for the initial lamp lumens (at 100 hours burning) to be taken into account.
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