Lighting specification and Part L: 2010

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.

The latest version of 'Approved Document L: Conservation of Fuel and Power' will become valid in October 2010, and there are some fascinating changes in the way that the lighting design criteria have been altered. There are still the same four parts: 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.

To save you the annoying business of looking for (and failing to find) the actual design criteria inside the Part L documents, let me tell you ….. they're not there. You need to access a copy of the Part L Compliance Guides and that's where you'll find the numbers.

Changes to Part L1 Design Standards

Firstly, the energy efficiency standards have been tightened up, shifting the minimum luminous efficacy rating from 40 lamp lumens/circuit Watt to 45 lamp lumens/circuit Watt. So far, so expected, but it's the next bit that comes as a surprise ….
In the 2006 edition a reasonable provision of low energy lighting was achieved if the designer ensured that either one luminaire in four used a dedicated low energy source, or that there would be one low-energy lamp per 25m2 of dwelling space (excluding garages)
In 2010, however, the new standards require three luminaires out of four to be fitted with low-energy lamps - but these can be any type of low-energy lamp provided their luminous efficacy meets the 45 lm/W requirement. Luminaires can be fitted with conventional lampholders (Edison Screw or Bayonet Cap) - and that's a major shift in assumptions about the general acceptability of low energy light sources.

But there's also a very big but, and one that I'm not at all sure about. The 2010 edition has allowed an exemption for any luminaire that has a power requirement of less than 5 circuit Watts - something that doesn't relate to compact fluorescent sources, but which is obviously aimed at LED fixtures. I think I know why this has come about, and I suspect my own design schemes reflect the need for such a change. This is what happens: I've been using small LED fixtures to provide a glimmer of over-night illumination in corridors and bathrooms, the justification being that we need only a tiny amount of light to enable us to navigate around the house at night, so why have to switch on unnecessary illumination when a 1W device can provide more than enough to get you where you're going. (And let's not get into melatonin suppression and illumination levels at this juncture - let's just acknowledge that sleep is very important to us all). Of course, every one of those little buttons of light got rounded-up into the 1-in-4 Part L headcount, so it wasn't difficult to deliver a compliant scheme.

The question, though, is why set the barrier at 5 circuit Watts? There are plenty of 'general lighting' LED fixtures available that fall within that figure that are being promoted around the place. They are not very good and they don't deliver sufficient illumination and I worry that there's a very real chance that some unscrupulous specifier/developer/contractor could fit-out an entire house with these inadequate luminaires and then claim a compliant lighting scheme.

As regards external lighting, the energy standards have once again been tightened-up, with the requirement that lamp capacity should not be more than 100 lamp-Watts, that they should be automatically controlled to switch off when there is no one around, and that they are fitted with a daylight sensor to prevent their use when they are not needed. All good stuff.

  

Changes to Part L2 Design Standards

 
Once again, the focus is on a tightening-up of the luminous efficacy ratings; general lighting for offices, industrial and storage areas now requires luminaires to have an initial efficacy of 55 luminaire lumens /circuit Watt, an increase of 10% over the 2006 edition - putting more of a squeeze onto luminaire designers to deliver a better performance.
General lighting in other non-domestic spaces will require light sources to have an average initial efficacy of 55 lamp lumens / circuit Watt, again a 10% uplift from 2006, while display lighting gets a bigger hit by having its compliance limit lifted from an initial efficacy of 15 lamp lumens/ circuit Watt to 22 lamp lumens / circuit Watt.; a 50% increase, and rightly so.

There are also minimum lighting control standards to be met, from requiring a light switch by the door to a small room, to a fully-managed system using time-based or processor-based controls. I'm not sure that the writers of Part L have a real, deep and heart-felt, understanding of lighting controls, or whether it's such a complex thing that they've gone for the simplest options. Technology is such that there are so many more exciting possibilities available to us when it comes to controlling the energy usage of our lighting installations - and proposing a switch by the door feels as 21st century as a rush-light.

There's also a cute reference to the control of display lighting, which can be 'switched off when people will not be inspecting exhibits or merchandise or being entertained'. Yeah - right. That piece of absurdist comedy really entertained me. And when the department store sees its merchandise displays as if they're in a particularly quiet gallery of the V&A, then I'll quit.

But my chief concern regarding Part L2 relates to the lighting design aesthetic. A target performance figure of 55 luminaire lumens / Watt calls for a robust and unforgiving style of lighting performance, usually associated with high-output modular fluorescent luminaires and recessed downlights. These types of fixture are capable of squeezing a lot of light out of a lamp and into the lit space, but it's a very mechanistic approach to space illumination. CIBSE has lobbied for many years to attenuate the starker aspects of this kind of lighting - we've seen it time and again in lower specification offices where 'Cat2' modular fixtures have been used to deliver a visually harsh environment.
Softer, more civilising, illumination cannot be delivered at 55 luminaire lm / circuit Watt, but it can be delivered at 45 lamp lumens / circuit Watt, and that's what I shall be looking for in my designs.


  

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 Watt^2a.

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.