What should a lighting specification look like?


Sophie Parry

March 6th, 2020
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Lighting is becoming an increasingly complex part of building services and project delivery. The reason for this increase is due to several factors:

  • The development of LED lighting technology
  • Methods of controlling the lighting
  • Energy efficiency
  • Circular economy considerations
  • Emerging trend of wellness

These key advances mean that the application of lighting, both internally and externally, needs to be considered with care. The lit effect can make or break the look and stature of a building, notwithstanding the background compliance engineering and validation required once the concept of the proposed lighting scheme has been decided.

Internal lighting specifications for residential premises

The type of interior (residential or commercial) and the activity taking place or likely to take place in the space is the first consideration.

An interior designer will likely add a residential lighting scheme as a high level so that the overall ‘look’ of the finished residence is enhanced during the hours of darkness and is delivered to the expectation of the actual or future occupants. Before we delve into the technicalities, you should consider lighting of spaces such as hallways, lounges, kitchens and bedrooms as subjective. Your opinion of what makes a great lighting scheme may not be the opinion of someone else, so if you are working directly with the client, your job will be easier when agreeing the selection of the luminaires, this is what we in the lighting world call light fittings. If the development is speculative, you will need to select and specify luminaires and create a lit effect that is going to appeal to the majority of potential buyers or tenants.

So that’s the aesthetics considered. At this stage of the project, the luminaires have likely been selected from catalogues or ideally by engaging with a supplier or manufacturer to view samples. Remember to look objectively at luminaires in terms of the aesthetic when switched off and the lit effect when switched on before making the final decision.

The next stage of the specification development is to consider the compliances required and how you will control the luminaires. For residential interior lighting there are very few legislative compliances that need to be complied with, other than ensuring the energy consumption of the installation complies with the current edition of Building Regulation Part L for dwellings and the current edition of the IET Wiring Regulations.

However, there are other technical considerations to consider when specifying luminaires and lamps. These considerations can be summarised as follows:

Light output

Gone are the days where lamps were specified by wattage. LED lighting is specified based on the lumen output. LED lamps are much more energy efficient than the now defunct filament light bulbs of yore and also even back in the day, wattage was never a measure of light output, just power consumed. The wattage is still shown on LED lamps but the only reason is for the benefit of the electrical engineer checking circuit loads for compliance. The lumen output will depend on the luminaire location, how much space you need to light and to what level of light output.

Colour temperature

This is the term most people in a residential context will already know as warm white or cool white. The term temperature may also be used and is going to be more accurate as it refers to the lamp output in temperature as measured on the absolute Kelvin scale for temperature.

Luminaire or lamp specifications may refer to correlated colour temperatures as Kelvin – so what does this mean? A rough guide goes something like this:

  • For cosy, warm lighting in a relaxing environment such as a lounge or bedroom, you will most likely specify a warm lighting effect that typically is in the range from 2200-2700 Kelvin
  • An optional reading light would typically have a higher temperature of 3000-5000 Kelvin to make reading easier on the eye if reading a traditional paper based publication, rather than direct from an e book or smart phone
  • In areas like kitchens, bathrooms and study areas, there are tasks to be performed which require a higher lamp temperature to enable the person to see what they are doing with a degree of accuracy, so the colour temperature of choice is likely to be 3000-5000 Kelvin

Hopefully by now you realise that the generic terms warm white and cool white could be subjective and not necessarily create the lit effect required.

Colour rendering

When you solely depend on electric lighting, that lighting may distort the true colour (as seen in natural light) and could be a minor inconvenience if you pull clothes out of your wardrobe and step outside only to find your outfit is less than colour co-ordinated.

Colour rendering is not often talked about in residential lighting, but it should be. Colour rendering is expressed as CRI or Ra (scale 1-100- 1 very bad- 100 daylight quality). Residential lighting should be specified as at least a colour rendering index (CRI) of 70-80 for relaxing areas, such as a lounge or bedroom, but where tasks are carried out in areas such as the dressing table, kitchen, bathroom or study, the CRI needs to be in the 80-90 range.

Controlling the lighting

Now that we have developed our lighting scheme, we need to think about how we want to control the lighting. Control can be as simple as a manual wall switch or a rotary dimmer. In recent years, the trend has been to do more with controls as technology costs and creative solutions have become more commercially viable. Dimming switches that ‘chop’ the input power to the lamp have been around for many years, but with the arrival of LED lighting, it is important to ensure the proposed powerline dimmer is compatible with the LED lamps it will control, otherwise the dimming effect ill be less than smooth and the dimming switch will likely be emitting a buzzing sound as a prelude to failure. Other, more elegant options include the use of more sophisticated LED lamps with drivers that can accept a separate signal input to provide a dimming feature and that use a 0-10 volt controlling signal. Again, do ensure the lamp and driver is compatible with the control method to be specified.

Going beyond hard-wired controls, we enter the world of Bluetooth or wireless control. The same rules apply regarding lamp and lamp driver compatibility with the chosen wireless system. The provision of a controlling device such as a tablet with appropriate software or a dedicated remote control device will also be required. In some cases the residents that own smartphones can run the required control app, but what if you have guests?

What about outside?

We’ve considered the internal parts of the residence, but the external areas are also increasingly being lit as the market and demand for external residential luminaires continues to grow.

The main consideration with external lighting, notwithstanding compliance with the current building regulations and the current IET Wiring Regulations, is that of light trespass.

A few years ago, it was all about a dainty coach light at the front door and maybe a few big flood lights front and back to add a sense of security and to cause possible intruders to think again.

Security is still a consideration with external lighting and you may also need a minimum light level to support CCTV camera operation or at a local level, to illuminate locked gates, doors or intercoms so the user can use these security features without trying to find the torch app on their phone.

Light trespass (upsetting the neighbours) should be reduced or eliminated by careful selection of luminaire types and insuring the light output is only projected to the area you want to light and not over the property boundary. Additionally, the light output should also only shine outwards and/or downwards so as to prevent unnecessary contributions to the phenomenon known as sky glow.

On larger projects, local authorities will need to see evidence at the planning application stage that the more ambitious external lighting schemes meet the appropriate zoning requirements before granting planning permission. Post completion arbitration and remedials regarding light trespass can be both costly and time-consuming.

The luminaire types come in many styles. Be sure to specify luminaires that have a degree of ruggedness relative to the local environment. The luminaire needs to have been constructed and have a finish suitable to survive the extremes of the seasons for many years, and more technically to support the luminaires reliability over time. Look for or ask about the IP rating. IP or ingress protection is a method of determining if moisture and dust will be able to enter the luminaire and affect the luminaire reliability and performance.

A typical IP rating for an external luminaire should be IP 64. If you are lighting under water (fountains and pools) you would need IP-68 luminaires and be sure to additionally check that the depth rating is compatible with the depth you plan to install the luminaires at.

If vandalism is a concern, then there is the IK rating, which is a measure of robustness relative to mechanical shock. The scale is IK-0 to IK-10. External luminaires that could be subject to vandalism should have IK ratings from IK-8 to IK-10 to reduce the potential for damage or failure from vandalism.

Residential lighting conclusion

So these are the considerations for internal and external residential lighting. As with most things, you get what you pay for, but by engaging with experienced lighting professionals, the lit effect should enhance the residence and meet all the less obvious compliances.

A lot of what we understand and think about lighting stems from our own experiences in the home and therefore shapes our perceptions to a degree when working professionally on residential and non-residential projects.

What’s different about lighting a commercial project?

In a nutshell, it’s a whole different ball game. Some of the luminaire performance features that were mentioned for residential lighting such as lumen output, colour temperature, colour rendering and how we control the lighting are also key performance considerations. External lighting is also subject to the rules of limiting light pollution, but that’s where the similarities end.

Each type of commercial project should be considered as an application when it comes to lighting. The project is being lit for a specific task or series of tasks and the requirements for appropriate lighting have been developed over many years and have also had to track and adapt to the changes in technology and energy constraints applied to all other building services.

The net result is that there are best practice design guides for lighting each application which have usually been written by that industries umbrella organisation (i.e. British Council for Offices (BCO), Department for Education, Sports governing bodies such as the Amateur Swimming Association (ASA) etc, as well as the professional societies such as CIBSE/SLL (Chartered Institute of Building Services Engineers/ Society of Light & Lighting) or the ILP (Institute of Lighting Professionals).

In addition, there may also be specification requirements for the lighting to contribute points to BREEAM or WELL certification that also need to be taken into account.

The other big difference on commercial lighting projects is the requirement for emergency lighting, which only apply to residential projects in apartment blocks or sheltered accommodation where there are clearly defined landlord/tenant spaces and just the landlord or communal spaces will require emergency lighting.

The other thing to note about emergency lighting is that although it does not add to the project aesthetic, and so could be considered a ‘grudge’ buy, it is required by law and has to be maintained to be fit for purpose should it be required to operate under emergency conditions. The continued operation of emergency lighting is the legal responsibility of a nominated responsible person who is responsible in law for ensuring the emergency lighting is ready for operation at all times during the occupation of the premises, otherwise prosecution for failure to comply is likely. There is recent case history of such prosecutions where upon inspection, emergency lighting has been found to be in disrepair and not deemed fit for purpose.

Image credit: iStock.com/Dvoinik

About Sophie Parry

Sophie, a qualified electrical engineer of 30 years, has spent much of her career specialising in lighting and currently works for Zumtobel Group providing lighting technical application research, guidance, and training in the UK & Ireland. Sophie is a published author, international speaker, Fellow of the Society of Light & Lighting, and member of SLL’s technical and publications committee.

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