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Good Practice for Energy Efficiency: Lighting
Artificial lighting is an essential part of our lives; approximately 20% of all electricity in UK commercial and industrial buildings is used in lighting (Carbon Trust, 2017). However, almost three in four buildings have outdated lighting installations. Accordingly, the most popular recommendation from the first phase of the UK's Energy Savings Opportunity Scheme (ESOS) assessments was the installation of a new lighting scheme.
Using efficient lighting products could save up to 75% of the electricity consumed for lighting in the UK each year (LIA, 2015) and correspondingly reduce lighting energy costs. Upgrading lighting can also improve the productivity, mood, health and safety of people working in and occupying these spaces.
+ Who is this guide for?
Are you a facility manager, financial director, engineer or other professional that oversees lighting upgrades?
Has your organisation decided to improve lighting to:
- Save on electricity costs, as identified (for example) by an energy audit
- Improve employee well-being or productivity
- Address health and safety risks
- Refurbish, or improve lighting maintenance
- Change interior design or rebrand?
Do you want ensure that the new lighting system:
- Is fit for purpose
- Is the most energy efficient
- Provides best value for money?
This guide is designed to help you.
+ What does this guide do?
This guide provides:
- A road map for overseeing a lighting upgrade
- Questions to ask a potential supplier or manufacturer
- A checklist of what should be included in a tender response
- Signposts to further reading including existing standards and detailed guidance
Note: The content of this guide is based on the Lighting Module of the Energy Institute Level 2 Energy Management Training course. The guidance was developed in the United Kingdom, but most of its recommendations can be applied anywhere.
To view the Guide's content, scroll through and click on the cards below.
What criteria should be considered when choosing a lighting designer?
Before contracting for a selected lighting project, you'll want to ensure that a lighting designer can provide an integrated, holistic solution that considers functional, aesthetic and energy-efficiency aspects of lighting design. To check that the lighting professional is sufficiently qualified and experienced:
- Verify their membership status in the Society of Light and Lighting (MSLL), or other industry associations
- Ensure that they hold an SLL lighting diploma or equivalent
- Review their portfolios and testimonials from past contracts
- Look for a designer that can demonstrate a diversity of completed projects
- Enquire how they keep up-to-date with the latest trends and technologies
Is there a design benchmark for lighting?
The lighting design process should take into account:
- Illuminance levelsIlluminance (or light) levels indicate the amount of light required to perform a task in a safe and efficient manner.
- Illuminance uniformityTo create a more comfortable and productive environment, it is recommended that task areas are illuminated in as uniform a way as possible. A qualitative expression of illuminance uniformity is the uniformity ratio, which is defined as the ratio of minimum illuminance levels to average levels. Typically, a ratio of 0.7 is required for creating a comfortable visual environment and avoiding glare. Illuminance uniformity is often achieved by installing light sources spaced in a regular grid over the area.
- Luminance distributionThis refers to the variations in brightness within the field of view, between the task area and its close and distant visual surroundings.
- Colour renderingThe Colour Rendering Index (CRI) is a measure of the ability of a light source to accurately portray the colours of the objects and surfaces it illuminates. The higher the CRI value, the more accurately the colours will be reproduced. Often, CRI values are referred to as Ra (average rendering) values.
- Colour temperatureThe term describes the overall colour of a light source. Different types of natural and artificial light sources produce different degrees of ‘warmth’ (towards yellow) or ‘coolness’ (towards blue). For example, the diffused light from the sky on a cloudy day is perceived by the human eye as being white in colour, whereas the direct light from the sun on a day with clear sky is perceived as yellow or orange in colour. Artificial light sources are categorised on the basis of their colour temperature in a similar way.
- Appropriate use of interior light surfaces, e.g. walls or ceiling
- Additional aspects such as glare and flickerGlare is defined as the sensation produced by intense light in the field of view (which lowers illuminance uniformity). Flickering refers to rapid and repeated changes in the brightness of light, that can cause distraction and possibly physiological effects such as eye strain or headaches.
In the UK, the Society of Light and Lighting (SLL) ‘Code for Lighting’ is considered one of the most comprehensive standards for lighting design. The Code for Lighting presents a holistic approach to lighting design, including energy efficiency, visual function, architectural integration, visual amenity, and both capital as well as operation and maintenance costs.
- SLLCL SLL Code for Lighting: www.cibse.org
- Lighting Digest, A list of British Standards related to the lighting industry: www.lightingdigest.co.uk
- CIBSE, Lighting for people, energy efficiency and architecture – an overview of lighting requirements and design (1999): www.cibse.org
- Waveform Lighting, Guide to the Color rendering index: www.waveformlighting.com
Does the lighting design(s) meet Health and Safety standards?
Well-designed lighting improves the working environment by allowing people to more easily see and avoid potential health and safety hazards and by ensuring they can carry out tasks safely and efficiently.
Poor lighting, on the other hand, can be detrimental to your business by causing Sick Building Syndrome (SBS), which may include eye strain, migraine, tiredness or poor concentration of people working in that environment.
In the UK, under the Health and Safety Executive in HSG 38: Lighting at Work, employers and people in control of non-domestic premises have a duty to ensure that lighting is safe and does not pose a health risk to employees and others who use their premises. A range of health and safety-at-work aspects include meeting minimum illuminance levels for various tasks (see Back of the envelope below), lamp replacement and disposal, emergency lighting systems and emergency lighting levels.
The recommended maintained illuminance levels vary for different activities. They are measured in the standard unit of lux, which defines the amount of light output reaching a given surface. Ask your lighting designer if they have worked out the appropriate maintained illuminance for each use of your lighting installations.
Cable tunnels, indoor storage tanks
Corridors, changing rooms
Foyers and entrances, dining rooms
Libraries, lecture theatres
Engine assembly, laboratories,
small retail shops
Assembly of minute mechanisms,
finished fabric inspection
- For more details on recommended minimum lighting levels and other factors of lighting in the workplace affecting H&S, please read Health & Safety Guide 38: Lighting at Work: www.hse.gov.uk
Does the proposed lighting solution comply with current building regulations?
In the UK, any new construction or major refurbishment project must comply with the 2013 Building Regulations. Regulation requirements include:
- A minimum efficiency for lighting fixtures at 60 lumens per circuit-Watt in the system. Lower efficiency luminaires are permitted only when fitted with particular types of lighting controls
- sufficient illuminance levels for each work task Illuminance (or light) levels indicate the amount of light required for performing a task in a safe and efficient manner. In the UK, illuminance levels are published primarily by the Society for Lighting and Light (SLL). Most publications, guidance and legislation refer to these or are in line with them. Please see examples of activities and their associated maintained illuminance levels in the card titled Check whether your lighting design meets the standards of the Health and Safety Executive's 'HSG 38: Lighting at Work.'
- appropriate ‘unified glare rating’ (UGL) factor The luminance from the lamps divided by the background luminance from the room's walls and ceiling. This varies depending on elements such as the dimensions of the space and the technical properties of its lamps and luminaires. According to the ‘SSL Lighting Guide 07: Offices’ the unified glare factor for office spaces should not exceed 19.
- appropriate contrast levels between different areas of a building
- appropriate brightness levels of various surfaces such as walls and ceilings
Another method for complying with the 2013 Building Regulations’ energy efficiency requirements for lighting systems is the Lighting Energy Numeric Indicator, LENI.
The LENI method calculates the energy performance of a lighting system in terms of energy consumed per square metre of floor area per year (kWh/m2/yr). Use of LENI promotes efficient use of lighting, not just efficiency of individual lighting components, as was the case for the previous edition of the Building Regulations. In doing so, it recognises the importance of lighting control.
What is the most cost effective and energy efficient design solution?
Several factors should be considered when evaluating the cost effectiveness and energy efficiency of a proposed lighting design:
- Access to daylight: The cost and energy efficiency of your lighting system will depend on natural light availability. Whenever possible, a lighting designer should examine how best to leverage daylight, as this will allow you to avoid switching on artificial lighting.
- Technology: Lighting technology has developed quickly in recent years, with lamps providing great improvements in lighting efficiency. Traditional incandescent bulbs are being fast replaced by a new generation of lighting such as compact fluorescent lamps (CFLs) and light-emitting diodes (LEDs). LED lighting, with lamp lifespans exceeding 50,000 hours of operation and with a possible output of 200 lumens per watt (power), stands out as the most cost and energy efficient technology for many uses. Considering the light output (lumens), the power (watts) used, or total cost of ownership, they consume approximately 80% less energy than halogen lamps and 60 to 70% less than traditional fluorescent lamps. Some LEDs offer additional functionality, for example embedded sensors allowing the user to monitor energy use or the operation and maintenance of lighting fixtures, as well as the potential for wireless data communication over the visible light spectrum (LiFi).
- Lighting Control: Lighting efficiency will depend on the compatibility of your new lamps with the lighting control system, e.g. timers, motion detectors and dimmers. Without suitable lighting control, even the newest generation of lighting will incur unnecessary energy costs. Conversely, teaming a control system with compatible efficient light sources can yield significant savings. Digital lighting control systems allow energy managers to better understand how lighting is used in a building, improve system design and optimise energy efficiency.
When choosing the most appropriate control method, it is important to take into account:
- Type of space, ranging from ‘owned’ (e.g. a small consulting room) through ‘shared’ (e.g. an open-plan office) to ‘managed’ (e.g. a restaurant) spaces
- Occupancy level and how the space is used
- Amount of daylight available, considering such influences on lighting as skylights, daylight harvesting, type of window glass, wall colour etc.
- Presence control: acoustic or movement detector
- Time control: time switch or programmed control
- Daylight linked: simple photocell or photocell plus regulator
If the control system does not perform as designed, energy savings may not be realised. This includes too-stringent controls; a system that is too aggressive in switching on/off and dimming can result in occupant complaints, reduced lamp life, and may lead to automatic controls being manually over-ridden.
The CIBSE Commissioning Code L: Lighting presents standards of good practice in this area. The Code provides guidance on how to set up a commissioning plan for a project, to manage the process of ensuring that the design intent is realised and that the users of the lighting installation are aware of the operation and benefits of the lighting installation, as apply to their particular use of the building.
The following figure summarises the main characteristics of example relatively-efficient light sources:
- Carbon Trust, Lighting: Bright ideas for efficient illumination: www.carbontrust.com
- Energy Saving Trust: www.energysavingtrust.org.uk
- ESTA, Lighting and Lighting Controls: www.esta.org.uk
- The Lighting Industry Association’s (LIA) Lighting Control Guide (available for registered members only): www.thelia.org.uk
- Simple Measurement for Energy and Water, Fuel Efficiency Booklets: www.cibse.org
- The Lighting Controls Authority: Introduction to the Commissioning Process: www.lightingcontrolsassociation.org
- CCL Commissioning Code L: Lighting: www.cibse.org
What should be included in the project’s cost?
For any lighting project, both the capital cost and the operational and maintenance costs must be estimated. Projects are often evaluated on a life cycle cost basis, as an installation with a higher capital cost but a lower operating cost may be more cost-effective over its lifetime than an alternative option that has a low capital cost and higher operational costs. For example, when considering LEDs with burn times of 50,000 hours, compared to other lamps which may last 18,000 hours or less before replacement, life cycle costing can be key to deciding which of these two systems is more cost-effective over its lifetime.
Life cycle cost analysis should provide you with an overview of the cost of the lighting design project throughout the whole project life, from the procurement stage, through installation, commissioning and testing and finally operation and maintenance.
Typically, the initial capital cost includes the cost of the design process, procuring the equipment and the installation process including commissioning and testing the installation.
The operational costs include the electricity consumption and maintenance (such as cleaning and replacing lighting components) throughout the life of the installation. Budget may also have to be set aside for the disposal of redundant equipment.
How can I understand the operational lifetime of a selected lighting system?
Various lamps have different lifespans referred to as “Average Rated Lifetime Hours” (ARL). The term indicates how long it takes for a certain percentage of light bulbs in a test batch to fail and is measured in hours. For example, if 100 bulbs were tested and 50 (or 50%) of them failed after 1,000 hours, this bulb would have an average rated life of 1,000 hours. Hence the ARL is popularly known as half-life.
ARL of traditional lights are highly predictable (please see the previous card for more information). However, LEDs don’t have the same type of failure. They are long-lasting light bulbs that do not normally burn out; instead their brightness slowly decreases over time. This phenomenon is called lumen depreciation, i.e. the time at which it degrades in light output to a given percent of its initial value. A typical LED’s rated life is when a lamp reaches 70% of initial brightness. This designation is represented by a label L70.
The rated life of light sources is different from the lumen maintenance life. While the former serves as a reliability value that is required by luminaire makers and end users, the latter compares the amount of light produced by a brand new lamp with its light output at a specific time in the future. See the Back of the envelope for more information about lumen maintenance life.
Each different type of lamp has a different average lumen maintenance life, as seen in the example chart below. This information is useful when considering whole-life cost of a lighting system, appropriate warranty coverage, and maintenance schedules.
- Light Bulb Average Rated Life Time Hours: www.thelightbulb.co.uk
- LEDs Magazine: Understanding the difference between LED rated life and lumen-maintenance life
What product warranties should be specified in a proposed lighting solution?
Before going ahead with an installation, make sure that you understand suppliers’ warranty policies to avoid those that are not appropriate for your project. Policies should guarantee that if sold products fail to operate in accordance with warranty, a supplier will provide a free replacement of a failed product, within the validity period of the policy and subject to the warranty terms and conditions. You should provide your supplier with details of factors which may impact the lifespan of the lighting for your particular use, e.g. switching and dimming patterns, the ambient temperature, humidity in the installation, cleaning and so on.
The following enquiries should be made:
- Does the warranty cover a minimum 5 years for a product and 12 months for the installation?
- Does improper installation affect or potentially void the warranty?
- How reliable is the business offering the warranty? What is the age of the business and its financial stability?
- Does the warranty specify a maximum number of burn hours per annum?
- Does the warranty provide a clear definition of “failure” of the light source?
- Does the warranty policy indicate the lifespan of a lighting unit?
- Does the warranty cover the maintenance cost?
- Does the warranty cover labour costs?
- Does the warranty clarify who bears responsibility and cost of replacing failed products?
- What lighting components does the warranty cover?
Consider the below example to evaluate whether an offered warranty policy is appropriate for your lighting system.
You purchase an LED lamp with 5-year warranty and of an L70 lumen maintenance rating of 30,000 hours. It is also stated in your warranty policy that the burning period must not exceed 6,000 hours per year.
The lighting operates 15 hours per day, 365 days per year. Your annual burn hours are thus 5,475, resulting in 27,375 burn hours for 5 years. Hence, your warranty policy expires a few months before your lighting system will reach the L70 rated life.
If your LED lamp fails within the first 5 years of operation, it could be then assumed* that it was defective or faulty rather than over-burned. You should be then entitled to a replacement, repair or other compensations agreed in the warranty policy.
*Subject to other terms and conditions agreed with your supplier.
- Regency Lighting, How long does LED lighting really last and what is actually covered by your warranty? insights.regencylighting.com
How can I maximise energy savings of the installed lighting system?
Lamps and lighting systems deteriorate and their light output depreciates over time. The lighting output of the system also progressively decreases due to accumulation of dirt on lamps, reflectors, lenses and room surfaces. Therefore, the performance of any lighting installation can be compromised without regular maintenance including simple tasks, such as cleaning luminaires and especially lenses, reflectors and panel diffusers.
In designing systems, a suitable maintenance factor should be included to ensure that the lighting levels are maintained over their lifetimes. Where previously lamp and ballast replacements would need to be factored into the maintenance regime, LEDs reduce frequency of the former but both lamps and ballasts may still need changing in the long term. Information such as the lamps' depreciation, or lumen maintenance life, is useful when calculating a lighting installation's maintenance schedule and whole life costs. For more information on lamp depreciation, see the Estimate the capital costs and the operational costs of your lighting project card.
I have performed an energy audit and want to upgrade my lighting - now what?
The missing gap between an energy assessment such as ESOS and a lighting quotation from a lighting supplier / manufacturer is referred to as a ‘Lighting Feasibility Study’.
The 'Lighting Feasibility Study', i.e. the action plan, should be ideally undertaken after an existing energy audit or an ESOS assessment has been completed, and where a client is wanting to replace or upgrade an existing lighting installation within their building.
This study assesses the lighting requirements in a particular space or entire building, enabling an accurate lighting design quotation to be prepared.
Often a client will just use the good will of a lighting manufacture to undertake a free lighting survey in a building and then install the manufacture's products. However, without looking at the rest of the market, the client may not be getting a lighting scheme which provides the best visual environment whilst being the most energy efficient.
Ideally a client should utilise the skills of an independent lighting consultant who does not represent or have any allegiance to any lighting manufactures.
This study should be performed by a qualified, independent and experienced lighting consultant, for example from the Energy Institute Register of Professional Energy Consultants (RPEC), or other relevant energy / lighting professionals such as Chartered Energy Managers, members of the Society of Light and Lighting who are holders of their association’s diploma, and members of the Institution of Lighting Professionals.
The lighting feasibility study will include all or the majority of the following aspects below in its assessment of the existing lighting system:
- What is the overall condition and age of the existing lighting installation?
- Does the existing lighting system still meet the latest design requirements?
- Has the existing lighting system been maintained?
- Are the lamps and diffusers dirty or missing?
- An assessment of the workplace areas and availability of daylight into the space/room, including an assessment of the daylight factor
If a client decides to replace or upgrade an existing lighting installation, the feasibility study should provide:
- A verification whether alternative lighting designs were considered and how the different types of lighting solutions meet the client’s requirements and aspirations
- An assessment if all necessary parameters are included in the lighting design solutions include illumination levels, uniformity, etc.
- An assessment whether and if so, what kind and quality of lighting control solutions have been included into design
- An assessment of compliance with the Building Regulations’ energy efficiency requirements of the considered lighting design solutions
- A verification whether a LENI calculation have been produced with accurate total lighting power, daylight factor, illuminance factor or occupancy factor
- An assessment whether health and safety requirements have been considered, including whether the lighting design(s) meet the HSE minimum lighting design requirements
- A verification whether the project costings include life-cycle cost analysis (LCCA) or SPP
- A verification whether the commissioning requirements have been considered, for example, to monitor whether movement sensors or time clocks operate when they are programmed to
- A verification whether a maintenance plan has been considered which takes into account regular lamp cleaning and replacement and whether it has been included in the life-cycle cost analysis (LCCA)
- A verification whether sub-metering requirements have been considered?
List of abbreviations and technical terminology
Ballast: a device used in order to regulate the amount of electric current that is supplied to a light source. It is essential to all types of discharge light sources. Typically, a ballast is placed in the lamp fitting.
Colour rendering: the Colour Rendering Index (CRI) is a measure of the ability of a light source to accurately portray the colours of the objects and surfaces it illuminates. The higher the CRI value, the more accurately the colours are being reproduced.
Colour temperature: a term that describes the overall colour of a light source. For example, diffused daylight on a cloudy day is perceived by the human eye as being white in colour.
Daylight Factor (Fd): a variable which takes into account the amount of energy that can be saved when daylight dimming control systems are in place.
Glare: the sensation produced by intense light in the field of view, which can prevent the task from being performed, reduce visibility and lead to visual stress and fatigue.
High-pressure sodium lamp: a type of discharge light source, which uses sodium, mercury and xenon to produce electric discharges. Their efficacy levels are relatively efficient, typically around 100 lumens per Watt. They are mainly used for outdoor application such as street lighting and security lighting.
Illuminance levels: a factor that indicates the amount of light required for performing a task in a safe and efficient manner. There is prescriptive guidance available for illuminance levels. Examples of these levels include 150 lux for loading bays, 300 lux for offices where mainly screen based work is carried out and 500 lux where paper-based work is carried out.
Illuminance uniformity: in general lighting applications, it is recommended to illuminate the task areas in a uniform way as much as possible. A qualitative expression of illuminance uniformity is the uniformity ratio, which is defined as the ratio of minimum illuminance levels to average levels. Typically, a ratio of 0.7 is required for creating a comfortable visual environment and avoiding glare. However, the ratio varies depending on the type of task. Illuminance uniformity is often achieved by installing light sources spaced in a regular grid over the area.
Illuminance: essentially, a measure of how much light illuminates a surface. Technically, the amount of luminous flux that reaches a given surface. This is the amount of light per unit of time and per unit area of the lit surface. The SI unit of illuminance is lux (lx), which equals to lumens per square meter.
Induction lamp: a lamp that produces electric current within the discharge gas tube through the use of electromagnetic fields. They are characterised by relatively high energy efficiency and a long lamp life (more than 100,000 hours). They are used in hazardous environments (such as the oil and gas industry) since they can be safer than other types of discharge light sources.
LED: a Light Emitting Diode, uses a different technology to emit light than a discharge light source. The technology is based on a scientific phenomenon known as electroluminence. It refers to the emission of light through a material that is activated by an electric current. In the case of LEDs, the materials used are semiconductors, e.g. germanium. Energy is released in the form of photon. LEDs provide a wide range of advantages over other lighting technologies, such as lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching. LEDs are expected to eventually dominate the lighting industry.
Light Output (luminous flux): the measure of the power of light, as perceived by the human eye.
Light Intensity (luminous intensity): the measure of the power of light that is emitted by a light source in a particular direction. The SI unit of luminous intensity is the candela (cd).
Lumen: the SI unit of light output, or luminous flux.
Luminaire: a complete electric light fixture, including the lamp(s), mechanisms for inserting or holding the lamp(s), wiring, socket and other protective components.
Luminance: it describes the amount of light per unit of time (i.e. power of light) that passes through, is emitted or reflected from a given surface in a particular direction. It refers to light that “goes away” from a surface (either through emission, reflection or transmission). The SI unit for luminance is candela per square metre.
Luminous efficacy: is a measure of how well a light source produces light. It is defined as the ratio of the light output to the electricity required either for just the lamp (i.e. light source) or the whole lighting system to operate. In the first case, this will give us a unit of lumen per Watt (lm/W – referring only to power of the lamp) whereas in the latter case, it will give us a unit of lumen per total circuit Watt (lm/TCW – referring to the whole lighting system). The higher the value of the efficacy, the greater proportion of energy that is converted into light.
Lux: the SI unit of illuminance, which equates to lumens per square meter.
Metal halide lamp: a discharge lamp that uses a blend of vaporised mercury and other metals known as halides to produce electric discharges. Halides are mainly comprised of halogens. In the EU, a halogen bulb phase-out came into force on 1 September 2018.
Unified glare rating (UGR): the luminance from lamps divided by the background luminance from a room's walls and ceiling. It varies depending on elements such as the spatial dimensions and the technical properties of lamps and luminaires. According to the ‘SSL Lighting Guide 07: Offices’, the limiting unified glare factor for office spaces should not exceed 19.
- Energy Institute: Level 2 Energy Management Professional, Module 8: Lighting
- Carbon Trust: Lighting: Bright ideas for efficient illumination
- CIBSE: Lighting for people, energy efficiency and architecture – an overview of lighting requirements and design
- CIBSE: Simple Measurement for Energy and Water, Fuel Efficiency Booklets
- Energy Managers Association (EMA): Light and Lighting Control, Buyer’s Guide
- Energy Saving Trust: The right light introduction for designers and house builders. Selecting low energy lighting
- ESTA: Lighting and Lighting Controls
- HM Government: Non-Domestic Building Services Compliance Guide 2013
- HSE: Health & Safety Guide 38: Lighting at Work
- LEDs Magazine: Understanding the difference between LED rated life and lumen-maintenance life
- The Lighting Controls Authority: Introduction to the Commissioning Process
- The Lighting Industry Association (LIA): How to select your energy saving bulb
- The Lighting Industry Association (LIA): Lighting Control Guide
- The Lighting Industry Association (LIA): Mini Guide to Part L for the Building Regulations
- Regency Lighting: How long does LED lighting really last and what is actually covered by your warranty?
- Regency Lighting: LED Buying Guide
- Thorn Lighting: The Thorn Case Study Booklet
- Waveform Lighting, Guide to the Color rendering index: www.waveformlighting.com