Low Energy Artificial Lighting

Transcription

1 Contents Why do we even need artificial lighting?... 1 Artificial lamp types... 2 Controlling Luminous Output: From Lamp to Luminaire... 5 Design Requirements for Artificial Lighting... 9 Visual Function and Amenity Sustainability Integration Maintenance Cost Lighting Control The Future for Artificial Lighting Why do we even need artificial lighting? Providing light by means other than the sun and sky are not new. Burning oil has been traced back as far back as 70,000 years although it was not until wick developments in the late 18 th century that significant efficiency gains were made. The Romans produced the first candle with a wick and gas lighting was common in the 19 th Century initially for street lighting, and then large public buildings followed by domestic settings. Almost every large town in Britain has a gas works for provision of lighting. However, all these methods were relatively extremely expensive, and hazardous. Prior to the invention of the incandescent light in the late 19 th Century, and then the leap in efficiency resulting from the development of fluorescent lighting, daylight was the predominant means of lighting interiors. Although natural light is free and well liked by building users, artificial lighting has many unique benefits: 1. Light can be available whenever it is required e.g. outside of daylight hours 2. Light can be provided wherever it is required e.g. in areas far from the building envelope. This has had a radical impact on the possibilities of form in modern architecture. 3. Light can be provided however it is required i.e. in any quantity and with any distribution. This can be tailored to provide a variety of requirements e.g. task lighting, display lighting, general ambient lighting 4. The light provided is stable in output, unlike daylight, so where precise control is required of light quantity and quality e.g. colour, this can be guaranteed with an artificial system. 5. Light can be provided independently of increased heat loss and gains from windows. Sadly, in many cases the ready availability of artificial lighting as an engineering solution has disassociated both building designers and users with their ability to use daylight as the predominant/sole light source when appropriate. 1/25

2 A successful artificial lighting scheme will have appropriate control to ensure that it is not utilised when it is not required (e.g. during daylight hours or where there is no occupancy), and that it provides an appropriate lit environment to the activity being undertaken, in as most efficient way as possible, when it is required. Artificial lamp types Artificial light can be produced by a number of different processes, and this has resulted in a range of different lamp types. The main types used today are as follows 1 : Incandescent: A filament is heated to a very high temperature so that it emits light, with the most common form being the General Lighting Source (GLS). The filament is a coiled (to reduce convection losses) tungsten wire located in a bulb whose size is set so as to not get too hot and to reduce blackening from the tungsten emitted from the filament over the lamps life. The bulb is filled with an inert gas, normally argon, to reduce heat loss from the filament. GLS lights have poor efficacy and short operating lives. Figure 1 Producing light in an incandescent lamp (Source: SLL) Tungsten Halogen: A tungsten filament is heated to a higher temperature than a GLS resulting in a greater luminous output. To reduce blackening from the tungsten, halogen at higher pressure than GLS needs to be introduced to the bulb, and the higher temperatures mean the walls need to be made of quartz or hard glass. They are more efficient, longer living, and more compact than standard GLS, though more expensive. Fluorescent: Light is produced through electrical discharge. Electrons within a tube containing a mixture of noble gases and mercury vapour collide with the mercury molecules which results in the generation of UV radiation, which in turn strikes the inside surface of the tube which is coated in a phosphor. This converts the UV radiation to visible light. The electric current supplied to the discharge has to be regulated using control gear to maintain stable lamp operation. Traditionally this has been using magnetic ballasts, though now high frequency electronic ballasts are normal. There are three types of phosphor mix used on the inside surface of the lamp, which can be mixed to give different colours: 1. Halophosphates Emit light in a wide band, though only reasonably efficient and colour rendering is poor 2. Tri-phosphates Mixes of three narrow frequency band light. Generally they have colour rendering indexes above 80, high efficacy and good lumen maintenance 3. Multi-phosphors Mix of usually five phosphors which results in a colour rendering index of above 90, though this comes with lower efficacies than tri-phosphor. 1 This section draws from the SLL Lighting Handbook 2/25

3 Linear tubes come in three diameters T12 (38mm), T8 (25mm) and T5 (16mm) the number after the T being the number of 1/8 th inches of diameter as well as compact fluorescent (CFL) fittings, often which have integrated control gear and so can be retrofitted into existing incandescent fittings. Figure 2: Producing light in a fluorescent lamp (Source: SLL) Metal Halide: Discharge occurs in a quarz discharge tube containing mercury vapour and metal halides which produces visible light and UV radiation which is converted to visible light as it strikes a phosphor on the inner surface of an outer bulb. They are compact come in a range of powers, and can have excellent colour rendering and efficacy. Low Pressure Sodium: Similar to fluorescent lighting except the mercury vapour is replaced with sodium and is run at a higher temperature. The discharge produces visible light directly without the need for phosphors. The emitted light occurs in two very narrow frequency bands close to the peak of the Photopic sensitivity curve, therefore lighting efficacy is very high, though as the light is effectively monochromatic colours are not rendered, and as such this lamp is rarely used in new installations. It is typically found in street lighting. High Pressure Sodium: Similar to low pressure sodium but operated at higher pressures. This has the effect of broadening the colour spectrum which means that reasonable colour rendering can be achieved, though this is at the cost of efficacy. In spite of this, efficacy is still high. White HPS has a spectrum with minimal output in the yellow part of the spectrum which makes colours appear more vivid. It therefore has useful applications in the retail sector. Light Emitting Diodes: Current is passed through a semiconductor chip which produces radiation in a variety of colour depending on the material of the chip. Commonly white LEDs are produced by adding a phosphor layer in front of a blue or UV chip. LEDs have very long lamp lives and good efficacies. Heat needs to be conducted away from the chip in order to maintain efficacies, as efficiency drops with increased operating temperature. Figure 3: Conversion of light from a blue LED chip using a yellow phosphor either dispersed in a moulding material (left) or on the chip s surface (right) (Source: LIF) 3/25

4 Designing lighting in a low carbon building requires specifying the right light source for the job, which includes not only energy efficiency but a number of other considerations. An efficient but inappropriate (e.g. photometrically or start-up time) lamp cannot be considered to be sustainable. Important parameters where lamp types differ include: Light output (luminous flux): This will affect the amount of light and therefore illuminance levels in a space. Different lamps will also have different lumen maintenance factors meaning that end of life output must be considered as well as initial output Power demand: This should include not just the lamp, but all associated circuitry. This should also include the power factor as for some lamps the voltage multiplied by the current may exceed the rated lamp power. Most high wattage lamps have a power factor of greater than 0.85 Luminous efficacy: The amount of light output per unit of power input. This should include any power consumption associated with control gear Lamp Lumen Maintenance Factor: The light output of lamps decreases as they get older. Lamps with poor LLMF therefore will result in greater power consumption as a lighting system is initially over-specified to account for the loss in light output at end of life Lamp Life: A longer life will reduce cost of replacement of both lamp and associated installation/maintenance costs. Lamp life is often quoted in terms of economic service life (hours) which is often the point at which the LLMF multiplied by the lamp survival factor (percentage of lights that will survive a certain number of hours) falls below 0.7. Life can be affected by temperature, switching and supply voltage. Colour: Generally described in terms of colour rendering index (often a minimum value/class is required depending on task) and colour temperature (chosen for atmosphere). Run-up time: The time taken for light output to reach 80%, which is virtually instant for GLS though may take as long as 20 minutes for low pressure sodium Dimming: Dimming is not possible for all lamps, and in some cases it is only possible to dim to a certain percentage of maximum output. It may also require special control gear. These are summarised for a range of lamp types. 4/25

5 Figure 4: Properties of various lamp types (Source: SLL) Controlling Luminous Output: From Lamp to Luminaire Having established that light can be produced by passing a current through a lamp, this can be practically applied to real situations by placing the lamp into a luminaire. The luminaire carries out many functions including connecting the electricity supply to the lamp, fixing the lamp to the building and protecting it from damage, as well as distributing the light in the desired manner. Optic control of light output is achieved by a combination of various optical controllers: 5/25

6 Reflectors: These redirect the light source to produce beams and light distributions of various angles or intensities depending on the shape and surface properties (e.g. specular, dimpled or rough) of the reflector and the relative position of the lamp within it. The reflector material used typically has reflectance values of , meaning that significant amounts of light from a lamp emitted in the direction of the reflector are converted to heat. Refractors: Control light distribution by refracting light using either prisms or lenses. Some energy is lost through the refracting material. Diffusers: Transparent materials, normally opal glass or plastic that scatter light in all directions in order to reduce the brightness of the luminaire. Some energy is lost through the diffusing material. Baffles: Can be used to hide the lamp (thus reducing the risk of glare), reduce light spill and control the light distribution. If it is used to hide the lamp and control distribution then the baffle material is made from a specular material and shaped to direct the light downward. As a rule of thumb, the finer the mesh the better the control, though the lower the light output ratio (see below). On a related note, Category 2 luminaires relate to the maximum luminance limit at an angle of 65 o to the downward vertical (cutoff angle), and were introduced in 1996 as a means of demonstrating that rooms where Visual Display Terminals (VDT) are used do not suffer from glare problems. However, an over-reliance on specification of Cat 2 lights which resulted in gloomy rooms (dark walls and ceilings) together with improvements to screen technology has meant that this categorisation system was scrapped in For modern screens with positive polarity (i.e. dark characters on a light background) a luminance limit of 1,500 cd/m 2 at a 65 o angle is permitted. Filters: Used in display and decorative lighting to change the colour of a light source, though with a large energy penalty. Modern LED luminaires can vary the light colour by varying the combination of red, green and blue LEDs on in a luminaire. Figure 5: Light distribution of a circular reflector with a point source at its focus (Source: SLL) Figure 6: A baffle used with a fluorescent tube. The shielding angle is the cut-off angle minus ninety degrees (Source: SLL) 6/25

7 The fraction of luminous flux produced by a luminaire relative to the bare lamp is known as the Light Output Ratio (LOR). The LOR should be obtainable from luminaire manufacturers. This can be used to give a better indication of overall efficacy of a lighting installation. For example Part L of the Building Regulations sets performance standards in terms of luminaire lumens per circuit-watt where the luminaire lumens are obtained by multiplying the lamp lumens by the LOR. The above principles of light distribution are incorporated into luminaires which can be broadly classified into the following types: 1. Direct luminaires distribute light mainly downwards and are used where ceiling heights are restricted. This is the most efficient way of delivering a required working plane illuminance but there can be problems regarding uniformity and dark ceilings 2. Indirect luminaires distribute light upwards which provides better uniformity and reduced glare, though using the ceiling as a secondary reflector comes with a large energy penalty. Generally only effective for ceiling heights above 2.75m. 3. Direct/Indirect luminaires combine the advantages of the direct and indirect types, by distributing some light downwards and some upwards. Generally only effective for ceiling heights above 2.75m. 4. Downlights are a form of direct luminaire characterised by a small aperture, and are commonly used with tungsten halogen bulbs and CLFs. Can provide sparkle and interest, though illuminance distribution is poor and ceilings can appear dark 5. Wall washers have an asymmetric light distribution so that large areas of wall can be washed evenly. Careful design and aiming is required to obtain the correct effect. 6. Task lighting can be used to supplement general ambient lighting. This can give users additional control, and may also enable illuminance levels from the ambient system to be designed to lower resulting in reduced energy consumption. a b c d e f Figure 7: Different luminaire type including (a) direct, (b) indirect, (c) direct/indirect, (d) downlight, (e) wall washer and (f) task light (Source: SLL) 7/25

8 LEDs are slightly different. They can be configured in a number of ways: 1. Packages: The LED die (or chip) is contained in a suitable package allowing simplified electrical connection or assembly 2. Module: the LED together with mechanical and optical components making a replaceable item for use in a luminaire 3. Luminaire: A complete light fitting that uses LEDs as the light source 4. Retrofit LED lamps: Used as direct replacements for existing light sources A B C D Figure 8: Configurations for LEDs (Source: LIF) Luminaires are then utilised in lighting strategies that can be broadly grouped into three approaches. General Lighting System: This usually consists of either direct, indirect or direct/indirect luminaires to provide a design illuminance for a working plane. Of the three direct lighting will be most energy efficient though may make a space appear gloomy. The main advantage of this approach is that it offers flexibility of use for the space e.g. work could be equally well undertaken anywhere. A typical engineer will probably design this type of lighting system unless instructed to otherwise by the client. Figure 9: A general lighting system employs a regular array of luminaires to provide uniform illuminance on a working plane (Source: CIBSE) Localised Lighting: Higher illuminance is provided around work areas from either ceiling mounted or hung luminaires, or free standing sources. In an office, desks account for 25-30% of space and so this approach offers potential energy savings, although perhaps with a loss of flexibility. This can be mitigated to an extent by using luminaires that are reloadable as part of a ceiling tile system, or relocated on a track system for suspended fittings 8/25

9 Figure 10: A localised lighting system uses luminaires located adjacent to workstations to provide both task and ambient lighting. Additional luminaires can be deployed to top up ambient and/or task lighting as required (Source: CIBSE) Local Lighting: Ambient lighting is provided by a general lighting system with task lighting at workstations topping up to required illuminance levels. The ratio of task to ambient should be around 2:1, therefore for an office with a design illuminance of 500 lux, the general system can be sized to provide 250 lux. Figure 11: A local lighting system uses a general lighting system to provide ambient illuminance (at a lower level than in solely a general lighting system) with additional luminaires at workstations to provide task illuminance (Source: CIBSE) With modern dimming and control systems, it is now possible to design a lighting scheme to be able to provide the light output of a general lighting system, but to create scenes with lower ambient light output that would therefore support localised or local strategies thereby providing energy savings without compromising flexibility or future adaptability. Design Requirements for Artificial Lighting Designing an artificial lighting system, as with any process of design, involves resolving a series of often conflicting objectives. It is vital that the client expresses their priorities to the design team, and that in term the design team is capable of expressing the potential conflicts and compromises that may result. It is important to remember that there are actually very few legal requirements governing internal lighting design (excluding emergency lighting). Part L of the Building Regulations sets minimum requirements for lighting efficacy and the Workplace Regulations state that every workplace should have suitable and sufficient lighting, but that aside there is the flexibility to trade-off design objectives against one another. This section discusses some of the main design requirements for internal lighting design. 9/25

10 Figure 12: Objectives for artificial lighting design (Source: SLL) Visual Function and Amenity The Workplace Regulations requires suitable and sufficient lighting which is often interpreted as meeting the design targets set in CIBSE publications, for example the CIBSE Code for Lighting and the various CIBSE Lighting Guide series e.g. LG5 The visual environment in lecture, teaching and conference rooms. Specific clients may also have produced their own design requirements e.g. Building Bulletin 90 for lighting in schools. This is reinforced by schemes such as BREEAM which provides a credit for meeting such standards. It is very important to remember that these standards are not mandatory and even within them there is often an element of flexibility, and that designers should be empowered to modify these requirements depending on the project objectives and context. For example, in the CIBSE Code for Lighting in discussion about relative wall illuminances it is stated: These values are not sacrosanct, and there are reasons a designer may wish to deviate from them. Bright walls can make a room seem larger and more spacious, whereas dark walls can make it seem small and possibly cramped, or intimate. Bright ceilings and dark walls may give the impression of formality and tension, whilst the reverse (bright walls and dark ceiling) may create an informal and relaxed or sociable atmosphere. These are not hard and fast rules, but are supported by experimentation. The format of CIBSE standards is generally to state minimum illuminances on a working plane and then to set relative illuminances for the walls and ceiling in order to avoid gloomy interiors. This is shown in Figure 13. There will also be additional standards relating to uniformity, glare and colour rendering. The correct interpretation of illuminance and uniformity design criteria appears to be commonly misapplied in lighting design. The standards only apply to task areas, and so where desk layouts are known the illuminance only needs to be calculated at the task positions and uniformity calculations made for the task area and immediate surround (0.5m zone). This could result in more appropriate, cheaper, and lower energy consuming schemes. Even where desk layouts are not known, illuminance and uniformity are considered for hypothetical sample points on the overall working plane. The standards do not refer to obtaining the average illuminance and uniformity over a whole horizontal plane in a room, 10/25

11 which would be tempting to use as these are numbers that are automatically output from commonly used software programs. This is demonstrated in Figure 14. In addition to the practical functionality of the lit environment, there will also be a need (whether it is stated or not) for the space to be visually amenable (agreeable or pleasant). This will require consideration of lightness of the room, which is linked to the brightness of vertical surfaces, and visual interest which refers to planned non-uniformity within the space. For example by highlighting displays in a retail outlet. Other factors which will affect the visual look and feel of a space is the colour rendering of the lighting installation, and the lamp colour used e.g. < 3000 K is warm and may be appropriate in a hotel, whereas a temperature of around 4000 K may be more appropriate in a commercial environment. Figure 13: Recommended surface illuminances and reflectances in an office (Source: SLL) Figure 14: An example room plane demonstrating how to calculate diversity and uniformity from a simulated grid of illuminances at the working plane when the task locations are unknown. Illuminance should be calculated at each of the points in the diagram, e.g. using computer software. Sample desks are then taken to be at the points of highest and lowest illuminance. At each of those two points a 0.5 x 0.5 task area that is subdivided into a 0.25 x 0.25 grid (blue zones) represents a task area, and a 0.5 x 0.5 m zone around that corresponds to an immediate surrounding area (green areas). Illuminances for the blue and green areas are then compared to design criteria (e.g. for an office desk blue zone should be 500 lux, green zone 300 lux), and uniformity is calculated only within each blue area (e.g. should exceed 0.8). The worst calculated uniformity is taken to be representative of the room. This is significantly different to calculating the uniformity by dividing the minimum illuminance in the room by the room s horizontal illuminance average. 11/25

12 Sustainability Energy efficiency is a key requirement of sustainable lighting design. It is estimated that lighting is responsible for 19% of electricity consumed in the UK, about 64 TWh/year 2, which equates to 32 million tonnes of carbon dioxide. Two factors affect energy consumed by a lighting installation its power consumption in use, and the length of time it is used for, with the latter being dictated by occupancy, daylight integration, and controls. Benchmark data is available (e.g. from CIBSE though it can be outdated) which state target installed power and energy consumption for a range of applications. Installed power is often normalised for illuminance and expressed as W/m 2.100lux. Figure 15: Lighting power targets from CIBSE Guide F which itself is based on CIBSE Code for Lighting 2002 (Source: CIBSE) Figure 16: Lighting energy benchmarks from CIBSE Guide F originally from ECG (Source: CIBSE Guide F) For a new lighting installation, the Building Regulations will need to be met. At a minimum this will require meeting the requirements of the secondary document the Non Domestic Building Services Compliance Guide. This states that efficacy should be at least 55 lamp 2 From SLL Lighting Handbook 12/25

13 lumens per circuit-watt for general lighting or 22 for display lighting. The efficacy can be adjusted if photocells and/or presence detection is used to control the lighting. In addition, there are minimum requirements for metering and control of lighting. This does mean that inefficient luminaires and maintenance schedules can be set, though this will penalise performance under criterion 1 (SBEM calculation). However, these are just minimum requirements. For the design of a new building, compliance is achieved by outperforming a hypothetical notional building which has fixed efficiencies for its building services. Under the 2006 version of Part L, office type spaces in the notional building had installed power densities of 3.75 W/m lux, whilst circulation spaces had densities of 5.2 W/m lux. The 2010 recast of Part L complicated the underlying workings of the methodology. The notional building is assumed to have an efficacy of 55 luminaire lumens per circuit-watt, which is estimated using a formula that is based on the room geometry. For typically shaped rooms, this results in an installed power density of about W/m lux. In addition to this, the notional lighting system has photoelectric lighting control for certain rooms (e.g. daylit office type space). In other words, the installed power densities of new lighting designs should aim to be no higher than this range; otherwise compliance would need to be achieved by making bigger savings against the notional building in other areas e.g. reducing heating demand, or providing additional renewable energy. At present it is realistic to achieve 1.6-2W/m 2.100lux for new lighting schemes if purely aiming to efficiently deliver light to a horizontal working plane 3. Figure 17: The installed lighting density of the notional building (blue curve) as a function of room geometry in the 2010 Part L. The red circle represents the zone for typical room proportions (R) which results in typical installed power densities of W/m lux for the notional building (Source: CEE) 3 Conversation with Ian Macrae, Head of Global Lighting Applications Management for Thorn Lighting (27/1/11) 13/25

14 The Lighting Industry Federation (LIF) has produced a technical statement on the definition of Ultra Efficient Lighting (UEL) which is being adopted by the lighting industry. It is based on the reasoning that for ultra efficient lighting the right light in the right place at the right time, by the right lighting system needs to be provided. Ultra Efficient Lighting means the lighting scheme design needed to fulfil the lighting requirements specified in the relevant lighting application standard and the resulting installed scheme to use an energy efficient lighting system consisting of lamps/light sources, ballasts, luminaires and lighting controls to deliver the scheme lighting requirements without increasing the environmental impact. In order to qualify as UEL the energy efficiency of the system needs to be in the top 20% of the range of lighting energy efficiency ratings measured using LENI (see below) and the lighting scheme is compliant with all regulations and standards at any time with particular reference to the SLLs Code for Lighting. This is an important point to consider it is important to reduce energy consumption, but doing this at the expense of lighting quality may be counterproductive. LENI is the Lighting Energy Numeric Indicator as defined in BS EN 15193, and is essentially a calculation of normalised (to floor area) annual energy consumption based on installed power for lighting and parasitic power (which includes lighting controls and emergency lighting) and operating hours including adjustment for controls. This is a broadly similar calculation to the one used in Part L, although the Building Regulations does not address emergency lighting, and has assumed occupancy profiles whereas LENI is based more on the actual intended use of the building. When designing for energy efficiency (both for new buildings and retrofitting) it is important to specify appropriate lighting. The example in Figure 18 shows new lighting installed to a toilet block where old T12 luminaires were replaced with more efficient T5s. The original installation consisted of a T12 40 W bare batten fluorescent tube with magnetic ballast, so total power would be about 50 W. This was replaced with a 2 x 54 T5 enclosed refracting luminaire with electronic ballast, so the total power would be about 120 W almost 2.5 times greater! The higher efficacy of the T5 coupled with the higher installed power means illuminance in the room is much higher though it didn t need to be. Of course, given the large windows, the lights should be off most of the time though this does not happen due to a combination of manual switching with poor energy management. 14/25

15 Figure 18: Before (left) and after (right) lighting installations in a toilet (Source: CEE) It is tempting to consider the sustainability of lighting systems purely in terms of reducing carbon emissions, but the safe disposal of lighting equipment should also be a consideration. In particular for fluorescent lamps, this will require them to be recycled, primarily to divert toxic mercury from ending up in landfill sites. Disposal of commercial lamps, luminaires and control systems is now covered under the WEEE Directive. Advice on disposal can be sought from Recolight 4 or Lumicon 5. Integration A low energy lighting scheme will require the successful integration of the daylight and artificial lighting strategies. The normal order would be to design the building to maximise daylight potential (whilst reconciling this with other design requirements e.g. thermal) and then to integrate the artificial lighting scheme such that its operation maximises the daylight contribution, and that the physical fixtures themselves are integrated into the architecture in a harmonious manner. Best practice would involve sizing windows based on quantatively investigating the trade-offs between heat loss and gain, daylight admittance, and artificial lighting consumption. Maintenance A lighting installation begins to deteriorate from its first use. It is therefore important that there is a maintenance strategy that is implemented. This should be conceived in discussion with the client and stored in the buildings O&M manuals. The lighting installation should also be designed in accordance to the planned maintenance, which has a significant effect on the /25

16 specification of the luminaires. Lighting standards are expressed in terms of maintained illuminance, which is the average maintenance on the reference surface at the time maintenance is carried out. It is calculated by applying a multitude of factors to the initial illuminance delivered by the installation which are as follows: Lamp Lumen Maintenance Factor (LLMF): Over time, the light output of a lamp will deteriorate. This will vary according to lamp type and hours of use. In the case of tungsten lighting, due to short lamp life the lamp will generally fail before it experiences significant loss in light output. Specific values of LLMF can be obtained from lamp manufacturers. Figure 19: LLMF as a function of typical discharge lamp type and operational hours (Source: SLL) Lamp Survival Factor (LSF): If planned maintenance consists of group replacement rather than spot replacement, that is, the entire installation is replaced after an agreed period, then the LSF is used in the maintenance factor calculation to account for the fraction of lamps that have not failed after a set period of time. Specific values of LSF can be obtained from lamp manufacturers Figure 20: Typical LSF for a range of commonly used discharge lamp types (Source: SLL) Luminaire Maintenance Factor (LMF): Light output from a luminaire will decrease over time as dirt accumulation absorbs emitted light. This is affected by the luminaire type, with dustproof and vented luminaires deteriorating least, the frequency with which the luminaires are cleaned, and the cleanliness of the operating environment. It is recommended that cleaning occurs every year. 16/25

17 Figure 21: LMF for typical luminaires in a normal operating environment (Source: SLL) Figure 22: Dirt e.g. dead fleas can build up in luminaires which will reduce light output. Increased cleaning frequencies are important in ultra low carbon buildings. Room Surface Maintenance Factor (RSMF): Illuminance will decrease over time as dirt builds up on room surfaces. This is more pronounced when the lighting strategy used is indirect (i.e. reflecting light off of the room surfaces), and when cleaning frequency increases. 17/25

18 Figure 23: RSMF for different room shapes based on luminaire type and cleaning interval (Source: SLL) Maintenance is therefore an important energy efficiency consideration in the design of artificial lighting. For example, for a general lighting system the table below shows that the luminaires chosen and the maintenance regime can more than double installed power. Scenario A (good maintenance factors) Scenario A (poor maintenance factors) Triphosphor fluorescent, 10,000 hours LLMF: 0.85 Halophosphor fluorescent, 10,000 hours LLMF: 0.76 LSF: 0.85 LSF: 0.85 Open top ventilated luminaire LMF: 0.86 Closed top ventilated luminaire LMF: 0.61 cleaned every year in normal cleaned every 3 years in normal environment, room index over RSMF: 0.96 environment, room index over RSMF: 2.5, direct luminaires 2.5, indirect luminaires 0.72 Maintenance Factor: 0.60 Maintenance Factor: 0.28 Design illuminance 500 lux Design illuminance 500 lux (maintained) (maintained) Initial Illuminance 833 lux Initial Illuminance 1786 lux Assumed efficacy (W/m Assumed efficacy (W/m lux) lux) Installed power (W/m 2 ) 25 Installed power (W/m 2 ) 53.7 Cost The cost of a lighting system needs to be carefully considered. Normally decisions are made purely on capital costs of potential systems. However, greater savings could be possible if decisions are made based on a whole life costing approach, which would include the benefit of designing systems with better efficiency (through reduced energy bills and associated costs e.g. the CRC), and longer lamp life and maintenance periods. Designing a lower energy lighting system may also be beneficial regarding meeting and exceeding the Building Regulations, as larger energy savings from the lighting system may mean less costly measures are required, for example photovoltaic panels. Lighting Control Energy is not saved by daylighting; energy is saved by dimming down or switching off electric lights that are not needed because of daylight 6 In order to provide artificial light at the right time, that is, when there is a demand for light by an occupier that cannot be met by natural light alone, then an appropriate control strategy is 6 Leslie R 2003, "Capturing the daylight dividend in buildings; why and how?", Building and Environment, vol. 38, pp /25

19 required. In its simplest form, a lighting control is an on/off switch. Experience has shown us that this type of control alone results in significant energy wastage. Lighting controls also allow scene setting, and over time the control strategies for energy efficiency and scene setting have converged as dimming of luminaires has become more feasible and control interfaces have become more sophisticated. The correct control strategy will depend on the type of space, frequency of occupancy, and the availability of daylight. The BRE has produced an information paper (BRE IP498) which is also referenced from Part L of the Building Regulations that proposes the most effective control strategy for these combinations. The type of space is divided into six types as is shown in Figure 24. Each type will have its own requirements and challenges for lighting control. Lighting zones should be designed to correspond to different areas of use, occupancy and daylight availability. Figure 24: Example floor plan showing different types of occupancy (Source: BRE) Figure 25: List of occupancy spaces from above example (Source: BRE) The main categories of lighting control are: Manual control: Switches (or remote controls) operated by a building user. Part L requires such switches to be no more than 6m or twice the room height whichever is greater from the luminaire. In addition, luminaires adjacent to a window wall require separate switching control. It is vital that switches are intuitively labelled so that users 19/25

20 can effectively operate them. Banks of unlabelled switches by a door will inevitably all end up getting turned on, even if they needn t be. Occupancy based control: Strategies include presence detection, which will automatically turn on when occupancy (movement) is detected, or absence detection which automatically turns off when a lack of occupancy is detected. Absence detection offers greater energy saving potential as a user is required to turn the lights on if they are required. The occupancy sensors used can be PIR (passive infra-red) which operates on a line of sight from the sensor, or microwave or ultrasonic which detects shifts in frequencies of reflected waves (Doppler effect). Most PIR sensors are sensitive to hand movement up to a distance of about 3m, arm and upper torso movement up to 6 m and full body movement up to about 12m. To calculate lighting efficacy for criterion 2 of Part L of the Building Regulations, a control factor of 0.9 is applied for absence detection (not presence) where a space is likely to be unoccupied for a significant number of hours. Presence detection should not be used in daylit areas where there is likely to be high occupancy as it is highly likely that in that scenario the artificial lighting system would often be on needlessly. Photoelectric control uses a photocell to send a signal based on daylight availability, which can be used to switch or dim luminaires. Dimming will save more energy than switching and is likely to be better liked by occupants as sudden changes in illuminance are avoided. Daylight zones are generally considered to be within 6m of a window wall. The correct positioning of the photocell is vital. For photoelectric dimming the photosensor should view neither the brightest or darkest spot in the room, and not directly view the artificial lighting of windows. The dimming response time, i.e. the time it takes the system to respond to a sudden change in light level, is typically set to about 30 seconds to avoid unnecessary response to temporary conditions, e.g. moving clouds. To calculate lighting efficacy for criterion 2 of Part L of the Building Regulations, a control factor of 0.9 is applied for photoelectric dimming or switching control. A control factor of 0.85 is applied when used on conjunction with absence detection as above. Timed control: Where the operating hours of a space are known, then lighting can be timed to turn off outside of those hours. Care should be taken to limit timed switching during occupancy hours as this can cause unacceptable disturbances to occupants. The BRE suggest which control strategies are most appropriate in any given scenario (Figure 26). Two example buildings are also given Figure /25

21 Figure 26: Suggested control strategies for different combinations of occupancy and daylight availability. ** denotes a recommendation, * denotes that the suitability should be assessed for a particular installation (Source: BRE) Figure 27: Example buildings and suggested lighting control strategies. (Source: BRE) 21/25

22 Automated lighting controls are a potentially important part of meeting Part L of the Building Regulations. For example, the notional building has photoelectric dimming for certain room types e.g. a daylit office. Therefore unless photoelectric dimming is used in the proposed design, larger carbon reduction will need to be made elsewhere to compensate. At present the National Calculation Methodology for the Building Regulations assesses energy reduction due to photoelectric dimming (and switching) by approximately calculating the daylight factor for a zone and calculating the additional required artificial lighting based on the external illuminance and the design illuminance for the zone. The calculation divides the zone into a front and rear half with potential separate control of each. However, the latest version of SBEM does not allow control to the rear of a space using a photocell (the option is disabled 7 ). An analysis for a classroom sized room with varying glazed fraction to the window wall showed that realising any energy saving benefits of larger windows using photocells is only achievable if the lighting to the rear of the zone can be controlled. As it cannot at present, it is concluded that the present regulations reward facades with low glazed fractions (20%), as thermal performance will be better and lighting energy use will not be significantly worse than with a 60% facade. A photocell controlling the front half of a daylight zone can under the NCM expect to use about 70% of the energy compared to having no control a significant saving. Figure 28: The percentage of time artificial lighting is on as a function of glazed fraction (ranging from 20%- 60%), hours of occupancy, design illuminance, and whether there is photocell to the front of the zone (top three lines) or to the rear as well (bottom three lines) for a 7m x 8m x 3m room in London (Source: CEE) More modern lighting systems can utilise the DALI protocol to enable plug and play type installation and individually configurable components. This can allow interface with a building BEMS system and can result in optimal use of lighting, easy commissioning and simple modification or adaptation to future use. An example schematic for a building is shown in Figure Conversation with SBEM technical team January /25

23 Figure 29: Schematic of DALI lighting control used for a whole building (Source: DALIcontrol.com) Irrespective of what lighting controls are designed, it is vital that they are effectively commissioned at the handover staged, and that there is an ongoing programme (such as the Soft Landings Framework) to ensure the design intent is actually realised. The Part L requirement that lighting circuits need to be metered should significantly assist with ongoing analysis for new buildings. The Future for Artificial Lighting Given the rapid improvements in LED efficiency to date (Figure 30), and the technical potential, it is expected that the predominant near to medium term trend is for the further development and uptake of the technology. Figure 30: Efficacy of different light sources. By comparison, the luminous efficacy of a candle is only 0.3 lm/w (Source: LIF) 23/25

24 At present, LED has become widespread for several applications. For example, the entertainment industry was the first to embrace the technology. Increasingly, it is being used for external architectural lighting due to its long life, good colour rendering and scene setting potential, and hotels where the long lamp life results in lower maintenance costs. It is approaching the point where parity is being achieved with fluorescent efficacies in commercial settings, however, at present the cost of LED is significantly greater. When assessing the feasibility of LED for a new project compared to other light sources it is also very important to consider the energy efficiency of whole systems (including all optics and control gear), as this will give a true understanding of expected energy consumption. For example, whilst lighting efficacies for LED chips are very high, this drops significantly once translated into a luminaire. Various projections (Figures 30-32) for the market penetration, cost and efficiency of LED technology tend to predict that it will come to dominate artificial lighting. It is not clear however, exactly when this tipping point will occur, and it is a point lighting manufacturers disagree upon. Figure 31: Projections for a 90% reduction in energy consumption (Source: Environmental Change Institute) Figure 32: LED market forecasts (Source: Philips) 24/25

25 Figure 33: LED cost and efficacy projections. The package does not include the drop in lighting output when placed in a module/luminaire (Source: US DoE) 25/25