A well designed and managed lighting system can lead to significant improvements in energy efficiency relating to office tenancies.
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Lighting typically accounts for 30 per cent of a commercial office tenancy’s power consumption.
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Energy savings on lighting in the range of 20 per cent and 70 per cent can be achieved in a typical office with paybacks of investment in around 5 years, depending on the current installation and usage patterns.
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Carefully engineered savings measures will usually provide corresponding maintenance savings and provide opportunities to significantly improve visual conditions for occupants.
This document is only intended as background information and is current as at October 2010.

Although it varies from office to office, lighting can typically account for 30 per cent of power used in commercial offices. Coupled with the fact that lighting is often something that tenants can control, it is an obvious candidate for energy efficiency improvements.
Example of power usage in a commercial office tenancy
Luminaire - a light fitting complete with all lamps and other necessary parts and wiring.
Lamp - a generic term for a light source that otherwise might be called a bulb or a tube.
Troffer - a luminaire constructed from an inverted metal trough. Most luminaires in office buildings are troffers. Other common luminaire types include downlights and surface mounted battens.
It is common for modern design-and-construct processes and certain energy rating schemes to focus on features lists of equipment that may or may not be installed and commissioned in a way that is energy efficient as a whole. However, the choice of a particular lighting product alone does not necessarily provide lower energy usage or a good NABERS rating. The way products are utilised is just as significant as product choice in achieving energy savings and improving building performance.
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The lighting system is the one thing that you lease from the building owner that will affect your NABERS tenancy rating. All of the other things that affect your rating like computers, printers, kitchen equipment and the like are installed by you during fit out.
Therefore, it is important that you understand the basic efficiency of the lighting system and how it might affect your eventual NABERS tenancy rating at the beginning of your lease negotiations.
Illumination power density (IPD) is an important performance indicator. An IPD of 6-
7W/m² is considered best practice. If the IPD is greater than 10W/m², you should consider getting it improved if you want to achieve a decent NABERS tenancy rating.
New leases and lease renewals offer the best opportunity to get this improvement paid for by the building owner. Building owners will want to get or retain your business and the $30-40/m² cost of upgrading a lighting system may be an acceptable price to pay to secure your rental income for the years ahead.
If the market is tight and your negotiating position is poor, you may not be able to get the building owner to fund the upgrade. In those cases, you should look at the business case for implementing the upgrade yourself. Lighting upgrades typically pay for themselves from savings in energy and maintenance costs in five years or less, so they should be implemented as early as possible in your tenancy period to maximise your benefits.
Achieving a 4.5 star NABERS tenancy energy rating
The NABERS tenancy energy rating is a measure of the efficiency performance of a tenancy space. Lighting energy consumption is only one but nonetheless a significant factor in determining the NABERS rating of the space. A lighting system with an illumination power density of less than 10W/m² and a control system that matches operating hours to occupancy is all that is required to achieve 4.5 stars in a space with typical levels occupancy and equipment loads. However, if there are large amounts of office equipment or appliances, or these are not well controlled to turn off when not required, then a more efficient lighting system may be required to get the desired rating.
If in doubt about the impact of the lighting system on your potential NABERS rating, get a specialist in NABERS and lighting energy efficiency to develop a simple model of your tenancy and calculate a NABERS rating estimate. This will tell you whether you need to improve the lighting system and by how much. As an added benefit, the estimate will also highlight other areas of potential improvementin addition to the lighting system.
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Illumination Power Density (IPD) is the number of watts required by the lighting system per square metre of floor area. This measure is used to determine the overall power loading from lighting within the space and sets the baseline power consumption when all luminaires are switched on.
In a commercial office using 2x36W T8 troffers, each luminaire nominally consumes
84W. For the typical luminaire spacing of 2.4m x 2.4m, each light is illuminating an area of 5.76m². Therefore the base IPD would be (84W / 5.76m²) = 14.6W/m², which is almost 50 per cent higher than the maximum of 9W/m² specified under section J6 of the
Building Code of Australia (BCA).
IPD is not factored to allow for the amount of illumination supplied, so a fundamental key to reducing IPD is to reduce illumination levels where ever possible. Since IPD is applied to the whole space (building floor), it is useful to have areas of low IPD to offset areas requiring task lighting, special displays, feature lighting, etc.
Single lamp luminaires
Generally a lighting system based on single lamp luminaires is more likely to deliver both a low IPD and high quality illumination than a system base on luminaires with two or more lamps.
Maximising the performance of the lighting depends on matching the occupant’s usage and requirements as closely as possible. Generally, it is more effective and less costly to install a highly efficient lighting scheme with simple controls, than to over-illuminate the space and then attempt to correct excessive power consumption using complex controls. Therefore the most important initial aspect is for the occupants to decide and confirm the usage for each part of the tenancy – in this way the lighting systems can be configured and optimised to suit those specific requirements. By illuminating areas in a commercial office such aas walkways and the background to the levels recommended by the Australian Standards, this strategy alone could be used to lower the IPD of nonworking areas by more than 50 per cent with no adverse effect on working conditions.
Lighting Control Systems
Lighting control systems are also important in determining the energy performance of a lighting system. Control systems including manual switches, timer systems, reset systems, occupancy detection, and daylight control. The important thing to look for is a control system that minimises lighting operating hours when the space is unoccupied.
Manual and timer systems are generally not good at this, however, automatic “reset systems” can work quite effectively providing that the switching zones are small and
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switches are local. Occupancy detection systems are very effective but can be frustrating if they are not sensitive enough and the lights keep going out.
Lighting control systems that switch luminaires off do not improve IPD, although the BCA and some energy rating schemes allow a small dispensation (typically 10 per cent) for these measures.
Provide flexible controls in large spaces
During the initial design stage it is incredibly difficult to determine the eventual usage of each space, and revisions are common. If the lighting is to be optimised for each task application, and wastage eliminated, then lights must be moved and switching configurations changed accordingly. Due to poor design and trying to save capital costs, a significant number of lighting control systems are completely hard-wired and provide no flexibility to make revisions in the future.
A system using individually addressable luminaires provides the ultimate in ongoing flexibility – each light fitting can be controlled and revised at any time using software reprogramming. However, apart from increased capital costs, individually addressable systems also require a significant ongoing maintenance commitment; even the simplest changes must be performed by a programmer, not an electrician.
Owners and occupiers therefore need to carefully assess how much flexibility they require, and balance the cost and complexity with the potential savings. It may be found that a revision to the hard-wired lighting system to add more switches and some simple
240V controls will provide excellent return on investment.
Controls generally
Give consideration to:
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Providing multiple switches to reduce the number of lights that come on at any one time. Using one switch to turn on all the lights in a large area is very inefficient.
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Placing switches at the exits from rooms and using two-way switching to encourage lights to be turned off when leaving the room.
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Using ‘smart’ light switches and fittings which use movement sensors to turn lights on and off automatically. These are useful in rooms used infrequently where lights may be left on by mistake, or for the elderly and disabled. In areas with natural daylight, make sure they have a built-in daylight sensor so that the light doesn’t turn on unnecessarily.
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Occupancy sensors with switches which must be turned on manually and turn off automatically, but with a manual over-ride, are preferable in most situations. Be aware that the sensors use some power continuously.
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Using timers, daylight controls and motion sensors to switch outdoor security lights on and off automatically. Controls are particularly useful for common areas,
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such as hallways, corridors and stairwells, in multi-unit housing.
Advantages of intelligent control systems include:
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Opportunities for energy savings
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Potential for flexibility
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Potential to personalise lighting for occupants
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Facility for fault reporting
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Facility for performance reporting
Energy Efficiency Control strategies include:
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Occupancy sensing
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Scheduling
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Lumen maintenance
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Daylight linking/harvesting
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Load shedding
However, control systems require consideration of:
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Higher capital cost
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More skills required to design, install and commission
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More skills required to manage/operate the system
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Ongoing scheduled maintenance costs
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Equipment failures are more expensive, and require specialist installation and commissioning
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Difficulty in capturing (quantifying) the savings that have been made from each measure
Other control strategies
In buildings or tenancy spaces with security systems, a simple and effective way to save power is to provide an interface between the alarm panel and the lighting system, so that all lights are forced “off” when the security system is armed. This simple system will provide 100 per cent after-hours power savings, compared to occupancy-based systems that could leave the lights on for an hour or more after the last person leaves. If there is an existing control system, make sure that all lights are forced “off” when the alarm is enabled.
Cleaners can add considerable after-hours usage to the lighting scheme, especially if they use a “master switch” to turn on all the lights prior to work. It is preferable to install dedicated “cleaners switches” that illuminate a small local zone (perhaps to a reduced lighting level), which is easiest implemented on buildings with lighting control systems.
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Australian Standard 1680.2.2 states
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:
Cleaning of most offices is a daily task, usually occupying between one and three hours each night. It is not unusual for full office lighting to be switched on during this period, representing a significant cost and waste of energy. As the tasks involved in cleaning are less visually demanding than many office tasks, lower illuminances can be adopted appropriate to the tasks performed.
It is recommended that the switching of general lighting systems be arranged so that approximately one third of the normal lighting level can be provided by the operation of ‘cleaners’ light switches. These switches may be used to operate multipole contactor switching devices to minimize the number of separate switches required.
If there are multiple circuits in each area, some can be labelled as “cleaners lights”, if not consider re-wiring circuits to allow this to occur. In any case, you should work together with the cleaners to define a procedure that will minimise the running times for lighting.
In any design, light level estimations are calculated based upon stipulated maintenance schedules, since lamps, luminaires and room surfaces all decrease in effectiveness over time. Modern lamps can last more than five years but cleaning and maintenance should be performed on luminaires and room surfaces more often.
To maximise energy efficiency, a scheduled cleaning and re-lamping program for luminaires must be implemented and this is most easily handled by using a control system to track running hours. In a typical office space running 3,000 hours per annum, it would be good practice to perform a full clean of all luminaires every two years and total re-lamp every four or five years.
By committing to perform maintenance in this organised way, the initial lighting design doesn’t need to allow for huge depreciation of illumination levels from dirty luminaire surfaces and for lamps being run until total failure.
In practical terms, a design based on strict scheduled maintenance can allow the initial lighting levels to be up to 30 per cent lower – which in turn means that the energy costs will be 30 per cent lower over the entire life of the building. Furthermore, maintenance costs are significantly reduced, because the cost to replace all lamps at the same time is lower than numerous spot replacements performed every time a lamp fails.
Below is a summary of the recoverable and unrecoverable losses associated with the building maintenance.
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AS/NZS1680.2.2:2008 - Clause 10.4.2 (c)
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Lamp output (lumens from lamp decrease)
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Lamp survival (lamp failure)
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Luminaire maintenance (unclean reflecting and transmitting surfaces)
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Room surfaces (unclean walls, ceiling etc)
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Deteriorating room surfaces
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Voltage and temperature (which affects the lamp’s output)
Although under the Green Star rating scheme one point is allowed for “Individually
Addressable Ballasts”,this provision does not necessarily provide energy savings. In fact, the special ballasts and associated controls add additional quiescent loadings that increase overall system power. To take advantage of the opportunities that these systems allow, the luminaires must be commissioned and programmed correctly.
When used in conjunction with timers, Building Management System integration, and other strategies, lighting systems with individually addressable ballasts can provide tangible power savings. However, like all automated systems, these schemes also require continual consultation with the occupants, good quality commissioning, and a significant commitment to ongoing servicing and adjustment.
If tenanting an office with a control system, attempt to have the owners include a sixmonthly control review and reprogramming in the lease agreement so that the system can be optimised once the usage patterns have been established. In any case, resources must be allocated by the tenants towards fine tuning the lighting controls to maximise effectiveness and energy efficiency.
Fluorescent luminaires with DALI ballasts can be dimmed. There is a common preference in Commonwealth government offices, especially those that use heavily screen based tasks, for lower light levels. DALI dimming systems can provide those lower light levels on an individual or group basis and result in energy savings. This is much better than the common approach of de-lamping either partly or completely, which can reduce the lighting on neighbouring workstations to unacceptable levels.
Properly designed occupancy-based control systems are very effective in areas with spasmodic usage and where occupants have poor discipline to switch off lights.
Typically the best results are achieved in storerooms, stairwells and other areas where lights have the tendency to be left on, and savings of up to 80 per cent are possible.
In large office spaces the savings are not as significant, due to the normal movements of
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workers through the space. In many cases such systems need to be deactivated during normal working hours, so potential savings only come after-hours. Because any movement will trigger the lights to remain on for half an hour or more after the last trigger event, occupancy-based controls may actually extend operation compared with (well disciplined) manual switching.
Depending on usage patterns of the tenants, it may be as effective to provide time-clock based controls. Lights in executive offices and similar spaces may benefit from occupancy-based controls; however there is a risk that the lights may go off during meetings. For the same reason, careful consideration must be given to using occupancy-based controls in meeting and conference rooms, as they probably will require the ability to over-ride the automatic controls both “on” (for meetings) and “off”
(for video presentations).
While dimming of luminaires may provide energy savings, there are overheads that need to be considered and allowed for. Systems that use luminaire ballasts to switch off (eg:
DALI and DSI) will continually consume power, even when apparently switched off.
Therefore, using such control systems for basic switching alone will increase power consumption compared to conventional switching methods.
Moreover, electronic ballasts do not have a linear relationship between light and power, and Australian MEPS requirements state that Dimming Ballasts (Class EEI=A1) consume a maximum of 50% power at 25% light output
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. Also, there is additional power consumed by the lighting control system itself, which must be operated continuously. It is definitely not worthwhile to over-illuminate a space, and then use dimming to compensate or to meet energy efficiency targets.
Control systems cannot compensate for poor lighting design or inappropriate luminaire selection. Dimming and digitally controlled lighting systems must therefore be carefully evaluated to determine if supplier’s claimed savings projections will actually be achieved.
Often, a better lighting design that doesn’t rely on such features will provide higher overall efficiency at a lower cost, and therefore release capital that can be spent on additional energy efficiency measures.
The first step in evaluating the feasibility of dimming schemes is to verify the amount of over-illumination, and for what periods the dimming could be applied. If total power savings greater than around 30-40 per cent are anticipated, the base lighting scheme should be reviewed because it is almost certainly over-specified – it will be less expensive and less complex to provide a base lighting scheme that properly matches the occupant’s requirements.
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AS/NZS4783.2-2002 Clause 5.3.2
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The most energy efficient light is natural sunlight. The science of day lighting involves the deliberate use of daylight to displace electric light. Large savings are possible in offices and other non-residential buildings when the relative amounts of daylight and artificial light are regulated by sensors and a control system. Done correctly, there will be a net saving of energy consumed by the building.
Done incorrectly, the heat load on the building will increase and there will be a net increase in cooling energy consumption. If the daylight control system is poorly implemented, building occupants will have to deal with glare and/or thermal discomfort using the most expedient means at hand, such as closing blinds, which in turn usually cancels out any of the benefits that daylighting might have offered.
The introduction of daylight to a work environment requires careful consideration of workstation placement, interior configuration and colours, so that glare and excessive contrast do not compromise visual conditions. Generally, workers will need to be facing parallel to windows; therefore daylight schemes must be included in an overall fit-out design and furniture layout.
Australian Standard 1680.1 provides comprehensive guidance about the integration of daylight, including the following
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:
Both sunlight and skylight can be used to illuminate interiors directly through openings (windows, rooflights, etc.) or indirectly by being reflected from external surfaces or devices (ground, building facades, shading controls, etc.).
In working interiors, sunlit glazing should be externally screened with overhangs or louvres; or internally shaded with blinds or other suitable devices. Unwanted sunlight penetration usually causes excessive contrast rather than excessive luminance.
When external horizontal louvres are used, they should preferably admit light reflected from below outside the building. This upward light when re-reflected from a white or near-white ceiling penetrates deep into the interior and is inherently glarefree. Similarly, a suitably angled internal venetian blind can reflect the sun’s rays upwards to the ceiling surface.
Control of sunlight penetration with the aid of overhangs and louvres is an exact science and various aids exist for the design of these. External architectural features known as light shelves can be an effective means of window shading while using a large surface to reflect sunlight onto the ceiling through a highlight window.
The successful integration of daylight and electric light in other than the smallest of window-lit rooms and some systems employing rooflights will depend not on the balance of daylight and electric light illuminances, but on the achievement of a satisfactory brightness distribution, including the effects of sky glare.
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AS/NZS1680.1:2008 - Clause 10.2.7 Control of sunlight penetration, and Clause 10.6 DAYLIGHT-ELECTRIC LIGHT
INTEGRATION
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There is no “best” lamp – there are a multitude of alternatives and each has advantages and disadvantages; good design utilises the correct product for each application. For example, in applications where lights are required to switch on and off quickly, Metal
Halide would be an inferior choice to Tungsten Halogen because, even though it is more efficient, the Metal Halide lights would need to be left on continuously.
In general terms, large diffused light sources are best for general illumination, whilst small bright light sources are best where intense and highly-focussed beams are required. Inefficiencies often come from choosing the wrong type of lamp to suit an application, even if that lamp may appear more “efficient”. While high powered lamps are more efficient, to provide quality lighting comfort it is usually better to use a larger quantity of less-powerful lamps.
Linear Fluorescent lamps provide the best balance between output and efficiency for general lighting. There is no significant difference between the energy performance of
T5 and T8 lamps of equivalent nominal size when running on similar control gear.
Fluorescent lamps on electronic ballasts provide instant flicker-free light although a few minutes warm-up time is required before full output is achieved. With a quality “pre-heat” type electronic ballast the lamp life is not significantly affected by frequent switching making them ideal for use with occupancy sensors.
Fluorescent can be dimmed with excellent results, offers a range of lighting colours, and provides efficacy (efficiency) of around 90 lumens per Watt. Rated lamp life on electronic ballasts is around 16-20,000 hours, and Lumen Maintenance is 90 per cent so the light output only drops 10 per cent over life. Since the lamp is reasonably large, glare control is less critical than with other light sources, however T5 lamps are unsuitable for use in most spaces without shielding.
Compact Fluorescent (CFL) lamps offer most of the advantages of linear fluorescent; however efficiency, life and lumen maintenance are all compromised due to the smaller package size. CFL lamps are best in downlights for general illumination, if the shape of a linear fluorescent is unsuitable. Due to the relatively large physical size, CFL lamps require large optical assemblies to achieve good lighting control. The smaller the luminaire the less efficient it will be, and the small low-wattage CFL lamps intended to replace Tungsten Halogen downlights have particularly poor performance.
A distinction should be made between dedicated compact fluorescent lamps that use external ballasts, and the “retrofit” CFL lamps with integrated ballasts that are intended to replace household bulbs and offer lower performance levels. The life of retrofit lamps is generally only about half that achievable from dedicated CFL fixtures with remote electronic ballasts and there are other significant compromises as well.
Metal Halide (MH) lamps provide a tiny, intense point of light which makes them ideal for use within reflectors to provide spotlighting effects. Metal halide takes up to 10 minutes to achieve full brightness, and up to 20 minutes to restart if power is interrupted, which makes them only suitable when the lights are to be left on continuously. While some high-powered lamps provide efficacy higher than fluorescent, the inability to switch quickly means that running hours and energy consumption can be significantly higher.
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MH lamps are not easily dimmed, and certain surface colours may appear distorted under MH lamps. Apart from their inability to switch and dim, the harsh glare from the extremely bright arc-tube is the main reason for not using MH lamps for general lighting within offices. However, providing that the luminaire has good optics, they are the best light source for spotlights and downlights that are used for display lighting.
Incandescent and Tungsten Halogen lamps are excellent light sources for some applications but their extremely low efficiency and relatively short life makes them unsuitable for use in commercial office spaces. With the ongoing improvements in performance of CFL, LED and MH lamps, it is economically viable to exchange incandescent and halogen luminaires with more efficient products.
CFL lamps are best where a wide beam, general illumination is required but be aware of the reduced performance of small retrofit lamps. Where decorative effects and sparkle is needed, LED lamps are often the best option even though their total output is not equivalent to the common 50W Halogen lamps. In commercial spaces like foyers and for display lighting, Metal Halide lamps provide the best efficiency, output and beam control.
An alternative lighting solution such as indirect/cove fluorescent lighting is also an option.
Light Emitting Diodes (LEDs) are an emerging technology, and are being heavily promoted by the semiconductor industry. In certain applications, they provide exceptional opportunities for energy savings compared with conventional light sources but since they are a point source they are generally not the best choice for illumination of large spaces. Unfortunately, as with many traditional luminaires, not all LED-based luminaires provide reliable performance. Even if the LED itself has good quality and performance as a bare device, its integration into a luminaire and that luminaire’s installation environment are key to the final product performance and whether it will stand up to customer expectations.
As with any electronic component, the primary enemy of LEDs is temperature, and effective heat dissipation is the key to long life. Unlike traditional light sources LEDs do not radiate heat with the light that they produce and therefore a conduction path must be created to remove the intense heat created at the semiconductor junction or the chip will fail. An enclosed luminaire and/or non-ventilated ceiling space provide extremely adverse environments for LEDs, and elevated internal temperatures dramatically reduce
LED performance over life. Heat will always remain the greatest challenge in a satisfactory LED scheme.
There are two general types of LEDs – specialised “Power LEDs” are mounted directly onto a heat sink assembly and are engineered for constant lighting applications.
Specifiers should be wary of any lighting devices using individual 3mm or 5mm diameter
“Indicator” style LEDs, as these individual LED packages have low output and are not designed to dissipate heat from continuous operation. Designers should also be wary of the performance claims made by LED lamp suppliers. The United States Dept of Energy
“Caliper” program
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has found that a large percentage of LED suppliers over-state initial
lumen output and colour stability, and under-state lumen depreciation. Similar studies in
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US Department of Energy CALIPER program - http://www1.eere.energy.gov/buildings/ssl/caliper.html
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Australia
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have identified similar problems.
In 2008 the Illumination Engineering Society (USA) developed standards to aid in determining lamp life and light output of Solid State Lighting. These are LM-80
“Approved Method: Measuring Lumen Maintenance of LED Light Sources” and LM-79
“Approved Method: Electrical and Photometric Measurements of Solid State Lighting
Products”. LM-80 provides a controlled method for undertaking a 6,000 hour test which then can be used to predict light performance out to 36,000 hours. Based on this standard, a “L70” life can be estimated, which is the number of hours of operation by which time light output has dropped to 70 per cent of its original.
While LEDs are promoted as having a long lifetime, their light output continually decreases throughout life. LEDs “fail” by becoming too dim, rather than actually stopping working like traditional light sources. Since lighting standards stipulate minimum lighting levels, the lamps’ lumen depreciation characteristics (within the luminaire, at the installed operating temperature) must be known and be allowed for in all lighting design calculations. This provides considerable challenges for designers, who should insist on LED performance reports as a complete luminaire system and tested to the relevant performance standards like IESNA LM-79 and LM-80 or equivalent.
At the time of writing, the long-term performance of LEDs is still insufficient to make them feasible as replacement for Metal Halide or Fluorescent light sources. If long lamp life is required, currently the most efficient, reliable and lowest cost system is using “long-life” linear fluorescent that has a rated life of up to 90,000 hours (eg: Philips Extreme, Osram
XXT, Aura lamps).
T5 lamps and luminaires are frequently proposed as being intrinsically more efficient than T8 luminaires. However, an objective review of data provided by lamp and ballast manufacturers does not support this assertion. To a large degree the misconception results from the marketing efforts of lamp manufacturers who wish to promote the newer and more profitable T5 technology, together with propagation of market hype and misinformation by some specifiers.
Unlike other countries, such as the United States, the underlying technology of both T5 and T8 lamps sold in Australia is identical. Specifiers should be cautious of suppliers comparisons between new T5 equipment and outdated T8 technology using wire-wound ballasts
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and tubes
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that have already been banned under MEPS requirements (2004).
T5 lamps must be run on electronic ballasts and can appear more efficient compared with a T8 lamp running on magnetic ballasts. When both are running on electronic ballasts, the efficacy is similar.
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“LED lighting as a substitute for the fluorescent tube” (Bruce Rowse, Carbonetix, Nov. 2009)
6
MEPS Requirements for Ballasts for Linear Fluorescent Lamps - http://www.energyrating.gov.au/ballasts2.html
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MEPS Requirements for Linear Fluorescent Lamps - http://www.energyrating.gov.au/lamps2.html
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The following table summarises the typical performance of the most commonly used nominally 1200mm long tubes:
Ballast type
Rated lamp life (IEC test cycle)
Lamp Output at 25°C (lumens)
Power Consumption (Ballast + Lamp)
System Efficacy (Lumens per Watt)
Typical luminaire performance (LOR) at
25°C
Total net output (luminaire)
Overall luminaire efficiency
36W T8
Triphosphor
Wire-wound
12,000 hrs
3350 lm
42W
79.8 lm/W
75%
2510 lm
60 lm/W
36W T8
Triphosphor
Electronic
20,000 hrs
3200 lm
35W
91.4 lm/W
75%
2400 lm
68.6 lm/W
28W T5
“High
Efficiency”
Electronic
20,000 hrs
2600 lm
32W
81.3 lm/W
85%
2210 lm
69.1 lm/W
54W T5
“High Output”
Electronic
20,000 hrs
4450 lm
61W
73.0 lm/W
85%
3780 lm
62 lm/W
It can be seen that the performance of equivalent T5 and T8 luminaires is virtually identical, so the choice between T5 and T8 lamps comes down to the amount of light required to suit the particular application.
T5 “High Efficiency” (HE) lamps are smaller, and have lower light output than a similarly sized T8, and therefore are useful where T8 lamps would over-illuminate the space.
Since T5 HE lamps have approximately 50 per cent higher surface brightness than T8, additional measures are required to ensure glare and other visual problems are minimised. It should also be remembered that since T5 luminaires have approximately
10 per cent lower output than an equivalent T8 system, a corresponding 10 per centadditional fixtures are required to achieve a similar light level.
T5 “High Output” lamps have much higher output, but are over 10 per cent less efficient and far more likely to cause glare. These characteristics make them more suitable for industrial applications and certain indirect lighting applications where lamps cannot be directly viewed. Be cautious of designs that use 1x54W T5 lamps in office spaces, and ensure that glare index falls within the limits stipulated in the Australian Standards. This is the exception to the one lamp luminaire rule of thumb that was referred to earlier.
In a standard open plan office space, if recessed troffer luminaires are installed at standard 2.4m x 2.4m centres then a 1x36W T8 lamp will provide sufficient illumination and achieve an Illumination Power Density (IPD) of around 6.1W/m². At the same spacing a 1x28W T5 would not give enough light, whilst using 2x28W luminaires would produce an IPD of 10.8W/m² (higher than allowed under the BCA).
In open plan areas, 1x28W T5 troffer luminaires will usually be required at 2.4m x 1.8m or 2.1m centres to provide a similar light level to 1x36W T8 luminaires at 2.4 x 2.4m centres. Therefore more fixtures are required which increases initial costs and long term maintenance. Using 2x28W T5 luminaires at wider spacing will introduce shadowing and uniformity problems at normal 2.7 to 3.0m ceiling heights.
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Whilst some upgrade options may appear to be a viable strategy and sometimes be the only reasonable option, great care should be taken in applying these technologies. Due to various inherent design and performance compromise, numerous application limitations and safety and compliance issues, the installation of these products should only be undertaken with the advice from experienced professionals. If the upgrade proves unsatisfactory, further advice needs to be sought before undoing the implementation to ensure that the luminaires are actually returned to their original state.
For the same reason, only deal with long term, reputable supplier companies that are likely to be around to honour their warranties and liabilities
There are a huge number of so-called “retrofit lamp” options flooding the market, commonly from Asian suppliers with limited experience in lighting. Whilst these products often initially seem to be easy and effective solutions, there are numerous compromises involved in the devices. Since these devices are intended to minimise or eliminate skilled trade labour, the luminaires internal electrical components are commonly retained, so this invariably leaves a legacy of antiquated internal wiring components.
Maintenance costs are generally far higher when the retrofit component fails, as the complete retrofit assembly must be replaced rather than a standard off-the-shelf replacement.
It must also be considered that a retrofit lamp will almost certainly compromise the original design intent of the luminaire or installation in one or many ways; so it must be assumed that the retrofit lamp cannot ever improve an existing lighting scheme. The original luminaire optics may be completely unsuitable for the retrofit device (even if it physically fits) so light distribution and glare will be adversely affected. Assessment of the suitability becomes the responsibility of the installer, who may not be skilled in evaluating whether the resultant installation complies with the relative lighting standards.
Lighting devices such as lamps, ballasts and LED Drivers are subject to a variety of
Australian Standards, and many retrofit products have not been certified for MEPS, C-
Tick or other mandatory requirements. In all cases the installation of retrofit devices will nullify all Statutory Approvals that applied to the original luminaires. Irrespective of any
“type approval” that some retrofit devices might have obtained, the installer and operator of the facility are still responsible for legalities and duty of care relating to the luminaires and installation. Therefore the new luminaire/lamp combination must be re-tested and approved.
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There is also the problem that retrofit lamps allow occupants to easily revert back to less energy-efficient light sources, so these devices cannot be considered a “permanent” energy-savings measure. Considering the unproven long-term performance, high maintenance costs and serious implications resulting from non-compliance with regulatory standards, retrofit lamp devices should are not generally recommended in commercial buildings.
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Lighting Council of Australia - Retrofitting Fluorescent Luminaires to Improve Energy Performance
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Voltage reduction devices like dimmers and autotransformers reduce energy consumption by reducing the mains voltage applied to the existing lighting equipment.
Generally they start the luminaires at full voltage, and then after a few minutes warm up they switch to so-called “economy mode” voltage of around 200V (about 15 per cent reduction). For linear fluorescent lamps, the characteristics of the inductive lamp/ballast circuit responds in a non-linear way so the power consumption is reduced at a higher percentage than the reduction in light output.
For example, a 2x36W T8 fluorescent luminaire with low-loss ballasts nominally consumes 84W at 240V, and the lamps produce 6700 lumens. Connected to a VRD at
204V the same combination will only consume 64W (24 per cent less) and the lamps will provide approximately 5,700 lumens (15 per cent less). This provides performance almost identical to a 2x28W T5 luminaire (63W for 5200 to 5800 lumens), without introducing problems of glare that can occur with T5.
These characteristics make VRD a simple and economical method of lowering energy consumption where a full upgrade is not warranted in non-critical areas with minimal or no switching, or to compensate for over-illumination resulting from installation of new triphosphor tubes. Typically these devices are appropriate for car parks and large banks of lighting, and are far less suitable for commercial office spaces, where there are often many different types of luminaires on the same circuits. Application considerations include:
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VRD should not be used in combination with electronic ballasts or occupancy sensors, as the reduced voltage may affect the operation of these devices.
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VRD should never be used with emergency lighting, as operation outside of nameplate voltage will nullify all compliance and classification of the emergency lighting system.
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Most VRDs feature down line switching detection circuitry which helps to identify when a new load (room) has been switched into circuit, and causes the line voltage to revert back to 100 per cent for a timed period so the lamps can strike. This can be frustrating to occupants of the main space, as they will notice the light level increase then decrease again.
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In most cases the minimum load on the switched circuit needs to be 8 or even 16 lamps, which makes the VRD unsuitable for use for small offices, toilets and other spaces in commercial buildings that require individual switching.
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The VRD devices have a limited operating life of 8 to 10 years, and failure modes are often catastrophic.
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These devices can only achieve energy savings in the range of 20-30 per cent, whilst full lighting upgrades can often achieve energy savings well in excess of 50 per cent.
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Lovett Tower
The lighting system in Lovett Tower was based on 2x36W recessed luminaires with low brightness louvred diffusers and installed at an average 2.4m x 2.0m centres (4.8m² of floor area per luminaire). Each 36W lamp used a low loss magnetic ballast for control and overall luminaire power was 84W. Therefore the nominal illumination power density was
17.5W/m² and an obvious candidate for improvement.
The luminaires had air slots on each side for supply and return air. Air handling luminaires are costly to buy and install and it was difficult to build a financial business case for replacing the existing luminaires. An option to upgrade the existing luminaires was then considered and adopted. This option involved stripping the existing control gear and wiring and replacing it with a pre-wired gear tray that contained a single 28W T5 lamp and ballast and a specular reflector to improve light output and manage the photometric performance of the luminaire.
In this project a T5 lamp was chosen because the solution required a shorter lamp and the light output from the lamp matched the requirements of the installation. To minimise the potential for glare from the high surface brightness of the T5 lamp, a Y5 opalescent flat refractive diffuser panel was installed to replace the low brightness metal louvre.
Luminaire power dropped from 84W to 31W and the illumination power density fell to
6.5W/m², an improvement of 63 per cent.
The main tenant of Lovett Tower is the Department of Veterans’ Affairs, who was able to get building owner funding for the project through the lease renewal process.
Tuggeranong Office Park
The lighting system in Tuggeranong Office Park was based on 2x36W recessed luminaires with low brightness louvred diffusers and installed at an average 2.4m x 2.4m centres
(5.8m² of floor area per luminaire). Each 36W lamp used a low loss magnetic ballast for control and overall luminaire power was 84W. Therefore the nominal illumination power density was 14.6W/m² and a candidate for improvement.
These were air handling luminaires with side slots for supply and return air. Air handling luminaires have a higher replacement cost and this project had a financial requirement to pay for itself before the end of the lease so a rebuild option was adopted. This option involved stripping the existing control gear and wiring and replacing it with a pre-wired gear tray that contained a single 36W T8 lamp and ballast and a specular reflector to improve light output and manage the photometric performance of the luminaire.
For this application a T8 lamp was selected because the existing layout required a higher light output than could be provided by a T5 lamp. T8 lamps are also cheaper and have a lot lower surface brightness than a T5 lamp. A Y19 clear prismatic refractive diffuser panel was installed to replace the low brightness louvre. Luminaire power dropped from 84W to
35W and the illumination power density fell to 6.1W/m², an improvement of 58 per cent.
The Department of Families, Housing, Community Services and Indigenous Affairs is the tenant of Tuggeranong Office Park.
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