Energy efficient lighting strategies

Sunday, 15 July, 2007

Electrical contractors can implement many strategies in commercial buildings to minimise greenhouse gas emissions and save their clients money. But steps taken to conserve energy must be future-proof. Today's actions shouldn't prevent tomorrow's solutions being implemented.

What an environmental paradox: social and political attitudes have changed in favour of energy conservation, but worker habits have changed towards longer working hours spread across a wider period of time. Office tasks have evolved from isolated, individual processes to technology-based interactive communication tasks. In effect, workers are consuming more energy for longer periods of time.

There are many devices and systems intended to reduce lighting energy consumption in commercial buildings and significant savings are achievable using a combination of these strategies. A holistic approach to solving the problem considers all factors that contribute to wasted lighting energy, including luminaires (new or existing) and non-lighting factors that might influence natural light entering the space.

Symptoms of under-controlled lighting include sharp rises in electricity consumption before most workers arrive, no observable energy reduction when workers go to lunch or when daylight penetration peaks and near-maximum energy usage continuing late into the evening or even overnight.

General strategies

Simple things electricians can do to improve the efficiency of lighting installations include installing tri-phosphor tubes and high purity reflectors, replacing lay-in panels with louvres and replacing conventional control gear with electronic or digital ballasts.

Removing lamps from multi-lamp fixtures to reduce consumption should be applied only to fixtures with three or more lamps. In two-lamp fixtures, photometric distribution is severely affected. A drop of 50% light output across an entire office will inevitably generate insufficient light in areas.

When aligning lighting to the floor plan layout, provide higher lighting density over workstations than corridors. It's practical to maintain illumination levels at desks while reducing unnecessary corridor lighting.

Most installations neglect cleaning and re-lamping fluorescent lights, opting to only change failed lamps. It's advisable to clean and re-lamp every few years.

Control strategies

Sophisticated lighting control can minimise energy consumption, providing significant cost savings, while providing users with control over their environment.


Lighting layouts are often designed around the lowest performance of luminaires. Over time, lamp efficiency decreases and dust accumulates on fittings, reducing light output. So the new lighting design to replace the less-than-optimal existing layout often results in over-lit workspaces. 'Designed Illuminance Management' optimises work area light output using automatic dimming control to continuously monitor and adjust levels. Without this, many offices are subject to excessive light levels from luminaires burning at full power, with energy bills to match. Digital controls like DSI and DALI enable continuous light level adjustment, indiscernible to occupants.

Daylight harvesting

Lighting control enables the strategic substitution of artificial light with natural light, slowly dimming lights parallel to daylight entry, achieving considerable energy savings while maintaining comfortable lighting levels.

Time control

Office energy usage patterns should reflect their occupancy profiles. In reality, this is rarely the case. Implementing time control practices ensures lighting doesn't operate overnight, wasting energy while buildings are unoccupied.

Manual control

Combined control merges acceptable user and manager inputs. A facilities manager can set broad time-based functions globally and the user can still manually intervene for unique requirements of the occupant's immediate environment.

Occupancy detection

Low circulation areas often consume energy unnecessarily. Conversely, a pre-programmed system shuts down lighting at preset times, without consideration of after hours workers. Occupancy detection eliminates both of these issues, by providing light when and where it is required.

Energy management systems

Energy management systems, such as Dynalite, utilise distributed processing architecture, interconnecting various devices over a network to form a complete control solution. Command and status information passes to all devices over the network and integrates with HVAC, BMS, security, fire and other systems. In most cases, network components operate autonomously and simply respond to or issue messages relating to their configuration. The broadcast event-based network ensures alterations or additions can be made after installation, without having to reconfigure or rewire the entire system.

'Smart' sensors such as photo-electric (PE) and motion detectors respond dynamically to time-based and environmental factors. PE detection is used in daylight harvesting. Motion detection can perform different routines according to time of day. During office hours, sensors might dim workstations by 20% when occupants have been gone for five minutes. After hours, the same sensors would switch workspaces off, or keep them and their associated egress paths illuminated if occupants are working late. Gradual closure after all movement has ceased ensures energy isn't wasted after their departure.

Ballast controllers can be installed in switchboards to control fluorescent and incandescent lighting fitted with electronic dimmable ballasts or transformers.

Time clocks store events like time of day, sunrise, sunset or specific dates, to advise devices of non-standard time issues such as public holidays, so local intelligent devices can modify their behaviour patterns.

Most offices have banks of switches near their main entry. Usually the first person arriving switches them all on and the last to leave forgets to turn them off. A better solution is a single prominent entry panel comprising two buttons: 'Day' which notifies the system that someone is in the office, illuminating corridors and amenities and changes device behaviour to suit normal working day requirements; and 'Night' which enables the last person to activate an orderly lighting shutdown when they leave. If neglected, a hibernation sequence is activated.

The savings

Dramatically different energy usage can be achieved by implementing strategies such as these, reflected on a facility's bottom line.

Issues Strategies
Unnecessary lighting used outside normal hours Switch off or dim to limit usage with occupancy sensors, dimming and time control.
Deterioration of light fittings Optimise light output with luminaire efficiency upgrade.
Excessive lighting design to allow for partitions, lamp ageing and dirt accumulation Illuminance-based design with grid relocation, de-lamping, dimming and occupancy sensors.
Sunlight/artificial light balance sensitive to occupants Daylight harvesting using PE sensors, occupancy sensors and dimming.
After hours activity After hours workers detected and given illuminance and automatic closure on departure.
Life-cycle operating costs Programmed lamp maintenance and replacement.
User input Globally set functions overridden as required by users through local or web browser control.
Status reporting System monitoring of individual fixtures for trends and early detection of component failure.
Inter-system communication HVAC, BMS and security can send/receive commands to/from lighting zones through central control.
Low utilisation areas (store rooms, amenities) Occupancy sensors and time control.
Tariff sensitive control Respond to changing energy costs and maximum demand constraints through central control.
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