This article explores how trimming of excess street lighting, the use of constant light output settings, optimised switching, off-peak dimming and adaptive lighting strategies can turn LED upgrades into an ongoing energy-saving asset.
Australian councils have spent much of the past decade converting mercury vapour, high-pressure sodium and various types of fluorescent street lights to LED, and the results have been dramatic. Depending on the starting point, councils have reduced electricity consumption by 50-80% compared to their legacy lighting. But LEDs are only part of the story. Layering smart controls over an LED network is where the next round of savings sits.
As confirmed by a Berg Insight Study, more than 30,000,000 smart controls are deployed around the world. Smart street lighting controls are perhaps the world’s most successful smart city technology. However, due to the metering capabilities of smart street lighting controls not being recognised until now, Australia has been a late adopter of smart controls.
The IPWEA SLSC Program identifies more than 25 benefits of smart controls. Beyond energy savings, smart controls can deliver:
- safer streets through 24-hour monitoring for faults as well as more consistent and well-maintained light levels;
- optimised maintenance planning and a range of other asset management benefits; and
- reduced light pollution with better outcomes for both nocturnal wildlife and residents living near lighting
But it is the energy savings — measurable, verifiable and directly tied to costs and emissions reduction — that most often makes or breaks the business case for smart controls.
The recent adoption of a new metering approach in the Australian National Electricity Market, called Type 9 metering, is intended to help councils and road authorities accurately measure street lighting energy consumption and thereby secure energy savings on their bills from trimming, dimming and other energy-saving strategies.
In summary, there are five control strategies that can help save the energy used in street lighting, particularly those lights found on main roads.
1. Trimming Excess Lighting
The real world is messy. Pole spacings are irregular and lighting choices come in lumpy outputs. This leads to a lot of over-lighting above the standard. It can also lead to highly uneven lighting. By permanently trimming off this excess lighting, road authorities will not only be saving energy but also greatly improving lighting uniformity. This is likely to be a significant safety benefit. Because trimming is implemented from sunset to sunrise, it can often be the biggest source of energy savings.
2. Constant Light Output (CLO)
Traditional lighting design has always been over-specified. Because old light sources faded steadily as they aged, lighting engineers designed to deliver compliant lux levels at the end-of-life. This meant that every new luminaire was significantly brighter — and used more energy — than the standard required for most of its operating life.
In contrast, fully controllable LED luminaires with smart controls let councils remove this built-in buffer, setting the output closer to the actual design requirement from day one and then gradually ramping up the power to keep the lighting level at the compliance point throughout the life of the luminaire. The implementation of CLO is something that AS/NZS 1158 now recognises as a valid strategy.
3. Optimised Switching
Traditional photocell controls and timed switches were often inaccurate, turning lights on too early and switching them off too late. Smart controls can optimise switch on/off times and, in some cases, have been used to gradually ramp up output in response to the calculations of diminishing ambient lighting levels.
4. Dimming in Off-Peak Hours
Traffic and pedestrian activity on most residential and collector roads falls sharply after 10pm or 11pm and stays low until the morning peak. Indeed, by 11pm most roads show traffic volumes 80-90% below their peak. Many councils and road authorities around the world have therefore asked why the same lighting level is needed when traffic volumes are massively reduced. Like other international road lighting standards, AS/NZS 1158 now recognises off-peak dimming as a valid lighting strategy provided off-peak dimming occurs between recognised lighting sub-categories.
The UK has led on this internationally with more than 70 local governments and county councils dimming in the off-peak or shutting off lighting in the off-peak (typically in rural areas). So, beyond the energy savings, what have the results been? The UK LANTERNS project —a collaborative national study led by the London School of Hygiene & Tropical Medicine and University College London —found that dimming and part-night regimes did not increase crime or road traffic accidents. France's massive national dimming and switch-off programs, run across thousands of municipalities, have reached similar conclusions at much larger scale.
5. Adaptive Lighting from External Inputs
Perhaps the most technically advanced approach to saving energy with smart controls involves using real-time conditions and data rather than a fixed clock. Central management systems (CMS) can adjust lighting output across a network using inputs such as vehicle counts (from traffic data services or sensors), ambient light levels, weather sensors and even event data. Adaptive lighting may offer additional savings on top of static dimming schedules, particularly on low-traffic roads. However, the costs of implementation need to be carefully considered in comparison to the additional benefits.
Importantly, none of these five strategies require replacing LED infrastructure already installed. Most modern LED luminaires are dimmable and ready to take a smart controller. The main task for asset managers is ensuring lighting design and CMS settings are all aligned with AS/NZS 1158 requirements.
Councils considering their own smart controls business case can find detailed guidance, roadmap documents and case studies through IPWEA's SLSC Program at slsc.org.au, alongside the Department of Climate Change, Energy, the Environment and Water's updated AS/NZS 1158 energy metrics guidance. The 2020 energy metrics in AS/NZS 1158 — the Power Density Indicator and Annual Energy Consumption Indicator — give councils a standardised way to measure and demonstrate these savings, scheme by scheme.
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