Taking a dim view of waste

Traditionally, limited opportunities for controlling exterior lighting have resulted in significant waste of energy and money but it’s now time to take a look at the latest technologies and clamp down on that waste.

All of us are now operating within an environment where energy consumption and costs are of paramount importance to public and private sector organisations alike. In many cases, driven by legislation and other initiatives, there is also an imperative to make improvements in these areas relatively quickly.


I would suggest, therefore, that an obvious priority is to identify areas of wasted energy, which also waste money, and deal with them. I further suggest that street and amenity lighting is very often guilty of wasting considerable amounts of energy and money. Not through complacency on the part of the owners of those installations (in most cases) but simply because the opportunities to exercise effective control of high intensity discharge (HID) lighting have been very limited.

That situation is changing, however, as new digital control technologies come onto the market that are able to dim HID light sources. This dimming ability has been available for indoor HID lighting for some time and can now be applied to exterior lighting. So it’s worth considering how such functionality can offer real benefits.

The key to reducing wasted energy is to match the use of the lighting to demand, a principle that has been applied to more general lighting applications for many years. So, for example, one element of a lighting control strategy inside buildings would be to use occupancy detection to switch lighting off in unoccupied areas.

In the case of external spaces it is more practical to think in terms of periods of reduced demand and, perhaps, situations where the weather may influence the lighting requirement. So, for instance, there are many motorways and other roads that are only lightly used after midnight. However, when it was suggested recently that lighting in these areas is switched off during the small hours a considerable amount of concern was expressed. Dimming the lighting instead of switching it off completely is clearly an excellent compromise.

The same is true of smaller roads and many other open spaces where the lighting is also of importance to pedestrians. Again, dimming the lighting at times when there will be hardly any foot or road traffic is a sensible course of action. And when you think there are over 7.5 million street lights in the UK this could go a long way to helping local authorities cope with the pressures on their budgets as well as reducing their carbon footprint.

In parallel, improved controllability can also be used to increase lighting levels in accident black spots, perhaps at times of day when accidents are most likely, and light levels can also be increased in bad weather. The overall effect is that these lighting systems become responsive to changes in demand, rather than remaining static irrespective of what’s happening.

While street lighting perhaps offers the biggest savings across the country there are also many amenity spaces that are also lit throughout the night when there is nobody there to benefit from it. So the same principles can be applied to any external space that is lit for long periods but has variable use during that time.

In all such cases, in addition to the energy savings, there will be further benefits through the longer lamp life that results from less use. Extended re-lamping cycles will reduce maintenance costs and there will be fewer lamps to send for recycling through the life of the lighting system. As HID lamps are classified as hazardous waste and are more expensive to dispose of than some other light sources, this will result in even greater financial savings – and reduced environmental impact.

The recent development of digital dimming systems for exterior HID lighting have made all of this possible – going way beyond simply providing a dimmable ballast to exploiting all the benefits of digital control technologies to create an intelligent and versatile lighting control system. Furthermore, such systems allow all street lanterns and amenity luminaires to be controlled via the digital interface – making them very responsive.

These systems allow the luminous flux of HID lighting to be adjusted from 40% to 100% via DALI (Digital Addressable Lighting Interface) or DSI (Digital Serial Interface) signals, depending on the type of HID light source being used. In addition, a specific luminous flux value can be selected in ‘step dimming’ mode via an additional 230V control line to achieve energy savings of up to 50%. The brightness level can also be lowered via a digital power changeover switch at defined times without control lines.

So now that this technology is here, I urge any organisation that operates exterior HID lighting to take a fresh look at how the energy performance of that lighting can be optimised.

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