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Energy Saving in Street Lighting

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Wednesday 28th February, 2018

With recent increases in the cost of electrical energy, and current budget cuts, local authority decision makers have been pushed to review their policy on street lighting in order to minimise the impact of rising energy costs. An increasing awareness of the environmental impacts is also driving these changes.

Whether saving money or saving the planet is the primary concern, nobody in our industry is immune from the requirement to reduce the amount of energy currently required to light our streets. While there is general acceptance of the need for such action, as a society we have become accustomed to relatively high artificial lighting levels, and there are some very real concerns to consider.

Potential difficulties arise in relation to important social issues such as personal safety, security, access and wayfinding – all of which are improved by lighting. Street lighting sets the tone not only for vehicle users but all those who use the spaces around roads and has a major impact on the environment after dark. Good lighting brings its surroundings to life, increasing night-time footfall, which in turn brings the benefits of both increased revenues and greater safety, through the presence of larger volumes of people.

So far-sighted authorities are now looking to technological advances to achieve savings. But, while new-build schemes can incorporate new technology from the start, retrofitting it into older equipment can be difficult and, in some instances, extremely costly. Various measures are currently being adopted to reduce energy costs. These might involve innovative light sources, such as LEDs, or techniques for adjusting and controlling existing street lighting to reduce burning hours. Examples of these are:

TRIMMING

Photocells could be replaced so that exterior lighting switches on later in the evening and off earlier in the morning; turning lighting on 15 minutes later and off 15 minutes earlier each day can save approximately 90 burning hours per annum.

DIMMING

Considerable savings can be made by dimming street lighting along main traffic routes during quieter periods. However this will require some capital investment in pre- programmed electronic ballasts and their installation into existing lighting. Traffic schemes are currently designed around levels of traffic flow and based upon the highest anticipated concentration. When flows reduce dramatically after midnight, and stay low until around 5.00am, the lighting can theoretically be dimmed to align with the reduced flow. This can reduce energy consumption by as much as 25%.

SWITCHING OFF

Another all-too-obvious alternative is to switch off street lighting during these pre-dawn hours. In fact several local authorities (particularly in rural areas) have taken the bold step of trialling the complete switch off of selectedstreet lighting schemes.

However, the consequences of a major road traffic accident during these hours need to be considered, particularly in locations such as roundabouts. Again, there may be a need for extra capital investment to improve safety on affected roads and some trials have required the installation of LED cats’ eyes and warning signs.

Anecdotal evidence suggests that night-time accident rates have actually increased and that the extra costs of making safety improvements have all but cancelled out any savings made in energy costs. In the long-term too, permanently switched off lighting columns have to be disconnected from the electrical supply and removed, on safety grounds. This can cost some £500-£600 per column – or the equivalent of 15-20 years’ electricity savings for each street-lamp on secondary roads or residential streets. Hardly good economics.

LUMINAIRE DESIGN

The specification of modern, well sealed, high performance lanterns can both save energy – and dramatically reduce the environmental impact of a lighting scheme. Whether through flat glass optics, efficient reflectors or precise lens technology, the elimination of waste light is an important factor in any holistic assessment of street lighting impacts.

NEW LIGHT SOURCES

Sales of energy efficient lamps are now increasing – Cosmopolis from Philips being the most widely adopted example. There are several other new white light sources becoming available from other suppliers. These lamps, coupled with design standards that now allow the design of lower lighting levels, when using light sources with good colour rendering, allow further savings to be made.

LEDS

Many claims are being made about LEDs and their valuable energy saving contribution to street lighting schemes. However, while there may be gains in the quality of light life expectancy and energy consumption, claims of dramatic cost savings have yet to be independently substantiated – and the initial capital investment is high.

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