Changing the colour of night on urban streets - LED vs. part-night lighting system
Introduction
Streets lit by technologies dating back to the 1960s are one of the largest energy drains for the municipalities in the United Kingdom (UK) that is approximately 40% of their total electricity consumption [1]. The electricity costs for street lighting are a significant expenditure for a small city like Coventry in the UK with approximately 32,000 lighting columns [2]. There is a substantial increase in the electricity cost particularly through the rapid increase in the cost of oil and gas (much of which comes from abroad) that generate around 80% electricity in the UK [3]. For promoting energy efficiency at street lighting, focus should be given on the consumption, production patterns and program costs ensuring the minimisation of electricity consumption as well as high quality lit environment and safety for the people. The UK cities are upgrading the streetlights to white light-emitting diode (LED) lamps to ensure not only the energy efficiency but also to help fight crime and promote safe cycling despite the objections from some city dwellers for its brightness and changing the colour of night on urban streets. For example, Kent County Council is installing 118,000 LED lamps, Leicestershire plans to have 68,000, Manchester will have 56,000 and Gloucestershire will have 55,000 LED lamps on the streets.
Several studies [[4], [5], [6]] assessed the energy efficiency of LED lamps comparing to the traditional fluorescent lamps. Escolar et al. [5] claimed that LED lamps could improve energy efficiency by up to a factor of five without altering light intensity levels that is appealing to lighting authorities for significant energy savings on street lighting. Higher electricity savings cause less carbon footprint as electricity is still mostly generated from fossil fuel. Bilec et al. [4] stated that LED lamps could reduce 25% emission of airborne toxins and particulates comparing to the metal halide and High-Pressure Sodium (HPS) lights. Iveland et al. [6] compared different street lighting systems and argued that LED lamps were more efficient on urban streets because of not only consuming less energy but also ensuring safety by providing bright lights. Zhang et al. [7] examined the technology on proficiencies of different lighting foundations through laboratory examinations of visual performance as well as brilliance awareness and concluded that LED lamps are more appropriate for highways comparing to other lights.
Cost effectiveness due to longer lifespan and less maintenance operations is another advantage of LED lamps [8,9]. In addition, LED lamps can be remotely controlled by a central computer system such as the system developed by OSRAM Licht AG. This allows a specific selection of lights to be simply switched on and off from one location, which also aids in implementing a part-night lighting system. Also, LEDs aren't restricted to on or off states: the ability to dim an LED light can be built. Several studies [[10], [11], [12]] examined the benefits of LED lamps on the urban streets in the UK. Falchi et al. [10] and Sacks et al. [11] ascertained that LED lamps significantly reduced the road accidents and crimes on major roads in the UK. Welsh and Farrington [12] found the similar findings after assessing the impact of LED lamps on the crime rates at five cities in the UK and argued that street lighting was more plausible than surveillance and deterrence since it increased the community pride and informal social control. In addition, higher ambient light levels of LED lamps increase the effectiveness of other security measures, such as closed-circuit television (CCTV) and automatic number-plate recognition (ANPR) at night.
Installation of LED lamps on urban street requires higher installation costs and a long-term period to payback benefits of replacing outdated streetlights in terms of energy savings and costs. To achieve the short-term energy efficiency of urban streetlighting, city councils sometimes adopt a ‘part night’ lighting system particularly in the residential areas where lights of relatively lower importance (in respect of traffic accident and crime rate) are dimmed or switched off at times during the night when they are least likely to be needed [13]. The city councils require strategies to upgrade the street lighting considering the budgetary constraints and ability to develop, implement and evaluate the programmes of installing the LED lights on the streets. The Coventry City Council recently replaced 29,701 existing sodium lights with LED lights of which the current total energy usage is 8,290,965 kWh. This paper performs the economic analyses to understand the economic feasibility of two street lighting systems: LED lamps and part-night lighting system on the streets in Coventry city during the twenty-year period (2010–2030) assuming that the return of investment period is twenty years. Data were collected from the Traffic and Network Management and Street Lighting departments of the Coventry City Council. Data were also collected from Balfour Beatty who are in partnership with Coventry City Council carrying out the installation of 28,700 new LED lighting columns on the streets of Coventry city that was started on the 1st November 2010.
Section snippets
Energy efficiency of new LED lighting project in Coventry city
The projection of energy usages by existing, new LED lamps and part-night lighting system during the period of twenty years starting from the year of 2010 is shown in Fig. 1. The prediction of energy usages assumed that the existing lights would be replaced by LED lamps evenly across the first year (year 2010) accounting for the energy usage of 6,003,173 kWh. During the period of 2011–2030, all 29,701 lighting columns have new LED lamps resulting in a total energy usage of 4,568,799 kWh per
Safety and health issues of LED lamps
Despite the energy efficiency and lower carbon emissions, people including Public Health England are decrying the long-term negative impacts of LED lamps on people's eyesight and leaving them with disruption of the circadian system (sleep cycle) that eventually have adverse impacts on people's wellbeing and safety. For example, after the replacement of around 185,000 yellow HPS street lights with LED lamps in Rome on March 2017, residents of the city described the new whiter lights as harsh and
Conclusions
Increasing energy demand urges for sustainable energy solutions to mitigating the climate changes and ensuring energy security especially for countries like the UK who are mostly dependent on other countries for the generation of electricity. Many cities in the UK upgrading the streetlights to white LED lamps for reducing the electricity costs since lighting urban streets costs approximately 40% of total electricity consumption in a city. Installation of LED lamps on urban street requires
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