led siijalice2bPublic lighting takes a big part of finances and costs in budgets of cities and communities. The costs are those for construction, maintenance, management, and electrical energy costs.

Better energy efficiency can be made through using the light sources with bigger energy effectiveness, appropriate optics which don't scatter the light, and with appropriate management and regulation of lighting according to current and real lighting needs (REGEA, 2014.2).

Classical type of lamps

There are two classical ways of artificial light generation: thermal and luminescent radiation. According to this, lighting sources are also divided into two groups. The first type of light is generated by passing the electrical current through the material which is heated to the temperature at which is possible to obtain visible light spectrum. Luminescent radiation is characteristic for light bulbs with gas discharge. Gas discharge in glass tube filled with gas as a result makes electrons movement which collides with gas atoms under the action of magnetic field (REGEA, 2014.2). These light bulb types are mostly used for public lighting. Public lighting can be divided into three groups: road lighting (lighting of roads and tunnels), urban lighting (lighting of squares and pedestrian zones), reflector lighting (lighting of facades and prestigious buildings) (Bilal, 2015.14; REGEA, 2014.2).

The most commonly used lamps for public areas lighting are incandescent lamps (least efficient), halogen and low pressure sodium lamps (Culver, Kitira, 2009.7). They have poor color rendering factor since they radiate yellow light that deadens the atmosphere and makes people feel sleepy. Mercury lamps are the oldest discharge lamps. They generate light by discharge in mercury gas and its utilization is 60 lm/W. Lighting up takes 3-6 minutes, re-lighting up of the hot bulb takes about 5-10 minutes. Its lifetime is 16 000 hours. Because of their mercury content, there are efforts for prohibition of these bulbs in Europe, while in the USA they are already prohibited. Mercury that these bulbs contain is very dangerous for people's and animals' health, and it may be released during its maintenance, storage, transport, installation, recycling or disposal (Culver, Kitira, 2009.9).

Discharge by sodium lamp is done in sodium vapor in addition of xenon for easier start and small amount of mercury. Biggest utilization for these lamps is 150 lm/W. Average lifetime is 32 000 hours. Lighting up takes 5 minutes, and re-lighting up of the hot bulb takes about 1-2 minutes (Radulović, 2015.31-34.).

Light pollution is every useless emission of artificial light in regions out of the zone that needs to be illuminated (street, road, monument, advertising, etc.). It comes as a result of inappropriate installation or lamps design. It causes pollution of the sky and environment with an excess of light. Light pollution can be avoided using the ecological lighting, and those are the lamps which meet these conditions:

-        Reduced power consumption compared with conventional light sources, and reduced greenhouse gas and other harmful gases emissions,

-        Appropriate lamps design and installation.

Non-ecological luminaries are those which emit light in all directions with very poor utilization of the emitted light (10-30%) - (REGEA, 2014.4).

LED lighting

White light sources that are very similar to natural sunlight such as LED (Light Emitting Diode) are very increasingly used for high-quality and energy-efficient space lighting. There are so many advantages of this technology which has been used in various industrial applications, mobile phones, computers, internal lighting, and now days her large benefit in public lighting area is revealed (REGEA, 2014.3).

LED is illuminated semiconductor diode that emits focused light due to the effect of electroluminescence. It is a special type of semiconductor diode, and it is made up of semiconductor LED chip, cathode and anode, reflector, lens and housing (Žunić, 2008.1). Public lighting LED lamps consist of a matrix of small LED diodes that gradually weaken in intensity, so not all at once (Culver, Kitira, 2009.27).

LED opcenitoMain LED diode elements (Source: Encyclopedia Britannica, 2010)

Street lighting is a public service which isn't negligible at all. In fact, the consumption of electricity to illuminate streets consumes up to 40% of the city budget for energy. Replacing existing street lighting lamps with LED lamps energy consumption and maintenance costs could be reduced up to 50%. In order to use all the advantages of LED diodes completely, these lamps should be networked. This allows remote control and performance improvement with the possibility of street light dimming and street light time of action control according to the conditions (e.g. short/long days). The principle of controlled action founded on networking brings additional 10-20% energy savings in addition to those savings made only by using LED lamps. Networking enables easier failure detection, and thus maintenance and repair costs reduced with more precise dispatching. Networked LED lamps have some bigger investment costs, but they have more advantages than only installed LED lamps. There are two main groups of LED lamps benefits: energy savings and operational costs savings.

Energy savings

The largest benefit of using LED street lights are the lower energy costs, which result from the following features:

-        Low wattage: LED lamps provide significant energy savings by delivering the same or enhanced light quality at lower wattage than classic bulbs.

-        Dimming: Due to the high light output, LED lamps can be dimmed to 50% in the beginning of installation. Dimming can be made according to circumstances such as low traffic times, unpopulated areas in the middle of the night, etc. So, there is a possibility of light intensity regulation.

-        Reduced burn time: With on/off scheduling capabilities, street light operation can be easily modified to coincide with changing sunrise/sunset times, reducing lamp burn time.

Result of these features is that networked LED lamps can reduce energy consumption for street lighting 60-74%.

Operational costs reduction

Operational savings from networked LED lamps vary according to the costs that operators have for current maintenance.

-        Long lifetime: LED lamps have 3-4 times longer duration than classical lamps (it is 50 000-100 000 hours, compared with classical lamps whose lifetime is about 10 000-15 000 hours) (Culver, Kitira, 2009.28), so these lamps require less frequent replacement.

-        Remote monitoring and management: Street light management software provides insight in street light operations and also gives possibility for control through dimming and on/off state planning.

-        Automatic outage detection: Street light software for management gives possibility of instant outage notification. With precise outage information number of false alarms and related costs can be reduced, non-working lamps can be easily discovered and dispatching is also easier.

-        Proactive maintenance: Some software provide other advantages such as predictive information alerting operators which lamps are very close to its end-of-life, so replacement can be planned proactively. These features provide concept of „intelligent lighting“ (Silver Spring Networks, 2013.1-5).

Other advantages:

-        Very low percentage of initial defects

-        Utilization of these lamps is up to 150 lm/W

-        Resistance for vibration and shock, high reliability under severe conditions

-        There is no ultraviolet or infrared radiation

-        Low voltage, instant turning on of the light and no flickers (Culver, Kitira, 2009.28)

-        No heat generation, it doesn't harm the insects because it represents cold lighting source (REGEA, 2014.3)

-        Small dimensions, creative and compact design

-        Environmentally friendly because it doesn't contain harmful elements (lead, mercury, cadmium, yttrium, arsenic, etc.), and it also has a simple degradation and recycling after the end of service life

-        Infrastructure financing through the savings

Disadvantages:

-        High production costs and costs of the products which are compensated by energy savings and long lifetime

-        There is an adverse effect of humidity and high temperatures on LED lamps (Culver, Kitira, 2009.28)

Public lighting design should be implemented according to standards (EN 13201, UNI 10819) (REGEA, 2014.7).

Author: MSc. Edina Hasanspahić

Source: BhDOCumentary

Literature and Internet

  • www.silverspringnet.com, Silver Spring Networks, The Business Case for Smart Street Lights, California, September 2013, 1-5,

  • Bilal Ermina, Savremena energetski efikasna rasvjeta, Faculty of Electrical Engineering in Sarajevo, Sarajevo, July 2015, 14-20.
  • Regionalna energetska agencija sjeverozapadne Hrvatske (REGEA) u saradnji s OSRAM, Suvremena energetski učinkovita javna rasvjeta, Zagreb 2014, 1-8.
  • Žunić Nusret, LED i OLED osvjetljenje, Brčko, October, 2008, 1-3.
  • Culver Alicia, Kitira Vincent, LED Exit Signs, Street Lights, and Traffic Signals, Responsible Purchasing Guide, USA, 2009, 7-28.
  • Radulović Milovan, Električna rasvjeta, Arhitektonski fakultet Podgorica, Crna Gora, 2015, 31-34.
  • www.britannica.com/technology/LED/images-videos, Encyclopedia Britannica, LED Images and Videos, 27.12.2015.

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