LIGHTING ON DEMAND. SUSTAINABLE LIGHTING SYSTEMS IN PUBLIC SPACE

Nunes, J., Landscape Architect, PROAP – Landscape Architecture (joao.nunes@proap.pt) Jacinto, N., Landscape Architect, PROAP – Landscape Architecture (nuno.jacinto@proap.pt)Campos, T., Landscape Architect, PROAP – Landscape Architecture (tiago.campos@proap.pt)Caroço, F., Lighting Technician, Schréder – Lighting S.A. (filipe.caroco@schreder.pt)Zoilo, I., Architect, PROAP – Landscape Architecture (inaki.zoilo@proap.pt)

Lighting on Demand (LoD) is a lighting concept based on the creation of a light wave that follows users according to their movement along the public space. It can be used in different sorts of spaces, according to the distinct appropriations they foster. The methodology within this paper seeks to assess the advantages of LoD applicability in public spaces, both in economic and environmental terms, through analytical and systematic comparisons between four theoretical scenarios: traditional lighting; LED lighting; LED lighting produced from photovoltaic panels; LoD concept. The four scenarios were applied in a case study in Tejo and Trancão Urban Park, Lisbon, Portugal. Conclusions demonstrate significant reductions, both in terms of total annual energy consumptions as in the annual CO2 emissions. Reductions of up to 80 per cent, when comparing traditional lighting with LoD, and up to 20 per cent, when comparing LED scenarios. On the other hand, LED-based lighting fixtures also require lower maintenance levels and, therefore, maintenance costs, especially when compared to traditional systems.This study proves its importance especially if LoD operates as a premise for an integrated public space design. Furthermore, it is a system independent from light sources and communication mechanisms currently available in the market, which proves LoD’s flexibility. This paper seeks to initiate a fruitful discussion around the role of public lighting in achieving sustainable solutions for the public space, especially when concerning its strong potential for a more dynamic linkage of public space use and lighting is revealed.

Keywords: lighting, light wave, sustainability, LED, public space

1. Introduction

Figure 1: Lighting on Demand (LoD) concept as a light wave that follows user according to their movement.

The present research seeks new solutions for public space lighting by implementing an innovative lighting system: Lighting on Demand (LoD). This paper seeks to initiate a fruitful

discussion around the role of public lighting in achieving sustainable solutions for the public space, pointing in the direction of new approaches to reduce energy consumption and enhance more dynamic and adapted to different users’ needs.

LoD concept is based on the creation of a light wave that follows users according to their movement along the public or private space. Its conceptual flexibility lies in its potential application to different sorts of spaces (circulation paths, leisure areas, contemplation areas, activities and socializing areas), different sorts of users and different hierarchies of spatial appropriation (Figure 1).

The results reported here result from the assembling, interpretation and systematization of information on the public lighting system of a 90.000 square meters urban park with approximately fifteen years of existence – Tejo and Trancão Urban Park, Lisbon, Portugal.

The comparative analysis and methodology within the present reasoning make use of the light technologies available in the market, namely Light Emitting Diodes (LED), as well as the most recent innovations in terms of connection mechanisms and communication of lighting fixtures in public space.

The emergence of several intelligent lighting systems, both for public and private uses, demonstrates the importance of the theme in socio-economic terms. Programs such as LITES project, an European based program which presents a public lighting systems that uses LED technology in order to reduce energy consumption are already being put up to the test, expecting a potential for energy saving of approximately 70 per cent. (LITES. Led-basedintelligent street lighting for energy saving)

However, the system presented here is independent of the technologies above mentioned and one expects it to suffer an evolution process accordingly to the successive technologies discovered. The considerations on the applicability of this system are described in the final considerations chapter.

Furthermore, this paper addresses a potential project that is in fully compliance with the Action Plan adopted by the Commission in 2006 as a reference for Community policy in energy consumption and aiming at achieving a 20 per cent reduction in energy consumption by 2020 (ADENE).

2. Lighting fundamentals

According to human beings physiological functioning, “all objects are seen by contrast, either dark against a light background, or light against dark background”. Our ability to see depends on the existing contrast and the lower the existing light or the greater precision of the detail seen, the greater the need for that contrast. “Unless the objects are self-luminous, their contrast with the background comes from the amount of light directed at them which is returned to the eye of the user (…).” 1

Without the intention to make a detailed analysis of biometric parameters to assess the quality of light in human beings, several variables must be considered with regard to light’s perception by the human body: the assumption that the perception of the surrounding light changes throughout the day, throughout the year and throughout the life cycle; the conscience that, even though every human being experiences the difference between night and day, light

1 CIE, Road Transport Lighting for Developing Countries, page 5.

is perceived in many different ways; the awareness that light as a profound influence on human’s biological, biochemical and even psychological processes (hormonal changes, mood, sleep, digestion, sense of safety, stabilization of human cycles, etc.). (Licht.de-Fördergemeinschaft Gutes Licht, 2010, pp. 6-15)

In this chapter some basic concepts will be presented, as that they are considered throughout the research process and how to define methodological assumptions.

2.1. Basic illumination concepts

Light’s variables and units are expressed in physical terms by several basic lighting quantities. Avoiding an exhaustive analysis of such lighting principles, only some of the most important basic concepts, which clearly express the light’s physical relations, are presented here: luminous flux (φ); luminous intensity (I); luminance (L); Iluminance (E), Color Rendering Index (CRI) (Licht.de-Fördergemeinschaft Gutes Licht, 2007, pp. 5-6) (Figure2).

Luminous flux (φ) is the rate at which light is emitted by a source of radiation, e.g. a lamp. It is measured in lumen (lm) and it defines the visible light radiation from a light source in all directions.

Luminous intensity (I) is V as candela (cd). The spatial distribution of the flux emitter defines the shape of the light beam emitter by a physical device, e.g., luminaire, reflector lamp or LED.

Luminance (L) is the brightness of a luminous or illuminated surface as perceived by the human eye. For an object to be seen, some of the light striking has to be scattered in the direction of the eye. The differences in luminance between various objects ant their background determine how visible they are. It is measured in cd/m2 or cd/cm2, and expresses the intensity of the light emitted or reflected by a surface per unit area.

Illuminance (E) is the luminous flux from a light source falling on a given surface. The flux from a luminaire travels in various directions through space until it strikes a surface. The amount of light falling per unit area of the surface is called the illuminance and is measured in lumens per square meter, or lux (lx). Where an area of 1 square meter is uniformly illuminated by 1 lumen of luminous flux, illuminance is 1 lux.

Figure 2: Four basic lighting principles.

Color Rendering Index (CRI) is the ability of a light source to reproduce the colors of different objects it illuminates light faithfully in comparison with the ideal or natural light source. (ADENE, Agência para a Energia,, 2011)

2.2. Basic electro-technology concepts

The concepts here presented are a mere tool to give the reader the full ability to comprehend this document’s content and methodology. As mentioned above, an extensive analysis of the concepts related to physical lighting devices is not sought, as it clearly goes beyond the scope of this research. The concepts discussed in this chapter are: light source, light fixture, luminous efficacy and real reflection.

Light source is the basic source of radiation that converts electrical energy into electromagnetic radiation visible to the eye, or light. Filament lamps or LEDs are among the most known light sources.

Light fixture is an electrical device that illuminates a specific area, through the use of artificial light (electric light source). It is composed by a lighting device, a light source and support structure. Luminaires and lanterns are examples of light fixtures.

According to the 2007 CIE’s report, basic lamps are rarely used by themselves, and this is especially important in outdoor lighting systems. The light flux is directed by reflection mechanisms (combination of mirrors) and refractions mechanisms (combination of prisms and lenses). These articulated systems are protected inside a protective and resistant structure and the whole system is called a luminaire. “In some countries, when a luminaire is specifically designed for roadway lighting, is called a lantern” (INTERNATIONALCOMMISSION ON ILLUMINATION, 2007, p. 5).

Luminous efficacy of a Light source is the ratio between the total luminous flux emitted by the source and the power absorbed by it. It is measured in lumens per Watt (lm/W).

Real reflection is a combination of three basic sorts of reflection: specular reflection, diffuse reflection and retroreflection. In specular reflection, the light leaves the surface in one direction only, without scattering, such as a very wet road. On the contrary, in diffuse reflection, light is scattered in many directions in such a way the luminance is the same for all angles of viewing. Finally, in retroreflection, light is returned back in the exact direction of the source, with a very small spread in the area surrounding this particular direction (Figure 3).

Figure 3: Basic sorts of reflection.

But in fact, most surfaces display a combination of specular and diffuse reflections, “with the specular becoming increasingly noticeable for large angles of incidence and observation”. (INTERNATIONAL COMMISSION ON ILLUMINATION, 2007, p. 7)

2.3. Qualities of the source of light

An adequate lighting system is the one that caters to human needs. This applies both indoors and outdoors. Lighting systems must be tailored to human being’s physiological requirement, ergonomic standards, as well as promote a wide sense of comfort (Licht.de-Fördergemeinschaft Gutes Licht, 2008, p. 28) (Figure 4).

The main criteria for outdoor lighting are: luminance distribution, illuminance distribution, glare, direction of light, light colour and colour rendering, light flicker.

Luminance, and the way it is distributed, plays a key role when it comes to the adequate outdoor level of brightness. Balanced luminance distribution determines adequate physiological behaviours, such as visual acuity, contrast sensitivity and efficient ocular functions (accommodation, convergence, pupillary change, eye movement, etc.). A correct luminance distribution also allows important visual comfort. As luminance greatly depends on illuminance, an adequate illuminance distribution is also fundamental, “influencing the speed and reliability with which a visual task can be registered and addressed”

Glare is produced by bright surfaces in the field of vision. There are two kinds of glare: discomforting glare (psychological effect) and disabling glare (physiological effect). When it is caused by light bouncing off reflective surfaces, it is generally known as reflected glare. In order to avoid errors, fatigue and accidents, it is important to control glare, by using suitable luminaires and matt surfaces whenever possible, by limiting luminaire’s luminance and by enlarging the luminous surfaces of the luminaires.

Modelling is a term used to describe the balance between diffuse and directional light and, accordingly to Licht.wissen 13 report (Licht.de-Fördergemeinschaft Gutes Licht, 2007, p. 6), it is considered to be an important lighting quality criterion. “Modelling is achieved when light comes predominantly from one direction, although care should be taken to avoid creating harsh”.

The colour of the light source is expressed by correlated colour temperatures. Colour temperature (T) is a characteristic of visible light determined by comparing its colour saturation with the one of an ideal black radiant body, that is, the temperature at which a blackbody radiates the same color as the light source. It is usually measured in Kelvin (K). The concept of hot or cold light relates to the tone colour with which the light source presents itself to the environment. 2

2 According to international standards, light sources can be classified as: warm (T < 3300); medium (3300< T < 5000); cold (T > 5000)

Figure 4: Quality criteria for adequate lighting.

The selection of the light colour is essentially an aesthetical matter of great subjectivity, with implications in the psychological spatial perception. Even though, light colour determines light source luminous efficacy, which is reflected on lighting system final costs.

Other important effects influence the qualities of the source of light, namely: flicker and stroboscopic effects (which can be distracting and give rise to physiological complaints, potentially causing dangerous situations on movement’s perception); other disruptive effects (physiological complaints, such as trouble sleep and headaches, negative impacts on fauna and flora, etc.

3. Light Emitting Diodes (LED)

LED was firstly introduced in the market in 1962, and the range of solutions existing today is wide. Throughout this sub-chapter a brief analysis of the key features of LED technology is presented, citing existing comparative analysis with other sorts of light sources, as far as possible.

In the last part of this sub-chapter LED is studied in articulation with intelligent lighting and management systems. This analysis becomes important when realizing that the greatest potential of LED technology is achieved only with this integration.

3.1. LED characteristics and comparative analysis with traditional lighting

It is now accepted worldwide the revolution brought about by the introduction of LED technology in lighting systems. It has proven to be operative both indoors and out, with decorative or functional purposes, a wide scope for application, a great flexibility of shape and colour dynamics and with an exceptional performance in terms of efficiency and longevity.

According to CIE last report on Workshop 5 - Led for Quality, “due to the increased luminous flux and efficacy, LEDs now start to compete with current light sources such as linear and compact fluorescent lamps and compact high intensity discharge lamps in luminaires for general lighting and for accent lighting.” (INTERNATIONAL COMMISSIONON ILLUMINATION, p. 1).

LED is a source of light different from the common halogen or energy-saving lamps. Instead of working by heating, filaments or gas discharge, LED is a considerable small electronic chip of special semiconductor crystals. This is the main reason why so very little energy is needed to induce LEDs to emit light (when comparing with traditional light sources). Even though light produced by LED is not hot, it is wrong to assume it does not generate heat. In fact, only a small part of the incoming energy is transformed into light; the rest generates heat inside the semiconductor (Figure 5).

Figure 5: LED’s composition.

Electroluminescence is induced when electric current is passed through the solid crystal; the diode starts glowing, emitting what is often mentioned as “cold light”.

To protect them from external influences, the semiconductor crystals are embedded in a plastic case, which enhances the production of higher light densities, making spreads of 15 to 180 degrees possible.

LEDs produce a monochromatic radiation. All the colours of the emitted light are determined by the semi-conductor material in use. The production of LEDs varies greatly, as do the light colours. Changes have to be introduced in the manufacturing system, in terms of the concentration and chemical composition of the phosphor material, or simply by adding colour mixing (using multi-LEDs), in order to achieve the required colour. Nowadays a great variety of colours and tones is available in the market.

Among other proven positive characteristics of LEDs, some of the most important are:

- Extremely long life and lower maintenance requirements (when compared to traditional street lighting, such as high-pressure mercury lamp (HPM), high-pressure sodium vapour lamp (HPS) or metal halide lamp); (Licht.de-Fördergemeinschaft Gutes Licht, 2005,p. 07).- High efficiency (LEDs have an operating life of five thousand hours or more, that is, six years of maintained operation of up to forty-five years of light for three hours a day, compared to a one thousand hours lifetime of incandescent lamp or a eighteen thousand hours lifetime of a fluorescent lamp) ; - Relative low installation costs (Licht.de-Fördergemeinschaft Gutes Licht, 2005, p.09;19);- White and coloured light with efficient colour rendering possibilities; - Insensitivity to vibration; almost no heat generation or IR and UV radiation; - Instant, flicker-free lighting with dimmable properties; - Compact design systems;- No mercury content and no end-of-life disposal problems.

3.2. Intelligent lighting systems with LED technology

Although LED technology is highly efficient, the greater potential of efficiency and energy saving is achieved only when it is combined with intelligent lighting and management systems. It is considered that systems designed for day-light and presence-dependent regulation can save up to 80 per cent, even in outdoor lighting, where it is proven that losses are higher than indoors.

Electronic regulators integrated in the luminaires are the first step to ensure LED’s efficiency, as they guarantee the constancy of light output and that illuminance never falls below the minimum levels required. Recent studies refer that “these regulators alone cut energy requirements and costs by 15 per cent”. 3

The mechanisms of lighting control today available are also responsible for important energy savings, as they allow LEDs to be dimmed when little energy is required, on the on the hand and, on the other hand, to power the energy up when sensors register the presence of pedestrians, cyclists or even automobiles. They can go even further: according to the

3 Licht.wissen 17, chapter ‘LEDs for City and Street’, page 11

information received by the sensors located inside the luminaires, instead of powering up the whole street (or cycle route), particular sections can be illuminated, in a succession similar to the detected movement.

LED systems can be incorporated in ‘telemanagement’ systems and it is believed that, with currently available technology, it is possible to implement wireless communication systems between luminaires, with a methodology similar to the one with cabling systems.

There are already a number of embryonic programs that aim to implement these sorts of integrated systems. One good example is the European program LITES – LED-based intelligent street lighting for energy saving, with four pilots implemented across Europe (France, Poland, Latvia and Portugal) (LITES. Led-based intelligent street lighting for energysaving). Even though, further research in communication mechanisms within intelligent lighting systems will be needed.

4. Light pollution in the context of global energy consumption

According to the International Energy Agency (IEA), almost 19 per cent of global energy consumption is used for lighting (IEA, International Energy Agency, p. 48). This conscience acquires even more importance when acknowledging that in 2010 energy consumption in the G20 grew more than 5 per cent, opposing the slight decrease in 2009. The electricity market followed the trends of other markets, experiencing consistent growths (Enerdata, 2010).

In the EU-wide Environmental Acceptability Requirements, an extensive body of rules and regulations, European Union (EU) defines four priority areas: climate protection, nature and biodiversity, environment and health, sustainable use of natural resources and waste management. The global community is now aware that, in order to fight against the number-one climate modifier, greenhouse gas CO2, global energy consumption must be sharply reduced (Licht.de-Fördergemeinschaft Gutes Licht, 2007, p. 12).

Experts have determined that more than a third of street lighting is over thirty years old. This obsolete technology (not only considering light sources, but luminaires as well) is, in part, responsible for low efficient uses.

LED technology acquires importance in this context as it has proven the ability to save up to 30 per cent of global energy consumption for lighting. In fact, LED solutions can reduce up to 60 per cent of the total amount of energy required to a lighting system (when compared to traditional light sources), especially when combined with precise light control integrated lenses.

The statistics only emphasize the importance of intelligent lighting systems when referring to energy efficiency. As mentioned in Licht.wissen 19 report, “lighting systems must take into account luminaires and light sources with a high power efficiency rating and dimming properties”4. While ensuring effective lighting and a sense of wellbeing, intelligent lighting systems help conserve energy (Licht.de-Fördergemeinschaft Gutes Licht, 2010, p. 26).

LoD represents a positive contribution when it comes to evaluating a system’s sustainable performance, as it helps decreasing energy supply and enhances more dynamic and adapted users’ needs.

4 Licht.wissen19, chapter ‘Lighting quality and energy efficiency’ page 26.

This technique improves sustainability assessment as it reduces energy consumption, by maintaining or even increasing lighting’s quality level. Moreover, it diminishes carbon dioxide emissions and maintenance costs.

Environmental Certification assessment tools, such as the World Sustainability Society (WSS) 5 or the ESTIDAMA Program 6, grant significant beneficial inputs to these “efficient infrastructures”, when evaluating energy efficiency.

5. The role of lighting in the context of safety in public space

Outdoor lighting systems address the same tasks as indoors, ensuring visual task performance, sense of safety and wellbeing, however the design requirements differ.

According to Licht.wissen 13 report, “during the day, our eyes provide around 80 per cent of the sensory impressions we register. But at night, the visual acuity of the eye drops to just three to 30 per cent of its day-time level – depending on lighting.” (In reality, daylight illuminance ranges from 5,000 to 100,000 lx. On a moonlit night, however, it reaches only 1 lx at most) (Licht.de-Fördergemeinschaft Gutes Licht, 2007, p. 04).

Furthermore, during the night period, spatial orientation and field of vision are reduced; the risk of glare is significantly higher; and even our biometric performances decrease sharply. In this context, lighting plays a key role in safety, especially when considering public space.

When considering outdoor lighting systems, although vehicle headlights are considered to be more effective, on or off the road, as they appear brighter than the background, fixed luminaires of variable sizes also play an important safety role, working largely by making the ground surface brighter than objects upon it. In either case, “light coming directly from the light source into the eye (glare) has to be kept minimum to reduce the sensation of contrast”.7

There are several reports on the criteria for good lighting in external spaces and, further, to pedestrian connections in residential industrial and commercial areas. One of the reports considered in this research is the CIE 136-2000, which settles that lighting projects should give the users the ability to anticipate difficulties and danger along their path, as they acquire the aptitude to sense movement and make facial recognition.

The EN 13201 document, the European standard rule for public lighting, was revised and simplified into the CIE 115:2000 report, by reducing the number of necessary analysis parameters. In short, these rules settle different lighting classes, in accordance to prevalent uses, movement speeds, and potential conflict zones (ADENE, Agência para a Energia,,2011, pp. 22-27).

Among other characteristics, lighting systems are ought to:

- Prevent users from accidents (seeing and being seen);- Provide adequate visual performance and colour discrimination to enhance visual

performance;- Provide accurate contrast sensitivity;

5 WSS is a non-profit foundation which the main goal is to create an universal measure of sustainability that allows to quantify the impacts of human activities on the natural resources.6 Program managed by Abu Dhabi Urban Planning Council (UPC) to promote sustainability and enhance liveability in the emirate under the ambit of Abu Dhabi Vision 2030.7 CIE, Road Transport Lighting for Developing Countries, 2007, page 05

- Reduce glare;- Create conditions for visual acuity; - Provide the required illuminance levels in order to let contrasts to be perceived ;- Afford correct illuminance levels allowing human’s eyes adaptation time.

6. Methodology

FIgure 6: LoD light wave along a cycle route.

LoD concept is based on the creation of a light wave that follows users according to their movement (Figure 6). Use of high quality of light standards is maximized, regarding both color temperature, and CRI.

To obtain systematic data, potentially interpreted statistically and compared with the other scenarios, a light source with large capacity and high-dimming relationship lm/W was considered.

Although LED technology is accepted as the existing light source in the market with the most accurate characteristics, it is not mandatory its use to fully operate with LoD. In reality, this research sustains this system’s ability to adapt to the characteristics of almost all light sources available, showing different performances, costs and environmental impacts.

In order to prove the validity of LoD, the study focused on the comparative analysis of four different lighting scenarios:

- Scenario 1 (S1): lighting using traditional light systems (with HPM); - Scenario 2 (S2): LED lighting, meeting the initial design requirements; - Scenario 3 (S3): LED lighting at the expense of energy production through

photovoltaic panels; - Scenario 4 (S4): Lighting using the ‘Lighting on demand’ concept.

To obtain a credible comparison between the four above mentioned scenarios, an accurate analysis must be undertaken, relating energy balance calculations, economic feasibilities,

light pollution productions and required maintenances, both in terms of luminaires’ spare components and communication systems.

When referring to a cost comparison, several fields must be considered in order to guarantee a sensible and realistic analysis: quality of the systems, service life, serviceability, maintenance requirements of luminaires, availability of spare parts and compliance with lighting quality features.

Along this document, precise lighting system planning are assumed for each given situation, that is, all the prerequisites for each given systems are optimized to their fullest potential, showing the greatest energy savings, costs reductions and pollution levels reductions possible. (Licht.de-Fördergemeinschaft Gutes Licht, 2007, p. 54)

The necessary systematic data to compare the LoD scenario (S4) with the other three was obtained from a case study located in the city of Lisbon, Portugal: Public lighting system in Tejo and Trancão Urban Park.

7. Case study: Public lighting system in Tejo and Trancão Urban Park

7.1. Analysis of existing situation

Figure 7: Tejo and Trancão Urban park, Lisbon, Portugal.

Tejo and Trancão Urban Park is a ninety-thousand square meter urban park, with almost fifteen years of existence, located in the eastern part of Lisbon, Portugal. It is a mature park, with proven aptitudes to accommodate a wide range of clearly defined areas, users, and settled appropriation mechanisms (Figure 7).

The park currently meets not only urban functions, but metropolitan as well, solving the seam of the urban fabrics between two suburban municipalities – Lisbon and Loures. This park is set in the context of the Parque das Nações new urban centrality, born of a plan with about twenty years, which accommodated the International Exhibition of 1998. Today, the park shows dynamic intense experience, hosting approximately one million visitors annually.

Due to its size and complexity, the analysis was concentrated on main pathways, crossing the park from north to south, and secondary pathways, which connect the first ones.

Figure 8: Different sorts of luminaires referenced in the intervention area.

In terms of lighting project the design team made the following choices (Figure 8):

- In the main pathways, the placement of four meter high post-top luminaires (L1) with HPM with 250 W;

- In the secondary pathways, the placement of three meter high bollards (L2) with HPM with 125 W.

In overall study area ninety-one (91) light fixtures from L1 type and two hundred and eighty (280) from L2 type were counted.

7.2. Application of the case study scenarios. Discussion of the results

Data collection for statistical treatment were obtained throughout 2010, from counts made on site in different days of the year and during the periods of the day with greater potential use (between 8.00 and 11.00 AM and between 8h00 and 11.00 PM).

The counts focused on two variables:

- Quantity and quality of light fixtures in primary and secondary roads;- Number of users and quality of movement.

When referring to the second variable, uses were systematized in three categories: walking, running and cycling.

Comparative analysis of the above mentioned four scenarios (S1 to S4) focused on the following variables:

- Light sources used and their powers;- Total power absorbed, dimming level and total power absorbed with dimming;- Number of luminaires, linking annual hours of operation (fully operational and with

dimming) and energy costs.

Three sorts of comparative results were sought: total annual energy; total energy consumption; annual CO2 emissions.

The results can be viewed in the data table below:

Characteristics S1 S2 S3 S4Luminaire type L1 L2 L1 L2 L1 L2 L1 L2Lamp type HPM HPM LED LED LED LED LED LEDRated lamp [W] 125 250 38,4 96 38,4 96 38,4 96Total power absorbed [W] 150 300 38,4 96 0 0 38,4 96Dimming level [ percentage ] 0 0 0 0 0 0 50* 50*Total power absorbed dimming [W] 0,00 0,00 0,00 0,00 0,00 0,00 19,20 48,00Number of luminaires 280 91 280 91 280 91 280 91Annual hours of operation** 4380 4380 4380 4380 4380 4380 4380 4380Annual hours at 100 per cent 4380 4380 4380 4380 4380 4380 0 0Annual hours with dimming 0 0 0 0 0 0 4380 4380Energy costs IP [2007] [€/kWh] 0,1000 0,1000 0,1000 0,1000 0,1000 0,1000 0,1000 0,1000Total annual energy consumption [€] 18 396,00 11 957,40 4 709,38 3 826,37 0,00 0,00 2 354,69 1 913,18

Total annual energy [kWh] 183 960 119 574 47 094 38 264 0 0 23 547 19 132Annual CO2 emissions [kg/year] 90 140 58 591 23 076 18 749 0 0 11 538 9 375* These values are based on estimated hours of luminous flux, present in the existing chart below.** It is considered an average daily operating period of twelve hours.

The dimming levels presented in S4 were calculated from the estimated hours of luminous flux, and are shown in the chart below:

19:00 20:00 21:00 22:00 23:00 0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:000

102030405060708090

100

Estimated dimming levels

NIghtime (h)

Med

ium

% o

f lum

niou

s flux

(%)

From the data table, one firstly concludes that the simple replacement of the light source, from traditional HPM to LED, implies an approximate reduction of total annual energy consumptions of 40 per cent when considering L1 and of 30 per cent when referring to L2. Reductions in annual CO2 emissions are of the same range.

When comparing S1 and S4, reductions are more significant: reductions of up to 80 per cent, both in total annual energy consumptions, such as the annual CO2 emissions.

However, it is extremely important to emphasize at this point that, for lighting systems currently designed, the analysis should focus on the comparison between S2 and S4: reductions within the range of 20 per cent in both variables mentioned above.

The system of communication between devices considered here is based on a 'master and slave' lighting scheme, consisting of two distinct systems, a 'power line' and a 'command line'.

Control of luminous flux, in this case, is assured through the 'pulse with modulation system (PWM), assuring the proposed dimming levels.

As mentioned in sub-chapter 3.2 (Intelligent lighting systems with LED technology), today’s available technologies on the market allow the opportunity to formalize the constructive system of the LoD concept based on wireless intelligent communication. Nevertheless, the technical validation to operationalize this hypothesis requires further investigation in the field of communication technologies, which goes beyond the scope of this research.

8. LoD in the context of Landscape Architecture

LoD’s potential in Landscape Architecture projects is vast, both in the terms of solutions, as across the range of scales of intervention. The range of scales merges with the wide range of interventions within this discipline: one recognizes the applicability of the concept in urban interventions – urban and metropolitan parks, cycling and pedestrian routes, highways and main roads – and, similarly, its effectiveness in smaller scale projects - public squares, streets, or even private gardens.

Alongside the dynamic landscape features, introduced by solutions with living matters – water, vegetation, wood, stone, light, wind, sound –, which create daily, seasonal and life-time evolutionary fluctuations – LoD also introduces dynamism into the night reading of the landscape (Figure 9).

Figure 9: Examples of LoD’s applicability in streets (above) and in gardens (below).

LoD innovative nature lies not only in cost savings, in terms of implementation and management, and CO2 emissions reductions, but also and, above all, in the relation between users and spaces that respond more directly to their presence, their movement and their own appropriation mechanisms.

9. Conclusions and considerations

Adapting public space to new lighting technologies implies significant changes, when admitting that a fifth of the electricity generated in the world is used for artificial lighting.

Most recent reports figuring in several specialized lighting websites (such as LICHT.DE, CIE or Enerdata) point out that innovative lighting technologies, along with modern light sources

and efficient regulation and communication lighting mechanisms help to reduce energy consumption and, at the same time, enhance lighting quality.

When combining the potential LED dimming properties with an adequate communication mechanism, LoD becomes an effective lighting system adapted both to users’ fluxes as types of movement. In the absence of movement, the whole system has the ability to fallback, allowing important energy savings. The reductions have significant impact not only in total consumptions, but in CO2 emissions and light pollution levels as well.

On the other hand, LED-based lighting fixtures also require lower maintenance levels and, therefore, maintenance costs, especially when compared to traditional systems.

When generalized, the case study results provide extraordinarily positive results for systems built from scratch (comparative analysis between S2 and S4), both considering the use of LED technology. However, it is necessary to take into account that the effectiveness may decrease when it comes to the conversion of existing systems. In these last cases, additional care is recommended with the replacement of traditional light sources by LEDs, since the values of lighting and electrical equipment differ substantially.

S3 scenario may be economically viable only when considering L1 luminaires. With L2 luminaires the cost might be unbearable in most public spaces. Moreover, the continuity of lighting during the night period could be jeopardized when there is not enough energetic accumulation.

LoD system is independent from specific lighting and electrical technologies, that is, the concept is applicable to a great variety of lighting fixtures and sources of light, which attests to its viability in future scenarios of lighting within the international panorama.

This study proves its importance especially if LoD operates as a premise for an integrated public space design. Conclusions here drawn illustrate the actual enhancement of sustainability in two vectors: environmental and economic. This is a system in which user’s movement is linked and consecutively followed by lighting. A strong potential for a more dynamic linkage of public space use and lighting is, therefore, revealed.

10. References

ADENE, Agência para a Energia,. (2011). Eficiência Energética na Iluminação Pública-Documento de Referência. Lisbon: ADENE.

Enerdata. (2010). Global Energy Intelligence, World energy use in 2010. Philadelphia: Enerdata.

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Licht.de-Fördergemeinschaft Gutes Licht. (2007). Outdoor Workplaces. licht.wissen(13).

Licht.de-Fördergemeinschaft Gutes Licht. (2007). Roads, Paths and Squares. licht.wissen(03).

Licht.de-Fördergemeinschaft Gutes Licht. (2008). Lighting with artificial light. licht.wissen(01).

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11. Main author’s biographies

JOÃO NUNES

Lisbon,1960

Founder and CEO of the Landscape Architecture Studio PROAP, which gathers a vast group of professionals in a cross-disciplinary team, with distinguished levels of expertise in landscape, in its most inclusive conception.

As International Director is responsible for the strategic, executive and tactical leadership of the three international offices: Lisbon (Portugal), Luanda (Angola) and Treviso (Italy). Develops PROAP’s conceptual and creative design and defines the strategic orientation of the research processes.

Has been lecturing at the Instituto Superior de Agronomia in Lisbon (Agronomics Institute, Technical University of Lisbon) since 1991. Currently also lectures at the Istituto Universitario de Architettura de Venezia, Politecnico de Milano, Politécnico di Torino, Roma La Sapienza, Roma Ludovico Quaroni, Facoltá di Architettura di Alghero.

IÑAKI ZOILO

Zaldibia, 1972

Partner at the Landscape Architecture Studio PROAP, which gathers a vast group of landscape architects, architects, designers and plastic artists, part of a core oriented by João Nunes.

Involved in PROAP’s strategic direction and management, oversees research and design projects to assure conceptual and artistic coherence.

As senior overall project manager is responsible for the coordination and implementation of all projects. Leads the organisation and the development of the design competition teams in their conceptual and technical execution.

Frequently participates as guest lecturer in international design and art workshops, representing PROAP.

NUNO JACINTO

Lisbon, 1975

Partner at the Landscape Architecture Studio PROAP, which gathers a vast group of landscape architects, architects, designers and plastic artists, part of a core oriented by João Nunes.

Involved in PROAP’s strategic direction and management, coordinates the Construction Detailing and Technical Site Completion Processes. Supervises the Design Review, Verification and Validation Processes.

Director of PROAP SA, Proap’s local office in Luanda, Angola. Project Manager of all African projects, assures client and technical team liaison.

Frequently participates as guest lecturer in international workshops and conferences, representing PROAP.

TIAGO TORRES CAMPOS

Lisbon, 1982

Research Manager at the Landscape Architecture Studio PROAP, which gathers a vast group of landscape architects, architects, designers and plastic artists, part of a core oriented by João Nunes.

Managing Editor for PROAP’s publications. Jointly runs the international communication processes, manages graphic and written project information sent to media requests worldwide.

Participates tactically in the creative processes, review and critique of projects.

Frequently participates in international workshops and conferences, representing PROAP.