Lighting on Demand. Sustainable Lighting Systems in Public Space

Lighting on demand. sustainable lighting systems in public space

Nunes, J., Landscape Architect, PROAP – Landscape Architecture ()

Jacinto, N., Landscape Architect, PROAP – Landscape Architecture ()

Campos, T., Landscape Architect, PROAP – Landscape Architecture ()

Caroço, F., Lighting Technician, Schréder – Lighting S.A. ()

Zoilo, I., Architect, PROAP – Landscape Architecture ()

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-based intelligent street lighting for energy saving)

However, the system presented here is independent of the technologies above mentioned and oneexpects 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.Lightingfundamentals

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 is perceivedin 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 consideredthroughout the research process and how to define methodological assumptions.

2.1.Basic illuminationconcepts

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 faithfullyin 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”(INTERNATIONAL COMMISSION ON ILLUMINATION, 2007, p. 5).

Luminous efficacy of a Light sourceis 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 toLicht.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]

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.LightEmittingDiodes (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 COMMISSION ON 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).

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 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.