Led-based Public Lighting System Reliability

Led-based Public Lighting System Reliability for a Reduced Impact on Environment and Energy Consumption A. Lay-Ekuakille(1), G. Vendramin(1), M. Bellone(1), A. Carracchia(1), D. Corso(1), M. De Giorgi(1) A. Deodati(1), D. Laforgia(2), V. Pelillo(2), E. Petrachi(1), A. Sarcinella(1), A. Trotta(3) (1) Dipartimento di Ingegneria dell’Innovazione, Università Degli Studi del Salento Via Monteroni, 73100 Lecce, Italy, giuseppe.vendramin@unile.it, http://smaasis-misure.unile.it (2) Energy and Environment Research Center, Dipartimento d’Ingegneria dell’Innovazione, Università Degli Studi del Salento (3) Dipartimento di Elettrotecnica ed Elettronica, Politecnico di Bari, Via Orabona 4, 70100 Bari, Italy Abstract - Light Emitting Diodes (LEDs) contain solid_state technology made in Silicon Valley using similar technologies that are used in the latest microprocessors. These solid_state devices have no moving parts, no fragile glass environments, no mercury, no toxic gasses, and no filament. There is nothing to break, rupture, shatter, leak, or contaminate. They are playing a significant role in energy saving policy; since private and public lighting are indicators of development in many countries. Developing policy must be envisaged in order to reduce impact on environment and energy consumption without sacrificing an important part of economic growth. This research outlines results of a campaign which has been conducting in the Town of Leporano, in the district of Taranto (Apulia Region, Italy) in cooperation with the local government. Different led system have been located on public posts. Keywords - LED, light, streetlight, light pollution, HME lamp, HPS lamp, public lighting. I - Introduction Since LED based light sources last at least 10 times longer than a normal light source, there is no need to replace the light source, reducing or even eliminating ongoing maintenance costs and periodic re-lamping expenses. Light emitting diodes are solid state devices containing no moving parts and no filaments to break. As such, LEDs handle rough environments including heavy vibration and impact. Unlike conventional light sources, which typically contain a fragile filament enclosed in a breakable glass enclosure, LEDs are built using solid state technology made in Silicon Valley using similar technologies that are used in the latest microprocessors. These solid state devices have no moving parts, no fragile glass environments, no mercury, no toxic gasses, and no filament. There is nothing to break, rupture, shatter, leak, or contaminate. The solid state nature of LEDs make them extremely rugged and durable an excellent choice for applications where reliability and dependability are paramount. Conventional light sources (as well as some LEDs) contain invisible radiation as well as the visible component of light in the beam. This radiation can be very short wavelength blue, known as ultraviolet light, or long wavelength red, known as infrared, which causes heat. Ultraviolet light can, and will, damage materials, cause color changes and eventually breakdown many materials. Museums and other applications where ultraviolet light is a liability use expensive low flexibility light pipes to filter out this harmful component of the generated light. Frequently the light sources used for these light pipes is a very bright, hot, incandescent or halogen sources, generating most of their light as heat. Infrared light can damage displayed objects, increases air conditioning costs, decreases environmental comfort, and when reflected off reading surfaces increases eyestrain. II - Fondamentals and juridic aspects LEDs have now enabled never before possible applications which traditionally used HID and halogen bulbs. LED applications include roadway, pathway, warehouse security, parking lot (indoor and outdoor), landmarks, architectural and canopy lights to list a few. LEDs have quickly improved in light output over the last few years. Within solid state lighting systems they provide better energy consumption and lower maintenance costs compared to traditional light sources. A typical solid state Exterior Wide Area Lighting system consists of LEDs, secondary optics, heat sinks and a power supply. System efficiency is the ability to capture as much light as possible produced by the LUXEON® LED, and project it onto the intended target. Large omni-directional light sources allow light to escape the reflector. This results in light that is not managed and misses the desired area of illuminance. LEDs are small directed light sources which can be coupled very efficiently with a secondary optic. Increased system efficiency means less wasted light and more light where you need it. Fig.1 - Utilization efficiency comparison Wasted light can lead to light pollution such as glare (the result of excessive contrast between bright and dark areas in the field of view). Fig.2 – Light pollution: glare effect Fig.3 – Light pollution: light trespass Light pollution is excess or obtrusive light created by humans. Among other effects, it causes adverse health effects, obscures stars to city dwellers, interferes with astronomical observatories, wastes energy and disrupts ecosystems. Light pollution can be construed to have two main branches: (a) annoying light that intrudes on an otherwise natural or low light setting and (b) excessive light, generally indoors, that leads to worker discomfort and adverse health effects. Specific categories of light pollution include light trespass, over-illumination, glare, clutter, and sky glow. It is common, however, for annoying or wasteful light to fit several of these categories. Light trespass occurs when unwanted light enters one's property, for instance, by shining over a neighbour's fence. A common light trespass problem occurs when a strong light enters the window of one's home from outside, causing problems such as sleep deprivation or the blocking of an evening view. Over-illumination is the excessive use of light. Specifically within the United States, over-illumination is responsible for approximately two million barrels of oil per day in energy wasted. This is based upon U.S. consumption of equivalent of 50 million barrels per day of petroleum. Equivalent barrels per day of petroleum is simply an easy to visualize representation of energy use from all sources. It is further noted in the same U.S. Department of Energy source that over 30 percent of all energy is consumed by commercial, industrial and residential sectors. Energy audits of existing buildings demonstrate that the lighting component of residential, commercial and industrial uses consumes about 20 to 40 percent of those land uses, variable with region and land use. (Residential use lighting consumes only 10 to 30 percent of the energy bill while commercial buildings major use is lighting.) Thus lighting energy accounts for about four or five million barrels of oil (equivalent) per day. Again energy audit data demonstrates that about 30 to 60 percent of energy consumed in lighting is unneeded or gratuitous. Glare is the result of excessive contrast between bright and dark areas in the field of view. For example, glare can be associated with directly viewing the filament of an unshielded or badly shielded light. Light shining into the eyes of pedestrians and drivers can obscure night vision for up to an hour after exposure. Caused by high contrast between light and dark areas, glare can also make it difficult for the human eye to adjust to the differences in brightness. Glare is particularly an issue in road safety, as bright and/or badly shielded lights around roads may partially blind drivers or pedestrians unexpectedly, and contribute to accidents. Fig. 4 – Components of light pollution Clutter refers to excessive groupings of lights. Groupings of lights may generate confusion, distract from obstacles, including those that they may be intended to illuminate, and potentially cause accidents. Clutter is particularly noticeable on roads where the street lights are badly designed, or where brightly lit advertising surrounds the roadways. Sky glow refers to the "glow" effect that can be seen over populated areas. It is the combination of light reflected from what it has illuminated and from all of the badly directed light in that area, being refracted in the surrounding atmosphere. This refraction is strongly related to the wavelength of the light. Rayleigh scattering, which makes the sky appear blue in the daytime, also affects light that comes from the earth into the sky and is then redirected to become sky-glow, seen from the ground. As a result, blue light contributes significantly more to sky-glow than an equal amount of yellow light. Lighting consumes one fourth of all energy consumed worldwide, and case studies have shown that commonly 50 to 90 percent of building lighting is unnecessary for the purposes required. Energy is wasted when light does not fall on its intended target, as when lighting fixtures allow light to go up instead of (as is generally preferred) downward. Waste also occurs when more light is generated than needed. Many governments are looking for ways to reduce energy use after signing the Kyoto Protocol, and individuals, organizations and local authorities are increasingly improving lighting efficiency in order to reduce energy consumption. III - Experimental facility description The 45-watt Home-Made Street Light is capable of providing 2,025 lumens output (45lm/W). It is currently the best performing outdoor LED lamp developed with more power and brightness output than before. Demonstrating the SMAASISLIGHT ver.1 system-in-package LEDs technology for outdoor application, it can well-control the LEDs junction temperature (Tj) at under 70 °C (lab measured and tested) (Fig. 4). The LEDs junction temperature (Tj) must be kept low, and also must eliminate the hot spots caused by cluster effect. It is also important to maintain all LEDs with the same temperature conditions within the P-N junction, and control at the same decay rate, so the brightness output stays uniform across. Fig. 4 – Temperature properties of Led Streetlight Lamp Fig. 5 – Temperature properties of HPS Lamp The design had to take into account to include for driver box, control, electrical circuits, power supply and other engineering components. It is essentially a very difficult challenge for current high-power LEDs approach to figure out a workable solution, for building a real LED street lighting device with enough brightness output for outdoor application. There are technical barriers to overcome, particularly in ultra-high power dissipation and junction temperature control. It is important to have protection from dust, water, and humidity, while able to efficiently conduct the LEDs generated heat away as well. The head module comes to 700 mm (L) x 450 mm (W) x 200mm (H), conforming to most dimensions of standard outdoor lighting fixtures in current use. It is constructed with a base slot for mounting to lamp post of up to 8 meters in height. They have been located on public posts. Fig. 6 and fig. 7 illustrate used LED support switched-off and switched on respectively. Fig. 6 – Support of LEDs in the lab Fig. 7 - Switched – on LEDs in the lab Fig. 8 - Located support on post Fig. 9 - Switched - on LEDs on street Fig. 8 and fig. 9 show one of the located armour before and after illumination along Luogovivo street in Leporano. LEDs-based post illuminates in a correct and appropriate way the street, allowing major safety. Fig. 10 - Comparison between traditional and Led-based posts From fig. 10, it is possible to admire the difference between a traditional equipped post and a LEDs-based support one. IV - Methods Intensity is one of the most commonly used characteristics used to indicate the light output of LEDs. However, the construction and packaging of an LED create special difficulties in specifying and measuring a meaningful value for intensity. The flux Φ is meant to be that flux leaving the source in a particular direction and propagating in the element of solid angle Ω containing the given direction. Fig. 11 – Defining geometry for the quantity Intensity (I) The input aperture (of area A) to the detector, together with the distance d of the aperture from the source, defines a solid angle 2d A=Ω for the measurement. If we use this detector, and measure the flux Φ at any angle θ , keeping the distance d constant, we will obtain the same director measurement value at all angles. This is useful, since it does mean that we do not require a critical alignment of our measurement system with respect to the angle θ . Fig. 12 – Point Source: The Intensity is the same in all directions Fig. 13 – Polar plot showing the Intensity I of a point source as a function of angle Θ around the point source The intensity information is usually presented on a polar plot where the length of the radius is the value of the intensity I of the source measured from some defined center of the source. The intensity is plotted as a function of angle θ about the source measured from some defined direction ( )0=θ with respect to some characteristic feature of the source. The intensity is usually normalized to some value 0I such as the maximum value, or the value in some direction of interest. Intensity information for LUXEON LED (lambertian) is plotted in Fig. 14. Fig. 13 – Lambertian Source: Polar plot showing the Intensity I of a Lambertian source as a finction of angle Θ from the normal to the source surface Fig. 14 – Intensity information for LUXEON LED The equation for the intensity distribution of a Lambertian source is ( ) ( )θθ cos0II = , where 0I is the maximum value of the intensity, in the direction normal to the surface. To produce light, LEDs are operated with a forward bias. In this condition, the current through the device must be limited externally and LEDs are usually operated at a constant current from a DC power supply. The typical operating current, for the new high power LEDs, has been approximately from 350mA up to 700mA. It should be noted that the LED light output should be stabilized by stabilizing the current through the device, rather than regulating the power applied to the LED. The general equation for the relation between the current, voltage, and temperature for a diode is given by:    −  = 1exp0 kT eVii β (Eq. 1) where i is the current through the diode, 0i is the reverse saturation current, e is the charge of electron, V is the voltage across the diode, k is the Boltzmann constant, T is the temperature of the diode, and β is an ideality factor which varies between 1 and 2, depending on the semiconductor and temperature. This equation is used to monitor the temperature stability of the LED. Fig. 15 – Thermal design graph One of the mathematical tools used in thermal management design is thermal resistance (RΘ). Thermal resistance is defined as the ratio of temperature difference to the corresponding power dissipation. The overall RΘJunction_Ambient (J_A) of a LUXEON Power Light Source plus a heat sink is defined in Eq . d ambientjunction JA P T R − ∆=θ (Eq. 2) where: ∆T = TJunction - TAmbient (°C), Pd = Power dissipated (W), and Pd = Forward current (If) * Forward voltage (Vf). Heat generated at the junction travels from the die along the following simplified thermal path: junction to slug, slug to board, and board to ambient air. For systems involving conduction between multiple surfaces and materials, a simplified model of the thermal path is a series thermal resistance circuit, as shown in Fig. The overall thermal resistance (RΘJ_A) of an application can be expressed as the sum of the individual resistances of the thermal path from junction to ambient (Eq. 3). The corresponding components of each resistance in the heat path are shown in Fig. 16. The physical components of each resistance lie between the respective temperature nodes. BASBJSJA RRRR θθθθ ++= (Eq. 3) Where: Fig. 16 - components of each resistance in the heat path RΘJunction_Slug(J_S) = RΘ of the die attach combined with die and slug material in contact with the die attach. RΘSlug_Board (S_B) = RΘ of the epoxy combined with slug and board materials in contact with the epoxy. RΘBoard_Ambient (B_A) = the combined RΘ of the surface contact or adhesive between the heat sink and the board and the heat sink into ambient air. Eq. 4, derived from Eq. 3 can be used to calculate the junction temperature of the LED device. ( )( )JAdAJunction RPTT θ+= (Eq. 4) where: TA = Ambient temperature. Pd = Power Dissipated (W) = Forward current (If ) * Forward voltage (Vf ). RΘJ_A = Thermal resistance junction to ambient. In our case: WCR oJA /45=θ (Eq. 5) Many questions and concerns exist in the measurement of LED clusters and arrays. Two groups are active in preparing recommendations for these. CIE TC2-50 has recently started to prepare a technical report for measurement of the optical properties of visible LED clusters and arrays, to give recommendations for definitions and measurement methods and conditions for various clusters and arrays of LEDs including static displays and signs. Also, within the Illuminating Engineering Society of North America (IESNA), the Testing Procedures Committee has Project 78 - Guide for Measurement of LEDs. The purpose of this project is to develop a guide for appropriate methods and equipment to measure the output of LED fixtures for lighting and signaling purposes. V - Results Measurements have been performed according to a pre- established grid and specific location as illustrated in fig. 17. These measurements, included in a campaign, yield to Fig. 17 - Architecture of measurement points 0 m 4m 8 m 20 cm 2 m 4 m 6 m 7 m 0 5 10 15 20 25 30 35 Lux Led streetlight 45W Fig. 18 - Traditional lamp on post 0 m 4m 8 m 20 cm 2 m 4 m 6 m 7 m 0 5 10 15 20 25 30 35 Lux HME lamp 125W Fig. 19 - New LED support on post results indicated in fig. 18 and fig. 19 for traditional structure and LEDs one. It is clear, the new feature produces more light, at the same distance, than traditional system, with less power engaged. Reliability evaluation is going on in order to assess minimum standards for public lighting infrastructure to be vested in Leporano town. Energetic and legal aspects according to current italian legislation are also included in the present research. SMAASIS led street light is also comparable with HPS lamp. High-pressure sodium (HPS) lamps produce light when gas contained in an arc tube (in this case, sodium) is excited into fluorescence. As can be seen from Fig. 20 , HPS lamps emit light across the visible spectrum. The majority of light generated falls between 550 nm and 650 nm, resulting in the lamp's characteristic orange cast with CRI = 25, with an efficacy equal to 67 Lumen/Watt . Fig . 20 - High-pressure sodium (HPS) lamps spectrum Fig . 21 – Led lamp spectrum The life-span of most HPS lamps between 50W and 1000W is rated at 24,000 hours. As a result, a HPS lamp can be expected to last 5,4 years.