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Led-based Public Lighting System Reliability for a Reduced Impact on Environment and Energy Consumption

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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.
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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
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 2
d
A
= 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 0
I 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
(
)
(
)
θ
θ
cos
0
II
=
, where 0
I 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:
=1exp
0kT
eV
ii
β
(Eq. 1)
where i is the current through the diode, 0
i is the reverse
saturation current, e is the charge of electron, V is the
voltage across the diode, k is the Boltzmann constant,
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
θ
θ
θ
θ
++= (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 o
JA /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
20cm
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
20cm
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. This makes HPS lamps the
longest lasting of any of the common types of lamps. This,
combined with its high efficacy and low cost, has led to
HPS lamps becoming the most popular type of exterior
luminaire in use today.
CRI (Color Rendering Index) for White Led types is 70 and
its life-span is rated at 60,000 hours, Led lamp can be
expected to last 12 years.
VI - Conclusions
New features of LEDs-based post for public lighting are
described in the present research that include automatic
system for controlling car traffic versus energy
consumption. Preliminary results got from current
campaign permit to be sure in reaching the pre-indicated
objectives. For general lighting applications, 70% lumen
maintenance, which corresponds to a 30% reduction from
the initial light output of a lighting system, is close to the
threshold for detecting gradual reductions to 70% of initial
light output are considered acceptable by the majority of
occupants within a space. Thus, this level is unlikely to be
problematic for a wide array of lighting applications.
Indeed, lumen maintenance values greater than 70% are
archieved by most successful general light sources
throughout their operating life.
Led streetlight lamp advantages versus traditional lamp:
Reduce utility costs
Meet public desire for or against street lighting
Replace old, dilapidated streetlights
Meet security requirements
Meet traffic and pedestrian safety requirements
Minimize glare
Increase nighttime visibility for motorists and
pedestrians
Limit light trespass
Reduce light pollution
Support and spur economic development
Improve aesthetics
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