10th International Symposium
“Topical Problems in the Field of Electrical and Power Engineering“
Pärnu, Estonia, January 10-15, 2011
A Concept of Using LED Lamps
in Conjunction with Traditional Light Sources
Irena Milashevski, Jelena Armas, Raivo Teemets
Tallinn University of Technology
renamilashevski@gmail.com, jarmas@hot.ee, raivo.teemets@ttu.ee
Abstract
As a result of gradual development, LED lighting
has been established commercially for nonpollution, long life, easiness of transport, and other
advantages. This paper proposes a concept of using
LED lamps in conjunction with traditional light
sources. Structure of the proposed lighting system
based on LEDs in conjunction with the traditional
light sources is introduced.
Keywords
LED, lighting, traditional light sources,
power supply for LED
Introduction
The artificial lighting consumes a considerable
amount of electricity generated in the world.
Together with the concern about the increase of
energy on consumption in various segments, the
development of more efficient lighting systems
becomes more important. Current market of lighting
devices is supplemented by novel light sources that
enable revolutionary improvements of lighting
options for lighting systems, and electrical
parameters of lighting systems while ensuring high
reliability and durability that is essential in energy
saving. One of these sources is the Light Emitting
Diode (LED).
Requirements imposed on electric power scheme of
lamps are stringent. The basic requirements in
creating lighting systems are: reliability of power
supply scheme, uninterrupted supply of electricity to
fixtures and the high value of a mean time between
failures of the used equipment. Requirements
described in operating standard documents, such as
limiting sizes and frequencies of voltage fluctuations
allowed for lighting networks are equally important
The frequency of voltage fluctuations in lighting
feeding line are limited depending on amplitude: no
restrictions if fluctuations is ±1,5%, less than
10 times per hour if fluctuations lies in range
between ±1,5 to ±4% and one per hour in case then
it is higher than ±4%.
Traditionally, the lighting network laid on the power
supply to the lamps is divided into two parts –
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supply and group [1]. Supply mains form a line laid
on substations to group boards and group network –
the line laid by the group panels to lighting fixtures.
There is a set of various power supply circuits of
lighting settings, and the choice of each of which is
rendered by influences of several factors. The main
ones are: the presence on a projected or existing
facility of the general or dividing transformers for
feeding of power and lighting consumers, lowvoltage circuit of the substation; types of
illumination accepted for a given object,
requirements for lighting controls, the nominal
voltage and power of a system which are accepted
for light sources. Lighting system design involves an
important requirement – the maximum value of ∆U
(equal to 5.0% Un) should not be exceeded. From the
statistics of working: in the supply network
1.5...2.0% Un, in the group network – 3.0...3.5% Un
is lost.
The introduction of LED lighting systems forces the
given concept to be reconsidered.
1. Light Emitting Diode
LEDs were proposed and described in detail in our
previous paper [2]. LED is a diode structure in
essence, so the current and voltage of the LED has
the exponential relationship, (see Fig. 1).
Fig. 1. Volt-Ampere characteristic of a LED
LEDs have become the most suitable solution for
replacement of traditional fluorescent lamps because
of their energy efficiency, the introduction of high
brightness
LEDs
with
white
light
and
monochromatic colours has led to a movement
towards general illumination. This revolutionizes the
optoelectronics market, enabling engineers to use
LEDs for general lighting applications as well as
medical, indoor lighting and automotive solutions.
So variable LED array modules were developed,
they are making great strides in terms of lumen
performance and reliability, however, the barrier to
widespread use in general illumination still remains
the cost or luminous efficiency, special requirements
concerning optical properties and optomechanical
layout have to be met.
LEDs offer many advantages over traditional
lighting sources. To point out which of the
advantages are most important depends on the
specific application, such as: very long lifetime
(50,000 hours); lower maintenance costs; efficiency
higher than that of incandescent and halogen lamps;
instant light-up; fully dimmable without colour
variation; direct emission of coloured light without
filters; complete spectrum of colours; dynamic
colour control and tuneable white point; total design
freedom with hidden light; directed light for more
efficient systems; vibration-proof lighting; no
mercury; no IR or UV radiation in visible light. The
market for LED solutions is expanding rapidly with
the significant efficiency increase of LED chips.
This revolutionizes the optoelectronics market,
enabling engineers to use LEDs for general lighting
applications as well as medical, specialty lighting
and automotive solutions, where previously less
efficient technologies had to be used [3].
Wide use of fluorescent lamps in households is well
known because of their energy saving, but they have
the serious shortcoming of mercury pollution which
restricts their applications. So LEDs have become
the most suitable candidate to replace fluorescent
lamps.
As white light LED products have become more
widely available, additional factors enter into light
source selection. The purpose of the paper is to
compare current LED products with conventional
lighting on the following basis: energy efficiency,
life, lumen depreciation, light output/distribution,
and colour quality.
2 Features of power supply system for
combined lighting system
A special LED module is commonly used for the
production of LED lamps. The LED module consists
of one or more LEDs, powered by direct current
whose value may change. Typical arrays use seriesconnected LED stacks to ensure equal current
through all devices (Fig. 2).
LEDs are current-driven devices whose brightness is
proportional to their forward current. But for normal
consumption, like for home appliances, AC power
sources are provided. LED is powered by a DC
source, and the voltage level depends upon the
number of LEDs to provide a constant current
control. Therefore, AC source should be converted
via converters to give the DC source for the LED.
Input voltage drivers are selected from some of the
standards of nominal values: 12, 24 or 48 V. For the
LED fixtures that can illuminate a room with a
ceiling height of 4 meters, and even used for outdoor
lighting, it is advisable to use a standard nominal
48 V. This nominal voltage is, in principle, quite
widespread. In addition, the power sources for
telecommunications applications with a rated output
voltage of 48 V are available and can be successfully
used in lighting systems due to their high reliability
and relatively low cost.
Fig. 2. A basic LED converter provides
constant current to series strings of LEDs
Traditionally, the power supply is with an input
voltage of 220 V AC and the LED module is located
in one casing that is dictated by the rare cases of
their application. Since lighting systems that utilize
traditional and the LED lighting sources can be
made, a selection of rated voltage level becomes an
issue and requirements for voltage fluctuations
should be considered.
Combination of power and lighting power lines used
now does not improve economic indicators and
creates an unsatisfactory mode of power supply for
lamps. The use of power lines for supplying the
lightning equipment is applicable only for small
buildings and with schemes of intermediate
transformation because of sensitivity of traditional
light sources to voltage fluctuations. Voltage drop of
1% causes a decrease in the flux from incandescent
lamp by 3...4%, from fluorescent lamps at 1.5%, for
mercury lamps at 2.2%. The voltage reduction of
10% causes a reduction of a light stream by
30...40% in luminescent lamps. At a voltage
reduction of 20% and more there is no ignition of
gas-discharge lamps. On the other hand, pressure
increase of 10% at lamps of incandescence and
luminescent lamps is reduced in terms of their
service to 25...30% [4]. Unlike traditional light
sources, LED modules do not have such problems:
the driver used in them is able to maintain the
required output parameters even when the voltage
level in power line is equal to 70% from the
nominal. In consequence, when light-emitting diode
modules are powered from the main power board it
is possible to observe necessary quality requirements
of the electric power for lighting devices with longer
group networks than earlier.
The scheme of a lighting part of an electric
equipment most frequently applied is shown in
Fig. 3 [6]. For large multipurpose complexes in
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which the structure also includes power equipment
and illumination systems multi circuit systems of
power supplies are often applied (Fig. 3).
Fig. 4. Block diagram of power supply unit (PSU)
and LED arrays
Fig. 3. Lighting part of an electric equipment
Regarding to the increase in a resource of light
sources and maintenance, qualitative illumination
fixtures have their own contour of power supplies
and get power from the guards of working
illumination. To increase of the reliability of power
supplies of fixtures a possibility of their switching
on consumption from the main guards 1 on the
power highway 4, serving in basic power, equipment
is provided. With large sizes of buildings it is
favorable to apply bus-duct 5 with a joint supply for
them both: a light-emitting diode and traditional
light sources.
3 Power supply for LED lighting
Unlike a conventional power or signal diode, ultrabright, high-power LEDs cannot be subjected to
reverse voltage. If exposed to such a condition, then
failure is certain. Also for long life, high peak
currents should be avoided. Hence, the simple option
of connecting anti-parallel LED strings to the mains
through current limiting impedances is not advisable
if long life is demanded. An array of LEDs must be
supplied from the mains via an AC/DC converter,
which protects them from reverse voltage and surges
whilst regulating output current.
For all electronic equipment connected to the mains
operating at levels of 50 W upwards there is a
concern about harmonic pollution introduced into
the mains supply. Recent legislation and updated
international standards [6] stringently enforce the
harmonic current limits that can be drawn by the offline equipment, so as to reduce supply voltage
distortion. With regard to the fundamental current,
since street lighting authorities pay a tariff for low
power factor, it is advisable also to provide power
factor correction. There are a number of techniques
that can be used to achieve both high power factor
and low harmonic pollution; the two main
approaches broadly fall into two categories, passive
and active.
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A detailed literature review revealed that in order to
achieve high power factor and low harmonic
distortion, whilst maintaining good reliability and
low cost, an active Power Factor Correction (PFC),
converter operating in the discontinuous current
mode could be implemented [7]. Further, electrolytic
capacitors should be avoided within the luminary, as
they will dry out at the high temperatures to be
found there. However, eliminating electrolytic
capacitors will have a severe impact upon the
operation of the PFC converter, since in order to
avoid 100 Hz stroboscopic effects, an energy store is
required from which the LEDs will be supplied
twice per cycle as mains voltage goes through zero.
Thus a non-electrolytic capacitor is required which
can operate at the elevated temperatures within the
luminary and, being inevitably lower in value than
an electrolytic capacitor, this capacitor must store
energy at a high voltage. This requirement instantly
narrows the PFC converter options to those that can
boost the output voltage.
A block diagram of the proposed luminaire PSU is
shown in Figure 4. It comprises a buck-boost PFC
input stage. Its output is fed to LED arrays via
individual current regulator circuits, which are buck
dc/dc converters. These buck converters regulate the
current through the LED arrays, enabling independent
operation modes.
4 Comparison of various light sources
Energy consumption and lightning parameters are
compared for the scheme presented on Fig. 3 for
different types of used luminary. At traditional
illumination by incandescence lamps a capacity of
3.9 kW is required. In case of compact luminescent
lamps with the power of 36 W the 1.40 kW power is
required, but replacing incandescence lamps with
LED lamps with the power of 20 W with
corresponding lighting characteristics, the power
decreases to 0.80 kW that is near 20% of first case
and only 46% of power required for luminescent
luminaries if losses in networks are not taken into
account [8].
Preliminary data for comparison technical and
economical indicators for incandescence lamps,
luminescent lamps and LEDs are presented in
Table I. Estimated data for LED were based on
XLight LED luminaire.
Table 1. Preliminary data for comparison of different types of luminary
Power consumption
Measures Luminescent LED
W
36
20
Luminous flux
Real power consumption
Incandescent
2x100
Lm
W
2400
48
2000
22
2000
200
%
years
70
100
6
100
Installation cost per unit
Fixture unit cost with capital expenses
$
$
18
120
18
180
18
310
Replacement of one fixture unit cost
Number of hours in operation per year
$
hours
10
15000
10
50000
10
1000
Price of electricity
$/kWh
0.065
0.065
0.065
Operating efficiency of a luminous flux
Term of an estimation of investments (Tc)
The results of saving by replacing luminescent
lamps and incandescence lamps with LED (for one
fixture) are presented in Table 2. It is shown that
payback from replacing luminescent lamps for
LEDs will be reached on the second year, by
replacing incandescence lamps it will take less than
4 months.
Table 2. The savings by replacing luminescent and incandescence lamps with LED
Measures Luminescent Incandescent
Electricity cost savings from Tc for one LED
Estimated savings by the end of Tc for one LED
as compared with lighting source
Conclusions
In this paper a concept of using LED lamps in
conjunction with the traditional light sources was
presented. The structure of the proposed lighting
system based on LEDs in conjunction with the
traditional light sources was introduced. Advantages
and drawbacks of this solution were described.
The LEDs technology, considered a promising
alternative to the illumination systems, has been
significantly improved in the last few years. The
main advantages of using LEDs are: high average
life; high luminous efficiency; and simple drives,
when control and dimming systems are required.
Acknowledgement
This paper was supported by the Project DAR8130
“Doctoral School of Energy and Geotechnology II”.
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