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ISSN 1843-6188
Scientific Bulletin of the Electrical Engineering Faculty – Year 10 No. 2 (13)
WORKING MODELING OF FLUORESCENT
LAMPS USING VIRTUAL INSTRUMENTATION
Anca MIRON, Andrei CZIKER, Mircea CHINDRIŞ
Technical University of Cluj-Napoca, 15th C. Daicoviciu Street, 400020, Cluj-Napoca, Romania
E-mail: [email protected]
intensity of the radiation can be concentrated on a few
spectral lines at the characteristic frequencies determined
by the distribution of permitted energy levels of the
particular atoms, thereby making exceptionally efficient
light sources. Of all the gas discharge lamps, fluorescent
lamp is one of the most efficient and widely used [1].
Lighting currently consumes approximately 10–15% of
the global energy requirement [2]. Given the increasing
concerns about energy saving, an urgent need to improve
the efficiency of lighting systems proves to be of
significant importance.
For general lighting, fluorescent lamps are known for
decades to be an efficient light source mainly used for
home and office lighting. Today approximately 1.2 billion
units of these lamps are manufactured worldwide each
year [2]. A fluorescent lamp is essentially a low-pressure
mercury-argon discharge held in a cylindrical tube with
phosphor coating that converts the ultraviolet radiation
produced into visible light. Its relative merits compared to
incandescent lamps include energy saving and longer life.
During recent years, fluorescent lamps operating at high
frequency have emerged as energy-efficient alternatives
to replace the conventional 50/60-Hz systems and also
the incandescent lamps in the form of compact
fluorescent lamps (CFL). Advantages of driving
fluorescent lamps at high frequency include increased
light output, elimination of flicker and audible noise,
lower ballast power consumption and extended lamp life.
Fluorescent lamps and other types of arc discharging
lamps are studied in the framework of the Electrical
Energy Usage application classes (laboratories). Taking
in consideration the need to study fluorescent lamps, the
development of computer science, and particularly the
appearance of special programming software (as virtual
instrumentation), the authors have developed several
virtual instruments for the study of fluorescent lamps
working, that help the students to understand better these
electrical energy consumers.
The paper presents a synthesis regarding the fluorescent
lamps, their working and a virtual instrumentation
application for the simulation of fluorescent lamps
functioning.
The last section of the paper contains several conclusions
that underline the advantages of fluorescent lamps and
virtual instrumentation usage in education and for
educational software.
Abstract: In the latest years, the usage of fluorescent lamps
has grown especially due to the fact that they have a higher
luminous efficacy, longer life, lower heat, etc. In the
framework of the Electrical Energy Usage course, there is
studied the working of fluorescent lamps at different supply
voltages, using different ballasts and configurations. From
this point of view, and considering the development of
computer science and especially the virtual instrumentation,
the authors have developed several instruments dedicated for
the study of fluorescent lamps functioning. Thus in the paper
are described general aspects about the fluorescent lamps,
their working principles, electric parameters, and the virtual
instruments developed. In the end, are underlined the
advantages brought by the virtual instrumentation in the
education field of power systems learning principles and
physical phenomenon.
Keywords: fluorescent lamps, virtual instrumentation,
education, power quality, arc discharging
1. INTRODUCTION
Lighting is one of the most important achievements in
the industrialized history. Light is a kind of
electromagnetic radiation which stimulates the eyes and
enables seeing. Today most man-made light is generated
from electricity through an apparatus named as lamp.
There are mainly two types of lamps: incandescent
filament lamps and gas discharge lamps [1].
The incandescent lamp has a tungsten filament which
emits light when the electric energy flows through. The
spectrum of energy radiated from an incandescent lamp is
continuous. Unfortunately the major part of the energy is
radiated in the infrared region and is converted into heat.
Only a relatively small quantity of energy is emitted at
various visible lengths as light. Thus the efficiency of an
incandescent lamp is low although it may be more
convenient to use than gas discharge lamps.
All electric gas discharge lamps convert electrical energy
into light by transforming electricity into kinetic energy of
moving electrons, which in turn is converted into radiation
as a result of some kind of collision process. The primary
process is collision excitation of mercury atoms in a gas to
high-energy states from which they relax back to the
lowest-energy atomic levels by means of the emission of
electromagnetic radiation. The unique advantage of the
atomic radiation from a gas discharge is that by a suitable
choice of the atoms of which the gas is composed,
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Scientific Bulletin of the Electrical Engineering Faculty – Year 10 No. 2 (13)
ISSN 1843-6188
different types of oxides (Zn, Ca, Ba, etc.) in order to
raise the thermo-emission proprieties.
Fluorescent lamps require ballast and a starter to
stabilize the current through the lamp and to provide the
initial striking voltage required to start the arc discharge.
This increases the cost of fluorescent light fixtures,
although in many practical situations only one ballast is
shared between two or more lamps. In figure 2 is
illustrated the electric scheme of the connection circuit to
the supply grid of a fluorescent lamp.
2. FLUORESCENT LAMPS
The fluorescent lamps belong to the category of lowpressure mercury-vapour discharge lamps.
A fluorescent lamp or fluorescent tube is a gas-discharge
lamp that uses electricity to excite mercury vapour. The
excited mercury atoms produce short-wave ultraviolet
light that then causes a phosphor to fluoresce, producing
visible light. A fluorescent lamp converts electrical
power into useful light more efficiently than an
incandescent lamp.
In the next sub-sections are described the component
elements and the working principle of fluorescent lamps.
2.1 Constructive aspects
A fluorescent lamp is composed primarily of the
following elements (figure 1):
1. Discharging tube
2. Two electrodes
3. Electric connections
4. Two or four contact pins
Figure 2. The connection circuit to the supply grid of a
fluorescent lamp: 1 – fluorescent lamp; 2 – starter; 3 – ballast
2.2 Working principle
The fundamental means for conversion of electrical
energy into radiant energy in a fluorescent lamp relies on
inelastic scattering of electrons. An incident electron
collides with an atom in the gas. If the free electron has
enough kinetic energy, it transfers energy to the atom's
outer electron, causing that electron temporarily to jump
up to a higher energy level. The collision is 'inelastic'
because a loss of energy occurs. This higher energy state
is unstable, and the atom will emit an ultraviolet photon
as the atom's electron reverts to a lower, more stable,
energy level. Most of the photons that are released from
the mercury atoms have wavelengths in the ultraviolet
(UV) region. Ultraviolet photons are absorbed by
electrons in the atoms of the lamp's interior fluorescent
coating, causing a similar energy jump, then drop, with
emission of a further photon.
The basic processes inside the discharge tube are the
following [4]:
1. Heat generation. When the kinetic energy of the
electron is low, an elastic collision takes place and
only a small part of the electron energy is transferred
to the gas atom. The result of this type of collision is
an increase in the gas temperature. In this case, the
electrical energy is consumed to produce heat
dissipation. However, this is also an important process
because the discharge has to set in its optimum
operating temperature.
2. Gas atom excitation. Some electrons can have a high
kinetic energy so that the energy transferred in the
collision is used to send an electron of the gas atom to a
higher orbit. This situation is unstable and the electron
trends to recover its original level, then emitting the
absorbed energy in the form of electromagnetic
radiation. This radiation is used to directly generate
Figure 1. Fluorescent lamp constructive elements [3]
The discharging tube is made of transparent or
translucent material (glass, quartz); its roles are to isolate
the inside low-pressure atmosphere from the outside
environment, and to convert the ultraviolet light to
visible light. This last property is due to the fact that the
inner surface of the tube is coated with a fluorescent (and
often slightly phosphorescent) coating made of varying
blends of metallic and rare-earth phosphor salts. The
discharge tube is filled with a gas containing low
pressure mercury vapour and argon, xenon, neon, or
krypton. In the lamp, the optimum mercury vapour
pressure (which gives the maximum luminous efficacy)
is 0.8 Pa that is around 0.3% of the atmospheric
pressure. For the tube diameters normally used, this
pressure is reached at a wall temperature of about 40 °C,
not much higher than typical ambient temperature.
The arc discharge is maintained between the two
electrodes made of tungsten wolfram filaments that are
sustained by nickel wires. On the filaments are put
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ISSN 1843-6188
visible light. In other cases, ultraviolet radiation is first
generated and then transformed into visible radiation by
means of a phosphor coating on the inside wall of the
discharge tube.
3. Gas atom ionization. In some cases, electrons have
gained such a high kinetic energy that during a
collision with a gas atom an electron belonging to the
gas atom is freed, resulting in a positively charged ion
and a free electron. This freed electron can play the
same roles as those generated by the electrodes. This
process is especially important during both discharge
ignition and normal operation, because ionized atoms
and electrons are necessary to maintain the electric
current through the lamp.
1. The lamp is axially homogenous.
2. Only the positive column has been considered, the
electrode regions have been ignored.
3. The displacement of species through cataphoresis has
not been considered as this happens over a much
longer period of time than a 50-Hz cycle.
4. The lamp is already ignited, the model does not correctly
predict the breakdown stage, and however, it is capable of
predicting transient events once the lamp is lit.
5. The ions do not play a significant role in the discharge as
charge carriers, being much heavier than the electrons.
6. Volume recombination is negligible.
Various models exist that describe the resistance of a
fluorescent lamp [6].
The cubic model is given as,
2.3 Fluorescent lamps modelling
The low frequency of the mains is not the most adequate
power source for supplying fluorescent lamps. At these
low frequencies, electrons and ionized atoms have
enough time to recombine at each current reversal. For
this reason, the discharge must be reignited twice within
each line period. Figure 3 illustrates the current and
voltage waveforms, and figure 4 represents the I–V
characteristic of a TL-D 36W/54-765 lamp operated with
inductive ballast at 50 Hz.
200
1
100
0.5
u( t )
0
0.01
0.02
0.03
0.04
0.05
0.06
 100
 0.5
 200
1
u=A·i + B·i3
This is closer to the real model but more complicated to
use. An approximation is needed which is both simple
and accurate.
Parabolic function to model the non-linear lamp
resistance yields,
u=k·i2
R=K1/Irms + K2·Irms + K3
i( t )
3. VIRTUAL INSTRUMENTS
1
The virtual instruments were created using the graphic
programming environment LabVIEW. A virtual
instrument (vi) is composed of two parts: frontal panel
and block diagram.
The virtual instruments were firstly developed to help
Electrical Energy Use students to understand the working
of fluorescent lamps, but they can be used also in other
purposes, or they can further be completed in order to help
other future activities. Regarding the vi importance, they
don’t eliminate the realization of the physical circuit, but
the vi represent a supplementary help in the educational
process. They can be used to create more complicated
circuits and to make several experimental circuits, too.
There have been developed four vi dedicated to achieve
the previous presented purposes. Further on are described
the frontal panels and the block diagrams of the software
tools. In the next sub-sections, the roles of each vi and the
steps that users have to make in order to obtained the right
results are also underlined. The main advantage of the vi
is that the users don’t need to have programming skills,
only the basic PC operating knowledge.
0.5
0
 0.5
 100
0
100
(3)
where: K1, K2, K3 are constants of the lamp.
“The parabolic model allows for closed-form solutions
of non-linear differential equations describing different
fluorescent lamp output stages. A typical output stage
consists of a L in series with the lamp (figure 3)” [7].
t
1
 200
(2)
The parabola is a good fit for higher current regions of
the I-V curve, where most of the power is consumed by
the lamp. The parabolic model is comparable to the
cubic and easy to use.
Second order polynomial model I
Figure 3. Voltage and current waveforms of a TL-D
36W/54-765 fluorescent lamp
i( t )
(1)
200
u( t )
Figure 4. I–V characteristics of a TL-D 36W/54-765 lamp
The following models concentrate on the physical
processes that determine the electrical conductivity of
the lamp. In determining the lamps conductivity, there
are two important parameters: the number of electrons
available to carry current in the plasma and the mobility
of those electrons. The latter plays an important role in
determining the lamp’s nonlinear high-frequency
behaviour. As for any fluorescent lamp model, it is
necessary to make assumptions about the way in which
the lamp behaves. This model makes the following
assumptions about the lamp’s behaviour [5].
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It can be observed that the user can decide what to see,
the current or the voltage waveform. Figure 6 presents
the circuit current waveform, while in figure 7 is
illustrated the supply voltage waveform.
3.1 Frontal panel
The frontal panel is the interface between the user and
the PC (graphic user interface – GUI). Figure 5
illustrates the GUI of the vi representing the first
“window” that students come in contact with. In the
figure, the electric single-phase scheme of a classic
connection circuit of a fluorescent lamp is presented. It
can be seen that an inductive ballast is used.
Figure 7. The frontal panel of the electric source vi
The supply voltage is variable; its amplitude can vary
between 170 and 250 V. The inferior limit was chosen
because the starter begins to function at 180 V and on
the other hand the supply voltage is not recommended to
exceed ±10% from the nominal voltage (in the case that
the phase-to-phase voltage is 230 V).
After the student has chosen the supply voltage and the
number of signal periods (a signal period is of 20 ms), he
can visualize the voltage drops on the lamp or ballast, by
clicking on the corresponding circuit element. In figures
8 – 12 the display windows for the fluorescent lamp and
the ballast are illustrated.
Figures 8 – 10 display the voltage waveforms between
the fluorescent lamp terminals. In order to underline the
lamp functioning at different supply voltages, figure 8
presents the lamp voltage for a 190 V, figure 9 for a 230
V, while figure 10 for a 245 V supply voltage.
Figure 5. Frontal panel of the main virtual instrument
So, the first step is to create the electric scheme of the
circuit whose function the user wants to simulate. This
activity is very simple: after the software is brought to
the running state, by clicking on the drawing space,
appears a library with circuit electric elements from
which user can choose the right elements (in the picture
there were chosen a supply source, a fluorescent lamp
with starter, an inductive ballast and the appropriate
connecting conductors). After this stage is completed
(the electric circuit is the right one and contains all
appropriate component elements), the user must click the
“Drawing” button in order to go to the next stage. This
action is understood by the vi as the end of the first
stage, the drawing stage, consequently the electric
scheme cannot be changed. In the next stage, the
students are able to introduce/change different
parameters of the scheme or to visualize the voltage and
currents characteristics in diverse points of the circuit.
So in order to see the electric source characteristics, the
user has to click the source symbol from the scheme. In
figure 6 is presented the window (frontal panel virtual
instrument) that contains the electric source
characteristics, and also different parameters:
 Supply voltage.
 Power factor.
 Number of periods.
 Current and voltage waveforms.
Figure 8. The vi frontal panel that shows the voltage drop
on the lamp at a supply voltage of 190 V
Figure 6. The frontal panel of the electric source vi
Figure 9. The vi frontal panel that shows the voltage drop
on the lamp at a supply voltage of 230 V
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Scientific Bulletin of the Electrical Engineering Faculty – Year 10 No. 2 (13)
Figure 13. Main virtual instrument block diagram
Figure 10. The vi frontal panel that shows the voltage drop on
the lamp at a supply voltage of 245 V for two periods of time
The current though the circuit for a supply voltage of 190 V
on one period can be observed in figure 11, while in figure
12 is displayed the voltage waveform on the terminals of
the inductive ballast at the same supply voltage.
Figure 14. Supply source virtual instrument block diagram
Figure 11. The vi frontal panel that displays the current ballast
Figure 15. The hierarchy tree of the virtual instruments
Figure 12. The vi frontal panel that displays the voltage on
the ballast terminals
4. CONCLUSIONS
All electric gas discharge lamps (including fluorescent
lamps) convert electrical energy into light by
transforming electricity into kinetic energy of moving
electrons, which in turn is converted into radiation as a
result of some kind of collision process. Use of
fluorescent lamps brings the following advantages:
 They last longer. On average, a fluorescent tube has a
lifespan six times longer than a regular incandescent bulb.
They tend to burn less after continuous use, and can be
turn on and off without being afraid of burning them.
 Fluorescent lighting is 66 percent cheaper than regular
lighting while providing the same brightness. When it
is considered that a quarter of any home's electrical
consumption is done through light bulbs, the savings
can add up considerably.
 Fluorescent lamps do not give off heat, which makes
them great for area lightning and for areas where
additional heat can cause equipment to malfunction or
bother the users.
3.2 Block diagram
The block diagram represents the part of the virtual
instrument that is not accessible to the user; it is the vi
component that contains the source code. In order to
build the block diagram graphic elements that are
specific for the G graphical programming language are
used. The block diagrams of two vi are presented in
figures 13 and 14; in figure 15 is illustrated the hierarchy
tree of the developed virtual instruments.
The block diagram from figure 13 illustrates the
programming connections of the main virtual instrument,
whose frontal panel is illustrated in figure 5. Figure 14
presents the block diagram that is in the back of the
virtual instrument whose GUI is illustrated in figures 6
and 7. The connections between the virtual instruments
and their subordinated relationships are presented in
figure 15 through the hierarchy tree.
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Virtual instrumentation represents a real revolution in
the field of experimental research. Mainly the
applications of virtual instrumentation (virtual
instruments) simulate the functions of real laboratory
apparatus. Virtual instruments are characterized by their
versatility and low cost, so they are very suitable for
educational applications. Nevertheless, the operation rate
of these instruments is limited by the general-purpose
orientation of the hardware.
The virtual instruments presented in the paper are used
to simulate the working state of fluorescent lamps at
different supply voltage values, with several kinds of
ballasts and in diverse configurations.
The advantages of using virtual instrumentation in
education and in particular, for the simulation of
fluorescent lamps are:
 The ability to see inside the instrument and to
understand how it works.
 Data is already available within the PC.
 Possibility of testing new “ideas” before the actual
construction.
 It is easy for use as: oscilloscope, variable supply,
digital multi-meter, prototype board.
 It is a truthful support for the real simulations made
during the application classes, offering the students a
better understanding of the physical phenomenon.
ISSN 1843-6188
5. REFERENCES
[1] http://en.wikipedia.org/wiki/Fluorescent_lamp
[2] E.E. Deng, Negative incremental impedance of
fluorescent lamps, Simple high power factor lamp
ballasts, PhD. Thesis, California Institute of Technology,
Panadena, California, 1996.
[3] Loo Ka Hong, et al. A dynamic conductance model
of fluorescent lamp for electronic ballast design
simulation, IEEE Transactions on Power Electronics,
Vol. 20, No. 5, September 2005, pp 1178 – 1185.
[4] http://arch1design.com/blog/wp-content/uploads
/2009/08/fluorescent-lamp-1.gif
[5] Muhammad H. Rashid. Power electronics
handbook, Academic Press, 2001.
[6] Holloway, Arran J., et al. Physically based
fluorescent lamp model for a spice or a Simulink
environment, IEEE Transactions on Power Electronics,
Vol. 24, No. 9, September 2009, pp 2101-2110.
[7] Thomas J. Ribarich and John J. Ribarich, A New
High-Frequency Fluorescent Lamp Model, IEEE Industry
Applications Society Annual Meeting, St. Louis,
Missouri, October 12-16, 1998, pp 6.
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