Basic Electrical Engineering

1. Maharashtra Institute of Technology,
Aurangabad
LABORATORY MANUAL
Practical Experiment Instruction Sheet
EXPERIMENT TITLE : Study of Fluorescent Tube light.
EXPERIMENT NO.3 : MIT(T)/ETC/Basic Electrical Engineering /Manual No.1
FY(All) DEPARTMENT: Electronics & Telecommunication Engineering
LABORATORY : Basic Electrical Engineering Location Part I Page 21
Aim: Study of Fluorescent Tube light.
Theory :
A fluorescent lamp or a fluorescent tube is a low pressure mercury-vapour gas-discharge lamp that
uses fluorescence to produce visible light. An electric current in the gas excites mercury vapour which
produces short-wave ultraviolet light that then causes a phosphor coating on the inside of the bulb to
glow. A fluorescent lamp converts electrical energy into useful light much more efficiently than
incandescent lamps. The luminous efficacy of a fluorescent light bulb can exceed 100 lumens per watt,
several times the efficacy of an incandescent bulb with comparable light output.
Construction
A fluorescent lamp basically consists of a long glass gas discharge tube. Its inner surface is coated with
phosphorous and is filled with an inert gas, generally argon, with a trace of mercury. The tube is then
finally sealed at low pressure with two filament electrodes each at its both ends. These electrode
filaments are used to preheat the tube and initiate a rapid conduction of electrons between the two end
electrodes. The process initially requires a relatively high amount of power. The energy also converts
some of the mercury from a liquid to a gas. Electrons then collide with the gaseous mercury atoms,
increasing the amount of energy. As electrons return to their original energy level, they begin to release
light. However, the light they emit is ultraviolet, and not visible to the naked eye, so another step needs
to take place before we can see the light. So the tube is coated with phosphorous. Phosphors will give
off light when exposed to light. When exposed to the ultraviolet light, the particles emit a white light
which we can see. Once the conduction of electrons between the electrodes is complete, no more
heating of the filaments is required and whole system works at a much lower current.
Prepared By: Mr. S.S. Chate Approved By: Dr. G.S. Sable

2. Maharashtra Institute of Technology,
Aurangabad
LABORATORY MANUAL
Practical Experiment Instruction Sheet
EXPERIMENT TITLE : Study of Fluorescent Tube light.
EXPERIMENT NO.3 : MIT(T)/ETC/Basic Electrical Engineering /Manual No.1
FY(All) DEPARTMENT: Electronics & Telecommunication Engineering
LABORATORY : Basic Electrical Engineering Location Part I Page 22
Construction of tube light
Principle of Operation
The fundamental means for conversion of electrical energy into radiant energy in a fluorescent lamp
relies on inelastic scattering of electrons when an incident electron collides with an atom in the gas. If
the (incident) free electron has enough kinetic energy, it transfers energy to the atom's outer electron,
causing that electron to temporarily jump up to a higher energy level. The collision is 'inelastic'
because a loss of kinetic 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 not
visible to the human eye, so they must be converted into visible light. This is done by making use of
fluorescence. 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.
Prepared By: Mr. S.S. Chate Approved By: Dr. G.S. Sable

3. Maharashtra Institute of Technology,
Aurangabad
LABORATORY MANUAL
Practical Experiment Instruction Sheet
EXPERIMENT TITLE : Study of Fluorescent Tube light.
EXPERIMENT NO.3 : MIT(T)/ETC/Basic Electrical Engineering /Manual No.1
FY(All) DEPARTMENT: Electronics & Telecommunication Engineering
LABORATORY : Basic Electrical Engineering Location Part I Page 23
The photon that is emitted from this second interaction has a lower energy than the one that caused it.
The chemicals that make up the phosphor are chosen so that these emitted photons are at wavelengths
visible to the human eye. The difference in energy between the absorbed ultra-violet photon and the
emitted visible light photon goes toward heating up the phosphor coating.
When the light is turned on, the electric power heats up the cathode enough for it to emit
electrons (thermionic emission). These electrons collide with and ionize noble gas atoms inside the
bulb surrounding the filament to form a plasma by the process of impact ionization. As a result of
avalanche ionization, the conductivity of the ionized gas rapidly rises, allowing higher currents to flow
through the fluorescent lamp. The fill gas helps determine the operating electrical characteristics of
the lamp, but does not give off light itself. The fill gas effectively increases the distance that electrons
travel through the tube, which allows an electron a greater chance of interacting with a mercury atom.
Argon atoms, excited to a metastable state by impact of an electron, can impart this energy to a neutral
mercury atom and ionize it, described as the Penning effect. This has the benefit of lowering the
breakdown and operating voltage of the fluorescent lamp, compared to other possible fill gases such
as krypton.
Wiring the tube light
Tube light fixture consists of a large heavy square "choke” or “ballast” and a small cylindrical
“starter.”
Prepared By: Mr. S.S. Chate Approved By: Dr. G.S. Sable

4. Maharashtra Institute of Technology,
Aurangabad
LABORATORY MANUAL
Practical Experiment Instruction Sheet
EXPERIMENT TITLE : Study of Fluorescent Tube light.
EXPERIMENT NO.3 : MIT(T)/ETC/Basic Electrical Engineering /Manual No.1
FY(All) DEPARTMENT: Electronics & Telecommunication Engineering
LABORATORY : Basic Electrical Engineering Location Part I Page 24
Wiring the tube light
• The choke is in fact a large inductor. It consists of a long copper winding over iron lamination.
• An inductor by nature always has a tendency to throw back the stored current in it, every time
the power through it is switched OFF. This principle of the choke is exploited in lighting a
fluorescent tube light.
• When an AC voltage is applied to a tube light fixture, the voltage passes through the choke, the
starter, and the filaments of the tube.
• The filaments light up and instantly warm up the tube. The starter is made up of a discharge
bulb with two electrodes next to it. When electricity passes through it an electrical arc is
created between the two electrodes. This creates light, however the heat from the bulb causes
one of the electrodes (a bimetallic strip) to bend, making contact with the other electrode.
Prepared By: Mr. S.S. Chate Approved By: Dr. G.S. Sable

5. Maharashtra Institute of Technology,
Aurangabad
LABORATORY MANUAL
Practical Experiment Instruction Sheet
EXPERIMENT TITLE : Study of Fluorescent Tube light.
EXPERIMENT NO.3 : MIT(T)/ETC/Basic Electrical Engineering /Manual No.1
FY(All) DEPARTMENT: Electronics & Telecommunication Engineering
LABORATORY : Basic Electrical Engineering Location Part I Page 25
• This stops the charged particles from creating the electrical arc that created light. However,
now that the heat from the light is gone, the bimetallic strip cools and bends away from the
electrode, opening the circuit again.
• At this point, the ballast or choke "kick's back" it’s stored current, which again passes through
the filaments and ignites the tube light once again.
• If the tube does not sufficiently charge up, subsequent kicks are delivered by the choke due to
rapid switching of the starter, so that finally the tube strikes.
• After this the choke only acts like a low impedance current limiter to the tube as long as the
light is kept illuminated.
A common problem associated with these types of fixtures is humming or buzzing. The reason for this
lies in the loosely fitted choke on to the fixture which vibrates in accordance with the 50 or 60 hertz
frequency of our AC mains and creates a humming sort of noise. Tightening the choke's screws may
instantly eliminate the problem.
The working principle of today’s modern electronic ballasts is to avoid the use of starters for the
preheating purpose. They are also very light in weight. These inhibit the initial flickering of the tube
light as normally seen in the ordinary tube fixtures by changing the frequency of the mains power to a
much higher 20,000 hertz or more. Moreover, electronic ballasts are very energy efficient.
Conclusion: Write your own conclusion.
Prepared By: Mr. S.S. Chate Approved By: Dr. G.S. Sable