Table Of ContentFLUORESCENT LAMPS
Philips Technical library
FLUORESCENT LAMPS
Edited by W. Elenbaas
MACMillAN
English edition © N.V. Philips' Gloeilampenfabrieken, Eindhoven, 1971
Softcover reprint of the hardcover 2nd edition 1971
First edition 1959
Reprinted 1962
Second edition 1971
All rights reserved. No part oft his publication may be reproduced or transmitted,
in any form or by any means, without permission.
SBN 333 054172
ISBN 978-1-349-00363-1 ISBN 978-1-349-00361-7 (eBook)
DOI 10.1007/978-1-349-00361-7
First published in English by
THE MACMILLAN PRESS LTD
London and Basingstoke
Associated companies in New York, Toronto, Melbourne
Dublin, Johannesburg and Madras
PHILIPS
Trademarks of N.V. Philips' Gloeilampenfabrieken
Preface
The 1962 edition of 'Fluorescent lamps and lighting' has here been brought
up to date. Since the extent of the subject has again increased, it was decided
not to deal with applications in this book.
The authors of the first nine chapters of the 1962 book have been joined
by Messrs. Moerkens and Vrenken. The sequence of the chapters has been
ch~nged somewhat.
We start with a chapter on 'gaseous discharges' and one on 'the discharge
of the fluorescent lamp'. Then follows 'luminescence' and 'luminescent sub
stances' after which a chapter 'lamp design and lamp manufacture' is in
serted. A chapter on 'colour and colour rendering' treats this subject, which
is so closely connected with the phosphors that we like to treat it here. The
'stabilisation' and the 'lamp types and circuits' are treated in the two next
chapters, after which chapters on 'invertors and convertors', on 'dimmers'
and on 'balast design' follow. The book is concluded with a chapter on
'installations' in which regulations, radio interference, heat problems, etc.
are treated. Electronics have become very important in the circuits used and
have therefore been given ample attention in this book.
The sections marked at the beginning and end with a dagger (t) are in
tended for those readers who are interested in a more detailed discussion.
If desired, however, these sections can be passed over without disturbing
the continuity of the remainder of the text.
W. ELENBAAS
Table of Contents
Preface
1 Gaseous discharges W. Elenbaas 1
Introduction - Electron emissiOn - Structure of the atom and
mechanism of radiation and ionisation in gaseous discharges - Elastic
and inelastic collisions - The potential gradient of the discharge -
The current-voltage characteristic - Stabilisation - Ignition
2 The discharge of the fluorescent lamp W. Elenbaas 19
Why the low pressure mercury vapour discharge? - Lamp dimen
sions-How much light can be expected from a fluorescent lamp? -
The energy balance of the fluorescent lamp - The efficiency as a
function of different parameters
3 Luminescence, fluorescence and phosphorescence
J. L. Ouweltjes 32
Incandescence and luminescence - Some practical aspects of the
luminescence of solids - The emission and absorption spectra of
solid substances - Some further considerations of the electron tran
sitions involved in luminescence
4 Luminescent substances J. L. Ouweltjes 41
Chemical composition of phosphors-Requirements for the practical
application of phosphors - Physical properties of phosphors - Pre
paration of phosphors
5 Lamp design and lamp manufacture L. E. Vrenken 52
Essential parts- Bulbs- Electrodes- Mercury and rare gas- Caps
- Lamp making - Coating the tube wall with a phosphor -Processing
in the lehr - Processing on the exhaust machine - Activation of the
electrodes
6 Colour and colour rendering
A. A. Kruithof, J. L. Ouweltjes 71
Blending of fluorescent materials - The fundamentals of colour
vision - Construction of the chromaticity diagram - Computing
colour points - Application of chromatics in the development of
fluorescent lamps - Choice of colours for general lighting fluorescent
lamps - Colour tolerances - Colour rendering-The specification of
the colour rendering properties - The shortcomings of the 'standard'
lamps - Data for some of the Philips de Luxe lamps
7 Stabilisation of the discharge Th. Hehenkamp104
Introduction - Direct-current supply - A.C. operation - Conse
quences of current distortion - Measurement of ballasts
8 Lamp types and circuits J. Funke, J. C. Moerkens120
Introduction - Starter switches - Lamp types for switch start opera
tion - Starter circuits - Lamp types for starterless circuits - Circuits
for preheat starterless lamps - Instant start circuits (cold starting) -
Lamp operation at higher frequencies -D.C. circuits and lamps -
Lamp types for special purposes
9 Inverters and converters Th. Hehenkamp181
Introduction - Principle of the transistor inverter - Inverter with
reduced switching losses - Cooling of the transistor - Applications
of transistor inverters - The thyristor as a switch - Inverter with
forced commutation - Self-commutating inverters - Applications of
thyristor inverters and converters
10 Dimming of fluorescent lamps J. C. Moerkens198
Introduction - The principle of dimming fluorescent lamps -
Influence of fluctuations in mains voltage - Control circuit with
stabilising effect - Symmetry of the lamp current - Controlling high
powers (central control unit) - Outdoor lighting (influence of the
temperature) - Automatic control - Auxiliary equipment - Dimmer
for low powers - Dimmer ballasts
11 Ballast Design Th. Hehenkamplll
Introduction - Iron circuits - Different types of core constructions
- Choke dimensions in relation to losses and insulation temperature
- Copper space factor - Relation between insulation temperature and
life - Cooling of the ballast - Ballasts of small cross-section - Con
struction of capacitors- Capacitor life- Ballast noise- Noise mea
surement
121nstallations J. Funke, J. C. Moerkens245
Temperature problems with ballasts - Radio interference- Higher
harmonics in the mains current - Lamp performance at low tem
perature - Dealing with audio frequency signals in the mains
Chapter 1
Gaseous discharges
W. Elenbaas
1.1 Introduction
In the fluorescent lamp the transfer of electric energy into visible light
takes place in two steps. First the electric energy is partly transferred into
invisible ultra-violet radiation mainly of wavelength 253·7 nm. The amount
of visible radiation produced by the discharge itself is small compared with
the ultra-violet radiation.
The ultra-violet radiation produced by the discharge falls on the fluores
cent powder, which is situated at the inner wall of the discharge tube and
is there transferred into visible light (in special lamps mainly invisible ra
diation is produced for special purposes). The production of radiation by
the discharge is thus the first step in the light production and we will there
fore start with a general treatment of gas discharges.
1.2 Electron emission
In gaseous discharges, charged particles - namely electrons and positive
ions - move in a gas between two electrodes. Negative ions occur in some
types of discharge, but these need not be considered here. Discharges without
electrodes in the gas (possible at high frequencies) are also not treated in
this book.
2 FLUORESCENT LAMPS
+
Fig. 1.1. Gaseous discharge tube in
series with a D.C. voltage V2 and a
resistor R. The voltage V1 serves to
heat the cathode.
Let us first look at the arrangement illustrated in Fig. 1.1, which shows a
lamp connected to a source of direct current; when the lamp operates, a
potential difference V, ( = V2 - IR) exists between the electrodes. On
average, the electrons travel from the negative electrode (cathode) to the
positive electrode (anode), whilst the positive ions, whose average rate of
progress is much slower than that of the electrons, move from anode to
cathode.
Since the average movement of the electrons is towards the anode, there
must be a continuous supply of electrons by or near the cathode. The pro
cess of electron supply by the cathode is known as electron emission. More
over, positive ions and electrons are created throughout the whole discharge
(see Sections 1.3 and 1.4).
The emission of electrons is a very important feature of a gaseous dis
charge; so much so, that the manner of the emission determines whether
the discharge will be called a glow discharge or an arc discharge. By glow
discharge is meant the discharge from a cold cathode, and by an arc dis
charge that from a hot cathode *.
Free electrons occurring in the metal of the cathode are not normally able
to emerge from the cathode into the surrounding medium; to make this
possible the electron requires a certain minimum amount of energy; this
energy is expressed in terms of the electron-volt, defined as the energy
acquired by an electron in changing its potential by 1 volt. If, for a given
metal, this minimum energy be q; electron-volts, q; is called the thermionic
work function of the metal.
The mechanical analogy of these electrical forces, which prevent the
electrons from leaving the metal is shown in Fig. 1.2. The box is filled with
marbles up to a level lying a distance h below the rim p of the box. Unless
some force acts upon them, the marbles cannot rise to the level p; to reach
this level a marble in the uppermost row must acquire an energy of at least
mgh (m = mass of the marbles and g = acceleration due to gravity). The
box may be taken to represent the metal in which the electrons are located,
whilst the rim is analogous to the space outside the metal to which the
p p Fig. 1.2. In the same way that energy is
required to move the marbles out of the
box, energy must be imparted to the
electrons to enable them to leave the
metal.
* Arc discharges with cold electrodes, as occur on liquid mercury or on copper electrodes
are left out of consideration. Here the cathode fall is also small (approximately 10 V)
which is characteristic for the arc discharge, whereas the cathode fall of the glow dis
charge equals some 100 V.
GASEOUS DISCHARGES 3
electrons cannot pass without energy being imparted to them. The dis
tance h and the quantity cp are wholly analogous; the difference is however
that the electrons move within the metal, whereas the marbles are stationary
in the box.
Let us now consider two ways in which the electrons can emerge from
the metal.
1.2.1 Arc discharge
When a metal is heated, the mean velocity of the electrons in the metal is
increased. The velocity for all electrons at any given moment is, however,
not the same. There exists a certain distribution of velocities covering both
slow and rapidly moving electrons, and those of the latter which move
quickly enough and moreover strike the surface are able to leave the metal.
If, furthermore, an electric field exists in the adjoining space and this field
is so oriented as to exert on the electrons a force in a direction away from
the metal, these electrons may move still further away from the metal. lf
the temperature of the metal is increased, more and more electrons acquire
a sufficient velocity to escape from the metal, and the emission thus increases.
Fig. 1.1 therefore includes a voltage V to maintain the cathode at an
1
elevated temperature. In Fig. 1.2 it is obviously an advantage if the dis
tance h is small, so that marbles whose kinetic energies are lower can also
reach the rim; in the case of electron emission it is thus advisable to employ
a substance having a low work function, and, in practice, this is achieved
by covering the cathode with a thin layer of an alkaline earth oxide such as
BaO, SrO or CaO or a mixture of these.
1.2.2 Glow discharge
Suppose that a projectile is shot into the box of marbles shown in Fig. 1.2.
One or more of the latter may then be ejected from the box, depending
naturally on the nature of the projectile, its direction and velocity, and the
distance h. In a glow discharge the projectile takes the form of a positive
ion, which is accelerated just in front of the cathode by reason of the electric
field in that region, and then alights on the cathode. By no means every
positive ion arriving at the cathode liberates an electron; the probability of
this happening depends on the ion velocity and also on the work function.
In actual fact it appears that the odds are about 1 to 100, that is to say,
for every 100 positive ions arriving, only about one liberates an extra elec
tron (one electron being used to neutralise the positive ion). For this kind
of emission the cathode need not be heated at all; however, its temperature
will increase somewhat owing to the bombardment of the positive ions, but
this temperature rise is not essential to the emission process. In this case,
therefore, we speak of cold-cathode emission. The electron emission per
square centimeter is very much lower than in the case of the arc discharge.
For the same current, thus, the cathode of the glow discharge must be con
siderably larger than that of an arc, and, in fact, it usually consists of a
sheet-iron cylinder. In order to maintain the advantage of a low work
function and thus enhance the chances of liberating electrons, these elec
trodes are sometimes coated with alkaline earth oxides. In spite of this, the
