IEC TR 62750:2012

IEC/TR 62750 ®
Edition 1.0 2012-02
TECHNICAL
REPORT
Unified fluorescent lamp dimming standard calculations

IEC/TR 62750:2012(E)
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IEC/TR 62750 ®
Edition 1.0 2012-02
TECHNICAL
REPORT
Unified fluorescent lamp dimming standard calculations

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
R
ICS 29.140 ISBN 978-2-88912-939-3

– 2 – TR 62750 © IEC:2012(E)
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Explanation of the dimming requirements . 5
2.1 General . 5
2.2 Additional heating. 5
2.3 Cathode heating limits . 6
2.4 Substitution resistors for electronic controlgear qualification. 7
3 Determination of limit values . 8
3.1 General . 8
3.2 Minimum sum-of-squares – SoS (I ≤ I < I ) . 9
min D30 D Dtrans
3.2.1 Lamp and electronic controlgear systems – SoS' . 9
min
3.2.2 Electronic controlgear qualification limits – SoS . 11
min
3.3 Minimum cathode voltage – CV (I ≤ I < I ) . 12
min Dmin D D30
3.3.1 Lamp and electronic controlgear systems – CV' . 12
min
3.3.2 Electronic controlgear qualification limits – CV . 12
min
3.4 Maximum cathode voltage – CV (I ≤ I < I ) . 13
max Dmin D Dtrans
3.4.1 Lamp and electronic controlgear systems – CV' . 13
max
3.4.2 Electronic controlgear qualification limits – CV . 14
max
4 Example of calculation for 54W HO lamps . 14
4.1 General . 14
4.2 Calculation of lamp and ECG systems – SoS' . 15
min
4.3 Calculation of lamp and ECG systems – CV' . 15
min
4.4 Calculation of ECG qualification limits – CV . 16
min
4.5 Calculation of lamp and ECG systems – CV' . 16
max
4.6 Calculation of ECG qualification limits – CV . 16
max
5 Glossary of symbols . 17
Bibliography . 20

Figure 1 – Fundamental circuit for SoS test . 10

Table 1 – SoS parametric values . 9
Table 2 – Fitted power law parameters . 11
Table 3 – Informative parameters for lamp and controlgear systems . 13
Table 4 – Datasheet parameters . 14

TR 62750 © IEC:2012(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
______________
UNIFIED FLUORESCENT LAMP
DIMMING STANDARD CALCULATIONS
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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The main task of IEC technical committees is to prepare International Standards. However, a
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data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC 62750, which is a technical report, has been prepared by subcommittee 34A: Lamps, of
IEC technical committee 34: Lamps and related equipment.
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
34A/1511/DTR 34A/1546/RVC
Full information on the voting for the approval of this technical report can be found in the
report on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

– 4 – TR 62750 © IEC:2012(E)
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

TR 62750 © IEC:2012(E) – 5 –
UNIFIED FLUORESCENT LAMP
DIMMING STANDARD CALCULATIONS
1 Scope
This Technical Report applies to fluorescent lamp dimming systems. It deals with the interface
of fluorescent lamps and dimming electronic controlgear. A unified framework for
standardization of fluorescent lamp dimming systems and the associated parameter
calculation method are described in this Technical Report.
Dimming of fluorescent lamps is becoming increasingly important as a strategy for conserving
global energy resources. This report is the result of many years of effort by global experts to
understand and test fluorescent dimming systems with the objective of standardizing these
systems to grow confidence and reliability in the marketplace. Two theoretical frameworks
have been merged to create this unified dimming standardization method: the SoS (sum of
squares of lead-in-wire currents) and CV (cathode voltage) models. The application of
dimming to actual fluorescent lamp and electronic controlgear (ECG) systems is the primary
concern for reliability in the application and end-user confidence. Characteristics of the
dimming parameter limits described in this report and observed in real system applications
such as in situ field diagnostics are offered as informative. The practical need to use
substitution resistors for ECG qualification is described in this report and also given as
normative parameters in the lamp and ECG standards. No attempt to treat the informative real
lamp-ECG system parameters as normative will be made in either the lamp or the controlgear
standards.
2 Explanation of the dimming requirements
2.1 General
This clause gives a general explanation of the dimming requirements found in the fluorescent
lamp and controlgear standards. Subclause 2.2 provides an overview of the theoretical
framework for the unified dimming standard. Subclause 2.3 provides an explanation of
informative limits for the cathode heating based on physical lamp and ECG systems.
Subclause 2.4 provides the basis for normative controlgear qualification using substitution
resistors. In this Technical Report, the use of primed quantities will signify values obtained
when measuring on actual fluorescent lamp and ECG systems. Unprimed quantities refer to
standardised quantities when testing ECG on substitution resistors. Although lead wire and
lamp discharge currents pertain to actual lamps, they will remain unprimed quantities in this
report.
2.2 Additional heating
It is a well-known fact that, when lowering the lamp current to decrease the luminous flux
(dimming) below a certain current value, the cathode is not heated sufficiently any more by
the lamp current. At these dimmed conditions without added ohmic heating, the cathode fall
will increase to sustain the lamp current and this results in an increased sputtering of the
cathode and thereby a decrease in lamp life. So additional cathode heating is necessary to
keep the cathode at a sufficiently high temperature for thermionic emission. The amount of
this additional heating current through the cathodes as a function of the lamp current is
however dependent on the controlgear circuit layout. There may be a phase shift between
these currents like in circuits with a capacitor parallel to the lamp. In other circuits, the
additional heating current is delivered by separate heating sources, in which case it is not
clear through which lead-in wire which part of the lamp current flows. For a generalized
description, these different circuits are included when describing the controlgear
requirements.
– 6 – TR 62750 © IEC:2012(E)
It has been found that measuring the root mean square (r.m.s.) currents through the two lead-
in wires to the cathode and calculating the sum of the mean squares of these two currents as
a function of the discharge current can estimate the cathode heating. The sum of squares,
SoS’, needed to keep the cathode at a sufficient temperature, is found to have a linear
dependence on the root mean square (r.m.s.) discharge current:
2 2
SoS’ = I LH + I LL = X’ – Y’ × I
1 1 D
where
I is the discharge current;
D
I is I lead high, which is the highest current through either lead-in wire;
LH
I is I lead low, which is the lowest current through either lead-in wire.
LL
Alternatively, it has also been found that it is possible to describe cathode heating in terms of
root mean square (r.m.s.) voltage applied across the cathode, CV’, while dimming. To a
reasonable approximation in the deep dimming range, the voltage necessary to keep the
cathode at a sufficient temperature is also a linear function of the root mean square (r.m.s.)
discharge current,
CV’ = X’ – Y’ × I ,
3 3 D
where the coefficients X’ and Y’ are constants, different from X’ and Y’ in the SoS’
3 3 1 1
expression.
The dimming range of discharge currents for which additional heating is necessary is given by
a maximum value, I , which defines the transition between normal and dimming
Dtrans
operation, and a minimum value, I , specified in the lamp standard. These values are
Dmin
expressed relative to the cathode test current, I , designated in the relevant IEC
test
datasheets. This cathode test current is defined in the relevant IEC standard as the current to
be applied when measuring the cathode hot resistance. An indirect measure related to the
overall cathode temperature is the ratio, R /R , where R is the “hot” resistance during
h c h
operation and R is the “cold” resistance at 25 ºC. For a nominally performing filament, the
c
measured hot resistance will usually correspond to a hot-to-cold resistance ratio, R /R , of
h c
4,75. The range of discharge currents, I ≤ I ≤ I , specified for dimming is typically
Dmin D Dtrans
~10 % of I ≤ I ≤ ~80 % of I for many lamp designs . For discharge currents above the
test D test
dimming range, I ≥ I , additional cathode heating is not required, but not forbidden as
D Dtrans
long as the value for the maximum current in any lead, I , is observed. Explicit values for
LHmax
the dimming range of discharge current and cathode test current are specified in the lamp
datasheets.
2.3 Cathode heating limits
The SoS model is developed from assumptions about the cathode hot spot. This is the
location where the discharge arc attaches to the electron-emitting region of the cathode. As
the discharge current is lowered into the dimming region, a hot spot remains localized until
the lamp current is lowered below I , approximately 30 % of I . In this region of dimming
D30 test
where the lamp current is greater than or equal to I , values for the critical “minimum SoS”
D30
(SoS’ ) are set to prevent cathode sputtering and the resulting short lamp life.
min
At low dimming currents, the discharge attachment becomes diffusely attached to the cathode
and the hot spot no longer is localized or stationary. Also, the hot spot tends to lose a well-
defined location when high or excessive heating currents are applied to the cathode.
___________
It is important to note that I is defined as a cathode related current parameter and does not necessarily
test
relate to the lamp discharge current or the dimming range for lamp designs in some regions.

TR 62750 © IEC:2012(E) – 7 –
Therefore, at low currents, or to describe the upper boundary of acceptable cathode heating,
the CV’ becomes a preferred approach to standardizing the cathode-heating requirement. In
the region of dimming where the lamp current is lowered below I , values for the minimum
D30
cathode voltage, CV’ , are set to prevent premature cathode destruction by sputtering.
min
Excessive additional heating will result in overheating of the cathode and thereby accelerated
end blackening of the lamp. To protect the cathode from overheating, resulting in excessive
barium evaporation (end-blackening) and possible mercury starvation in the lamp, a maximum
heating level should be set for the cathode voltage. This maximum cathode voltage, CV’ ,
max
is set to limit the cathode temperature below a temperature typically corresponding to a
cathode resistance ratio of R /R < 5,2.
h c
The uncoated part of the cathode can be overheated by the combination of high additional
heating and the discharge current itself (mainly in the higher dimming region). Setting a
, to the higher lead-in wire current, ILH, will protect these parts of the
maximum, I
LHmax
cathodes.
For controlgear design guidance, a target line SoS’ is also defined. It is a best setting for
tgt
the cathode heating to be sufficiently far away from the critical minimum and maximum.
To summarize, the cathode heating informative limits are given by the following set of criteria
uniquely defined over the dimming region of lamp currents. The voltage measured across the
leads of each cathode in the system should generally lie above the minimum heating line
CV’ and below the maximum heating limit CV’ . The measured SoS current values
min max
should lie above the minimum line SoS’ and the measured lead-in wire currents shall not
min
exceed the I limit.
LHmax
2 2
Lower limit: SoS’ [I + I ] = X’ – Y’ × I for I ≤ I < I
min LH LL 1 1 D D30 D Dtrans
Lower limit: CV’ = X’ – Y’ × I for I ≤ I < I
min 3 3 D Dmin D D30
Upper limit: CV’ , I for I ≤ I < I
max LHmax Dmin D Dtrans
2 2
Target: SoS’ [I + I ] = X’ – 0,3Y’ × I

tgt LH LL 1 1 D
2.4 Substitution resistors for electronic controlgear qualification
For normative ECG testing, the lamp discharge impedance is approximated using substitution
resistors, R , having values (R , R , R and R ) given at 10 %, 30 % and 60 %
L L10min L10max L30 L60
of the test current, I . Ambient temperature and lamp geometry are known to have a major
test
influence on the lamp impedance. At I = I a minimum, R , and maximum value,
D Dmin L10min
R , of the lamp substitution resistance is specified to allow for a rough approximation of
L10max
the thermal dependency of the lamp impedance. These resistor values are set at –30 % and
+ 30 % of the nominal lamp impedance at I = I . At I = 30 % (I ) and 60 % (I ) of
D Dmin D D30 D60
I , the nominal value of the lamp impedance is specified for the substitution resistance
test
value. These discharge current values have been chosen in the dimmed region where proper
setting of electrode heating is important for reliable lamp operation throughout the rated lamp
life. To summarize the lamp discharge substitution resistor set, the following abbreviations are
used:
• low impedance discharge at I : R ;
Dmin L10min
• high impedance discharge at I : R ;
Dmin L10max
• discharge impedance at I : R ;
D30 L30
• discharge impedance at I : R
D60 L60.
– 8 – TR 62750 © IEC:2012(E)
For any ECG that does not operate with a continuous range of dimming current (e.g. step
dimming controlgear), the lamp substitution resistor is selected to approximate the lamp
discharge impedance. This impedance approximation uses linear interpolations for R from
Lmin
R to R , R from R to R , and R from R to R for the range of lamp
L10min L30 Lmax L10max L30 L L30 L60
discharge current from I ≤ I < I in this report,
Dmin D Dtrans
(R − R )
L60 L30
R = ⋅(I − I ) + R for I < I < I
L D D30 L30
D30 D Dtrans
(I − I )
D60 D30
(R − R )
L10min L30
R = ⋅(I − I ) + R for I ≤ I < I
Lmin D D30 L30 Dmin D D30
(I − I )
Dmin D30
(R − R )
L10max L30
R = ⋅(I − I ) + R for I ≤ I < I
Lmax D D30 L30 Dmin D D30
(I − I )
Dmin D30
The selected resistor shall have a resistance value within 20 % of the calculated R ,
Lmin
R , or R value for the lamp operating current of the ECG under test. For normative ECG,
Lmax L
qualification test conditions are specified in IEC 60929.
In addition, the cathode impedance is approximated with substitution resistors. Since the
2 2
heating characteristics of resistors P~V or P~I , differ significantly from actual cathodes,
1,4 3,2
P~V or P~I , three substitution resistance values, R , R , and R , are given for
test1 test2 test3
each cathode for controlgear qualification tests. The R value, chosen to account for
test1
typical cathode impedance variation and provide most cathodes with moderate auxiliary
heating R /R ≥ 4,3 is used when testing the lower cathode-heating limit, SoS . The R
h c min test1
value is approximately equal to 4,6 R for typical T5 cathodes. Nevertheless, as a rule of
c
thumb, R should be chosen on the order of 4,75 R . Note that, due to the selection of
test1 c
R values exceeding the typical cathode impedance, values for cathode heating limits will
test1
differ from the informative physical lamp-ECG system values when qualifying ECG on
substitution resistors. The R value, chosen to approximate the cathode impedance with a
test2
high level of auxiliary heating R /R ~5,2, is used when testing the upper cathode-heating
h c
limit, CV and I . The R value is chosen to approximate the typical cathode
max LHmax test3
impedance when heated only with auxiliary current to a temperature corresponding to
R /R ~4,3. The R substitution resistor is used when testing ECG for the lower cathode
h c test3
heating limit, CV , at the deepest dimming lamp currents that provide only negligible heating
min
from the discharge current. This selection of R is the most accurate representation of the
test3
typical cathode at the deep dimming current and therefore provides a robust test of ECG that
may use different cathode heating circuit topologies.
The normative qualification of ECG is specified only at the values of cathode substitution
resistances defined above, not continuously along the lamp current dimming curve. Related to
these values, a test procedure and a test circuit are given in the performance standard for
electronic controlgear, IEC 60929.
3 Determination of limit values
3.1 General
This clause provides the details by which the limit values for SoS and CV are determined. It is
important to keep i
...