Energy and Power Engineering, 2010, 53-64
doi:10.4236/epe.2010.21009 Published Online February 2010 (http://www.scirp.org/journal/epe)
The Implications of Fluorescent Lamp Electronic
Ballast Dimming
—An Experimental Study
Sheryl G. Colaco1, Ciji P. Kurian2, V. I. George1, Anitha M. Colaco3
1Department of Instrumentation & Control Engineering, Manipal Institute of Technology, Manipal, India
2Electrical & Electronics Engineering, Manipal Institute of Technology, Manipal, India
3Electrical & Electronics Engineering, NMAMIT, Nitte, India
Abstract: In recent years, fluorescent lamp dimming controls are an integral part of daylight artificial light
integrated schemes intended for realization of energy savings. However, dimming, like any lighting option,
presents its own particular challenges and poten tial tradeoffs. In v iew of this, the present manuscript depicts
the preliminary work progress carried out to arrive at a comprehensive idea on dimming implications on key
factors: electrical characteristics, photometric distributions of lighting systems and influence on quality as
well as quantity of visual environment. The objective is to experimentally establish the acceptable range of
dimming control voltage that would satisfy both electrical and photometric performance of luminaire. The
vital part of the paper is devoted towards presentation of measurement results. For the experimental analysis,
three representative samples of different commercial analog 1-10VDC electronic dimmable ballasts and
fluorescent fixtures are compared and evaluated over their control voltage dimming range.
Keywords: dimming, power factor, power quality, chromaticity, light intensity, illuminance
1. Introduction
In the present scenario, electronic dimming ballasts are
crucial in automatic control and dimming function for
energy-management applications such as daylight harv-
esting [1]. Over many years, in spite of many reports and
case studies cite the advantages of daylight linked auto-
matic light dimming systems; comparatively very less
schemes have been implemented [2,3]. Part of the reason
could be attributed to the issues associated with lamp
dimming that have been debated during the last few
years. A number of literatures in print state that at some
stage during deep dimming; electronic dimming ballast
exhibit poor performance reflected by dramatic deterio-
ration of electric and photometric characteristics [4] Im-
portant concerns related to dimming include lamp life,
perceived brightness, perception of light level reduction,
color shift, power quality and energy efficiency [3].
Many past studies address these issues separately. The
effect of dimming on lamp life was investigated by Tetri
and Gligor [5]. Their experimental results indicate that
mortality was higher in the dimmed test groups than in
the undimmed test groups. Further their lamp life test
result showed that with electronic ballasts lamps reached
their nominal life even if the lamps are dimmed statically
or dynamically. A study by Akashi et al. [6] on the detec-
tion and acceptability of temporarily reduced light levels
showed that a reduction of 15% in illuminance levels is
the approximate threshold for noticing changes under
typical office lighting conditions. Further their study
revealed, light level reductions that are deemed accept-
able in an office environment ranges from approximately
33% to 50% depending on the office task and whether
the occupants were aware of the purpose and benefits of
dimming. Literature reports and utilities show an in-
creased concern about the power quality aspects due to
dimming of electronic ballasts [7,8]. Experimental tests
performed by National Lighting Product Information
Program (NLPIP)[9] on electronic dimmable ballasts of
T8 and CFL lamps document that progressive decrease in
dimming levels are associated with increase in voltage as
well as current THD accompanied by corresponding di-
minishing of power factor at minimum light output. In
their separate experimental study conducted by Benoit et
al. [10] and Doulos et al. [11] showed that power factor
decreases in function of dimming depth due to subse-
quent setting up of harmonics while dimming. Further,
inorder to quantify energy savings from dimming ballasts
Doulos et al. [11] performed various sets of electrical
and illuminance measurements on eighteen commercial

S. G. COLACO ET AL.
54
ballasts at different dimming levels. The authors [11]
developed polynomial functions between light output
and consumed power to reckon the relative differences in
energy savings. The chromaticity of a fluorescent lamp is
a supplementary parameter used to gauge light quality.
The adverse effect of dimming when it lowers the lum-
inous efficacy of the light source or changes its colour
requires careful inspection. The present communication
reports the preliminary study of an ongoing research
project on promotion of daylighting for energy conserva-
tion in a daylight artificial light integrated scheme. This
paper is organized as follows. Following a brief discus-
sion on problem statement in Section 2, the main sec-
tions of this paper includes experimental methodology in
Section 3, presentation of measurement results in Section
4 and finally, brief conclusions are deduced in Section 5.
It is envisaged that the information from these studies
would be of assistance to architect, the engineer, the
lighting designer or a combination of these during the
initial stage when different daylighting schemes and
concepts are bei ng developed.
2. Pr oble m Statement
The performance characteristic of lamps and ballasts
usually vary from one manufacturer to another. Therefore
prior to new lighting installations not only choice of the
lamp make is important but also there is a need to study
electrical and photometric characteristics of luminaire.
Obviously this could also serve as an important starting
datum for analysis and optimization of installations per-
formances in buildings. Issues related to electronic bal-
last dimming on fluorescent lamp and visual perform-
ance characteristics are the subject considered for dis-
cussions in this paper. This paper seeks to put into per-
spective the subject of fluorescent lamp dimming in a
manner that has not been discussed previously. The in-
tention is to ascertain th e preferable range of ballast con-
trol signal voltage that does not deteriorate electrical
characteristics, photometric distributions of lighting sys-
tems and visual environment quality as well as quantity.
For practical evaluation, three separate analogs dimming
ballast each supplied by different manufacturer and most
commonly employed for daylight responsive dimming
applications in Indian offices are analyzed.
3. Experimental Methodology
The methodology developed in this work combines elec-
trical; and photometric measurements including com-
puter simulations. The customary testing and measure-
ment procedures specified by CIE and IESNA were fol-
lowed [12–15]. The experimental tests were performed
under a standard set of conditions at the Photometry
Laboratory of Manipal Institute of Technology, Manipal
(India). Three 230V, 236W analog electronic dimming
ballasts with corresponding pairs of T8 fluorescent lamps
supplied by 3 different manufacturers Osram, Wipro &
Philips (labeled in this paper as EDB-A, EDB-B, EDB-C
respectively) were examined for practical comparison
and evaluation. In order to assess the performance char-
acteristic during dimming; twin 36W fluorescent lamps
were dimmed by manual adjustment of dimming ballast
control signal DC voltage from 1 to 10V (up or down)
with a digital 0-30V regulated DC power supply. Prior to
taking measurements the tested lamps were pre burned
for full light output for 100 hours before dimming with a
supply voltage of 230V a.c. 50 Hz and ballast control
voltage of 10V. The adjustment from one dimming level
to another level was done gradually. The lamps were
tested on 10 different ballast control voltages in step dif-
ference of 1 volt. To ensure that the temperature of each
lamp stabilized during testing, at each control voltage
level the lamps were operated for at least 10 min. All the
measurements were performed at an ambient temperature
of 26℃2。with a stabilized line vo ltage of 230V a.c.
To assess the performance characteristics; dimming
ballast control voltage (1-10V DC) formed the variable
parameter. The dependent variables include electrical
parameters (i.e., current, power factor, active power,
voltage and current harmonics) and photometric parame-
ters (i.e., luminous intensity, CCT, CU, chromaticity).
The following measurements were carried out to provide
the technical background for evaluating the electric and
photometric characteristics of tubular fluorescent lamp
systems all through dimming control signal voltage range
of electronic dimming ballast.
The luminous flux of the lamp in each dimming
mode was measured in an integrating sphere with an
inner diameter of 2.0 m. Power line voltage and line
current harmonic spectrum together with active power,
apparent power and power factor was recorded using
FLUKE 43B power quality analyzer. Lamp Chroma-
ticity coordinates were gauged using Konica Minolta
CL-200 Chroma meter contained in a Color chroma-
ticity coordinate measuring unit. The estimation of lu-
minaire luminous light intensity in C0-180 and C
90-270 planes involved collection of illuminance data
in both the specified planes in a darkroom at a fixed
distance of 5m from luminaires mounted on a swing
arm Goniophotometer. The luminous intensity was then
calculated from preceding illuminance measurement
using the inverse square distance law. Lighting calcula-
tion so ftware tha t this autho rs typic ally u ses are AGI 32
photometric toolbox for computation of CU chart and
Relux light simulation software for rendering of results
for visualization of the effects of dimming on quality
and quantity of illuminance in an interior. Luminaire
candela power distribution plots and 3D mesh plots of
work plane illuminance distribution were obtained us-
ing Matlab; a computational software [16].

S. G. COLACO ET AL.
55
4. Presentation of Measurement Results
Analog electronic dimming ballasts permit the light out-
put of the lamp to be continuously controlled over a ran-
ge of approximately 1% to 100% of full light output.The
main method of analog control utilizes a low voltage
control signal in the range 1-10V dc. A separate pair of
control cables runs from the controller to luminaires in
the controlled group. Dimming is accomplished by adju-
stment of control signal voltage of the ballast. This modi-
fies the amplitude of current flow in the fluorescent lamp
to achieve variation in emitted lamp ligh t output. Consis-
tent dimming behaviour varies among different ballasts
made by different manufacturers. The ensuing subsectio-
ns enumerate the impacts of dimming on performance
characteristics of fluorescent lamps.
4.1. Effect on Electrical Characteristics
Figures 1(a) and 1(b) illustrate the decrease in current
and subsequently r ed u ction in pow er co nsumptio n du ring
dimming down from 10V to 0V. All the reported ballast
lighting system has a maximum active power consump-
tion of approximately 72W. During dimming down
process the reduction in active power consumption
ranges from a maximum of 100% at 10V to a minimum
of 16%, 19% and 17% at 0V; for ballasts EDB-A,
EDB-B and EDB-C respectively. Figures 1(c) and 1(d)
depict the variation of percentage light output as a func-
tion of control voltage and percentage input power re-
spectively. It is noted that for all the ballasts neither the
light output nor the system power consumption has a
linear relationship with control voltage. Studies of Choi
et al. [17] report that this nonlinear variation in light o ut-
put with different dimming control voltage is one among
many other reasons for unreliability and inaccuracy of
daylight dimming systems, seeing that a particular con-
trol voltage cannot be predicted when a certain light
output is required. In order to achieve performance con-
sistency of electronic dimming ballast especially for PC
based light control algorithms, authors [17] suggests the
application of best fit functions using regression meth-
ods that would satisfy the relationship between control
voltage of dimming ballast and its corresponding light
output characteristics. As seen form Figure 1(d), at a
control voltage of 0V; all the test lamps emit approxi-
mately 1% of light output with a minimum power con-
sumption of approximately 20%. It is noticed during the
experiment that neither the lamp extinguish es nor flick-
ers at minimum control voltage. Figure 1(e) shows the
variation of luminous efficacy as a function of percent-
age active power consumption. The luminous efficacy
drops from a maximum of 43%, 45% and 42% to a
minimum of approximately 1% for EDB-A, EDB-B and
EDB-C lamps respectively. It is also observed from
Figure 1(e) that luminous efficacy of all the tested lamps
stays approximately constant with dimming until about
57% of input power; thereafter it decreases drastically.
(e)(d)
(c) (b)(a)
012345678910
50
100
150
200
250
300
350
Cont rol Voltage ( V)
Current (mA)
EDB-A
EDB-B
EDB-C
0 1 2 3 45 6 7 8 910
0
10
20
30
40
50
60
70
80
Cont ro l Vo ltage (V)
Power Consumption (W)
EDB-A
EDB-B
EDB-C
012345678910
0
10
20
30
40
50
60
70
80
90
100
Cont rol Voltag e ( V)
lumen output ratio(%)
EDB-A
EDB-B
EDB-C
010 20 30 40 50 60 70
0
10
20
30
40
50
Input Power(W )
Luminous Efficacy(%)
EDB-A
EDB-B
EDB-C
020 40 6080 100
0
20
40
60
80
100
Power Consumption ratio (%)
lumen output ratio (%)
EDB-A
EDB-B
EDB-C
(f)
0 1 23 45 6 78 910
0.75
0.8
0.85
0.9
0.95
1
Cont rol Voltag e ( V)
Po wer F acto r (lag)
EDB-A
EDB-B
EDB-C
Figure 1. Measured electrical characteristics over the control voltage dimming range

S. G. COLACO ET AL.
56
(a)(b) (c)
0100 200 300400 500 600 700
0
10
20
30
40
50
60
70
80
90
100
Harmoni c Frequency (Hz)
Current THD (%)
EDB-A THDr=6.4%
EDB-B THDr=6.2%
EDB-C THDr=5.5%
0100 200 300 400 500 600 700
0
10
20
30
40
50
60
70
80
90
100
Harmoni c Frequency (Hz)
Current THD (%)
EDB-A T HD
r
=7.0%
EDB-B THD
r
=6.4%
EDB-C THD
r
=6.1%
0100 200 300 400 500 600 700
0
10
20
30
40
50
60
70
80
90
100
Harmonic Frequency (Hz)
Current THD (%)
EDB-A T HD
r
=7.7%
EDB-B THD
r
=7.7%
EDB-C THD
r
=7.5%
0100 200 300 400 500 600 700
0
10
20
30
40
50
60
70
80
90
100
Harmonic Frequency (Hz)
Current THD (%)
EDB-A THD
r
=9.6%
EDB-B THD
r
=9.3%
EDB-C THD
r
=10.0%
0100 200 300 400 500 600 700
0
10
20
30
40
50
60
70
80
90
100
Harmoni c Frequency (Hz)
Current THD (%)
EDB-A THD
r
=11.3%
EDB-B THD
r
=11.1%
EDB-C THD
r
=11.7%
0100 200 300 400 500 600 700
0
10
20
30
40
50
60
70
80
90
100
Harmonic Frequency (Hz)
Current THD (%)
EDB-A THD
r
=15.1%
EDB-B THD
r
=12.1%
EDB-C THD
r
=16.0%
0100 200 300 400 500 600 700
0
10
20
30
40
50
60
70
80
90
100
Harmonic Frequency (Hz)
Current THD (%)
EDB- A THD
r
=17.5%
EDB- B THD
r
=14.0%
EDB- C THD
r
=18.3%
0100 200 300 400 500 600 70
0
0
10
20
30
40
50
60
70
80
90
100
Harmonic Frequency (Hz)
Current THD (%)
EDB- A THD
r
=25.7%
EDB- B THD
r
=20.1%
EDB- C THD
r
=26.2%
0100 200 300 400 500 600 700
0
10
20
30
40
50
60
70
80
90
100
Harmonic Frequency (Hz)
Current THD (%)
EDB- A THD
r
=30.0%
EDB- B THD
r
=26.7%
EDB- C THD
r
=32.4%
0100 200 300 400 500 600 700
0
10
20
30
40
50
60
70
80
90
100
Harmonic Frequency (Hz)
Current THD (%)
EDB- A THD
r
=36.8%
EDB- B THD
r
=42.0%
EDB- C THD
r
=46.1%
(d)
(e)(f) (g) (h)
(i)(j)
Figure 2. Current harmonic spectra at decreasing ballast dimming voltages a) 10V b) 9 V c) 8v d) 7v e) 6v f) 5v g) 4V h) 3V i)
2V j) 1V
Figure 1(f) demonstrates the deterioration of power fac-
tor with reduction in control voltage. The power factor
reduces from approximately 0.98 to 0.83, 0.8 and 0.78
for EDB-A, EDB-B and EDB-C lighting system respec-
tively. This decline in power factor is attributed to sur-
facing of lower odd order harmonics during dimming.
The influence of dimming on power quality is discussed
in next Subsection 4.1.1. A mathematical relationship
between power factor and harmonics is given by
Equation (1) [18 ].
2
1
.cos()
1
pf THD


 (1)
Additionally, the electricity supply companies require
that the power factor at which the supply is u sed shall be
maintained at not less than 0.9 lagging. Referring to
Figure 1(e), for dimming voltages below 3V power fac-
tor of the tested ballasts lies below 0.9.
4.1.1 Power Quality
Power quality issues are concerned with growing presen-
ce of line harmonic distortions characterized by poor po-
wer factor. Harmonics are frequencies that are integral
multiples of the fundamental frequency. Harmonics ema-
nate whenever the supply wave shape is distorted from a
pure sine wave. In electronic ballast system, the narrow
current pulses drawn by the conventional rectifier-capa-
citor type interface is rich in harmonics [19]. A common
measure of distortion in current and voltage is defined by
percentage Total Harmonic Distortion.
Industry standards for harmonic current distortion fro-
m electronic lamp systems have not been formally esta-
blished [2 0]. AN SI C8 2.77 s ets a maxi mum cu rrent THD
limit of 32% for the lighting equipment [21]. According
to IEEE 519 and IEC 61000-3-2 [22,23], the current
THD and voltage THD limits for electronic ballasts is
20% and 5% respectively. Current and voltage harmonic
spectra for the different lamps used in the study are pre-
sented in Figure 2 and Figure 3 respectively. Though the
investigated ballasts were equipped with harmonic sup-
pression filters by the manufacturers; the significantly
distorted current during dimming is possibly owed to the
construction me- thod in order to decrease the ballast size
and cost. The bar Figures 2(a)–(j) shows the individual
harmonic distortion expressed in percent of the funda-
mental current as defined by the formula in Equation (2)

S. G. COLACO ET AL.
57
(a)(b) (c)(d)
50150 250350 450 550 650
0
10
20
30
40
50
60
70
80
90
100
Harmonic Frequency (Hz)
Voltage THD (%)
EDB-A THD
r
=1.7%
EDB-B THD
r
=1.7%
EDB-C THD
r
=1.7%
50150 250 350 450 550 650
0
10
20
30
40
50
60
70
80
90
100
Harmonic Frequency (Hz)
Voltage THD (%)
EDB-A THD
r
=1.6%
EDB-B THD
r
=1.5%
EDB-C THD
r
=1.5%
50150 250 350 450 550 650
0
10
20
30
40
50
60
70
80
90
100
Harmonic Frequency (Hz)
Voltage THD (%)
EDB-A THD
r
=1.5%
EDB-B THD
r
=1.4%
EDB-C THD
r
=1.5%
50150 250350 450 550 650
0
10
20
30
40
50
60
70
80
90
100
Harmonic Frequency (Hz)
Voltage THD (%)
EDB-A THD
r
=1.4%
EDB-B THD
r
=1.4%
EDB-C THD
r
=1.5%
50150250350 450550 650
0
10
20
30
40
50
60
70
80
90
100
Harmonic Frequency (Hz)
Voltage THD (%)
EDB-A THD
r
=1.8%
EDB-B THD
r
=1.9%
EDB-C THD
r
=1.7%
50150 250 350 450 550 650
0
10
20
30
40
50
60
70
80
90
100
Harmonic Frequency (Hz)
Voltage THD (%)
EDB-A THD
r
=2.5%
EDB-B THD
r
=2.5%
EDB-C THD
r
=2.6%
50150 250 350 450 550 650
0
10
20
30
40
50
60
70
80
90
100
Harmonic Frequency (Hz)
Voltage THD (%)
EDB-A THD
r
=2.4%
EDB-B THD
r
=2.5%
EDB-C THD
r
=2.4%
50150 250350 450 550 650
0
10
20
30
40
50
60
70
80
90
100
Harmonic Frequency (Hz)
Voltage THD (%)
EDB-A THD
r
=2.1%
EDB-B THD
r
=2.1%
EDB-C THD
r
=1.9%
50150250 350 450 550 650
0
10
20
30
40
50
60
70
80
90
100
Harmonic Frequency (Hz)
Voltage THD (%)
EDB-A THD
r
=2.6%
EDB-B THD
r
=2.7%
EDB-C THD
r
=2.7%
50150250 350 450 550 650
0
10
20
30
40
50
60
70
80
90
100
Harmonic Frequency (Hz)
Voltage THD (%)
EDB-A THD
r
=2.6%
EDB-B THD
r
=2.7%
EDB-C THD
r
=2.7%
(e)(f)(g) (h)
(i)(j )
Figure 3. Voltage harmonic spectra at decreasing ballast dimming voltages a) 10V b) 9 V c) 8v d) 7v e) 6v f) 5v g) 4V h) 3V i)
2V j) 1V
14 2
2
1
n
n
I
THD I


 (2)
As depicted in Figure 2(a) through (j) when the lamps
are dimmed down from 10V to 1V the spectrum of cur-
rent is characterized by emergence and elevation of ma-
gnitudes of third and fifth order harmonic components
while dimming. Ballast B accounts a lower current THD
(except at 1V) compared to other ballast A and ballast C.
On an average for all the ballasts the line current THD
increases from a minimum of 6.0% at 10V to maximum
of 42.0 % at 1V. From the measurements results, it is
clear that for the reported ballasts; THD in current lies
within recommended IEEE 519 for control voltage above
3V. Similarly, for control voltage more than 2V current
THD is less than ANSI C82.77 limits. Bar Figures 3(a)–(j)
depicts the voltage harmonic spectra during lamp dim-
ming down proce ss. On an averag e for all the tested bal-
lasts line voltage THD lies between 1.6% at 10V to 2.6%
at 1V complying with IEEE 519 standard voltage limit of
5%. Additionally, it is observed during dimmin g that line
current and line voltage crest factor is below 1 .7 .
4.2 Effect on Photometric Characteristics
Table 1 illustrates the influence of dimming on candela
power distribution curves and CU values of luminaires
under examination. Light distribution curves are curves
defining variation of luminous intensity with angle of
emission in a C 0-180 and C 90-270 plane, passing thou-
gh centre of luminaire [24]. Furthermore specifiers use the
coefficient of utilization chart to assess how effectively
luminaire delivers light to a work plane. Referring to the
polar curves presented in column 2 of Table 1; whilst
dimming down from 10 to 1V, EDB-B has a lower light
intensity compared to EDB-A and EDB-C. The candela
power of the lamp EDB–A is downsized from approxi-
mately 2000 cd/1000 lm to approximately 65 cd/1000 lm.
For EDB-B and EDB-C lamps the light intensity value
decreases from approximately 1800 cd/ 1000lm to 60cd/
1000lm. It is observed that there is not much deviation in
the light distribution contour shape at different dimming
levels. However, it is noticed that the light distribution
pattern is sligh tly affected for control voltage less than 4V
for EDB-C luminaire and below 2V for EDB-A and
EDB-B lamps respectively, the luminaire efficiency while

S. G. COLACO ET AL.
58
Table 1. Effect of dimming on candela power distribution (II column) and on values of coefficient of utilization (III column)
for each dc control voltage (I column)
Control
Voltage Light intensity curves (cd/1000lm) Coefficient of Utilization (%)
10V
500
1000 1500
200
0
30
210
60
240
90270
120
300
150
330
180
0
EDB-A,%  =53.2
EDB-B,%  =43.5
EDB-C,%  =51.6
RC 80 70 50 30 10 0
RW 70 50 30 10 70 50 30 10 50 30 10 50 30 10 50 30 10 0
0 63 63 63 63 62 62 62 62 59 59 59 56 56 56 54 54 54 53
1 59 57 56 54 58 56 55 53 54 53 52 52 51 50 50 49 49 48
2 55 52 49 47 54 51 48 46 49 47 45 48 46 44 46 45 43 42
3 51 47 43 41 50 46 43 40 45 42 40 43 41 39 42 40 38 37
4 48 43 39 36 47 42 38 36 41 38 35 39 37 35 38 36 34 33
5 44 39 35 32 43 38 34 32 37 34 31 36 33 31 35 33 31 30
6 41 35 31 28 40 35 31 28 34 31 28 33 30 28 32 30 28 27
7 39 32 28 25 38 32 28 25 31 28 25 30 27 25 30 27 25 24
8 36 30 26 23 35 29 26 23 29 25 23 28 25 23 28 25 23 22
9 34 28 24 21 33 27 23 21 27 23 21 26 23 21 26 23 21 20
10 32 26 22 19 31 25 22 19 25 21 19 24 21 19 24 21 19 18
Effective Floor Cavity Reflectance 0.20
9V
500
1000 1500 2000
30
210
60
240
90
270
120
300
150
330
180
0
EDB-A,%=53.1
EDB-B,%=43.1
EDB-C,%=50.9
RC 80 70 50 30 10 0
RW 70 50 30 10 70 50 30 10 50 30 10 50 30 10 50 30 10 0
0 63 63 63 63 62 62 62 62 59 59 59 57 57 57 54 54 54 53
1 59 58 56 54 58 56 55 54 54 53 52 52 51 50 50 50 49 48
2 55 52 49 47 54 51 49 47 49 47 45 48 46 44 46 45 44 43
3 52 47 44 41 50 46 43 41 45 42 40 44 41 39 42 40 39 38
4 48 43 39 36 47 42 39 36 41 38 35 40 37 35 39 36 35 34
5 45 39 35 32 44 38 35 32 37 34 32 36 34 31 35 33 31 30
6 42 36 32 29 41 35 31 29 34 31 28 33 30 28 33 30 28 27
7 39 33 29 26 38 32 28 26 32 28 26 31 28 25 30 27 25 24
8 36 30 26 23 36 30 26 23 29 26 23 28 25 23 28 25 23 22
9 34 28 24 21 33 28 24 21 27 24 21 26 23 21 26 23 21 20
10 32 26 22 20 31 26 22 19 25 22 19 25 22 19 24 21 19 18
Effective Floor Cavity Reflectance 0.20
8V
500
1000
1500 200
0
30
210
60
240
90270
120
300
150
330
180
0
EDB-A,%  =49.2
EDB-B,%

=35.9
EDB-C,%

=45.8
RC 80 70 50 30 10 0
RW 70 50 30 10 70 50 30 10 50 30 10 50 30 10 50 30 10 0
0 59 59 59 59 57 57 57 57 55 55 55 52 52 52 50 50 50 49
1 55 53 52 50 54 52 51 50 50 49 48 48 47 47 47 46 45 44
2 51 48 46 44 50 47 45 43 46 44 42 44 43 41 43 41 40 39
3 48 44 40 38 47 43 40 38 42 39 37 40 38 36 39 37 36 35
4 44 40 36 33 43 39 36 33 38 35 33 37 34 32 36 34 32 31
5 41 36 32 30 40 36 32 30 35 32 29 34 31 29 33 31 29 28
6 39 33 29 27 38 33 29 26 32 29 26 31 28 26 30 28 26 25
7 36 30 27 24 35 30 26 24 29 26 24 28 26 24 28 25 23 23
8 34 28 24 22 33 28 24 22 27 24 21 26 23 21 26 23 21 20
9 32 26 22 20 31 25 22 20 25 22 20 24 22 20 24 21 19 19
10 30 24 20 18 29 24 20 18 23 20 18 23 20 18 22 20 18 17
Effective Floor Cavity Reflectance 0.20
7V
300
330 0
500
1000
1500 2000
30
210
60
240
90
270
120
150
180
EDB-A,%  =42.5
EDB-B,%  =33.7
EDB-C,%  =38.5
RC 80 70 50 30 10 0
RW 70 50 30 10 70 50 30 10 50 30 10 50 30 10 50 30 10 0
0 51 51 51 51 49 49 49 49 47 47 47 45 45 45 43 43 43 43
1 48 46 45 44 46 45 44 43 43 42 41 42 41 40 40 40 39 38
2 44 42 39 38 43 41 39 37 39 38 36 38 37 36 37 36 35 34
3 41 38 35 33 40 37 35 33 36 34 32 35 33 31 34 32 31 30
4 38 34 31 29 37 34 31 29 33 30 28 32 30 28 31 29 28 27
5 36 31 28 26 35 31 28 26 30 27 25 29 27 25 28 26 25 24
6 33 28 25 23 33 28 25 23 27 25 23 27 24 22 26 24 22 22
7 31 26 23 21 30 26 23 21 25 22 20 25 22 20 24 22 20 19
8 29 24 21 19 28 24 21 19 23 21 19 23 20 18 22 20 18 18
9 27 22 19 17 27 22 19 17 22 19 17 21 19 17 21 18 17 16
10 26 21 18 16 25 20 18 16 20 17 16 20 17 15 19 17 15 15
Effective Floor Cavity Reflectance 0.20

S. G. COLACO ET AL.
59
6V
500 1000 1500
30
210
60
240
90270
120
300
150
330
180
0
EDB-A,%=33.1
EDB-B,%=25.6
EDB-C,%=28.4
RC 80 70 50 30 10 0
RW 70 50 30 10 70 50 30 10 50 30 10 50 30 10 50 30 10 0
0 39 39 39 39 38 38 38 38 37 37 37 35 35 35 34 34 34 33
1 37 36 35 34 36 35 34 33 34 33 32 32 32 31 31 31 30 30
2 34 32 31 29 34 32 30 29 31 29 28 30 29 28 29 28 27 26
3 32 29 27 26 31 29 27 25 28 26 25 27 26 24 26 25 24 23
4 30 27 24 22 29 26 24 22 25 24 22 25 23 22 24 23 22 21
5 28 24 22 20 27 24 22 20 23 21 20 23 21 19 22 21 19 19
6 26 22 20 18 25 22 19 18 21 19 18 21 19 18 20 19 17 17
7 24 20 18 16 24 20 18 16 20 17 16 19 17 16 19 17 16 15
8 23 19 16 15 22 18 16 15 18 16 14 18 16 14 17 16 14 14
9 21 17 15 13 21 17 15 13 17 15 13 16 14 13 16 14 13 13
10 20 16 14 12 20 16 14 12 16 14 12 15 13 12 15 13 12 11
Effective Floor Cavity Reflectance 0.20
5V
EDB-A,%=21.8
EDB-B,%=16.6
EDB-C,%=18.5
80
0
30
210
60
240
90
270
120
300
150
330
180
0
400 600
200
RC 80 70 50 30 10 0
RW 70 50 30 10 70 50 30 10 50 30 10 50 30 10 50 30 10 0
0 26 26 26 26 25 25 25 25 24 24 24 23 23 23 22 22 22 22
1 24 24 23 22 24 23 23 22 22 22 21 21 21 21 21 20 20 20
2 23 21 20 19 22 21 20 19 20 19 19 20 19 18 19 18 18 17
3 21 19 18 17 21 19 18 17 18 17 16 18 17 16 17 17 16 15
4 20 18 16 15 19 17 16 15 17 16 15 16 15 14 16 15 14 14
5 18 16 14 13 18 16 14 13 15 14 13 15 14 13 15 14 13 12
6 17 15 13 12 17 14 13 12 14 13 12 14 12 12 13 12 11 11
7 16 13 12 11 16 13 12 11 13 12 10 13 11 10 12 11 10 10
8 15 12 11 10 15 12 11 10 12 11 10 12 10 9 11 10 9 9
9 14 11 10 9 14 11 10 9 11 10 9 11 10 9 11 9 9 8
10 13 11 9 8 13 10 9 8 10 9 8 10 9 8 10 9 8 8
Effective Floor Cavity Reflectance 0.20
4V
330
100
200
300
400
500
30
210
60
240
90
270
120
300
150
180
0
EDB-A,%  =13.1
EDB-B,%  =10.4
EDB-C,%  =11.5
RC 80 70 50 30 10 0
RW 70 50 30 10 70 50 30 10 50 30 10 50 30 10 50 30 10 0
0 16 16 16 16 15 15 15 15 15 15 15 14 14 14 13 13 13 13
1 15 14 14 13 14 14 14 13 13 13 13 13 13 12 12 12 12 12
2 14 13 12 12 13 13 12 12 12 12 11 12 11 11 11 11 11 11
3 13 12 11 10 12 11 11 10 11 10 10 11 10 10 10 10 10 9
4 12 11 10 9 12 10 10 9 10 9 9 10 9 9 10 9 9 8
5 11 10 9 8 11 10 9 8 9 8 8 9 8 8 9 8 8 7
6 10 9 8 7 10 9 8 7 8 8 7 8 8 7 8 7 7 7
7 10 8 7 6 9 8 7 6 8 7 6 8 7 6 7 7 6 6
8 9 7 6 6 9 7 6 6 7 6 6 7 6 6 7 6 6 5
9 8 7 6 5 8 7 6 5 7 6 5 7 6 5 6 6 5 5
10 8 6 5 5 8 6 5 5 6 5 5 6 5 5 6 5 5 5
Effective Floor Cavity Reflectance 0.20
3V
100 200 300
30
210
60
240
90
2
70
120
300
150
330
180
0
EDB-A,%  =7.9
EDB-B,%  =7.2
EDB-C,%  =6.8
RC 80 70 50 30 10 0
RW 70 50 30 10 70 50 30 10 50 30 10 50 30 10 50 30 10 0
0 9 9 9 9 9 9 9 9 9 9 9 8 8 8 8 8 8 8
1 9 9 8 8 9 8 8 8 8 8 8 8 8 7 7 7 7 7
2 8 8 7 7 8 8 7 7 7 7 7 7 7 7 7 7 6 6
3 8 7 6 6 7 7 6 6 7 6 6 6 6 6 6 6 6 6
4 7 6 6 5 7 6 6 5 6 6 5 6 6 5 6 5 5 5
5 7 6 5 5 6 6 5 5 6 5 5 5 5 5 5 5 5 4
6 6 5 5 4 6 5 5 4 5 5 4 5 5 4 5 4 4 4
7 6 5 4 4 6 5 4 4 5 4 4 5 4 4 4 4 4 4
8 5 4 4 3 5 4 4 3 4 4 3 4 4 3 4 4 3 3
9 5 4 4 3 5 4 4 3 4 3 3 4 3 3 4 3 3 3
10 5 4 3 3 5 4 3 3 4 3 3 4 3 3 4 3 3 3
Effective Floor Cavity Reflectance 0.20

S. G. COLACO ET AL.
60
2V
90
120
50 100 150
30
210
60
240
270
300
150
330
180
0
EDB-A,%  =3
EDB-B,%

=2.4
EDB-C,%  =2.4
RC 80 70 50 30 10 0
RW 70 50 30 10 70 50 30 10 50 30 10 50 30 10 50 30 10 0
0 4 4 4 4 3 3 3 3 3 3 3 3 3 3 3 3 3 3
1 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
2 3 3 3 3 3 3 3 3 3 3 3 3 3 2 3 3 2 2
3 3 3 2 2 3 3 2 2 3 2 2 2 2 2 2 2 2 2
4 3 2 2 2 3 2 2 2 2 2 2 2 2 2 2 2 2 2
5 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
6 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 1
7 2 2 2 1 2 2 2 1 2 2 1 2 2 1 2 2 1 1
8 2 2 1 1 2 2 1 1 2 1 1 2 1 1 2 1 1 1
9 2 2 1 1 2 2 1 1 1 1 1 1 1 1 1 1 1 1
10 2 1 1 1 2 1 1 1 1 1 1 1 1 1 1 1 1 1
Effective Floor Cavity Reflectance 0.20
1V
20 40 60 8
0
30
210
60
240
9
0
270
120
300
150
330
180
0
EDB-A,%

=2
EDB-B,%  =1.8
EDB-C,%  =1.3
RC 80 70 50 30 10 0
RW 70 50 30 10 70 50 30 10 50 30 10 50 30 10 50 30 10 0
0 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
3 2 2 2 2 2 2 2 2 2 2 2 2 2 1 2 2 1 1
4 2 2 1 1 2 2 1 1 2 1 1 1 1 1 1 1 1 1
5 2 1 1 1 2 1 1 1 1 1 1 1 1 1 1 1 1 1
6 2 1 1 1 2 1 1 1 1 1 1 1 1 1 1 1 1 1
7 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
8 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
9 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
10 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
Effective Floor Cavity Reflectance 0.20
10V
9V
8V
7V
6V
5V
4V
3V
2V
1V
0.32 0.330.34 0.35 0.36
0.32
0.33
0.34
0.35
0.36
x
y
0.33 0.340.35 0.36 0.37
0.33
0.34
0.35
0.36
0.37
x
y
0.33 0.34 0.35 0.360.37
0.33
0.34
0.35
0.36
0.37
x
y
Figure 4. Chromaticity diagrams and Mac Adam ellipses for a)EDB-A b) EDB-B and c) EDB-C lamps
dimming down drops from a maximum of 53.2%, 43.5%
and 51.6% to a minimum of 2%, 18%, 1.8% for EDB-A,
EDB-B, EDB-C respectively due to decrease in the bal-
last control voltage. Taking the representative case of
EDB-A luminaire, tabulated percentage CU values gen-
erated by AGI-32 Photometric toolbox is shown in third
column of Table 1 against each ballast control voltage.
The row labeled RC is the effective ceiling reflectance,
the row labeled RW is the wall reflectance and the first
column is the Room Cavity Ratio. For the ind icated ceili-
ng, wall and room cavity ratios, the tabulation shows the
percentage of utilized lu mens on the work plane. Clearly,
percentage CU value of the luminaire depreciates with
the reduction in th e control voltage.
4.2.1 Chromaticity and CCT
Chromaticity values are customarily used for character-
izing the color appearance of a light source. A metric
commonly used for quantifying perceivable color differ-
ence is the MacAdam ellipse, which is a contour in the
chromaticity diagram [25]. The ANSI specifies a 4-step
MacAdam ellipse as the acceptable chromaticity toler-
ance area for certain types of fluorescent lamps [26].
Almost all color-normal subjects will perceive a color
difference in source if the chromaticity coordinates of
experimental light source in the course of dimming; falls
beyond chromaticity tolerance area. Using the chroma-
ticity coordinates of maximum output as the centre of the
ellipse, 4 steps MacAdam ellipse plo tted for the reported
ballasts are shown in Figure 4 (a) through (c). As can be

S. G. COLACO ET AL.
61
1 2 3 4 56 7 8 910
4000
4500
5000
5500
6000
dimming voltage (V)
Col or Temp erat u re ( K)
EDB-A
EDB-B
EDB-C
Figure 5. CCT(K) versus ballast analog control voltage
seen from the Figure 4 all the experimental lamps in
question subjected to dimming confines their chroma-
ticity shift within 4-step MacAdam ellipse. Further it is
noticed that X- Y chromaticity coordinates remain essen-
tially constant throughout the dimming range. Figure 5
indicates the relative CCT shift for various dimming
control voltage of the ballast. It is observed that there is
no appreciable deflection in CCT all through the dim-
ming voltage range.
4.3 Effect on Visual Performance
This section highlights on the influence of fluorescent
lamp dimming systems on quantity and quality of inte-
rior illuminance. Figure 6 (a) through (j) portrays the
simulated view of standard office room (2.02.03.0m)
rendered by Relux lighting simulation software. In addi-
tion Matlab generated 3D mesh plot of interior horizontal
illuminance for each control voltage of the ballast is il-
lustrated in Figures 6(a)–(j). Reflections of the floors,
walls and ceiling are considered to be diffuse with reflec-
tion coefficients of 0.3, 0.5 and 0.7 respectively. For elu-
cidation, this paper documents the artificial lighting
analysis just with EDB-A luminaire. The results pre-
sented in this section concentrates on impact of T8 fluo-
rescent lamp dimming on quantity of quality of artificial
lighting without daylight intervention into the experi-
mental room under examination. Further, the assessment
of perceived discomfort glare due to lighting is not taken
into consideration. The simulated 3D illuminance takes
into account 0.5m offset from the walls at a horizontal
working plane 0.7m above the floor. The recommended
visual performance criterion advocates a minimum av-
erage illuminance value at the workplane as 300 lx and
uniformity (ratio of minimum illuminance to average
illuminance) above 0.8[27 ,28]. Rendered scen es depicted
in Figure 6(a)-(j) disclose that there is no perceptible
difference in the appearance of the light as well as gen-
eral appearance of the interior especially related to color.
The reason may be that, there is no significant deflection
in CCT as well as light distribution pattern of lamp all
through dimming as highlighted in the previous sections.
However in practical schemes the general brightness of
the room depreciates slightly during dimming which
could be perceived by the normal observer. This is due to
the fact that many working interiors appear dim for illu-
minance value lower than 200 lx which is the minimum
recommended illuminance for a work space. As repre-
sented in Figure 6, illuminance value lower than 200 lx
manifests for dimming voltages beneath 6V. Neverthe-
less through out dimming uniformity of illuminance in
the whole interior stays abo ve 0.8 as displayed in illumi-
nance distribution plots of Figures 6(a)–(j).
5. Conclusions
As an energy conservation strategy, dimming controls for
electric lighting have been one of the mainstays of the
effort to use daylighting. In view of this, the present
communication experimentally examined the fluorescent
lamp dimming implications on performance characteris-
tics of lighting systems from non manufacturer’s per-
spective. The purpose was to discover acceptable range
of dimming control voltage that would gratify both elec-
trical and photometric performance of luminaire. We
recognize that there may be a few high frequency elec-
tronic dimmable ballasts which are indeed as per national
/international specifications. However, our conclusions
are limited to the ballasts obtained from afore mentioned
manufacturers for our experiments. The following salient
points can be gleaned from the experimental results pre-
sented in this paper:
 The measurement on electrical characteristics
shows, all the tested lamps could be dimmed down from
100% to 1% of light output with a power consumption of
approximately 20% at 1V d.c. Further, neither the lamp
flickers nor extinguishes even at minimum control volt-
age of 0V d. c. During d imming d own on an a verage cur-
rent THD and voltage THD rises from approximately
6.0% to 45% and 1.4% to 2.7% respectively. As a con-
sequence the power factor deteriorates from approxi-
mately 0.98 at 10V to 0.8 at 1V.
 With respect to photometric performance char-
acteristics, it is inferred that during dimming there is no
significant variation in light intensity distribution pattern,
CCT and chromaticity shift. On an average for all the
tested lamps, the light intensity value drops off from ap-
proximately 2000 cd/1000lm to approximately 25cd/
1000lm. There is also a significant drop in utilization fa-
ctor values during dimming . Th e desired limits of u tiliza-
tion factor depend on task application.
 Rendered simulation results depict no signifi-
cant variation in visual performance characteristics dur-
ing dimming as; stan dards prescribed illu minance unifor-
mity criterion of 0.8 is met. During dimming, average
illuminance value dwindles from approximately 520 lx to
20 lx. However, in practical schemes the interiors appear
dim for illuminance values lower than 200lx. Therefore,
the judgment of desired lux level for a range of dimming

S. G. COLACO ET AL.
62
0.5
1
1.5
0.5
1
1.5
400
450
500
550
600
0.79 E
min
/E
max
=
0.86
Room Length(m)
E
min
/E
avg
= 520 lx E
avg
=
Room Width(m)
567 lx
E
max
=
446 lx
Interior Illuminance (lx)
E
min
=
460
480
500
520
540
560
0.5
1
1.5
0.5
1
1.5
400
450
500
550
600
0.81 E
min
/E
max
=
0.86
Room Leng t h(m)
E
min
/E
avg
=
519 lx
Room Width(m)
E
avg
= 559 lx E
max
=
444 lx
Interior Illuminance (lx)
E
min
=
460
470
480
490
500
510
520
530
540
550
0.5
1
1.5
0.5
1
1.5
400
450
500
550
0.81 E
min
/E
max
=
0.86
Room Length(m)
E
min
/E
av
g
= 481 lx
Room Width(m)
E
av
g
=
514 lx
E
max
= 416 lx
Interior Illuminance (lx)
E
min
=
420
430
440
450
460
470
480
490
500
510
0.5
1
1.5
0.5
1
1.5
360
380
400
420
440
460
0.81 E
min
/E
max
=
0.87
Room Length(m)
E
min
/E
avg
=
415 lxE
avg
=
Room Width(m)
442 lxE
max
= 360 lx
Interior Illuminance (lx)
E
min
=
360
370
380
390
400
410
420
430
440
0.5
1
1.5
0.5
1
1.5
180
190
200
210
220
230
0.81
E
min
/E
max
=
0.86
Room Length(m)
E
min
/E
avg
=
214 lxE
avg
=
Room Width(m)
228 lx E
max
= 185 lx
Interior Illuminance (lx)
E
min
=
185
190
195
200
205
210
215
220
225
0.5
1
1.5
0.5
1
1.5
280
300
320
340
360
0.81
E
min
/E
max
=
0.87
Room Length(m)
E
min
/E
avg
= 324 lxE
avg
=
Room Width(m)
347l xE
max
=
281 lx
Interior Illuminance (lx)
E
min
=
290
300
310
320
330
340
0.5
1
1.5
0.5
1
1.5
110
120
130
140
0.82 E
min
/E
max
=
0.88
Room Length(m)
E
min
/E
avg
=
128 lx
Room Width(m)
E
av
g
=
136 lx E
max
= 112 lx
Interior Illuminance (lx)
E
min
=
115
120
125
130
135
0.5
1
1.5
0.5
1
1.5
65
70
75
80
85
0.80
E
min
/E
max
= 0.87
Room Length(m)
E
min
/E
av
g
=
77 lx
E
avg
=
Room Width(m)
84 lx
E
max
=
67 lx
Interior Illuminance (lx)
E
min
=
68
70
72
74
76
78
80
82
0.5
1
1.5
0.5
1
1.5
24
26
28
30
32
0.80
E
min
/E
max
=
0.86
Room Length(m)
E
min
/E
avg
=
29 lx
Room Width(m)
E
av
g
=
31 lx E
m
a
x
=
25 lx
Interior Illuminance (lx)
E
min
=
25
26
27
28
29
30
0.5
1
1.5
0.5
1
1.5
16
17
18
19
20
21
0.81
E
min
/E
max
=
0.89
Room Length(m)
E
min
/E
avg
=
19 lx
Room Width(m)
E
av
g
=
21 lxE
max
=
17 lx
Interior Illuminance (lx)
E
min
=
17
17.5
18
18.5
19
19.5
20
20.5
(a)
(c)
(e)
(g)
(i)
(b)
(d)
(f)
(h)
(j)
Figure 6. Visualizing image and corresponding mesh plot of illuminance distribution depicts the influence of dimming on
quality and quantity of interior lighting at each dimming voltage a) 10V b) 9 V c)8v d)7v e) 6v f) 5v g) 4V h) 3V i) 2V j) 1V

S. G. COLACO ET AL.
63
control voltage requires particular attention based on task
application.
In summary it is concluded from our experimental
analysis that in order to achieve superior electrical,
photometric as well as visual performance from a lumi-
naire; the optimum control voltage range of ballast dim-
ming should preferably lie between 10V to 3V d.c. The
laboratory result of this paper demonstrate that fluores-
cent lamp dimming schemes are not an obstacle for
wider use of energy efficient daylight artificial light in-
tegrated schemes.
6. Acknowledgements
The present research is funded by Department of Science
& Technology under WOS-A scheme, Government of
India. The authors gratefully acknowledge this contribu-
tion. Any opinions, findings and conclusions or recom-
mendations expressed in this material are of the authors.
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Nomenclatures:

Luminaire efficiency

cos

Cosine of the phase angle between input volt-
age and current.
1
I
Fundamental current (A)
n
I
Current at harmonic order number n
pf Power factor given by

cos

THD Total Harmonic Distortion
CCT Correlated Color Temperature (K)
CU Coefficient of Utilization
Emin Minimum Illuminance (lx)
Emax Maximum Illuminance (lx)
Eavg Average Illuminance (lx)