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PLEA2012 - 28th Conference, Opportunities, Limits & Needs Towards an environmentally responsible architecture Lima, Perú 7-9 November 2012
Illumination Condition and Work Efficiency in the Tropics Study on production spaces of Ready-made garments factories in Dhaka
MD. MOHATAZ HOSSAIN
1, PROF. DR. KHANDAKER SHABBIR AHMED
1
1Department of Architecture, Bangladesh University of Engineering & Technology, Dhaka, Bangladesh
ABSTRACT: The Ready-made garment (RMG) sector of Bangladesh employs a large number of people who labour in the
production spaces of garments factory buildings throughout the day. The economic viability of this sector largely depends
on the performance of the workers. Demanding compliance standards of buyers from various countries and a challenging
energy supply and demand scenario in the sector poses questions of sustainability and building design. Appropriate
Illumination conditions of these production spaces, quality as well as quantity of lighting suitable for the production
processes, is a major requirement of a proper working environment. Industrial processes in such indoor environments are
becoming highly complex; workers working under poor lighting conditions are usually exposed to a range of visual
problems with operating machines, textile sewing activities, ironing and other activities. Visual comfort for various
illumination levels has impact on total physical comfort condition and any physical discomfort influences the human
behaviour and their work efficiency. The paper focuses on causality to identify the effects of the illumination condition of
production spaces on the work efficiency and to recommend illumination ranges that would facilitate optimum work
efficiency.
Keywords: Illumination condition, Work efficiency, Production space, Visual comfort, Ready-made garments.
INTRODUCTION
The readymade garment (RMG) sector is a fully export-
oriented industry [1] and Bangladesh is one of the largest
RMG exporters in the world. It plays a pivotal role in the
economy of Bangladesh by accounting for approximately
76% of the total export earnings and nearly 10% of GDP
[2]. Bangladesh, being a labour-abundant country, started
the process of industrialisation in the sector by
concentrating on labour-intensive products such as
clothing [3]. Hence, the economy of this sector depends
on the production by the workers. However, the
readymade garments have been heavily criticized during
1970 - 2000 for the poor working conditions particularly
in the production spaces. The poor luminous
environment in production spaces was one of the
concerns affecting the workers. Among the
environmental compliance factors Illumination condition
remain an important which must be ensured by the
factory owners. Illumination condition includes the
quality as well as quantity of the lighting. However, in
the production space (Sewing, Cutting, dyeing and
finishing), where illumination condition is very
important, the total luminous environment usually varies
with the type of lighting sources and location of the
sources. Poorly designed and maintained lighting can
result in glare and flicker that may cause vision
problems. When the lighting meets both quantity and
quality needs, it adds better working performance and
productivity [4]. Therefore, appropriate illumination
condition should be maintained not only for the visual
comfort but also for facilitating production targets..
The luminous environment acts through a chain of
mechanisms on human physiological and psychological
factors, which further influence human performance and
productivity [5]. Many factors, such as skill, education
and previous experience can affect productivity.
However, lighting is one of the least expensive and the
most important influences on human performance in the
work environment [6]. Providing workers with sufficient
light to perform visual tasks improves their accuracy,
thus increasing production speed and reducing waste of
materials and time. Total production process in the
garments factory constitutes several discrete stages of
activities which are linked in a progressive manner
forming a chain of labour intensive production process.
Therefore it is necessary to maintain an excellent work
environment for maximizing productivity [7]. While
considering the typical working environment of a
garments worker, light sources and illumination level at
the horizontal work plane are notable issues for this
research. Bangladesh National Building Code (BNBC)
and the local laws do not mention the means of achieving
recommended illumination levels. Since for compliance
needs, RMG factories in Bangladesh are increasingly
aiming to raise the lighting levels for various functional
needs like sewing, this is likely to increase energy
consumption substantially. Whereas, the general
PLEA2012 - 28th Conference, Opportunities, Limits & Needs Towards an environmentally responsible architecture Lima, Perú 7-9 November 2012
whose age group is around 18-25 years in common and
who have experiences from 1 month to over 2 years with
an average 9-10 working hours per day.
Figure 2: False coloured 3D visualization showing the lighting
layout of the production space 3 (Software: DIALux)
Figure 3: Illumination condition of selected production spaces
EXISTING ILLUMINATION CONDITION Illumination levels were measured at different positions
within the selected production spaces. One set of
measurement was taken with the artificial lights switched
on (Figure 3), before the lunch break, and another with
lights switched off during the lunch break to test the
daylight penetration and its contribution to the
illumination condition of the production spaces during
day. All data were measured at the height of horizontal
work plane at 2.5 feet (0.76 m) above floor level. The
surveyed production spaces were divided into grids with
reference to column or structural grid. Then the points
gained in the 2D plan of the production spaces were
selected for recording of the overall lighting levels as
well as lighting levels where only source is daylight. It is
observed that the illumination level in production space
type-3 is a bit higher than the other spaces (Table 2). The
main reason behind it can be the overall artificial lighting
layout (figure 2), higher window lintel height which was
observed only in this production space, location of the
windows, outdoor illumination level, depth of the
production space and any other features impacting the
luminous environment. But variation (uniformity ratio)
of the lighting levels also can be observed in this
production space.
Table 2: Illumination level measured at horizontal work plane
Production
space
Location or zone Average
Illumination
level
(Daylight),
Lux
Average
Illumination
level
(Daylight +
Artificial
Light ), Lux
Production
Unit 1
Near the window (Party Daylight) 166 873
Centre of the half depth of space
(Mostly Artificial Lighting)
3 588
Furthest from the Window
(Completely artificial Lighting)
0 532
Production
Unit 2
Near the window (Party Daylight) 258 953
Centre of the half depth of space
(Mostly Artificial Lighting)
9 672
Furthest from the Window
(Completely artificial Lighting)
1 581
Production
Unit 3
Near the window (Party Daylight) 287 1088
Centre of the half depth of space
(Mostly Artificial Lighting)
6 792
Furthest from the Window
(Completely artificial Lighting)
0 696
Table 3: Average Uniformity and Diversity of Luminance Production
Space 1
Production
Space 2
Production
Space 3
Uniformity of Luminance: (435/664)=0.66 (420/735)=0.57 (390/805)=0.48
Diversity of Illuminance: (1150/435)= 2.5 :
1
(1050/420)=2.5
: 1
(1490/390)=3.5
: 1
Table 4: Measured illumination levels and standards
Average illumination in survey Internatio
nal
Standards
( IESNA)
Internatio
nal
Standards
(IES
Code)
Local
Standa
rds
(BNBC
2006)
Produc
tion
space
1
Productio
n space 2
Productio
n space 3
Minimum
Illuminatio
n level at
work plane
(lux)
435 420 390 300 600 300
Maximum
Illuminatio
n level at work plane
(lux)
1150 1050 1490 1000 900 1500
While considering only the daylight in the production
spaces and uniformity ratio, it can be easily observed that
the uniformity ratio of daylight is very low in all the
production spaces. Hence, supportive artificial lights are
installed in the indoor spaces. These three production
spaces used florescent tube lights. Uniformity of
luminance, Diversity of Illuminance and Spacing Height
Ratio were calculated based on recorded illuminances
and other records during the surveys in the production
spaces. The mounted lights were at 7 feet (2.13 m) from
floor level at all the selected spaces. The Table 3 reveals
a uniformity of luminance of 0.48 in production space-3,
which is considered low. The diversity of Illuminance at
the work planes was also found high in production space-
3. The workers of the production space-3 may face more
PLEA2012 - 28th Conference, Opportunities, Limits & Needs Towards an environmentally responsible architecture Lima, Perú 7-9 November 2012
glare or contrast problem than other production spaces.
The value of SHR is low in the production space-1 which
indicates good and glare-free artificial lighting
environment.
Table 4 gives comparison between ‘International
illumination standards' and ‘local recommendations' for
sewing or equivalent works which was then compared
with the illumination measured in the surveyed
production spaces. The illumination level comparison
shows that in the surveyed cases the highest levels are
reached in the work planes, though international
standards require less lighting in the work plane areas.
The usually recommended uniformity of luminance
should not be less than 0.8. But none of the production
spaces met this standard. On the other hand, while
considering the diversity of Illuminance, all the results
were within the standard of 5:1.
PERFORMANCE ANALYSIS AND RESULTS
The two main variables were taken from same samples at
the same time and ‘correlation’ analysis with other
available evidence was done by Microsoft Excel Data
Analysis. Here, the independent variable is the
illumination level and dependent variable is the number
of defects per hour (%). While doing statistical data
analysis to observe correlation among the variables
(Distance between luminaire and work plane (ft), Product
Colour at work plane, Number of Errors per hr (%),
Illumination (at work plane), and Lighting Environment),
limited degree negative correlation were found between
Illumination at work plane, Lighting Environment,
Number of Errors per hr (%). Limited degree positive
correlations were also found between Lighting
Environment and Illumination level (at work plane).
Table 5 revealed that the number of defects per hours
(%) has limited degree negative correlation with
illumination level in all surveyed production spaces. The
correlation coefficients (r value) in production space 1, 2
and 3 are -0.6,-0.5 and -0.5 respectively. On the other
hand, the correlation coefficients number of defects per
hours (%) and Lighting environment or zone in
production space 1, 2 and 3 are -0.3,-0.4 and -0.5
respectively. When considering the correlation between
lighting environment and lighting level, the value of the
coefficients (0.5, 0.7 and 0.6 in the production space 1, 2
and 3 respectively) show that they have limited degree
positive correlation which reveals that inclusion of
daylight can cause increasing of total illumination.
To understand the causal relationship between these
two variables (dependent: number of defects per hours
(%) and independent: illumination level) the Scatter pot
chart with regression line and Detail regression analysis
were used. Relationship between the two variables can
also be exhibited graphically by scatter diagram. Figure 4
illustrates the linear relationship between the independent
variable (illumination level) and dependent variable
(Percentage of production defects per hour) within two
Axis X and Y respectively. From the comparison
between these individual scatter pot charts of three
production spaces, it can be observed that the mode of
the line, the slope of the equations have the similarities
and the illumination levels have moderate effect on the
efficient production. The Regression analysis statistics
can be shown by Table 6 where the values of ‘R Square’
were identified. In production space-1, R square value
reveals that illumination level had about 36% (0.362 out
of 1) causal effect on the production defects (output
variable). Rest of the cause could be other environmental
variables and personal factors. In production space-2 and
3, R square values shows that illumination level had
about 25% (0.251 out of 1) and 20% (0.201 out of 1)
causal effect on the production defects (output variable).
Table 5 Correlation coefficients among illumination levels,
lighting environment and production errors per hour
Su
rveyed
un
it
Variables
Distance
between
Luminaire
and work
plane
Product
Colour
at work
plane
Number
of
Errors
per hr
Illumination
level (at work
plane)
Lighting
Environm
ent P
rodu
cti
on
un
it 1
Distance between
Luminaire and
work plane 1.000
Product Colour
at work plane 0.618 1.000
Number of
Errors per hr 0.314 0.270 1.000 Illumination
level (at work
plane) -0.025 -0.098 -0.611 1.000 Lighting
Environment 0.265 0.074 -0.323 0.450 1.000
Pro
du
cti
on
un
it 2
Distance between
Luminaire and
work plane 1.000 Product Colour
at work plane 0.116 1.000 Number of
Errors per hr 0.145 -0.091 1.000 Illumination
level (at work
plane) -0.070 0.038 -0.514 1.000 Lighting
Environment -0.149 -0.162 -0.441 0.680 1.000
Pro
du
cti
on
un
it 3
Distance between
Luminaire and
work plane 1.000 Product Colour
at work plane 0.035 1.000 Number of
Errors per hr -0.264 -0.049 1.000 Illumination
level (at work
plane) 0.219 0.040 -0.463 1.000 Lighting
Environment 0.047 0.223 -0.476 0.591 1.000
From Regression of these two variable (independent
variable: Illumination level and dependent variable:
Production errors), coefficients (B value) were found as
well. It can be observed that increasing 1 unit of
illumination level, causes 0.009 units less defects in
production space-1, 0.007 units less defects in production
space-2 and 0.005 units less defects in production space -
3 (
PLEA2012 - 28th Conference, Opportunities, Limits & Needs Towards an environmentally responsible architecture Lima, Perú 7-9 November 2012
Table ). In terms of percentage, it can also be said that
increasing 10 unit of illumination level causes 9% less
defects in production space-1, 7% less defects in
production space-2 and 5% less defects in production
space -3. Frequency analysis of independent variable
(illumination level) of the samples with bin ranges from
200 lux to 1200 lux and more reveals that high frequency
samples had 401-1000 lux at their work-plane in
production space-1, 2 and 3. Frequency analysis in bar
charts explain that for production unit 1 and 2, the
desired lighting for effective production is 601~800 lux,
while for production unit 3, it is 801~1000 lux.
Figure 4: Scatter pot chart showing correlation between the
two variables with linear regression lines and linear equations
Table 6: Regression Statistics of two variables Surveyed Units Regression Statistics
Production unit 1 Multiple R 0.611
R Square 0.373
Adjusted R Square 0.362
Standard Error 2.296
Observations (N) 60
Production unit 2 Multiple R 0.514
R Square 0.264
Adjusted R Square 0.251
Standard Error 1.982
Observations (N) 60
Production unit 3 Multiple R 0.463
R Square 0.214
Adjusted R Square 0.201
Standard Error 2.747
Observations (N) 60
Table 7: Coefficients from Regression analysis Surveyed
Units
Independent and
Dependent Variables*
Coefficients
(B Value)
Standard
Error t Stat
Production
unit 1 Intercept 10.979 1.154 9.518
X Variable 1 -0.009 0.002 -5.876
Production
unit 2 Intercept 8.157 1.054 7.740
X Variable 1 -0.007 0.002 -4.563
Production
unit 3 Intercept 7.608 0.992 7.669
X Variable 1 -0.005 0.001 -3.975
* Independent variable: illumination level and dependent variable: production
defects per hours (%)
On the other hand, while considering location of the
sample workers in terms of lighting environment or zone,
highest numbers of the samples had low production
defects within partly natural light in the production
space-1. In production space-2, low production defects
were observed in mostly artificial lighting environment,
while in production space-3, low production defects were
notices in partly natural environment. The production
space configuration in terms of window location,
available daylight inside the production space can be one
of the reasons behind this result.
Table 8: Descriptive Statistics of effective lighting levels Illumination level (at work plane) with low production defects, Lux
Production unit 01 Production unit 02 Production unit 03
Mean 835.9 724.8 898.8
Standard
Deviation
159.6 145.6 265.9
Minimum 520.0 425.0 390.0
Maximum 1150.0 1028.0 1490.0
Count 20.0 35.0 33.0
On the other hand, while considering location of the
sample workers in terms of lighting environment or zone,
highest numbers of the samples had low production
defects within partly natural light in the production
space-1. In production space-2, low production defects
were observed in mostly artificial lighting environment,
while in production space-3, low production defects were
notices in partly natural environment. The production
space configuration in terms of window location,
available daylight inside the production space can be one
of the reasons behind this result.
Table 9: Frequency of only those lighting environment with low
numbers (0%~3%) of defects using bin function Lighting environment Bin* Production
unit 01
Production
unit 02
Production
unit 03
Completely Artificial
lighting environment -2 2 13 3
Mostly Artificial lighting
environment -1 0 18 5
Partly Natural lighting
environment 0 21 4 22
*Here,-2,-1 and 0 are the dummy variables (bin ranges within -2 ~0) for the
convenience of statistical analysis.
The correlation coefficients revealed that there were
causal relationships between the illumination condition
and the work efficiency. Through the regression analysis
the relationship established a linear equation y=mx+c,
where ‘x’ and ‘y’ are the two variables, ‘m’ is the slope
and ‘c’ is the intercept of ‘y’. Slopes are from -0.0091 to
y = -0.0091x + 10.979
0 1 2 3 4 5 6 7 8 9
10 11 12 13
300 400 500 600 700 800 900 1000 1100 1200
Per
cen
tag
e of
Pro
du
ctio
n d
efec
ts
per
hou
r (%
)
Illumination Level at work plane (Lux)
Production defects vs Illumination level (Production unit 1)
y = -0.0071x + 8.1569
0 1 2 3 4 5 6 7 8 9
10 11
300 400 500 600 700 800 900 1000 1100
Per
cen
tage
of
Pro
duct
ion
def
ects
per
hour
(%)
Illumination Level at work plane (Lux)
Production defects vs Illumination Level (Production unit 2)
y = -0.0049x + 7.6085
0 1 2 3 4 5 6 7 8 9
10 11
300 500 700 900 1100 1300 1500 Per
cen
tage
of
Pro
duct
ion
def
ects
per
hour
(%)
Illumination Level at work plane (Lux)
Production defects vs Illumination Level (Production unit 3)
PLEA2012 - 28th Conference, Opportunities, Limits & Needs Towards an environmentally responsible architecture Lima, Perú 7-9 November 2012
-0.0049 (Table 10). The minus (-) sign of the slope
indicates that increasing the illumination level decreases
the production errors. The value reveals that increasing 1
unit of illumination level causes 0.91%~0.49% less
defects. Within this scope of research, it was found that
probable efficient illumination ranges was commonly
601-800 lux. As the overall lighting levels in lighting
ranges were bit high in production space-3, the finding of
the ranges became high. Considering the mean values
and standard deviation from the mean values, it can be
said more specifically that the desired illumination level
at the work plane of the worker in production spaces to
achieve effective and quality production should be
around 700 lux (within range of 601~800 lux). However,
there must be no glare, veiling reflection or high contrast
at the work plane. Otherwise it could generate eye related
health hazards and reduce production.
Table 10: Comparative observation of the worker evaluation Terms Production
space-1
Production
space-2
Production
space-3
Sample
criteria
Number of Sample
workers
60 60 60
Sex M: 36%, F:
62%
M: 60%, F:
40%
M: 59%, F:
41%
Age group (Years) 18-25 18-25 22-29
Major Activity Name
(Sewing)
Operator
(75%)
Operator
(45%)
Operator
(43%)
Experience of sample
workers
More than 2
years
0.1-0.5 years 0.6-0.9 years
Total work hour
(hours/day)
9-10
hours/day
9-10
hours/day
9-10
hours/day
Linear
relationsh
ip
Causal relationship
between Illumination
level (x) and percentage
of production defects
per hour (y) , equation:
y=mx+c,
y = -0.0091x
+ 10.98
y = -0.0071x
+ 8.16
y = -0.0049x
+ 7.61
Ranges Illuminance ranges for
less defects (Lux)
601-800 601-800 801-1000
Mean Mean Illuminance for
less defects (Lux)
836 725 899
Standard
deviation
Standard deviation
(Illuminance for less
defects)
160 146 266
Quality of
light
Major Lighting
environment for less
defects
Partly
Natural light
(21)
Mostly
artificial
light (18)
Partly
Natural light
(22)
CONCLUDING REMARKS:
From this research, the following specific as well as
some general recommendations can be drawn for
production spaces of RMG factories in context of Dhaka
region, Bangladesh, in order to improve the luminous
environment as well as future study:
The illumination level at the work-plane of the workers
should be within 600-800 lux (average 700lux) especially
for Sewing Operators, Sewing Helper, Quality Controller
and others.
As illumination level and production defects have
negative linear correlations, low illumination level at
work plane must be avoided.
From this research it has been found that about
21~37% (0.21~0.373 out of 1) of the illumination
condition has the causal effect on effective production
capacity of the worker. Other aspects like thermal,
psychological, other environmental features should be
also considered during evaluation of the workers
performance with effective production in future research.
The luminaires layout and their spacing should be
designed by architects or designers in such a way that
uniform lighting and required lighting level with daylight
inclusion should be ensured at any point of the horizontal
work plane in the production space for flexible
production flow design.
Architects should design the production flow layout
within a production space in such a way that the critical
works, which require high lighting level to do the work
comfortably, can be placed near openings of the
production spaces to ensure better luminous environment
for the workers with better productivity.
This research was also conducted only in purpose
built RMG factories where the production spaces
maintain some certain environmental compliance.
Guidelines suggested in this paper can be considered by
the architects or designers while designing a standard
production space with accommodating compliances
possibly for LEED certification process or can be applied
during construction or renovation of the production
spaces.
ACKNOWLEDGEMENTS.
The authors acknowledge Bangladesh University of
Engineering & Technology and GIZ for their support.
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