A Method to Determine a Single Point Percentage Daylight Factor Value from Field Work Data S.F. Mohamed1*, E.M. Cik Harun2 and A.W. Abdullah3 1School of Housing Building and Planning, Universiti Sains Malaysia, 11800, Penang, Malaysia
2,3School of Technology Management and Logistic, College of Business, Universiti Utara Malaysia, Sintok, Kedah, Malaysia
*Correspondence: firstname.lastname@example.org ABSTRACT Background: The daylight factor is an established way to measure daylight level in an indoor space, whereby natural illumination level indoors (Ei) is compared to the simultaneous illumination outdoors (Eo). Objectives: This paper suggests a way to measure %DF using field work data taking samples of 2 rooms with the worst case scenario of facing directly East and West for comparison. Results: Two varied window to wall (WWR) and window to floor (WFR) ratios were tested for this experiment. The %DF values calculated from this research were in the range of 0.8 to 2.3% and natural illumination levels were found to be more than adequate for normal bedroom activities. Conclusion: The west room experiences slightly lower average %DF values compared to east room. From the average %DF values, how bright they translate into illuminance level in the rooms under the real Malaysian skies could be seen in the average, max and min Li data collected.
Daylight factor %DF, Window to wall ratio (WWR) window to floor ratio (WFR) INTRODUCTION The most popular and most used formula to measure and analyze day lighting performance in buildings is the percentage daylight factor [1,2,3]. The daylight factor quantifies daylight levels and distribution pattern in the interiors of a building. The formula assumes overcast skies condition and it does not consider the excessive illumination caused by direct sunlight penetration.
Eo is the simultaneous outdoor illuminance on a horizontal plane from an unobstructed hemisphere of an obstructed sky . By using relative values which compare indoor to outdoor illuminance, this factor is constant under widely varying outdoor sky and day lighting conditions 
METHODOLOGY A case study building was selected from one of the residential blocks of the Universiti Sains Malaysia campus called Fajar Harapan, which is located in Penang Malaysia. The rooms selected face the East and West direction directly (Figure 1). The rooms measure 2.9m by 4.43m with floor area of 12.85meters square. The window area is 4.43 meter square which makes up 50% of window wall ratio (WWR) and 35% of window floor ratio (WFR).
To get more %DF readings, the windows were also half covered using polystyrene boards (Figure 2) making 25% WWR and 17% of window floor ratio (WFR).
Indoor illumination were taken at mid points of east and west rooms (Le and Lw) using luxmeter probes located 1m above floor level. Readings were logged every 10 minutes using a data logger simultaneously with an outdoor weather proof light probe (Lo). Similar techniques were carried out with the window areas covered by half. All measurements were carried out from in March. March days were chosen as the sun path for the locality of Penang is more directly perpendicular to the room’s orientation.
Fig. 2: East and West room position and windows shape.
RESULTS AND DISCUSSION Indoor illumination at the East room usually peaked at around 9am while in the West room at around 5pm and this is an indication of some direct sunlight penetration according to the sun’s location and altitude at the particular times. In the field work daylight factor calculations ie Le/Lo X 100 and Lw/Lo X 100 the readings which were seen to have the influence of direct sunlight were disregarded . This is because the daylight factor calculations do not consider the component from direct sunlight and assumes completely uniform and overcast skies. Readings, which were too early in the morning and too late in the evening, were also disregarded due to the skies not being uniformly illuminated. Only readings from 10.30am to 3.30 pm (Figure 4) are considered as those are the approximate times that direct sunlight penetration do not occur in both rooms. This duration is derived through observation and pattern of data from field work
CONCLUSION Table 1 below summarizes the data collected and described above. It could be seen that the west room experiences slightly lower average %DF values compared to east room. From the average %DF values, how bright they translate into illuminance level in the rooms under the real Malaysian skies could be seen in the average, max and min Li data collected. Data on Lo, on the other hand describe the high illumination of the Malaysian skies. Here in Malaysia, 1%DF and even 0.5% DF may be sufficient for activities in a residential room like resting, reading or just taking a nap.
Table 1: Natural Illumination Level and daylighting factor
East Room 6 Days (10:30am - 3:30pm)
50% (10 - 15 Mar)
25% (16 - 21 Mar)
West room 6 Days (10:30am - 3:30pm)
50% (10 - 15 Mar)
25% (16 - 21 Mar)
ACKNOWLEDGEMENT The autors thanks Opik Taopiqurrohman, Agung Restu Susanto, Ube, Dedi, and Finy for their dedicated work in collecting data used in this article as a part of the objective of our research for rehabilitating the degraded peat land areas.
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