NATURAL LIGHTING OF STUDIO APARTMENT WITH EAST-ORIENTED OPENING

. Less optimized natural lighting would result in apartment residents being dependent on artificial lighting, thus increasing energy consumption. Building opening orientation considerably influences the natural light intensity. This research aimed to analyze the natural lighting pattern on apartment units with east-oriented opening orientation and determine methods to support the existing condition to be optimized. This research applied the descriptive analysis research method assumed from calculation outcome of the software DIALux. Results indicated a proportion of units in The H-Residence Apartment do not meet the requirements specified by SNI 03 6197-2011, predominantly in the kitchen area. The average light intensity in a day in units with east-oriented opening reached its peak at 08.00 – 09.00 a.m. and decreased towards 16.00 p.m. following the sun path. The light intensity in numerous areas exceeded the requirements significantly. Other factors influencing the natural light distribution are layout and interior element. Several ways to optimize the natural light intensity utilization are adding suitable shading device, using dark-colored interior elements, and considering the sun path in designing building openings.


INTRODUCTION
The building sector in Indonesia is the largest energy consumer after the industrial and transportation sector, reckoned at 24% in 2004 and still expected to rise to 39% by 2030. The energy consumption generated by the use of artificial lighting contributes about 15%-25% to building's total energy consumption [1]. In countries with tropical climate, lighting system that depends on natural lighting from the sun could decrease the use of artificial lighting, thus reducing energy consumption. However, excessive incoming light intensity might cause visual or thermal discomfort, therefore causing apartment residents to block incoming natural light with light control devices [2]. Less optimized natural lighting intensity might result in apartment residents being dependent on artificial lighting, accordingly increasing energy consumption per unit so as affecting the expenses paid by the residents [3].
One of the factors influencing the penetration depth of natural light is window or opening orientation [4], [5]. This theory is based on the sun path throughout the day that progresses from east to west, influencing the natural lighting received by building opening depending on its orientation. The optimal opening orientation for buildings in Jakarta that is located in the equator area would be facing south or north to avoid excessive radiation and high temperature [6,7].
This research aims to analyze natural lighting pattern on apartment units with east-oriented opening orientation and determine methods to support the existing condition to be optimized. Research simulation was run in natural lighting condition, meaning no lamps were switched on, and without assessing the glare factor. Regulation used to examine the average natural lighting intensity calculation result is SNI 03-6197-2011. This p-ISSN : 1412-114X e-ISSN : 2580-5649 http://ojs.pnb.ac.id/index.php/LOGIC research can be used as a recommendation in lighting system design and reference to advance the natural lighting issue on apartments or high-rise buildings so that it could be further optimized.

METHODS
This research was done on studio apartments in both empty and furnished setup in The H Residence Apartment located at Jl. MT Haryono Kav 6-7, Cipinang, Cempedak, East Jakarta. The studio unit area is 37 m 2 with 1.3 m 2 balcony and 2.7 m floor-to-roof height. Referring to Figure 1, the rooms inside consist of a bedroom, a kitchen area, and a bathroom.  As shown in Figure 2, the unit layout is divided in two types, one of them with balcony at the unit's south corner and the other at the north corner. A wall divides each unit's balcony, causing the south-corner balcony to end up with the wall on the right side, while the north-corner with the wall on the left. This research began with searching the unit property data consist of the size and materials used for the interior elements. Then, a model was constructed using DIALux evo 9 for units with both empty and furnished setup. Afterwards, a simulation was run in various conditions namely at 8.00 a.m., 12.00 p.m., and 4.00 p.m. on June 21 and December 21 2020. Working plane was set on 0.75 m from the ground [9]. Digital simulation was chosen because of the high accuracy rate and the ability to cover plenty parameters with realistic result [10].
This research applies the descriptive analysis method that shows detailed data through words [11]. Average natural lighting intensity acquired from digital simulation was compared to requirements stated in SNI 03-6197-2011 about Energy Conservation on Lighting System, specifically 250 lux for bedroom and kitchen [12]. Further calculation was done in Microsoft Excel, with the 15th floor representing other floors due to its central position.  Table 1 shows the comparison between material used in existing apartment and digital simulation. Aside from wall, floor, ceiling, and opening, a set of furniture was added with heavy reference to actual studio apartment presented in The H Residence Apartment. All materials used in simulation model were adjusted to match the actual model, using the materials provided by DIALux evo 9 library. Table 2 and 3 show the calculation result summary from DIALux software in which numerous areas do not meet the requirements specified by SNI, specifically the kitchen area. The kitchen area possesses low average intensity due to its location being far from window opening and surrounded by dark-colored interior elements, namely entrance and bathroom door      Figure 4 shows the same progress, although not as drastic as the empty setup, lighting intensity reaches its peak at 8.00 a.m. The area with highest lighting intensity, marked by the color red and orange, ranging from 2000 -7500 lux, is located near the window opening. While, the area with lowest lighting intensity, marked by the color purple to green, ranging from 0 -300 lux, is located around the kitchen area. shows that similar occurrence with Figure 4 happened, with the lighting intensity reaching its peak at 8.00 a.m. and gradually decreases throughout the day. However, intensity produced on December 21 is far higher than on June 21. The area with highest lighting intensity, marked by the color red and orange, ranging from 2000 -7500 lux, is located near the window opening. While, the area with lowest lighting intensity, marked by the color blue and green, ranging from 5 -300 lux, is located around the kitchen area. shows similar progress with Figure 5, although with far higher lighting intensity. The area with highest lighting intensity, marked by the color red and orange, ranging from 2000 -7500 lux, is located near the window opening. While, the area with lowest lighting intensity, marked by the color purple to green, ranging from 0 -300 lux, is located around the kitchen area.    Based on Figure 9, both units reached peak lighting intensity between 08.00 -09.00 a.m. in accordance with the sun path moving from east to west causing the culmination to happen in the morning. The average natural lighting intensity declines in the evening following the sun moving west [13]. Apartments with opening not meeting the requirements might result in unit receiving sufficient lighting intensity for only half a day since there will be a drastic decrease after noon.  Apartment number 1528 with south-corner balcony possesses higher average lighting intensity in comparison with apartment number 1530 with north-corner balcony. This occurrence is caused by a 3° deviation to the south on the building, therefore making apartment number 1528, with a wall dividing each studio located at the right side of the balcony, to receive more light from the sun.

Lighting Intensity Pattern
Average lighting intensity from both units far exceeded the minimum requirements stated in SNI. While maximum requirements are not mentioned, requirements of maximum 300 lux for bedroom and 750 lux for kitchen area are mentioned in IESNA [14]. Excessive average lighting intensity might cause visual discomfort such as glare and thermal discomfort or high temperature, causing the residents to block incoming light and using artificial light instead [15]. High average intensity might be caused by the area of window opening, creating visual discomfort [16].
Bigger opening area causes the window-to-wall-ratio (WWR) to exceed reasonable limit. While there is a research that states the energy used for artificial lighting increases as WWR decreases, it is possible for residents to cover openings instead to avoid glare and heat, thus increasing the use of energy for artificial lighting [17]. Other previous research states energy use will decrease as WWR decreases [18].
In both units, average intensity on December is considerably higher compared to June. Because the building coordinate is located at 6°14'S and 106°52'E, lighting intensity will differ between the two solstices. This happens because sun's latitude on June 21 is situated at 23.5°N and on December 21 at 23.5°S.

Figure 9
also indicates that empty unit possesses higher average lighting intensity compared to furnished unit caused by the dark-colored interior elements where the reflection factor is lower. Interior elements with dark colors might cause 50% decrease of lighting intensity [19]. Furthermore, the materials used also influence visual discomfort. Materials such as glass and wood can be used for interior wall, gypsum board can be used for ceiling and ceramic for tiles [20].

CONCLUSION
East-oriented opening possesses higher average of natural lighting intensity in the morning and decreasing throughout the day given the sun path moving from east to west. Average intensity received by all units exceeds the requirement stated in SNI 03-6197-2011 and SNI 03-6575-2011. Several ways that can be applied to optimize unit's natural lighting state are adding horizontal shading device and using dark-colored interior elements. Preliminary to designing building opening, a suitable opening orientation in accordance with the sun path must be considered. Further similar research to concern the unit layout aspect and external factors from surrounding environment.