Analyzing daylighting conditions for interior lighting setups
A little project set up by my friend Dilshan requiring an analysis for his office building in Sri Lanka. I’m typically used to the canadian sun light analysis so this posed a different approach since we are now much closer to the equator making it nearly impossible for daylight to ever reach deep spaces as the sun will always be above.
To get an idea of what the sunlight path would look like and the resulting shading we can use Ecotect (discontinued by Autodesk) which provides wonderful Solar tools to help understand these conditions. The following graphic demonstrates the differences between the lighting in Toronto and Colombo.
Toronto demonstrates that the light can reach further into spaces on one of the most extremes of sunlight conditions. During the summers, the sun is still going to reach the interiors however not as to the same extent.
The previous illustration depicts one of the most extreme of lighting conditions, as the drawing on the right demonstrates that the day light does not in fact reach far into the space as much as say Toronto.
Dilshan’s particular building is located on Sri Saddharma Mawatha, with clear views to the south east and a large wall in the rear that affects some of the light for the lower levels. It is a 3-storey building and we will be analyzing the second floor for the purposes of this exercise. The following diagrams demonstrate the overall lighting conditions for his building.
Looking at how limited the light gets into the space, its quite obvious that there will be a need for auxiliary lighting systems within the space, especially within the middle most bay during the entire day. The early mornings and late afternoons light will enter into the spaces closest to the windows, however as seen in the Annual Hourly Shadow Study, light in an overall sense does not really enter the space. The following diagram demonstrates this in a % of overall daylighting.
The interior will receive approximately 40–50% of all available daylight. This is far from enough to conduct work or reading within the spaces by relying solely on daylight.
To conduct any reasonable type of work, or reading the typical lighting levels for the interior spaces is required to be a minimum of about 500 Lux, which is typical lighting measurement unit used in demonstrating lighting atmospheric conditions within spaces. I have conducted two separate lighting distribution systems, one specified by Dilshan and one that I would think would work.
Case Study i: 5 Lights per Bay
This lighting condition allows for approximately 500–600 Lux levels at a height of 600 mm above Floor Slab. This is important as most table surfaces at on average at that height. So all measurements are conducted on table top heights. This set up is adequate throughout the day for work and reading.
Case Study ii: 4 Lights Per Bay
Conclusion:
In this scenario, the lighting fluctuates between 350–500 Lux which is inadequate for the conditions required. The previous scenario is far superior. The conclusion that can be made is that Case Study I is the correct lighting scheme, however to alleviate spots of darkness, T8 fluorescent tubes are preferable over spots as they allow for more evenly distributed lighting conditions and shadows under hands when writing and/or drawing are not as sharp.
This is just a basic guide on what goes on when doing Lighting Design Calculations and can go far further when given specific lighting fixtures with specific diffusers that produce complex lighting conditions. In such a situation, Ecotect plugs into a realistic ray tracer called Radiance which renders the lighting conditions accurately. I have used this for my building science thesis as my final dissertation for my bachelors in architecture to demonstrate methods of achieving maximum daylighting capabilities within an enclosed space.
