Metrics For Daylight Strategies

The Daylight Factor

As society came to terms and realization of the sustainable energy and benefits that natural lighting offer; it was essential to try and harness such a resource to its full potential. The concept of the daylight factor was established in the early twentieth century to assist architects and designers to be able to assess how daylight would interact with the dwellings and how they can use it to their advantage.

The Daylight factor represents the quantity of illumination that would be available indoors relative to the illumination present outdoors of the location under overcast skies; this factor is formed in a ratio. To calculate the factor a simple formula is used ; 

DF = (Ei/Eo) x 100 %

Ei stands for the indoor illumination and Eo represents the outdoor illumination. It is calculated as the above formula displays by dividing the horizontal work plane illumination indoors by the horizontal illumination outdoors on the roof of the building that is being questioned for its daylight intake and then multiplying the result by 100.

The higher the ratio the more natural light the location is exposed to. This helps the architects to evaluate where windows should be placed so that the interior is exposed to enough daylight. On the other hand if the building is already built the daylight factor helps designers to be able to manipulate the access points in order to have more exposure to daylight.

The illustrations below show how a building would be typically assessed using the daylight factor. The image on the left shows the ground level of the building and the amount of light that the floor would intake and the intensity of light that would integrate with the interior. The image on the right displays the first floor and the intensity of the light is also seen; even where access points are not integrated. 

 Another useful way to asses the daylight is through the use of luminance. By invoking a cross section of the building and analyzing its luminance a more dynamic overview of the exposure of natural lighting is gained. The study of daylight and its luminance can be calculated through daylight simulation programs such as; 

Radiance

§  Daysim

§  Desktop Radiance

§  IESve

§  DIALux

§  Relux

§  Ecotect

§  VELUX

§  LightCalc

Reference Links;

Daylight Site. 2015. DAYLIGHT ANALYSIS IN THE DESIGN PROCESS OF RESIDENTIAL BUILDINGS | The Daylight Site. [ONLINE] Available at: http://thedaylightsite.com/daylight-analysis-in-the-design-process-of-residential-buildings/. [Accessed 19 April 2015].

Daylight Factors | All Things Lighting. 2015. Daylight Factors | All Things Lighting. [ONLINE] Available at: http://agi32.com/blog/2014/03/05/daylight-factors/. [Accessed 19 April 2015].

Daylight factor. 2015. Daylight factor. [ONLINE] Available at:http://www.new-learn.info/packages/clear/visual/daylight/analysis/hand/daylight_factor.html. [Accessed 19 April 2015].

Daylight Factor | Daylighting Pattern Guide. 2015. Daylight Factor | Daylighting Pattern Guide. [ONLINE] Available at:http://patternguide.advancedbuildings.net/using-this-guide/analysis-methods/daylight-factor. [Accessed 19 April 2015].