Daylighting Factor and Its Value For Different Spaces

Source of light  is sun, but inside a building light from the sun may reach in the following ways:

• A - Diffused or skylight , ( through window or opening).
• B - Externally reflected light ( by ground or other buildings) through the same windows
• C - Internally reflected light from walls , ceiling  or other internal surfaces.
• D - Direct sunlight  along a straight path from the sun through a window top a given point.

Daylight Factor

It is the ratio of illumination in a given building to the simultaneous outdoor illumination. It is taken as a constant expressed as a %.

Its valid only under overcast sky conditions, i.e when there is no direct sunlight.

D.F = Ei/Eo *100
D.F = sky component + externally reflected component + internally reflected component

Design Sky – It is the illumination value for a particular location evaluated from records of illuamination taken over a long period of time which is exceeded in 90% cases in daylight hours.

Warm Humid Climates

• Direct sunlight is avoided for thermal reasons. Bright sky can provide sufficient light but also causes glare.
• View of the sky is screened using planters or shading devices. A view of the sky up to 15° from the horizon is permissible.
• Daylight must be reflected from ground or blades up to ceiling which should be of a light colour.

Hot and Dry Climate:

• Internally reflected light is the best form of daylighting. The small size of openings and blue skies reduce the sky component in such areas.
• Shading devices used should be non reflective and positioned so that they are not directly visible as they can cause glare.
• High level windows should be used. Low level windows are acceptable only if they open onto a shaded and planted courtyard.
• Strong luminance contrast between a sunlit view and window can be avoided by painting adjacent walls and inside of window frames white.

DAYLIGHT FACTOR FOR VARIOUS SPACES

To learn more about lighting, visit:

• Introduction to Lighting
• Glare and Factors Controlling It
• Lamps And Luminaires

This presentation was created by: Ankita Gupta, Vineet Goyal, Akhilesh Maurya, Biswajit Behra