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.
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
|TYPE OF BUILDING
||DAYLIGHT FACTOR (%)
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This presentation was created by: Ankita Gupta, Vineet Goyal, Akhilesh Maurya, Biswajit Behra