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

TYPE OF BUILDING
SPACE
DAYLIGHT FACTOR (%)
DWELLINGKITCHEN2.5
 LIVING ROOM0.625
 BEDROOM0.313
 STUDY1.9
 CIRCULATION0.313
SCHOOLSCLASSROOMS1.9
 LECTURE1.9-2.5
 LABORATORIES1.9-3.8
OFFICEGENERAL1.9
 DRAWING3.8
 ENQUIRY0.625-1.9
LIBRARYSTACK ROOM0.9-1.0
 READING ROOM1.9-3.8
 COUNTER AREA2.5-3.8
 CATALOGUE ROOM1.9-2.5
HOSPITALSGENERAL WARDS1.25
 PATHOLOGICAL LABS2.5-3.8

 

To learn more about lighting, visit:

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


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Comments

ASMITA N RAWOOL's picture
Member since:
30 October 2010

NICE WORK !!!