LIGHTING DESIGN: LECTURE - 5
Importance Of The Daylight
Luminance distribution
Sky conditions
Daylight Components
Daylight design methods
LIGHTING DESIGN LECTURE-5
DAYLIGHT : Importance Of The Daylight
Daylight is generally perceived as more attractive and comfortable than
artificial light. There are several reasons for this:
Light emitted by the sun covers a wide spectrum of colors. The blend
of these colors makes up white daylight. Artificial light sources cannot
exactly reproduce the color spectrum of the sun.
Daylight is dynamic. It varies through
the seasons and times of the day,
the position of the sun and cloud
cover. Artificial light is static.
LIGHTING DESIGN LECTURE-5
DAYLIGHT : Importance Of The Daylight
Artificial light in interior space is set at a level required for minimum
comfort. Daylight in interior spaces often reaches considerably
greater light levels.
Daylight is emitted by all sides of the
celestial hemisphere and by the sun.
Its distribution results in the illumination of the
environment which is comfortable for the eye.
Daylight has potential for energy saving.
All additional daylight not only means an
increase in visual comfort, but also an
energy saving in artificial lighting.
LIGHTING DESIGN LECTURE- 5
Three major reasons of Day lighting Design
Aesthetics (light and shadow, color, view)
Human performance (psychology and biology benefits)
Energy (sustainable design)
Daylight for the beauty
How much daylight (lux)
Quality of light
(glare and luminance ratios)
LIGHTING DESIGN LECTURE 5
Luminance distribution
Good daylighting is not simply a function of the quantity of light.
In fact, some techniques that increase the quantity of daylight can
actually decrease its quality.
two main quality issues
Glare
light distribution
Glare can be either disabling or discomforting.
disabling when it interferes with the ability to see.
discomforting when there is excessive contrast between light
and dark surfaces in a room
Glare does not nesessarily increase with increasing window size.
LIGHTING DESIGN LECTURE 5
Luminance distribution
The design is affected by conflicting requirements.
Increased reliance on day lighting, as an energy conservation
measure, may make a larger window desirable.
This may increase the risk of glare.
Even if sunlight is excluded, a view through the window of a sunlit
wall, a water surface, or sunlit clouds or a bright sky can cause
glare.
LIGHTING DESIGN LECTURE 5
Luminance distribution
The design is affected by conflicting requirements.
Increased reliance on day lighting, as an energy conservation
measure, may make a larger window desirable.This may increase the risk
of glare.
Even if sunlight is excluded, a view through the window of a sunlit wall, a
water surface, or sunlit clouds or a bright sky can cause glare.
If the sunlit device itself is visible (especially a white or bright metallic
device), it can cause glare.
If the shading device or a screen allows sun penetration in narrow
beams, producing alternating patches of sunlight and shade, it may be
worse than the unprotected window.
LIGHTING DESIGN LECTURE 5
Luminance distribution
Glare in day lighting can be reduced by :
1. Reduce luminance of the view by using low-transmittance glass
( 0.3), or by the use of blinds or curtains.
2. Increase the luminance of areas near the high luminance view,
e.g. by having windows in other walls to illuminate the surfaces
adjacent to the window or by using supplementary top lighting.
3. Increase the luminance of the windows surrounds by using
light color surfaces and contrast grading,
(With very large windows, this measure will not work.)
4. Use external protective devices
LIGHTING DESIGN LECTURE 5
Sky conditions:
Clear sky : Sky that is less than 30% cloud cover.
Overcast sky: Sky completely covered by clouds,
no sun visible
Cloudy sky: Sky having more than 70%
cloud cover.
LIGHTING DESIGN LECTURE 5
Sky conditions:
Typical illuminances E and luminances under
daylight and electric light.
LIGHTING DESIGN LECTURE 5
Components of the Natural Light (daylight flux) :
There are three separate components of the natural light that
reaches any point inside a building:
1. Sky Component (SC) - Directly
from the sky, through an opening such as a
window.
Sky Component (SC) depends on:
Width of the window
Distance between the point and
window
SC varies from 0.01 to 15%
LIGHTING DESIGN LECTURE 5
Components of the Natural Light (daylight flux) :
There are three separate components of the natural light that
reaches any point inside a building:
2. Externally Reflected Component
(ERC)
Reflected off the ground, trees or other buildings.
The luminance of obstrction is taken as 10-20% that of
the sky
3. Internally Reflected Component
(IRC)
The inter-reflection of 1 and 2 off surfaces within
the room.
Internally Reflected Component (IRC): is a half of SC
and is therefore significant
LIGHTING DESIGN LECTURE 5
Daylight design methods -1:
Daylight factor method
The ratio of day lighting illumination on a
horizontal point indoors to the horizontal
illumination outdoors, expressed as a For cloudy sky
percentage.
Design sky illuminance has been standardized as 5000 lx.
e.g. a 2% DF would mean
50002/100 = 100 lx indoor design illuminance (Ei)
For clear sky
LIGHTING DESIGN LECTURE 5
Daylight design methods -1:
Suggested daylight factor criteria (under overcast skies)
LIGHTING DESIGN LECTURE 5
Daylight design methods -1:
From a subjective perspective the following have suggested daylight
factors:
With a DF of less than 2%, a room will seem gloomy. Electric lighting
will be required for most daylight hours
With DF 2% - 5%, a room will feel that it is day lit, although
supplementary electric lighting may be needed.
With a DF greater than 5%, a room will feel vigorously day lit.
Electric lighting may not be necessary during daylight hours.
LIGHTING DESIGN LECTURE 5
DAY LIGHT DESIGN:
In day lighting design, for the positioning and sizing of apertures,
there are three main issues to be considered:
to satisfy the visual tasks (provide enough daylight)
to create the desired mood and provide visual focus
to integrate day lighting with the architecture.
LIGHTING DESIGN LECTURE 5
KEY ARCHITECTURAL ISSUES:
The daylight factor in a particular building space depends
upon a number of design factors including
1. size of daylight apertures (windows, skylights, etc.);
2. location of daylight apertures (side lighting, top lighting, etc.);
3. access to daylight (considering the site, building, and room
contexts);
4. room geometry (height, width, and depth);
5. location of the point of interest relative to apertures;
6. visible transmittance (VT) of glazing;
7. Reflectances of room surfaces and contents;
8. Reflectances of exterior surfaces affecting daylight entering
the aperture;
9. The effects of day lighting enhancements (light shelves..).
LIGHTING DESIGN LECTURE 5
Daylight design methods -2:
Total flux method
A room in the building is considered as a closed box, with an
aperture (a window) that will admit a light flux.
The illuminance on the plane of the window (EW) must be
known(assume 5000lx for calc.). If this is multiplied by the
window area (A), the total flux entering the room is obtained
LIGHTING DESIGN LECTURE 5
Daylight design methods -2:
This will however be reduced by three factors:
1. M, the maintenance factor, which allows for dirt or other
deterioration of the glazing in use.
2. G, or glass factor, allowing for the type of glazing, other than
clear glass.
3. B, bars or framing factor, allowing for obstruction due to
Solid elements of the frame and sashes, that would reduce the
effective area.
Thus, the effective flux entering will be
LIGHTING DESIGN LECTURE 5
Daylight design methods -2:
Data sheet d.2.2
Day lighting: correction factors
Effective flux
If this flux were to be uniformly
distributed over the floor area,
the Average illuminance would be
(where A is area)
