8
Natural Lighting
自然采光
It is necessary to provide a room with natural light
from the Sun or the sky.
Is Natural lighting just affect the
light environment in buildings?
NO!!

Daylight日光 is usually admitted into a building
by means of windows or skylights天窗;

but these windows also transmit heat, sound, and
perhaps air.

So the design of windows for a building, called
fenestration开窗法, affects almost all the environmental
variables.

The natural light can be used as the sole
source of interior lighting or can be combined
with artificial light.
This chapter is concerned with
8.1 Natural lighting sources 自然光源
8.2 Daylight factors 采光系数
8.3 Combined lighting 混合照明
8.1 Natural lighting sources
自然光源

All natural lighting comes from the Sun, by way of sky.

the light from the sky varies with the time of the day,
with the season of the year and with the local weather
Direct sunlight 太阳直射光

sunlight( 日光）
shadow
skylight 天空扩散光
Lightness

In parts of the world with predominantly (占主导
地位的）dry, sunny weather much of the natural
light inside building is direct sunlight

In the United Kingdom, and similar countries
where sunshine is unreliable , the overcast sky
（阴天） is consider as the main source of
natural light

Because the sky continually varies it is necessary
to define certain “standard skies”, with constant
properties, for use in design work.
Examples of different sky distributions
8.1.1 how to define “standard skies”
（1）Uniform standard sky 统一标准天空
Is a standard overcast 全阴 sky which is taken to have the
same luminance in every direction of view.

Viewed from an unobstructed point on the ground the sky
effectively makes a hemispherical半球的surface around that
point.

This surface emits light and the uniform sky assumes that
every part of the surface is equally bright.

Although the overcast sky of some countries is
not strictly uniform in luminance the model is
useful for some purposes.

The clear skies in sunny climates can also be
looked as a uniform standard sky.
（2）The CIE sky (CIE 标准天空)
is a standard overcast sky in which the luminance steadily
increases above the horizon.
This sky was defined by the Commission internationale
d’Eclairage 国际照明委员会
1
L  L Z (1  2sin  )
3
The luminance of the CIE sky at the zenith （顶点）is
three times brighter than at the horizon.
the CIE model is found to be a good representation of
conditions in many parts of the world.
8.2 what is Daylight factors 采光系数

Daylight factor is the ratio between
（the actual illuminance at a point inside a room ）
And
（ the illuminance possible from an unobstructed hemisphere of
the same sky）.

Unit : percentage
Ei
DF 
100%
Eo
Ei= illuminance at the reference point (lx)
Eo= illuminance at that point if the sky was unobstructed (lx)
Ei
DF 
100%
Eo
！！Direct sunlight is excluded from both values of
illuminance
8.2.1 Daylight factor components
采光系数的组成
the daylight
reaching a
particular point
inside a room is
made up of three
principal
components,

Sky components (SC) 天空扩散光

External reflected component (ERC)室外反射光

Internal reflected component (IRC)室内反射光

DF=SC+ERC+IRC
8.2.2

Daylight factor contours
采光系数等高线
Daylight factor contours represent the
distribution of daylight inside a room
by means of lines which joint points of
equal daylight factor
Ei
DF 
100%
Eo
What’ the use of daylight factor contours?
It can help us to judge the natural lighting in a building
Daylight Factor contours can help us to compare different
natural lighting designs
8.3 Combined lighting 混合照明
PSALI
Permanent Supplementary Artificial Lighting interiors.
室内永久辅助人工照明
Today’s homework
Exercises in class
1
A
B
C
D
fenestration开窗法 affects (
lighting environment
heat environment
sound environment
air quality in buildings
)
2 the light from the sky varies with (
A the season of the year
B the local weather
C the time of the day
D the sense of people
)
3 Uniform standard sky Is a standard
overcast sky which is taken to have the
same （
） in every direction of view.
A luminous flux
B luminous intensity
C illuminance
D luminance
4 The CIE sky is a standard overcast sky
in which （
）
A the luminance is constant
B the luminance at the zenith is three times brighter than
at the horizon
C the luminance steadily decreases above the horizon
D the luminance steadily increases above the horizon.
5 the daylight reaching a particular point
inside a room consists （ ）
A daylight factor
B sky component
C externally reflected component
D internally reflected component