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.

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 The natural light can be used as the sole source of interior lighting or can be combined with artificial light.

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 sunlight( 日光） Direct sunlight 太阳直射光 skylight 天空扩散光 shadow 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 全阴 Is a standard overcast 全阴 sky which is taken to have the same luminance in every direction of view. 半球的 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

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= illuminance at the reference point (lx) Eo= illuminance at that point if the sky was unobstructed (lx)

！！ Direct sunlight is excluded from both values of illuminance

天空扩散光 Sky components (SC) 天空扩散光 室外反射光 External reflected component (ERC) 室外反射光 室内反射光 Internal reflected component (IRC) 室内反射光 DF=SC+ERC+IRC DF=SC+ERC+IRC Daylight factor components 采光系数的组成 采光系数的组成 the daylight reaching a particular point inside a room is made up of three principal components,

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

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 室内永久辅助人工照明

Today’s homework

Exercises in class 1 fenestration 开窗法 affects ( ) A lighting environment B heat environment C sound environment D 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