6 Principles of Light
光学原理
Light and the effects of light are a major
element in the human sense of the environment.
Both artificial and natural sources
of light are used in buildings and these sources
can be supplied and controlled in many ways.
6.1 Natural of Light 光的性质
what is light?

Light is energy in the form of electromagnetic radiation
光是以电磁波形式传播的(辐射)能。


electromagnetic spectrum
电磁辐射波谱
UV：紫外线 is the short of (ultraviolet)
IR: 红外线 is the short of （infra-red)
how do light travel?
Light travel in straight lines but can be affected by the
following effects.
Reflection 反射
Refraction: 折射
Diffraction: 衍射
Light travel in straight lines
Reflection 反射
Refraction: 折射
Diffraction: 衍射
what is Visible radiation 可见光
nm_ nanometre 纳米10-9m
The wavelengths of electromagnetic radiation that are visible to
the eye range from approximately 380nm to 760nm .
380nm
760nm
What is white light?
什么是白光？
If all the wavelengths of light are seen at the same time the
eye cannot distinguish the individual wavelengths and
the brain has the sensation of white light.
380nm
760nm

White light can be separated into its component
wavelengths using a glass prism棱镜,
Monochromatic
and color
light 单色光 is light of one particular wavelength
what is Non-visible radiation 不可见光

Electromagnetic radiations with wavelengths outside the range
of visible wavelengths cannot be detected by the human eye.

Ultra-violet
Infra-red
Infra-red radiation 红外线
 Infra-red radiation has wavelengths slightly greater than those
of red light and can be felt as heat radiation from the Sun and
from other heated bodies.

Infra-red radiation is made use of in radiant heating devices, for
detecting patterns of heat emission, for “seeing ” in the dark,
and for communication links.
Ultra-violet 紫外线

Ultra-violet radiation has wavelengths slightly less than
those of violet light. It is emitted by the Sun and also
by other objects at high temperature.

Ultra-violet radiation helps keep the body healthy but excessive
amounts can damage the skin and the eyes.

Ultra-violet radiation can be used to kill harmful bacteria in
kitchens and in hospitals.

Certain chemicals can convert UV energy to visible light and
the effect is made use of in fluorescent lamps荧光灯.
6.2 Nature of vision 视觉特征
retina视网膜

the structure of the eye
Cone vision 锥体细胞 is adapted to normal levels of light and is
used to for seeing details and distinguish colour

Rod vision杆状细胞 is adapted to very low levels of light and is
very sensitive to light but cannot distinguish colour
terminology of vision视觉术语

Visual field视野 Is the total extent in space that can be seen
when looking in a given direction

Visual acuity视觉敏锐度 Is the ability to distinguish between
details that are very close together.

Adoption视觉适应 Is the process occurring as the eyes adjusts
to the relative brightness or colour of objects in the visual field.

Contrast视觉对比度 is the different in brightness or colours
between two parts of the visual field.
180
6.3 how to measure lighting 光的度量

Light is one form of energy and could be measured
by the standard units of energy.

But the effect of light on the human environment also depends
upon the sensitivity of the eye and a special set of units has
been developed for the measurement of light and its effects.

Luminous flux 光通量

Solid angle 立体角

Luminous intensity 发光强度

Illuminance照度

Luminance 亮度
which one can give more light?
Luminous flux光通量 is the rate of flow of Incandescent lamps
light energy
辐射体单位时间内以电磁辐射的形式向外
辐射的能量称为辐射功率或辐射通量
其中被人眼感觉为光的那部分成为光通量。

Unit : lumen (lm)

1lm= 1/683 W
fluorescent lamps
what is Solid angle 立体角


light can radiate in all three dimensions

the space around a point can be divided into “solid angles”
ds
d  2
r
The
ds r 2
1steradian 2  2  1
r
r
standard SI unit of solid angle is the steradian球面度(立体
角单位
A complete sphere contains
a total of 4  steradians
ds
d  2
r
which one would you choose?
F

Luminous intensity发光强度

Unit : candela (cd)

The candela is one of the base units in the SI
system.
I

Illuminance 照度
When luminous flux falls on a surface it illuminate that
surface.
Illuminance is the density of luminous flux reaching a surface

Unit : lux (lx)
1lx=1lumen/(meter)2

If light is falling a surface at right angles to the surface then the
illuminance is given by the following formula.
F
E
A
Illuminance 照度 in several
different cases
22
Figure 5.3 Summary of lighting measurements
McMullan
Inverse square law of illumination
照度的平方反比定律


The llluminance produced by a point source of light
decreases in inverse proportion to the square of the distance
from the source.
May be expressed by the following formula
I
E 2
d
Worked example 6.2
A lamp has a luminous intensity of 1200cd and acts as
a point source. Calculate the illuminance produced on
surfaces at the following positions
a) At 2m distance from the lamp, and
b) At 6m distance from the lamp
Know: I=1200cd
Using
I
E 2
d
d1=2m and d2=6m,
E=?
E1=1200/22=300lx
E2=1200/62=33.33lx
Cosine law of illumination照度的余弦定律

light strikes many surfaces at an inclined angle and
therefore illuminates larger areas than when it strikes
at a right angle.

I
Can be calculated using E  2 cos 
d
 Angle between direction of flux and the normal
Worked example 6.3
2.5m

2m
1.5m
A lamp acts as a point source with a mean spherical intensity of
1500cd. It is fixed 2m above the centre of a circular table which
has a radius of 1.5m. Calculate the illuminance provided at the
edge of the table, ignoring reflected light.
know: I=1500cd, E=?
Using :triangle laws三角形定律 d=2.5m
2
2
cos   
d 2.5
Note: you do not need to know the actual value of the angle in
degrees
Using
I
1500 2
E  2 cos  
 192lx
2
d
2.5 2.5
Reflection 反射
Diffusere
Specular flection
镜面反射
flection
漫反射
Reflectance 反射率is the ration of the luminous flux reflected
from a surface to the flux incident upon the surface
Worked example 6.4
A point source of light with a luminous intensity of
1800cd is set 3m above the floor and 1m below the
ceiling which has a reflectance of 0.5. calculate the direct
and reflected component of the illuminance on the floor
beneath the light
Know I=1800cd d=3m E=?
Using
Reflectance of 0.5
1m
I 1800
E  2  2  200 lx
d
3
3m
So direct component = 200 lx
d=1+1+3=5m
I
1800
E  2  reflectanc e  2  0.5  36 lx
d
5
which one is brighter ?
a fluorescent tube
a spot lamp聚光灯
have the same luminous intensity;
Self-luminous
The
sources 自发光光源
luminance is given by the following formula
Luminous intensity in a given direction
L
Area of source as seen from that direction
unit: cd/m2
亮度和照度有何区别？照了不一定亮！
Luminousflux reflected
Reflecting surface 反射表面
L
Area of reflectingsurface
unit: apostilb 阿波熙提(应用于扩
散表面的亮度单位)
where 1asb=1lumen/m2
反光材料，亮度高
吸光材料，亮度低
31
Self-luminous
sources 自发光光源
Reflecting surface 反射表面
cd/m2
1asb=1lumen/m2
the candela per square metre is the correct SI unit of luminance.
The apostilb is an alternative unit of luminance which is
convenient for some calculations
1 apostilb =1/

cd/m2
Draw out a list to compare these parameters
Solid
angle
立体角
Luminous
intensity
发光强度
Steradian candela
(cd)
球面度

ds
d  2
r
Luminous Illuminance Luminance
flux
照度
亮度
光通量
lumen (lm) lux (lx)
I
I
E
F
cd/m2
F
E
A
L
I
I
E  2 E  2 cos 
d
d
F

1lm= 1/683
W
1lm/m2
1 apostilb =
1/  cd/m2
Self-luminous
The
sources 自发光光源
luminance is given by
Luminous intensity in a given direction
L
Area of source as seen from that direction
Reflecting surface 反射表面
Luminousflux reflected
L
2
1asb=1lumen/m
Area of reflectingsurface
1 apostilb =1/

cd/m2
unit: cd/m2
A good light
environment
requires a
suitable light
distribution
what is Glare 眩光

Glare is the discomfort or impairment
损害of vision caused by an excessive
range of brightness in the visual field.

Glare can be caused by what?

lamps, windows and painted surfaces
appearing too bright in comparison with
the general background.
Glare Can be further described as
Disability glare 失能眩光
Discomfort glare不舒适眩光
how to measure Light?

A Photometer 光度计is an instrument that measures the
luminous intensity of a light source by comparing it with a
standard source whose intensity is known.

A photocell light meter 光电仪 is an instrument that directly
measures the illuminance on a surface.

The electrical resistance of some semiconductors , such as
selenium硒, changes with exposure to light and this property is
used in an electrical circuit connected to a galvanometer检流计.
This meter may be calibrated in lux.
Does light has Directional quality ?
光有方向吗？
We can describe its directional property
using the following parameters

Illumination vector 照明矢量

Scalar illuminance 照明标量

Vector/scalar ratio 矢量/标量比
Because of the limited time, we won’t talk too much
about these parameters
6.4 Color 色彩
please read this part by yourself after class











Spectral energy distribution figure 5.12
Colour systems
CIE color coordinates
Munsell system
Colour reproduction
Additive colour
Additive primary colours
Application of additive colour
Stage lighting
Colour television
Colour printing
6 Principles of Light
5.1 what is light?
5.1.1 how is light travel?
5.1.2 what is Visible radiation 可见光
5.1.3 what is Non-visible radiation 不可见光
5.2 Nature of vision 视觉特征
Cone vision 锥体细胞
Rod vision杆状细胞
Visual field视野
Visual acuity视觉敏锐度
Adoption视觉适应
Contrast视觉对比度
Inverse square law of illumination
5.3 Measure of lighting 光的度量
I
 Solid angle 立体角
E 2
d
 Luminous intensity 发光强度
Cosine law of illumination
 Luminous flux 光通量
I
 Illuminance照度
E  2 cos 
d
 Luminance 亮度
5.4 Colour 色彩 P122
Exercise in the class
1 Cone vision 锥体细胞 (
)
A is adapted to normal levels of light
B is adapted to very low levels of light
C is used for seeing details
D is used for distinguish
E is very sensitive to light
F cannot distinguish colour
2 rod vision 锥体细胞 (
)
A is adapted to normal levels of light
B is adapted to very low levels of light
C is used for seeing details
D is used for distinguish
E is very sensitive to light
F cannot distinguish colour
3(
) is the rate of flow of light energy
A solid angle
B luminous intensity
C luminous flux
D illuminance
E luminance
4 Link the following two columns by lines
1 Solid angle
2 Luminous intensity
3 luminous flux
4 illuminance
5 luminance
A cd/m2
B steradian
C apostilb
D lm
E cd
F lx
G lumen/m2