chapter 6.ppt

Chapter 6 Basics of Radiometry and Photometry
The optical system is the transmission system of radiant energy
The energy transfer ability has influence on brightness of the image
Radiometry: The study of testing, measuring and calculating the ic wave
Photometry: The study of testing, measuring and calculating the visible light
Solid Angle and its Applications in Photometry
Angle and Its Unit
the plane angle :
1 radian
B
A
O
the space angle: solid angle
s
Ω
o
The space contained in a closed conical surface of any shape is called the solid angle
Ω=
Take a radius of r to draw a sphere, if the conicoid cuts an area of on the sphere , the solid angle is a sterad (sr) .The whole area of the sphere is . Therefore
Ω= =4 π
Calculation of The Solid Angle
Assume that the slope angle of a cone is α, let us determine the solid angle of the cone:
Draw a sphere with a radius of r, assume to take a girdle corresponding with . Then the breadth of the girdle is ,the radius of the girdle is ,so the length of the girdle is ,and the total area of the girdle is
Basic Ideas in Radiometry and Their Measurement Units
Flux
The total energy a radiator radiates in a unit time---- radiant flux ,and the unit is watt.
:optical spectrum intensity curve
2. Radiant Intensity
We make a solid angle of in a given direction, the radiant flux in the scope of is , the ratio of and is called radiant intensity in the given direction and is denoted by .
The measurement unit of the radiant intensity is watt per sterad (W/sr).
It shows the characteristics of a radiator that radiates energy in different directions.
3. Radiant Exitance and Irradiance
Take a tiny area of around point A, we assume that the radiant flux emitted from the tiny area is , then the radiant exitance of point A is
A
ds
The measurement unit is watt per square meters
It shows the radiant characteristics of different positions on the surface of the radiator, regardless o