Double Ten science and technology about the basic concepts and importance of photometric measurement
Date：2022/8/3 11:07:31 / Read： / Source：本站
The measurement of photometry has high precision, which is the basis of accurate measurement of radiometrics. By thinking about people
The light effect function of the eye can be converted into a measure of radiation. Illumination and other optics can be used to measure illumination
The relationship of physical quantities to determine other optical quantities.
Photometric measurement is the corresponding radiation measurement in the visible band, taking into account the subjective factors of the human eye
Discipline. Since the human eye is a highly complex device, measuring the human eye's response to light is undoubtedly a very difficult task
Hard work. It involves many disciplines, including psychology, physiology and physics.
In 1924, the International Commission on Illumination d'Elairage (CIE) organized
The conference defined the average response value of the human eye to light, and photometry has since become a modern discipline. CIE sampling
A large number of people were tested, and the obtained data were plotted into Photopic curves. The curve shows the human eye
It is most sensitive to green light, but less responsive to violet and red light.
Experiments show that in the case of dark field, the human eye has completely different response values, in this case, the human eye
They can't tell colors. So, a series of tests led to a Scotopic curve,
The saccadic visual function is obtained.
With the spectral response curves of the human eye, CIE specifies the standard light source as the standard for light intensity measurement. The first one
The definition of CandlePower. In order to maximize the yieldability, in 1948, the metal platinum was quantified
The light emitted by melting redefines the criteria.
The basic content of photometric measurement is to define some physical quantities, and determine the corresponding measurement units and measures
Method. It is used in the research, design and manufacture of photometric instruments and radiation measurement, and the measurement of luminosity characteristics of light sources
It is widely used in optical industry, lighting industry, remote sensing and telemetry, colorimetry and atmospheric optics
And other fields. In addition, a variety of photosensitive and thermal detectors, infrared detectors also need to use photometric measurement technology
To determine its sensitivity and response characteristics.
4.2.2 Illumination standard
An instrument that measures illumination is called an illuminometer. An illuminometer made of photoelectric elements is independent of the state of the human eye, so
You can also measure irradiance. However, in the measurement of illuminance, due to the spectral response of the photoelectric element and the human eye
The difference in light effect function is relatively large and can only be eliminated by adding a correction filter. Spectrum of selenium photocells
The response is closer to the light effect function of human eyes, and its structure is shown in Figure 4.8. Figure 4.8 (a) shows one type of number
The illuminometer is displayed. Figure 4.8 (b) shows the selenium photocell of the illuminometer, and Figure 4.8 (C) shows the selenium photocell
The structure diagram of.
A layer of semiconductor selenium is coated on a metal base plate of iron or aluminum, and a second layer of conductivity and light transmission is coated on the selenium surface
Good metal film (such as gold, silver, etc.) as the collection pole, and then coated on the surface of the metal film a layer of protection
When light hits the semiconductor selenium through a thin metal film, it releases electrons. Electrons in the selenium shell
The flow of electrons creates an electric current, which is of magnitude 1O 'l
When the resistance is less than 200N, the current is linearly related to the incident light intensity. Waves in the spectral response of selenium photocells
It has a long range of 350^-75onm and is most sensitive at wavelengths around 55onm. A unit of light flux shines into a selenium cell
The resulting photocurrent is called the integral sensitivity of a selenium cell, in microamperes lumen 1 '(FtA"1m-1). general
The integral sensitivity of selenium cells is (2-5) X102 [LA-LM-1.
Its advantages are photocurrent directly proportional to radiation energy, good linear measurement: easy to use, portable and durable
The wood is low. The disadvantage is that the resistance is small, the current is not easy to amplify: the response is slow, only in the high-intensity radiation area is sensitive; long
After use, there is "fatigue" phenomenon.
The following analysis of the characteristics of selenium photocell, FIG. 4.9 is its equivalent circuit diagram.
When the luminous flux 0 hits the luminous surface of a selenium photocell, it produces a photocurrent IO, a portion of which 11 flows through the light
The internal resistance of the cell 1', the other part 1, flows through the load resistance of the external circuit where. 1, is the measured apparent photoelectric power
From the shunt principle
It can be seen that when the external circuit resistance RL<v', L, has a good linear relationship with the optical flux 0. So real
The illuminometer should be selected as a low resistance digital galvanometer for load.
The high internal resistance type has a resistance value of 105 orders of magnitude. It has good linear relationship, but low integration sensitivity. It is suitable for
High illumination measurement. The resistance value of the low internal resistance type is on the order of IO3N, and its integration sensitivity is poor, so it is only suitable for low illumination
When using illumination timing, a neutral filter should be attached so that the intensity of illumination above I ooolx can be measured. selenium
The integral sensitivity of the photocell is related to temperature, and should be measured at room temperature as far as possible, both too high and too low temperature
Large error is generated. The illuminometer should also be attached with an effective positive filter to correct the color temperature difference of various light sources. in
For large Angle incidence measurement, an Angle compensator made of glass or plastic should be attached to eliminate the shadow