Measuring principle of illuminance meter and index requirement
Measuring principle of illuminance meter
A photoelectric cell is a photoelectric element that directly converts light energy into electrical energy. When light is directed to the surface of the selenium photocell, the incident light passes through the metal film 4 and reaches the dividing surface of the semiconductor selenium layer 2 and the metal film 4, generating a photoelectric effect at the interface. The size of the generated photogenerated current has a certain proportionality to the illumination on the light-receiving surface of the photocell. At this point, if an external circuit is connected, a current passes through, and the value of the current is indicated from a microampere meter graduated in lux (Lx). The magnitude of the photocurrent depends on the intensity of the incident light. The illuminance meter has a variable speed device, so it can measure high illuminance and low illuminance.
Specification requirements for illuminance meters
● Compact Size, Light Weight
Compact size and light weight are the prerequisites for portable illuminance meters because they are used in a wide range of applications and often in different places.
Accuracy
The good and bad of the illuminance meter, and its accuracy has ** relationship. Of course, it is also closely related to its price, so a reasonable price to buy a higher accuracy of the illuminance meter is necessary, generally to the error does not exceed ± 15% is appropriate.
Color Compensation
The types of light sources are all over the place, some of them favor longer wavelengths of the red high-pressure lamps, or shorter wavelengths of blue-violet system such as Daylight fluorescent lamps; there is also a more even distribution of such as incandescent bulbs series, the same illuminance meter for different wavelengths of its sensitivity may be slightly different, so the appropriate compensation is necessary.
● Cosine Compensation (Cosine Compensation)
As we all know, the brightness of the illuminated surface is related to the angle of incidence of the light source. In the same way, when measuring with a light meter, the angle between the sensor and the incident light source will naturally have an effect on the reading of the light meter. Therefore, a good illuminance meter has a cosine compensation function should not be ignored.
The use of illuminance meter requirements:
① photocell application of good linearity of selenium (Se) photocells or silicon (Si) photocells; long working hours can still maintain good stability, and high sensitivity; high E when the choice of high internal resistance photocells, its low sensitivity and good linearity, not easily damaged by bright light irradiation
② paid within the V (λ) correction filter, suitable for illuminance with a different color temperature light source, the error is small
③ photocell before the addition of a cosine angle compensator (opal glass or white plastic) because the incident angle is large, the photocell deviates from the cosine rule
④ illuminance meter should work at room temperature or near room temperature (photocell drift with the temperature change and change)
