Types of illuminance meters and measuring principles
Types of illuminance meter and the principle of measurement Illuminance meter (or lux meter) is a special instrument for measuring luminosity, brightness. It is the measurement of light intensity (illuminance) is the degree of the object is illuminated, that is, the surface of the object received by the luminous flux and the ratio of the illuminated area. Illuminance meter is usually composed of selenium photocell or silicon photocell and microampere meter.
Illuminance meter measurement principle.
Photocell is a photoelectric element that converts light energy directly into electrical energy. When light is directed to the surface of the selenium photovoltaic cell, the incident light passes through the metal film 4 to reach the semiconductor selenium layer 2 and the metal film 4 on the dividing surface, in the interface to produce photoelectric effect. The magnitude of the potential difference generated is proportional to the illuminance 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 scaled in lux (Lx). The magnitude of the photocurrent depends on the intensity of the incident light and the resistance in the circuit. The illuminance meter has a variable speed device, so that it can measure high illuminance as well as low illuminance.
Types of illuminance meters:
1. Visual illuminance meter: inconvenient to use, not high precision, rarely used
2. photoelectric illuminance meter: commonly used selenium photocell illuminance meter and silicon photocell illuminance meter
Composition and use requirements of photoelectric cell illuminance meter:
1. Composition: microampere meter, shift knob, zero adjustment, terminal, photocells, V (λ) correction filter and other components.
2. Requirements for use
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-resistance photocells, its sensitivity is low and good linearity, not easily damaged by bright light irradiation
② paid within the V (λ) correction filter, suitable for the illumination of light sources with different colour temperatures, 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 or near room temperature (photocell drift with the temperature change and change)
