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Illumination meter is a special instrument for measuring luminosity and brightness. It is often used to measure illuminance of indoor lamps. The light intensity it measures is the degree to which the object is illuminated, that is, the ratio of the luminous flux obtained on the surface of the object to the illuminated area. Luminometer is usually composed of selenium photocell or silicon photocell and microampere meter. Illuminance measurement shall be made with an illuminometer not lower than Class I.
Photovoltaic cells are photoelectric elements that directly convert light energy into electrical energy. When light rays are incident on the surface of the selenium photovoltaic cell, the incident light passes through the metal film 4 to reach the interface between the semiconductor selenium layer 2 and the metal film 4, generating a photoelectric effect on the interface. The magnitude of the generated potential difference is proportional to the irradiance on the light receiving surface of the photovoltaic cell. At this time, if an external circuit is connected, a current will pass through, and the current value will be indicated from the microampere meter with Lux (Lx) as the scale. The photocurrent depends on the intensity of the incident light and the resistance in the loop. The illuminometer is a shift device, so it can measure both high illuminance and low illuminance.