Measurement principle and related technology of illuminometer
Illuminance meter measurement principle: Illuminance meter (or lux meter) is a special instrument for measuring illuminance. It is to measure 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. The illuminance meter is usually composed of a selenium photovoltaic cell or a silicon photovoltaic cell with a filter and a microammeter.
Illuminance calibration:
Calibration principle:
Let Ls irradiate the photocell vertically → E=I/r2, change r to obtain the photocurrent value under different illumination, and convert the current scale to the illumination scale by the corresponding relationship between E and i.
Calibration method:
Using the light intensity standard lamp, at a working distance similar to a point light source, change the distance l between the photocell and the standard lamp, record the readings of the galvanometer at each distance, and calculate the illuminance E by the inverse square law of distance E=I/r2, by A series of photocurrent values i with different illuminances can be obtained, which can be used as the change curve of photocurrent i and illuminance E, which is the calibration curve of the illuminometer.
Illuminometer
Factors that affect the calibration curve:
The photocell and galvanometer need to be re-calibrated when they are replaced; the illuminometer should be re-calibrated after a period of use (generally 1-2 times within a year); high-precision illuminometers can be calibrated with light intensity standard lamps; The calibration range of the illuminance meter can change the distance r, and different standard lamps can also be used, and a small range current meter can be selected.
Photovoltaic cells are photoelectric elements that directly convert light energy into electrical energy. When the light hits the surface of the selenium photocell, the incident light passes through the metal thin film 4 to reach the interface between the semiconductor selenium layer 2 and the metal thin film 4, and a photoelectric effect is generated on the interface. The magnitude of the generated photocurrent is proportional to the illuminance on the light-receiving surface of the photocell. At this time, if the external circuit is connected, there will be current flowing, and the current value will be indicated on the microammeter with lux (Lx) as the scale. The magnitude of the photocurrent depends on the intensity of the incident light. The illuminance meter has a shifting device, so it can measure high illuminance and low illuminance.
