What is the principle of measurement of the Illuminance Meter?
An illuminance meter (or lux meter) is an instrument specially designed to measure illumination.
It is to measure the degree of illumination of an object, that is, the ratio of the luminous flux obtained on the surface of the object to the illuminated area.
An illuminance meter usually consists of a selenium photovoltaic cell or a silicon photovoltaic cell combined with a filter and a microammeter.
Photocells are optoelectronic components that convert light energy directly into electrical energy.
When light strikes the surface of the selenium photovoltaic cell, the incident light passes through the metal film 4 and reaches the interface between the semiconductor selenium layer 2 and the metal film 4, producing a photoelectric effect on the interface.
The size of the photocurrent generated has a certain proportional relationship with the illumination on the surface of the photovoltaic cell.
6 If an external circuit is connected at this time, current will flow through, and the current value will be indicated on the microammeter with lux (Lx) as the scale.
The size of the photocurrent depends on the intensity of the incident light. The illuminance meter has a gear shifting device, so it can measure both high and low illuminance.
Categories of cited illuminance meters:
1. Visual illuminance meter: inconvenient to use, low accuracy, rarely used
2. Photoelectric illuminance meter: Commonly used selenium photovoltaic illuminance meter and silicon photovoltaic illuminance meter
When using a UV light meter, pay attention to the ambient temperature
When using, care must be taken to avoid receiving strong light, because if the photoelectric cathode is exposed to strong light for a long time, fatigue will occur, causing the photocathode to emit abnormally. Therefore, the protective cover of the window must be covered when the illuminance meter is not in use. In addition, the ambient temperature in which the UV illuminance meter works cannot be very high or very low. Especially for UV light meters that use thermoelectric effect elements as receivers, the requirements for ambient temperature are even more stringent (usually at 20°C); while when photoelectric tubes GD-5 are used as receivers, the requirements for ambient temperature are not very strict. Generally, the lower the temperature, the better; in order to reduce dark current. In addition, when measuring the radiation of the light source, it should be perpendicular to the window of the receiver. If it is tilted, a large error will occur. At this time, angle correction is required.
