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What is an illuminance sensor? Interpretation of the concept of illuminance and light intensity

by:Rika Sensors     2021-09-12
What is an illuminance sensor? Interpretation of the concept of illuminance and light intensity
The illuminance sensor is a kind of sensor that converts the magnitude of illuminance into an electrical signal, and the output value measurement unit is Lux. The illuminance transmitter has certain applications in many industries, such as the illuminance monitoring of the environment such as agricultural greenhouses, street lights on the street, and automated weather stations.

In terms of working principle, the illuminance sensor adopts the principle of hot spot effect. This sensor uses detection components that are highly responsive to low light. These sensing elements are like the photosensitive matrix of a camera, with winding plating inside. The surface of the multi-contact thermopile is coated with a black coating with high absorptivity. The hot junction is on the sensing surface, and the cold junction is located in the body. The hot and cold junctions generate a thermoelectric potential. In the linear range, the output signal is proportional to the solar irradiance. The visible light through the filter irradiates the imported photodiode, and the photodiode converts into an electrical signal according to the visible illuminance, and then the electrical signal enters the sensor's processor system to output the binary signal that needs to be obtained.

Of course, there are many categories of illuminance sensors, and some categories even optimize the structure described above, especially in order to reduce the influence of temperature. The illuminance sensor also applies temperature compensation circuits, which greatly improves The sensitivity and detection ability of the illuminance sensor are improved.

The concept of 'illuminance' is often confused with the concept of 'light intensityIn fact, there is no such a concept of 'light intensity' in photometry. Commonly used concepts of optical quantity are luminous intensity, illuminance, light output and brightness. 'Light intensity' is just a popular term, it is difficult to say which photometric concept corresponds to.

Several concepts mentioned above have strict physical definitions:

Luminous intensity: The luminous flux emitted by the light source in a unit solid angle, the unit is candela, that is, 1 lumen per steradian.

Illuminance: The luminous flux per unit area of u200bu200bthe illuminated surface, the unit is lux, that is, 1 lumen per square meter.

Light output: the luminous flux emitted by the unit area of u200bu200bthe light source, the unit is the same as the illuminance.

Luminance: the luminous intensity along the normal direction on a unit area, or the luminous flux emitted by a unit area in a unit solid angle in its normal direction, the unit is nits, that is, 1 lumen per square meter per steradian .

Because the luminous intensity and brightness are related to the direction, it is easy to deduce: the luminous intensity of the light source with the same brightness in all directions is the cosine function of the direction, and the luminous intensity is the largest in the normal direction, which is called a cosine radiator. Also called Lambertian light source. The brightness of a light source with the same luminous intensity in all directions is not equal.

These optical quantities all use luminous flux, which is the optical quantity corresponding to the radiant energy flux, because light is a kind of electromagnetic radiation. The equivalent luminous flux of 1 watt of radiant energy flux of electromagnetic waves of different wavelengths is different. When converting to luminous flux, the spectral sensitivity curve of the human eye must be considered, that is, the human eye does not perceive the same radiant energy flux of different wavelengths. Similarly, infrared light, microwaves, ultraviolet light, etc. are invisible to the human eye, while visible light with a wavelength of 400nm to 760nm is visible to the human eye.

In physical optics, 'light intensity' is also mentioned. It uses Maxwell’s equations to solve the electric vector of light. The square of the electric field intensity is the light intensity in physical optics, which is mainly used to calculate the patterns obtained by interference and diffraction effects. .

Light intensity is a relatively vague concept in various related disciplines of optics. Different branches have different opinions. Some are equivalent to luminous intensity, some are equivalent to illuminance, and some are equivalent to brightness.

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