Pyranometer

 A pyranometer is a type of actinometer used for measuring solar irradiance on a planar surface and it is designed to measure the solar radiation flux density (W/m2) from the hemisphere above within a wavelength range of 400 nm to 1000 nm(range may vary upon application).

Types of Pyranometer:
Pyranometers can be recognized and grouped into two different technologies: Thermopile Technology and Silicon Semiconductor Technology.

Thermopile Pyranometers:
It has a thermopile detector (a device that converts thermal energy into electrical energy) with strongly light-absorbing black paint that equally consumes all sun radiation. This creates a temperature difference between the black surface of the sensors and the body of the instrument and results in a small voltage at the sensor that can be measured and translated into W/m2.
Thermopile pyranometers follow the ISO 9060 standard, also adopted by the World Meteorological Organization (WMO). This standard discriminates between three classes. The latest version of ISO 9060, from 2018 uses the following classification: Class A for the best performing, followed by Class B and Class C, while the older ISO 9060 standard from 1990 used ambiguous terms such as "secondary standard", "first-class", and "second-class".

Semiconductor Pyranometers:
A semiconductor or silicon pyranometer uses a photodiode (a device that converts light into current) to create an electrical signal from the incoming solar radiation. It can detect the portion of the solar spectrum between 400 nm and 1100 nm.

The device measures radiation from the sun and the sky on a horizontal surface. When exposed to radiation, the silicon cell produces a voltage, and the current output is proportional to the radiation energy received. Now, this signal is sent to a device that converts this signal to a human-readable format. 

This device can be a data logger or a display unit.

To know more about data loggers follow the link below.
https://creativestudio1973.blogspot.com/2020/09/datalogger.html

Reference:
[1] https://en.wikipedia.org/wiki/Pyranometer