Photosynthetically active radiometer, also known as photon number, is mainly used to measure the amount of photosynthetically active radiation of natural light in the wavelength range of 400-700nm. It is simple to use and can be connected directly to a digital voltmeter or data logger. Use in all weather conditions. When illuminated by light, a voltage signal proportional to the intensity of the incident radiation is generated, and its sensitivity is proportional to the cosine of the right angle to the incident light. Each photosynthetically active pyranometer has its own sensitivity that can be read directly in w/m2. This table is widely used in agrometeorology and crop growth research.It can well promote the development of smart agriculture.