How is photosynthetically active radiation accurately measured?

Photosynthetically active radiation is the radiant energy in the solar radiation spectrum that can be absorbed, converted and used by the plastid pigments of green plants to synthesise organic matter. When green plants photosynthesise, they only absorb light in the wavelength range of 400-700nm, but little else. Therefore, photosynthetic radiation is directly related to the photosynthesis process and the final yield of the crop.

Photosynthesis is the process by which light energy is absorbed and converted by plant leaves. The photosynthetically active radiation absorption ratio (FPAR) is an important indicator of the balance of water, energy and carbon cycles in vegetation.

PAR sensors are mainly used in agriculture, forestry and other research and production sectors for the measurement of photosynthetically active radiation. When using PAR meters to make measurements, they are susceptible to conditions such as soil background, solar altitude angle, leaf and canopy size, vegetation type and cover, and to varying degrees under different background conditions. Photosynthetically active radiation is intercepted and absorbed or reflected and scattered by the vegetation canopy, so leaf area size has a direct effect on the photosynthetically active radiation absorption ratio (FPAR).