How is PAR measured?

PAR (Photosynthetically Active Radiation) is typically measured using a specialized instrument called a PAR sensor or quantum sensor.    These sensors are designed to detect and quantify the amount of light within the spectral range of 400 to 700 nanometers, which is the range of light that is utilized by plants for photosynthesis.

PAR sensors work by converting the incoming light energy into an electrical signal that can be measured.    The sensor is usually calibrated to provide readings in units of micromoles per square meter per second (μmol/m²/s) or watts per square meter (W/m²), indicating the intensity of light available for photosynthesis.

PAR measurements can be taken at various locations and heights above the plant canopy to assess the light conditions that affect plant growth.    Researchers, growers, and environmental scientists use PAR measurements to optimize light exposure for plants, adjust artificial lighting in controlled environments, and monitor natural light conditions in greenhouses, fields, forests, and other settings.

PAR sensors

In addition to measurements using PAR sensors, the rate of photosynthesis can be assessed indirectly by means of photosynthesis instrumentation (e.g., photosynthesizers), thereby inferring the effects of photosynthetically active radiation (PAR).  This approach usually involves measuring the rate of oxygen release or carbon dioxide uptake in plant tissues, thus providing information about photosynthetic activity.

PAR can also be measured using a photometer (radiometer), which is a broad-spectrum radiometer that measures light radiation over a specific range, including light in the PAR range.  PAR can be measured directly through the use of a well-calibrated radiometer.

Overall, tools such as PAR sensors, photosynthesis instruments, and photometers allow for a comprehensive assessment and measurement of the effects of light on plant growth and ecosystem function.