Question:
The instrument used for measuring photosynthetically active radiation (PAR) is
The instrument used for measuring photosynthetically active radiation (PAR) is
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Remember that photosynthesis is a quantum reaction, meaning plants respond to the number of photons rather than total energy.
Therefore, PAR is measured in units of \(\mu\text{mol}\cdot\text{m}^{-2}\cdot\text{s}^{-1}\) using a quantum sensor equipped with a bandpass filter for the 400--700 nm range.
Therefore, PAR is measured in units of \(\mu\text{mol}\cdot\text{m}^{-2}\cdot\text{s}^{-1}\) using a quantum sensor equipped with a bandpass filter for the 400--700 nm range.
Updated On: Jul 24, 2026
- Campbell stroke sun shine recorder
- Pyranometer
- Line quantum sensor
- Pyrheliometer
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The Correct Option is C
Solution and Explanation
Step 1: Understanding the Concept:
Photosynthetically Active Radiation (PAR) refers to the spectral waveband of solar radiation from 400 to 700 nanometers.
This specific band of light is absorbed by chlorophyll pigments and drives the light reactions of photosynthesis in plants.
To study crop canopy development, light interception, and photosynthetic efficiency, agrometeorologists must measure PAR precisely.
Step 2: Detailed Explanation:
Let us analyze the operational function of each instrument listed in the options:
- Campbell-Stokes sunshine recorder: This instrument uses a glass sphere to focus direct solar rays onto a heat-sensitive card.
It measures the duration of bright sunshine hours in a day, rather than light intensity or spectral quality.
- Pyranometer: This instrument measures the total global solar radiation (both direct and diffuse) incident on a flat surface across a wide spectral range, typically from 300 to 3000 nanometers.
- Line quantum sensor: This instrument contains a series of silicon photodiodes designed to measure the Photosynthetic Photon Flux Density (PPFD) specifically within the 400 to 700 nm band.
It counts the number of photons (in micromoles per square meter per second) rather than total energy, which is critical because photosynthesis is a quantum-driven photochemical reaction.
The linear design allows it to average the spatial variations in light intensity beneath a crop canopy.
- Pyrheliometer: This instrument measures direct beam solar radiation at normal incidence, excluding diffuse radiation, using a collimator tube.
Therefore, the line quantum sensor is the correct instrument for measuring PAR.
Step 2: Final Answer:
The instrument used for measuring photosynthetically active radiation (PAR) is the line quantum sensor.
Photosynthetically Active Radiation (PAR) refers to the spectral waveband of solar radiation from 400 to 700 nanometers.
This specific band of light is absorbed by chlorophyll pigments and drives the light reactions of photosynthesis in plants.
To study crop canopy development, light interception, and photosynthetic efficiency, agrometeorologists must measure PAR precisely.
Step 2: Detailed Explanation:
Let us analyze the operational function of each instrument listed in the options:
- Campbell-Stokes sunshine recorder: This instrument uses a glass sphere to focus direct solar rays onto a heat-sensitive card.
It measures the duration of bright sunshine hours in a day, rather than light intensity or spectral quality.
- Pyranometer: This instrument measures the total global solar radiation (both direct and diffuse) incident on a flat surface across a wide spectral range, typically from 300 to 3000 nanometers.
- Line quantum sensor: This instrument contains a series of silicon photodiodes designed to measure the Photosynthetic Photon Flux Density (PPFD) specifically within the 400 to 700 nm band.
It counts the number of photons (in micromoles per square meter per second) rather than total energy, which is critical because photosynthesis is a quantum-driven photochemical reaction.
The linear design allows it to average the spatial variations in light intensity beneath a crop canopy.
- Pyrheliometer: This instrument measures direct beam solar radiation at normal incidence, excluding diffuse radiation, using a collimator tube.
Therefore, the line quantum sensor is the correct instrument for measuring PAR.
Step 2: Final Answer:
The instrument used for measuring photosynthetically active radiation (PAR) is the line quantum sensor.
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