The Vernier PAR Sensor is calibrated before shipping and should not need user calibration.

However, you can calibrate the sensor using the Clear Sky Calculator (www.clearskycalculator.com). The Clear Sky Calculator for Quantum Sensors reports the theoretical PPFD at any time of day at any location in the world on a cloudless day. The application is most accurate at solar noon in the spring and summer.

To determine the theoretical PPFD at your location, you will need to know your latitude, longitude, altitude, time of day, air temperature and humidity. Complete the required fields in the web application. Record the Model Estimate of PPFD.

Please note that for best accuracy the sky must be completely clear if you are going to calibrate your Vernier PAR Sensor using the Clear Sky Calculator.

Take the PAR Sensor outside on a sunny and cloudless day. Make sure that you have calculated the theoretical PPFD for your date and location.

Note: The protective cap that comes with the sensor may not block all solar radiation. For best results during calibration, encase the outer part of the protective cap in aluminum foil when recording your ‘zero’ for PPFD.

  1. Connect the PAR Sensor to your computer with a Vernier computer interface (LaQuest – any model, LabPro, or Go! Link).
  2. Choose Calibrate > CH1: PAR from the Experiment menu and then click Calibrate Now.
  3. Verify that the PAR Sensor is placed in open sunlight. Verify that the protective cap is not on the sensor head of the PAR Sensor. Near the middle right of the calibration dialog box, you will see the potential output of the PAR sensor, in volts. Type the PAR value that you measured for open sunlight using the Clear Sky Calculator in the edit box. When the displayed voltage reading stabilizes, click Keep.
  4. Cover the sensor head of the PAR Sensor with the protective cap. The potential (voltage) will decrease rapidly. When the displayed voltage reading stabilizes, type 0 in the second edit box and click Keep.
  5. To store the calibration on the sensor itself, click the Calibration Storage tab. Note: If you wish to use the calibration only for the current experiment, skip to Step 8.
  6. Click Set Sensor Calibration. Make sure the Default Page corresponds to your new calibration. Click Set.
  7. Click Done. You will be prompted by the message, “Warning: You are about to change information in your sensor. Configuration data stored on the sensor will be lost. Pressing ‘Write’ will apply your changes to the sensor.” Click Write.
  8. Click Done to complete the calibration process.

You have now stored the calibration on the sensor itself. This new calibration will be used from now on, until you replace it by conducting another calibration or by reverting to the factory calibration.

You can set the PAR sensor back to its factory calibration by following these steps:

  1. Select Calibrate > CH1: PAR from the Experiment menu.
  2. Click the Calibration Storage tab.
  3. Click Set Sensor Factory Defaults.
  1. Connect the PAR Sensor to your LabQuest. The PAR reading will be displayed.
  2. Choose Calibrate > CH1: PAR from the Sensors menu and tap Calibrate Now.
  3. Verify that the PAR Sensor is placed in open sunlight. Verify that the protective cap is not on the sensor head of the PAR Sensor.
  4. Enter the PAR value that you measured for open sunlight using the Clear Sky Calculator in the field for known value 1. When the voltage reading stabilizes, tap Keep.
  5. Cover the sensor head of the PAR Sensor with the protective cap. The potential (voltage) will decrease rapidly. Enter 0 in the field for known value 2. When the voltage reading stabilizes, tap Keep.
  6. To store the calibration on the sensor itself, tap the Storage tab at the top of the screen. Note: If you wish to use the calibration only for the current experiment, skip to Step 8.
  7. On the Storage page, tap Save Calibration to Sensor. A message will appear: “Saving this calibration to the sensor will result in it being the new Custom Calibration 1”. Tap OK to proceed.
  8. Tap OK to complete the calibration process.

After you store a calibration to the PAR Sensor, this new calibration will be used automatically, regardless of the interface to which the PAR Sensor is connected.

You can set the PAR sensor back to its factory calibration by following these steps:

  1. Choose Calibrate > CH1: PAR from the Sensors menu.
  2. Tap the Storage tab.
  3. Tap Restore Sensor Factory Defaults.
Published: December 31, 2013. Updated: July 7, 2023.