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SpotOn® PAR SkyCheck™

Clear-Sky PPFD Reference Calculator
Compare a reading from your SpotOn® Quantum PAR Light Meter with the modeled clear-sky PPFD for the selected location, date, and time.
Model: ASCE-EWRI Appendix D clear-sky radiation
  • For the most accurate comparison
    Take your reading within about one hour of solar noon on a clear day with minimal haze, preferably from spring through summer. The PPFD conversion factor is calibrated for these conditions, so results may differ more when the sun is low.
  • If your reading differs by more than about 6%
    Compare readings across multiple clear days near solar noon. Clean the diffuser, make sure the meter is level, and test again.
  • Still seeing a difference?
    If the difference persists after a clean, level retest, contact Innoquest to discuss recalibration.

Input

Adds 1 hour to the offset above.

Pick your standard (non-DST) timezone, then check the box above if daylight saving is currently active for your location.

Used to estimate atmospheric water vapor — pull these from any local weather source. They don't need to be precise to the degree, just roughly right.

Reading 13:22

SUN ELEVATION — °
MODELED CLEAR-SKY PPFD — µmol/m²/s
YOUR MEASURED PPFD — µmol/m²/s
— Enter a measured value and calculate to see how your sensor compares to the modeled clear-sky reading.

About this calculation: This calculator uses the ASCE-EWRI Appendix D clear-sky radiation model. It estimates clear-sky solar radiation using the selected location, date, time, elevation, and atmospheric conditions, then converts the estimate to PPFD.

The result is a modeled reference for clear-sky conditions. Clouds, haze, obstructions, and local atmospheric conditions can affect actual readings. The calculator runs in your browser and does not rely on a live data feed.