Conversion – PPFD to Watts

NOTE: This conversion is for UV light in sunlight

*19 October 2016: UV conversion factor changed from 0.342 to 0.327 based on measured solar spectra for clear skies at multiple zenith angles and overcast skies. This new multiplier is 4.4 % lower than the old multiplier, which was based on the energy content of photons at 350 nm. The new multiplier was derived from spectral data, but corresponds to the energy content of photons at 366 nm. We recommend back correcting data when possible.

To convert units, multiply the measurement from the sensor, in units of µmol m-2 s-1, by 0.327 J µmol-1. This converts the UV measurement to units of J m-2 s-1, which is W m-2.

This multiplier is only suitable for sunlight measurements. If the UV sensor is used to measure different radiation sources (for example, electric lights), a different multiplier is required for unit conversion because the multiplier is dependent on the spectrum being measured. A spectral measurement is required to derive the conversion factor.