Posted on by Jason G Note: To be able to read PPFD or instantaneous PPFD will require an accurate quantum meter to take the readings, such as the Apogee MQ-500.

Most light meters measure the instantaneous photosynthetic photon flux density in µmol m-2 s-1 and yet plant growth is determined by the integrated daily photosynthetic photon flux density in mol m-2 d-1.

Here is how to convert from µmol m-2 s-1 to mol m-2 d-1 when using electric lights.

There are 3600 seconds in an hour. If the electric light output is constant, the instantaneous PPFD can be added up (integrated) over an hour.

Therefore 1 µmol m-2 s-1 = 3600 µmol m-2 h-1.

This must be divided by a million (1,000,000) to convert from micromoles to moles: 3600 µmol m-2 h-1 = 0.0036 mol m-2 h-1.

If the electric lights are on continuously (24 hours), the hourly PPFD must be multiplied by 24 to get the daily PPFD: 0.0036 mol m-2 h-1 = 0.0864 mol m-2 d-1.

There are 86,400 seconds in a day (3600 x 24 hours) so the daily PPFD can be calculated directly from the instantaneous PPFD from the following equation: µmol m-2 s-1 multiplied by 86,400 and divided by 1,000,000 = mol m-2 d-1.

So: 1 µmol m-2 s-1 = 0.0864 mol m-2 d-1 with continuous light

These conversions are accurate only under electric lights. The integrated daily PPFD from sunlight changes during the day so a single measurement cannot be used to estimate daily PPFD.

### Daily PPFD Reference Table

24-Hour Photoperiod

 Instantaneous PPFD (µmol m-2 s-1) Daily PPFD (mol m-2 d-1) 10 0.864 100 8.64 200 17.28 300 25.92 *600 *51.84 1000 86.40 2000 172.80

### 16-Hour Photoperiod

 Instantaneous PPFD (µmol m-2 s-1) Daily PPFD (mol m-2 d-1) 10 0.567 100 5.67 200 11.52 300 17.28 600 34.58 *1000 *57.60 2000 115.20

### 12-Hour Photoperiod

 Instantaneous PPFD (µmol m-2 s-1) Daily PPFD (mol m-2 d-1) 10 0.432 100 4.32 200 8.64 300 12.96 600 25.92 1000 43.20 *1300 *56.23 2000 86.40

*There are 50 to 60 moles per m2 day on sunny summer days in outside areas without any shade.

Reference: https://www.apogeeinstruments.com/conversion-instantaneous-ppfd-to-integrated-ppfd/

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