Conversion – Instantaneous PPFD to Integrated PPFD

How to Convert Instantaneous PPFD to Integrated PPFD

To accurately measure Photosynthetic Photon Flux Density (PPFD) or instantaneous PPFD, you will need a quality quantum meter such as the Treegers Quantum Par Meter

Most PAR light meters measure:

• Instantaneous PPFD
• Measured in µmol m-2 s-1

However, plant growth performance is determined by the:

• Integrated daily PPFD (DLI)
• Measured in mol m-2 d-1

Understanding this conversion is extremely important when setting up hydroponic grow lights and indoor grow room lighting schedules.

What Is PPFD?

PPFD stands for:

Photosynthetic Photon Flux Density

This measures the amount of usable photosynthetic light reaching the plant canopy every second.

PPFD is measured as:

• µmol m-2 s-1
• Micromoles per square metre per second

What Is Integrated PPFD or DLI?

Integrated PPFD, also known as:

Daily Light Integral (DLI)

Measures the total amount of photosynthetic light delivered to plants over an entire day.

DLI is measured as:

• mol m-2 d-1
• Moles per square metre per day

DLI is one of the most important measurements in hydroponic lighting performance.

Converting Instantaneous PPFD to Daily PPFD

Electric grow lights produce a relatively constant PPFD output, allowing growers to calculate daily light accumulation.

There are:

• 3600 seconds in one hour
• 86,400 seconds in one day

This means:

$1\ \mu mol\ m^{-2}\ s^{-1}=0.0864\ mol\ m^{-2}\ d^{-1}$

This conversion applies under continuous 24-hour lighting.

PPFD Conversion Formula

To calculate daily PPFD from instantaneous PPFD:

$\frac{PPFD\ (\mu mol\ m^{-2}\ s^{-1})\times86,400}{1,000,000}=DLI\ (mol\ m^{-2}\ d^{-1})$

Important Note About Sunlight

These conversions are accurate for electric grow lights only.

Sunlight intensity changes continuously throughout the day, so a single PPFD reading from sunlight cannot accurately estimate daily PPFD.

Daily PPFD Reference Table – 24 Hour Photoperiod

Daily PPFD Reference Table – 16 Hour Photoperiod

Daily PPFD Reference Table – 12 Hour Photoperiod

Outdoor Sunlight Reference

Sunny summer days outdoors in full sun commonly deliver:

• 50–60 mol m-2 d-1

This provides a useful benchmark when comparing hydroponic LED grow lights against natural sunlight.

Why PPFD & DLI Matter in Hydroponics

Understanding PPFD and DLI helps hydroponic growers:

• Optimise LED grow light placement
• Improve canopy penetration
• Increase photosynthetic efficiency
• Prevent under-lighting or over-lighting
• Improve flowering and vegetative growth performance
• Fine-tune hydroponic grow room environments

Correct PPFD levels are critical for maximising hydroponic plant growth and crop performance.

Reference: Apogee Instruments

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