The ALTA® by Monnit Photosynthetically Active Radiation (PAR) Light Meter monitors two essential measurements of PAR light for plant photosynthesis. This article will focus on photosynthetic photon flux density (PPFD). For more about the other PAR light metric—daily light integral—see this article.
What are PPFD and PPF measurements?
The PPFD measures radiation or PAR light that reaches the crop canopy from grow lights or sunlight ready to be absorbed by the plant, mainly through the leaves and flowers. In other words, it’s the number of photosynthetically active photons that fall and land on plants. A photosynthetic photon is a single particle of light that can take on various wavelengths within the PAR light spectrum.
Sensors like our PAR Light Meter that measure PPFD are often called quantum sensors due to the quantized nature of radiation. A quantum means the minimum quantity of radiation or one photon. In other words, one photon is a single quantum of radiation.
What is PPF? You may have seen a photosynthetic photon flux (PPF) specification or metric in your grow light description. The term PPF term defines the measurement of PAR as the total number of photons or the amount of light released from a light source per second.
What is PPFD? It’s the number of photons from the light source that land on a particular surface, preferably a plant. The measurement of PPFD indicates the amount and intensity of photons that land on a square meter of crops each second.
The PPFD unit is measured in micromoles (one micromole equals 62 quadrillion photons) per square meter per second (µmol/m2/s). This means PPFD is the amount of PPF that arrives on each square meter of your crop at any given second.
The value of measuring PPFD
Knowing both PPF and PPFD measurements can help you optimize grow space lighting for your specific crops. The measurements help establish precisely how much PAR light your grow lighting system must produce throughout each crop growing life cycle.
Naturally and simply, the closer to the light source the plant or plants are, the higher the PPFD reading. Plus, the center of a light’s beam has the highest PPFD reading. Adjusting the height and density of your light fixtures directly affects the PPFD and conditions of your crop canopy.
If you want to know how well your grow lights are working when it comes to their output and impact on your crops, then continually measure PPFD. Also, if you want to know the precise light intensity of a lamp over or on a growing area, be sure to determine the average of several PPFD measurements at a specific height.
Measuring PPFD can help you monitor the quality and quantity of PAR over, reflected, or under crop canopies in outdoor environments, greenhouses, grow houses, and growth chambers. You can also measure PPFD with our PAR Light Meter in aquatic environments, including saltwater aquariums where corals are grown.
For more about how PPFD and DLI monitoring work together, see this article.