When researching lighting in agriculture, Photosynthetic Photon Flux (PPF) and Photosynthetic Photon Flux Density (PPFD) are the two concepts that are extremely important. However, there are few growers who understand deeply about PPF and PPFD metrics; and almost all growers confuse these two concepts with each other.
Don’t worry! The below sections will provide you with some information about PPF vs PPFD in order to give you a solid understanding of these two concepts.
What are Photosynthetic Photon Flux (PPF) and Photosynthetic Photon Flux Density (PPFD)?
In order to clearly understand the two definitions PPF and PPFD, we need to answer the question “What is a photosynthetic photon?” first. A photon is an elementary particle carrying light quantum with different wavelengths. And a photosynthetic photon is a photo that is involved in photosynthesis (the photons whose wavelength is from 400 nm to 700 nm). Therefore, it is stated that the PPF and PPFD are two definitions used in the field of lighting for growing.
Photosynthetic Photon Flux (PPF) is the quantity of light produced from a grow light source each second, which means PPF measures the total amount of photosynthetic photon emitting from a light source used in growing plants in a second. The measurement unit of PPF is micromoles per second (μmol/s).
Photosynthetic Photon Flux Density (PPFD) is the quantity of light that reaches the plants, which means PPFD measures the total amount of photosynthetic photons created from a grow light source falling on a surface. The measurement unit of PPF is micromoles per second per square meter (μmol/s/m2).
***Watch video for more details about PAR, PPF and PPFD for finding the best LED grow light
PPF vs PPFD: What is the similarities and Differences
#1. Similarities of PPF and PPFD
From these above two definitions, it is easy to realize the two same points of PPF and PPFD. The first similarity of these two concepts is that both PPF and PPFD determine the quantity of photosynthetic photons that are beneficial for growing plants. The second point of similarity is that both PPF and PPFD measure the amount of light from both natural and artificial light sources such as the sunlight, LED grow lights, halogen grow light bulbs or incandescent grow light bulbs…
#2. The difference between PPF and PPFD
The main difference between PPF and PPFD is that PPF measures the total number of light emitted from a light source, while PPFD is a measurement of the density of light falling on the area growing plants.
When to use PPF and PPFD?
As the PPF measures the light intensity of grow light sources, therefore, it is useful to compare the different grow lights in the market when the growers select the most suitable one for their plants or gardens. In addition, as professional growers advised, it is also important to consider the beam angle when choosing the grow lights. Because the two lights with the same PPF and different beam angles will provide different PPFD.
PPFD measures the light that all the plants at a certain area receive from the light source. Therefore, PPFD was considered when choosing the light for specific plants because each plant needs different light brightness. It is recommended that the growers should take into account the distance from the light source to the plant and the location in order to calculate the most accurate PPFD.
***Read more: Best LED Grow Light For 3×3 Tent: Top 6 Expert Choice 2022
How to measure PPF and PPFD?
Measuring the PPFD is quite simple and does not cost much money. The growers can utilize handheld light meters or spectrometers so as to measure the PPFD. Furthermore, some modern technologies allow the growers to connect the handheld light meters/ spectrometers to their smartphones, which is much easier to measure.
On the other hand, measuring PPF is much more difficult than PPFD. In order to measure the light emitted from a light source in all directions, an ionosphere or integrating sphere that can capture light from all directions is necessary. However, these two devices are expensive and hard to use.
In practice, growers can calculate the PPF based on the specifications of grow lights that is provided by the manufacturer. For example, a LED grow light whose Photosynthetic Photon Efficacy (PPE) is 2.5 µmol/j, power rate is 600 Watts, its PPF may be:
PPF = PPE * Power rate = 2.5 * 480 = 1500 µmol/s
Then, the growers can easily divide PPF by area in order to find out PPFD. For example, the area is 2 m2, the PPFD may be:
PPFD = PPF / area = 1500 : 2 = 750 (µmol/s/m2)
***Read more: Top 7 Best Cheap Grow Lights 2022 [Top Highly-Recommended]
Frequently Asked Questions
Each stage of the plant needs different light intensity. Both too much and too less light can create negative impacts on the plants. As experts suggested, the seedlings, mother plants, clonal plants or weak plants need a gentle light whose PPFD is from 200 µmol to 400 µmol; the plants in the vegetative stage require a medium light whose PPFD is between 400 µmol and 600 µmol; and the plants in the budding, flowering and fruiting stage need a intensive light (PPFD from 600 µmol to 800 µmol).
The sun is the most important light source for plants on the Earth, therefore, many scientists have researched about the PPF and PPFD of natural sunlight. However, the light from the sun is very complicated; currently, human beings cannot measure the PPF of the sun. The PPFD of the sunlight is also dependent on many factors such as locations, seasons, clouds, atmosphere… At the equator, the PPFD of the sun in cloudless sky is about 2000 µmol/m2/sec. In other locations, the PPFD of the sun may be from 900 to 1500 µmol/m2/sec when the sun is directly overhead.
A mature plant needs from 600 to 800 µmol/m2 as PPFD. Therefore, if growing indoor plants, growers should find LED grow lights whose PPFD is in the above range. Please remember that PPFD should be less than 1000 µmol/m2 in order not to damage the indoor plants.
It is compulsory for professional growers to intensively understand the two concepts of PPF vs PPFD. If you have any questions about PPF, PPFDs or other concepts related to lighting, please do not hesitate to contact us to find out the answers. Goodbye and see you at other articles.