In this article, we will explain the meaning and importance of the term PPFD, which all cultivators hear too often these days. Some other terms you may see frequently are; Watt, Lumen, LUX, foot-candle, PAR, PPF and PE. The main purpose of the article, while sharing definitions of these terms and abbreviations, is to correct some common misconceptions and to help growers understand and interpret what values they should first examine for their garden and greenhouse lighting systems.
Most species perceive light differently and can use it for specialized purposes. Humans and most animals need light in order to see their surroundings. Our ears, which are another sense organ, have a different response to sound waves of different frequencies, thus, their sensitivity is different. You may find that very high-pitched sounds bother you more than very low-pitched ones. The response of our eyes to the color of light, that is, the sensitivity of our eyes to light of different colors, is similar to the phenomenon of sound frequency and hearing sensitivity of our ears. Our eyes are more sensitive to green light than to blue and red light. Lumen is a unit of measurement that takes the sensitivity of the human eye in consideration. The terms LUX and foot-candle are defined to measure light intensity in general lighting applications. The LUX unit is defined as Lumen/squaremeter and the foot-candle unit is defined as Lumen/squarefeet.
When measuring light intensity in agricultural lighting systems, the main problem experienced when LUX or foot-candle measuring devices are preferred is that the blue light (400 - 500 nm) and red (600 - 700 nm) light in the visible spectrum are not taken into account in the correct amount (Graph 1). We mentioned above that the human eye has low sensitivity to blue and red light. For this reason, LUX measuring devices mainly sensitive around the green band. but unlike humans, plants use red and blue light with very high efficiency in photosynthesis. Therefore, the use of LUX and foot-candle measuring devices will result in inability to measure red and blue bands, which are the most important ones in plant cultivation , and thus a misdirection. Scientific results should not be expected by measuring LUX and foot-candle in any agricultural application.
PAR stands for photosynthetically active radiation and expresses the wavelength interval of visible light (400-700 nanometers to nanometers) that stimulates photosynthesis. PAR is a very common (and often misused) term for agricultural lighting. PAR is not a metric unit of measurement like centimeters, inches, or kilograms. Instead, it defines the wavelength range of light needed to stimulate photosynthesis. PAR and the quality of the light spectrum are important issues to consider when cultivating plants.
Quantum PAR sensors are the main measurement tools used to measure the light intensity of agricultural lighting systems. These sensors utilize an optical filter to create reference sensitivity to PAR. Most devices can measure real time light intensity and record data.
PPF stands for photosynthetic photon flux. PPF is the total amount of PAR that a light source generates in one second. Special devices called integrating sphere and spectroradiometer are used to measure PPF. To express the PPF value, micromoles per second (μmol/s) must be measured. PPF data helps you to determine how efficiently your agricultural lighting system produces PAR.
PPFD measures the amount of PAR hitting the plant and stands for photosynthetic photon flux density. PPFD expresses the number of photosynthetic photons per second (μmol/m2/s) and usually measured at a specific point on the canopy. In order to obtain stable results in agricultural applications, PPFD measurements should be made from many different points with certain distances, not a single point of the greenhouse, garden or grow tent. Most lighting companies mislead growers by publishing PPFD values more than they measure, or by assuming that the values they measure in the center are measured in the entire field. There is no law or regulation controlling the PPFD values published by the manufacturers. For this reason, you can request video-proven PPFD measurements of the lighting systems you are considering investing in. As LEDWisdom, we share the PPFD measurements of all our products with 100% transparency.
PE stands for photon efficiency. It expresses how much of the electrical energy consumed by the lighting system can be converted into photons within the PAR, that is, the efficiency of the system. The PE value is calculated as PPF/W and its unit is umol/J. A Watt meter can be used to calculate the total power consumed by the system and the PE value is calculated using the W and PPF data. As can be understood simply, all lighting systems that use fans lose system efficiency significantly. As with LEDWisdom grow lights, agricultural lighting systems with high PE values offer you the highest quality and amount of harvest with the least electricity consumption.
Before investing in agricultural lighting systems for your big projects, you can request a contract with a PPFD guarantee from the lighting company. Taking this precaution saves you from dealing with companies that do not have a good understanding of their work or do unethical business. In your small investments, you can also request the lighting manufacturers or distributors to send the PPFD values of the grow lights you will invest in via video. As LEDWisdom, we present our spectrum and PPFD values with 100% transparency to all our customers and establish PPFD-guaranteed systems for your greenhouses. You can also reach all these details from our dealers.
-References:
1- Durazzo, Benjamin. (2021). Contemporary applications of light-emitting diodes in horticulture: A review on LED lighting technology and the use of wavelength band and irradiance modulation to study plant photobiology. 10.13140/RG.2.2.17101.77282.
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