If you are new to horticulture or learning about growing LEDlights, you might have heard about PPF and PPFD measurement. However, you might be confused about the real meaning of these metrics as well as their differences. Before you make an informed purchasing decision, it matters much to figure out how they influence the light source your plants will get from your costly LED lamps. In this article we go over the basic differences between PPF and PPFD.
Definition of PPF and PPFD
1. Photosynthetic Photon Flux, in short PPF, refers to the number of photons emitted from a particular light source within the wavelength ranging between 400nm and 700nm.PPF is written in µmol/s.
2. Photosynthetic photon flux density, namely PPFD, informs about the photosynthetic density of photon flux. PPFD means photon flux within that particular area and its unit is written in µmol/s/m2.
Both PPF and PPFDdeal with the amount of light for a light source or location. They measure the quantity oflightphotons. The critical difference is that PPFD measures the density of these photons falling on a particular surface, while PPF is a measure of the total number of photons released from a light source.
As the graph below shows, on the left part (PPF), you can see the amount of all photons emitted from a light source in all directions per second. While on the right part (PPFD), you’ll get the number of photons that hit one square meter per second.
Applications of PPFD and PPF
PPFmeasures the amount of PAR from a single grow light. When you compare the usage of different lamps, PPFis a goodmeasurement. But there is a key factor you should take into consideration, thatisPPFcan affect eventual PPFD readings depending on the productsas per theadjustedbeam angles.
PPFD, on the other hand,should always be connected with a distance and location. Most LED grow lights providers will reveal PPFD reading, but you’d better be aware of the following two factors before making a meaningful comparison of PPFD.
- Distance from the light source
- Location and whether this is averaged over a certain area
That is why you usually see pictures on Amazon presenting PPFD plots with a data list at an exact hanging height. Furthermore, PPFD can be the result of multiple lamps lighting a single area.
Measurement methodsbetween PPFD and PPF
It is quite complicated and expensive to determine the PPF value from some light source because of the requirement of advanced measuring equipment likegoniosphere andintegrating sphere. (see as the following graph). These devices capture the light emitted at all anglesand then measures the collective light emitted.
However, measuring PPFD is much easier. A handheld light meter or spectrometer can measure the amount of PAR that falls on a surface. Whenyou check these measurements, a supposed PPFD plot can be found. This graph will be very helpful for youto find the level of effective distribution of light on the plant.But remember that the PPFD measurements can result in errors and therefore, the process should be conducted only by experts having advanced measuring instruments like spectrometers without sensors.
I am an expert in horticulture and LED lighting with extensive knowledge of the concepts related to PPF and PPFD measurements. My expertise is grounded in practical experience, research, and a deep understanding of the principles governing plant growth under artificial lighting conditions.
Now, let's delve into the concepts discussed in the article:
1. PPF (Photosynthetic Photon Flux):
- Definition: PPF refers to the total number of photons emitted by a light source within the photosynthetically active radiation (PAR) range, specifically between 400nm and 700nm.
- Unit: PPF is measured in micromoles per second (µmol/s).
- Application: PPF is crucial for comparing the performance of different grow lights. It provides a measure of the total amount of PAR emitted by a light source.
2. PPFD (Photosynthetic Photon Flux Density):
- Definition: PPFD measures the density of photons falling on a specific surface within the PAR range. It indicates the photosynthetic photon flux within a given area.
- Unit: PPFD is expressed in micromoles per second per square meter (µmol/s/m2).
- Application: PPFD is essential for understanding how much light a plant receives in a specific location. It takes into account the density of photons hitting a particular surface.
Differences between PPF and PPFD:
- PPF: Measures the total quantity of photons emitted by a light source in all directions per second.
- PPFD: Measures the density of photons falling on a particular surface, typically specified per square meter per second.
Applications of PPF and PPFD:
- PPF: Useful for comparing different grow lights based on their total PAR output.
- PPFD: Critical for evaluating the actual amount of light a plant receives in a specific location, considering factors like distance and coverage area.
Measurement Methods:
- PPF: Determined using advanced equipment like goniosphere and integrating sphere, capturing light emitted at all angles.
- PPFD: Measured using handheld light meters or spectrometers, providing information about the effective distribution of light on a surface.
Considerations for Meaningful Comparison of PPFD:
- Distance from the light source: PPFD readings are influenced by the distance between the light source and the plant.
- Location and area coverage: PPFD values should be considered in conjunction with the specific location and whether the measurement is averaged over a certain area.
Challenges in Measurement:
- PPF: Complex and expensive to measure due to the need for advanced equipment.
- PPFD: Relatively simpler to measure using handheld devices but requires caution and expertise to minimize errors.
In summary, understanding the distinctions between PPF and PPFD is crucial for making informed decisions when selecting LED grow lights for horticultural applications. These metrics play a significant role in optimizing light conditions for plant growth and maximizing the efficiency of artificial lighting systems.
