Understanding PAR, PPF, PPFD, and PFD in LED Grow Lights

When growing plants indoors, it's important to provide the right amount and type of light. Over the years, different terms PAR, PPF, PPFD, and PFD have been used to measure light for plant growth, which can be confusing.

Let's break down these terms, which are commonly used when discussing LED grow lights and help you better understand their significance in plant growth.

PAR (Photosynthetically Active Radiation)

PAR is the type of light that plants use for photosynthesis. It's the light in the 400-700 nanometer range. In the past, PAR was measured using watts per square meter (W/m²), which didn't accurately represent the light that plants use.


PPF (Photosynthetic Photon Flux)

PPF measures the amount of light particles (photons) that plants use for photosynthesis. It's measured in micromoles per second (μmol/s). This term is more accurate than PAR because it counts the photons that plants actually use.

To put it simply, think of PAR as the total energy of the light that plants can use, while PPF is the actual number of light particles (photons) that plants can absorb and use for photosynthesis.

Here's an analogy about PAR and PPF that might help:

Imagine you have a bag of candy. PAR would be like measuring the total weight of the candy in the bag, while PPF would be like counting the number of individual candy pieces in the bag. While the weight can give you a general idea of how much candy you have, counting the actual number of pieces is a more accurate way to measure the amount of candy.

In the same way, PPF is a more precise measurement of the light that plants can use for photosynthesis compared to PAR.

PPFD (Photosynthetic Photon Flux Density)

PPFD is similar to PPF, but it also takes into account the area that the light covers. It's measured in micromoles per square meter per second (μmol/m²/s). This term is the most useful for indoor growers because it tells you how much light is reaching your plants at a specific point.

To understand the difference better, let's use another analogy for PAR and PPFD:

Imagine you have a watering can with a sprinkler head. PPF would be like measuring the total amount of water coming out of the sprinkler every second, while PPFD would be like measuring how much water is hitting a specific area of your plants every second.

In other words, PPF tells you the total output of your light source, while PPFD tells you how much of that light is actually reaching your plants at a specific point.

Why is PPFD important for indoor growers?

PPFD is the most useful measurement for indoor growers because it helps you determine if your plants are receiving the right amount of light.

Different plants have different PPFD requirements, so it's essential to know the PPFD output of your grow light and adjust the distance between the light and your plants accordingly.

By ensuring that your plants receive the optimal PPFD, you can promote healthy growth and maximize yields.

PFD (Photon Flux Density)

PFD is a newer term that includes a wider range of light wavelengths, not just the 400-700 nm range and can include photons between 300 and 800 nanometers.

This term is important because research has shown that other wavelengths, like far-red and ultraviolet light, can also affect plant growth.

Here's an analogy to help visualize the difference between PFD and PPFD:

Imagine you have a box of crayons. PPFD would be like counting only the crayons in the red, orange, yellow, green, blue, and violet colors (which represent the 400-700 nm range).

PFD, on the other hand, would be like counting all the crayons in the box, including the reds, oranges, yellows, greens, blues, violets, as well as the pinks, purples, browns, and blacks (which represent the wider range of wavelengths).

Why is PFD important for indoor growers?

Recent research has shown that light wavelengths outside of the 400-700 nanometer range can also have significant effects on plant growth and development.

Far-red light (700-750 nm) has been found to enhance leaf expansion, stem elongation, and flowering in some plants.

Ultraviolet light (100-400 nm) can influence plant morphology, stress response, and the production of secondary metabolites, which can affect plant flavor, aroma, and nutritional value.


In conclusion, when choosing an LED grow light, look for the PPFD value to determine how much light your plants will receive.

The higher the PPFD, the more light your plants will get. Make sure to adjust the distance between your light and your plants to achieve the optimal PPFD for your specific plants.

By understanding these light measurement terms PAR, PPF, PPFD, and PFD in LED Grow Lights, you can make informed decisions about your indoor grow setup and provide your plants with the best possible light for healthy growth.