Lumens, Lux, PAR, PPF and PPFD: What Is the Difference?

Lumens, Lux, PAR, PPF and PPFD: What Is the Difference?

If you’ve been delving into the field of horticulture lighting, you may have come across a plethora of acronyms such as Lumens, Lux, PAR, PPF and PPFD. At first glance, these terms can seem daunting, but they are actually fairly simple. In this guide, we will provide clear explanations for all these seemingly intimidating metric units. Only reliable manufacturers like us can keep you well informed of the meanings of these terms. After reading this article, you’ll feel more confident in selecting the optimal LED grow lights for your greenhouse or indoor plants.

What Is Lumens?


Lumens are relevant for white light in everyday applications. The lumen is a unit used to describe the amount of visible light a source produces. However, when it comes to grow lights for plants, lumens are not the appropriate metric. This is because lumens are based on the sensitivity of the human eye to green light, whereas plants are most responsive to red and blue light. Therefore, a light source may appear bright to humans based on lumens, but it may not provide the necessary intensity for plants.

To illustrate this, let’s consider two grow lights: one measures 500 lumens per square meter and has a high (blue) color temperature, while the other measures 1,000 lumens per square meter but falls within the green-yellow range. Based on lumens alone, one might assume the 1,000 lumen light is superior, but that’s not the case. Lumens don’t accurately reflect the light available for photosynthesis.

What Is Lux?

Lux is a unit of measurement that quantifies the number of lumens per square meter. It is useful for assessing the level of light in a given area and identifying areas that may require additional lighting. Lux provides a scale for understanding the intensity of light, with direct sunlight reaching around 100,000 lux, normal room lighting at 300 lux, and the light of a full moon at 1 lux.

Again, lux and lumens are not suitable for determining the intensity and potential of a grow light for plant growth.

What Is PAR?


If lumens and lux can not evaluate light for growing plants, what accounts for it? Well, PAR, that is Photosynthetically Active Radiation. PAR represents a range of light wavelengths from 400nm (violet-blue) to 700nm (red) that are essential for driving photosynthesis. Unlike lumens, which prioritize certain wavelengths based on human perception, PAR includes all wavelengths relevant to plant growth.

However, PAR alone doesn’t provide a complete understanding of the quality and quantity of light reaching the plant canopy. There are extra metrics to take into account. We will talk about them shortly.

How Do We Measure PAR Light?

Although measuring light can be challenging, it is essential to understand the output and efficiency of grow lights. When we refer to measuring light, we are essentially counting the photons released within a specific surface area over a given period. When we describe how much light is received from the sun in a day, we use the unit of moles. In the context of light fixtures, we use a smaller unit called micromoles, which is equivalent to one millionth of a mole.

In physics and chemistry, a mole is a unit of energy measurement. For light, a mole is approximately equal to 6.022140857 x 1023 photons. On the other hand, a micromole (μmol) is one-millionth of a mole, that is 6.022140857 x 1017 photons.

What Is PPF?


The Photosynthetic Photon Flux (PPF) refers to the total amount of light in the PAR range that a light source produces per second.

By knowing the PPF value of a grow light, you can estimate or calculate the number of lights needed per area to achieve the desired light level for your plants. Let’s consider the example of a strawberry grower conducting winter cultivation, aiming for a light level of 200 μmol/sm². Suppose each growing area has a total area of 40m². In this case, you would require 40m² x 200 μmol/sm² = 8000 μmol of light for that specific area. Now, let’s assume a single LED grow light emits a PPF of 2000 μmol/s. To meet the required light level, you would need 8000 μmol / 2000 μmol/s = 4 lights for each growing area.

Keep in mind that PPF represents the total number of PAR photons emitted by a light source in all directions, rather than the number of photons that will effectively reach your plants. To determine the number of photons that will reach your plants, you need to consider the Photosynthetic Photon Flux Density (PPFD) measurement.

How Do We Measure PPF?

The measurement of PPF involves conducting a sphere test. This test entails placing the light fixture inside a round sphere, where the emission of PAR photons in all directions is quantified. The sphere test continuously records the number of PAR photons emitted by the fixture per second, and the outcomes are typically represented as micromoles per second (μmol/s).

What Is PPFD?


PPFD, which stands for photosynthetic photon flux density, refers to the quantity of PAR photons that reach a specific surface within a given time. It offers useful information about the amount of PAR light received by plants at different measurement points. PPFD measurements are expressed in micromoles per square meter per second (μmol/m²/s).

Different plant species have specific PPFD requirements for optimal growth and yield. For instance, flowering plants like cannabis typically require around 300-600 μmol/s during the vegetative phase and 800-1000 μmol/s during flowering. These measurements represent the PPFD levels needed.

However, it’s important to note that PPFD has its limitations. One drawback is that it treats all photons within the 400-700nm range equally, even though red and blue light play a more significant role in driving photosynthesis.

Moreover, PPFD focuses solely on PAR within this range, disregarding the potential effects of UV and infrared light, which have been found to stimulate the production of secondary metabolites in plants.

Additionally, PPFD can be easily exaggerated. Manufacturers may list unrealistic distances between the plant canopy and the light source, leading to higher PPFD values. However, these distances are impractical due to factors such as heat generated by the lighting system.

Despite these limitations, PPFD remains the best available metric for assessing the effectiveness of LED grow lights. When comparing different lighting systems, it is crucial to closely examine the PPFD values to make informed decisions.

How Do We Measure PPFD?

PPFD is commonly assessed using a PAR meter, which can be positioned at different locations or heights to measure the actual light intensity at those specific spots. However, it’s important to note that a PAR meter primarily captures the direct light emitted by the source and may not accurately measure light from the sides. In many cases, it is advantageous to have a combination of direct and indirect light reaching the plants from various angles. This facilitates deeper light penetration into the plant canopy and promotes overall better yield.

In a small-scale cultivation setup, using a tent where light can bounce off the sides and directly illuminate the plants tends to be more beneficial. This allows for a more comprehensive light distribution within the limited space. On the other hand, in larger-scale operations with multiple lights, it is often more effective to suspend the lights at higher positions. This arrangement ensures that each plant receives light from multiple angles, optimizing the light coverage. Unfortunately, a standard PAR meter may not accurately measure this multidirectional lighting setup.

MokoLight-Your Reliable Supplier

Having a good understanding of these metrics will significantly assist you in selecting the right LED grow light for your crops. It will enable you to distinguish reputable manufacturers from cheap and unreliable ones right from the beginning. If you come across an LED grow light manufacturer that cannot provide these metrics or solely focuses on lumens, it’s advisable to steer clear of them.

If you’re unsure where to buy LED grow lights for your plants, we recommend exploring the LED lights line offered by MokoLight. We offer various LED grow light series designed for indoor plants, greenhouse cultivation, and vertical farming. All LEDs surpass average performance in terms of PAR, PPF, and PPFD metrics. Additionally, we provide a full spectrum, and some models even offer variable spectrum control, allowing you to provide your plants with the precise light they require at different growth stages. MokoLight is committed to supporting dedicated growers like you. Contact us right now!

Written by ——
Adelyn Ward
Adelyn Ward
Master of Science; professional electronic engineer with over 7 years of experience in electronic design and engineering projects; proven expertise of LED manufacturing processes, capable of communicating intricate ideas to a broad range of audiences. Reach Me Now>>
Adelyn Ward
Adelyn Ward
Master of Science; professional electronic engineer with over 7 years of experience in electronic design and engineering projects; proven expertise of LED manufacturing processes, capable of communicating intricate ideas to a broad range of audiences. Reach Me Now>>
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