It is no secret that light is a critical factor in farming - both in traditional fields and advanced indoor growing systems. However, not all light is equal when it comes to plant growth, and different measures are needed to fully understand and optimize light sources. Let’s dive into two of the most commonly used measurements for assessing light intensity: Lux and Photosynthetic Photon Flux Density (PPFD).
Lux is a measure of illuminance, or the intensity of light as perceived by the human eye.
One lux is equal to one lumen per square meter. In essence, lux quantifies the amount of visible
light in a specific area, giving us an understanding of what we, as humans, perceive as brightness.
This measure is useful in many contexts - from determining the necessary
lighting for a comfortable reading environment, to ensuring adequate
illumination for safety on roadways. However, when it comes to growing plants,
lux falls short. The reason for this is twofold.
Firstly, lux measurements are weighted based on human perception.
Humans are most sensitive to green light (around 555 nm), but plants
use a broader spectrum of light for photosynthesis, primarily in the red and blue
regions. Secondly, lux doesn't account for the number of photons reaching the plant surface,
which is a key factor for photosynthesis.
To address the shortcomings of lux for plant growth, scientists often turn to Photosynthetic
Photon Flux Density (PPFD). PPFD measures the number of photosynthetically active photons
(those in the wavelength range of 400 to 700 nm) that reach a specific area each second.
It is measured in micromoles of photons per square meter per second (μmol/m²/s).
Unlike lux, PPFD does not bias towards any particular part of the light spectrum.
It considers all photons within the photosynthetically active radiation (PAR) range equally,
regardless of their wavelength. This makes PPFD an excellent measure of the potential for photosynthesis,
the process through which plants convert light into energy.
Furthermore, PPFD considers the intensity of light reaching a given area, which is critical for indoor farming where light conditions can be tightly controlled. By using PPFD, growers can adjust their lighting systems to provide an optimal level of light intensity for their crops, enhancing growth rates and yields.
For outdoor farming, where the sun provides the majority of light, the differences
between lux and PPFD are less important. The full spectrum of sunlight naturally
provides a balanced range of wavelengths for photosynthesis. However, growers
still need to consider the angle and intensity of sunlight, cloud cover, and seasonal
changes, all of which can influence the PPFD values experienced by the plants.
In a Hybrid Farm, where both Sunlight and Grow Light together are responsible
for providing lighting for photosynthesis, using a spectrum independent measuring
system (PPFD) becomes utmost important. Using Lux system of measurement it is
absolutely impossible to compare two plant light sources or grow lights emitting
different spectra since Lux sensors offer different sensitivities to different
wavelengths of light. However, with PPFD sensors different light sources can be
measured and compared since it offers equal sensitivity to photons of all wavelengths
within the PAR band.
In indoor farming or controlled environments, the differences between
lux and PPFD become paramount. For example, if you were using a grow light
that emits a lot of green light, a lux meter might indicate that your plants
are receiving ample light. However, lux doesn't account for the total number
of photons reaching the plant surface so your plants may actually be under-illuminated.
By using a PPFD meter, you can ensure that your plants receive a
sufficient quantity of useful light. PPFD meters are designed to
measure the light intensity within the PAR range, providing a far
more accurate assessment of the light conditions for plant growth.
This allows growers to optimize their lighting systems, maximizing
plant health and yield.
Read more about what is PPFD (Photosynthetic Photon Flux Density) range.