The human eye perceives light completely differently than plants. Plants perceive light as particles that they can absorb. To utilize the full growth potential of plants, it is important to use grow lights, and there are several relevant units of measurement for light in horticulture that are worth learning about.
As a commercial gardener, you probably work with grow lights to optimize the growth of your plants. If so, you may have already come across a number of units and terms that all refer to light. But what do lumens, lux and watts mean? And what about the terms PAR, µmol, PFF, PFFD? Which unit should you use?
Let’s take a closer look.
Lumen: A standardized unit of measurement that indicates the total amount of light emitted from the light source. Simply put, the more lumens, the brighter the light.
Lux: A standardized unit of measurement that indicates the intensity of light distributed over a specific area.
Watt: Unlike lumen and lux, watt refers to the energy consumed by the product and not the light output of the product itself. This makes watt a unit of energy consumption, and thus the unit does not tell us much about how the light matches the plants’ growth needs. To keep the focus on the plants’ needs, we talk about PAR instead. This ensures that our LED matches the plants’ needs and growth potential.
PAR/µmol: Photosynthetically Active Radiation – or photosynthetically active radiation as it is called in Danish – indicates the amount of light plants can use for photosynthesis. This unit is the same as µmol, also known colloquially as micromol. PAR is not a unit of light measurement as such, but is a unit that provides information about the light spectrum the plant needs to grow.
PFF: Photosynthetic Photon Flux measures the amount of light emitted in a defined period of time. However, it does not tell us how much light actually reaches the plant itself.
PFFD: Photosynthetic Photon Flux Density measures how much light hits the plants themselves in a certain amount of time. If you see µmol/m2/s on our datasheets, for example, it indicates the light intensity per square meter every second.
Why lumens, lux and watts don’t tell us much about LED grow lights
The light plants capture – and the light we can see – is called visible light. Photosynthesis captures the energy from visible light, but it does not use the same amount of all the colors of the sun. On the contrary, plants primarily use light from the blue and red spectrum.
This is why DGT by Senmatic’s LED solutions are predominantly developed based on these two colors.
Okay, let’s get a bit more nerdy.
As mentioned, the way the human eye sees light is very different from how plants perceive light. Plants perceive light as particles that they can absorb – these particles are known as photons or quanta. This difference is why particles are measured in µmol/m2/s instead of lux, which is based on how the human eye sees light.
The improved knowledge of plant physiology compared to commercial performance and yield is reflected in the discussion of µmol/s instead of watts per m2. Micromoles are closely related to the photosynthetic needs of plants and can measure the full spectral distribution, including photosynthetically active radiation.
If you use lumens, lux or watts instead, you are measuring human light, whereas plant light is measured in photons using PAR/µmol, PFF and PFFD. Therefore, lumens, lux and watts do not tell us much about the composition of LED light as they do not optimally capture the blue and red spectrum.
Convert watt or lux to PAR
Because PAR (or µmol) measures the amount of light plants need for photosynthesis, we use that unit when determining the spectral composition and number of LED luminaires needed in your nursery and for your crops.
You can use the tables below to convert watt to PAR or lux to PAR:
From watts to PAR
From lux to PAR
Control the spectral distribution in DGT by Senmatics LED
Producing high-quality, healthy plants is about more than improving efficiency and accelerating photosynthesis. Flexibility and control are also extremely important variables, and factors such as plant appearance, growth stage and quality requirements make tuning the spectral distribution to your specific needs a golden opportunity.
This is why the spectral distribution can be tuned in DGT by Senmatics LED solutions.
When you change the spectral distribution, it means changing the composition of the colors emitted from the lamps. This is done by increasing or decreasing the percentage of blue light based on information about the plants’ needs.
How much you can adjust the colors depends on the LED solution, as all luminaires are born with different diode compositions to cover the different needs of plants. If you want detailed information about the possibilities to adjust the spectral distribution and what percentage is optimal for your particular culture, please contact our specialists.
All LED solutions except our Grow Horti have this feature.
Want to know more? Our specialists are ready to help
