Horticulture lighting 2

So a photon walks into a hotel. The desk clerk says, “Welcome to our hotel. Can we help you with your luggage?” The photon says, “No thanks, I’m traveling light.” Ok, ok settle down the point is every plant on Earth needs energy to grow and that energy come in the form of light. More precisely a photon. What does this mean? It means that we can use lighting fixtures like LED’s to grow plants without the sun. When looking at what is important in regards to LED fixtures and growing plants we should look at the basics which are fundamental in understanding LED grow technology. We will look at three in particular that are important. These three are PAR, PPF-> PPFD and Efficacy.

Let’s take a look at how light works as energy and what that means to grow lights. So a photon is energy but when useable it is referred to as radiation. Since plants use a process called photosynthesis to use radiation as energy to grow, knowing what kind of radiation is important. Radiation that it useable energy by plants is called Photosynthetically Active Radiation or PAR. So PAR is the only light radiation that’s important to growing plants. Since light is measured in wavelengths, which wavelengths are considered photosynthetically active? The short answer is 400 – 700nm. Now every plant is going to be a little different in which specific wavelength’s they use and when, but this means a full spectrum light is going to be the most affective light for growing any plant. Now that we have a grasp on what we need in a light to grow plants (PAR) let’s take a look at how to measure that useable energy.

Photosynthetic Photon Flux or PPF is a measure of the total PAR output by a lighting system per second. Photosynthetically active radiationThis is how we measure PAR, it is photon micromoles per second (umol/s). Again, what does that mean? Well, it means that’s how much useable energy is put off per second by a lighting fixture. This still doesn’t tell us how much of this light is getting to the plant, however. This is where we use Photosynthetic Photon Flux Density or PPFD. This is the real practical calculation in a grow light because it is the amount of PAR that arrives at the plant. PPFD is a PAR measurement on a specific point on the plant and is measured in micromoles per square meter per second (umol/m2/s). So if you have a light fixture you can move it up and down and side to side from your plant while taking this measurement until you have the optimal PAR.

LED Direct PhotonsLED horticulture color

Now that we can figure out the optimal PAR via PPFD how efficiently can we do it? Because after all if a system is not efficient enough it likely will not be cost effective. Just like white LED efficiency is referred to as efficacy. In the case of white LED it is simply efficacy meaning the amount of energy used in watts to produce x amount of light measured in lumens. For grow lights however this isn’t much use since lumens are not nearly as important as wavelength or PAR. So if we look at the PPF produced by the fixture divided by the energy in watts we get what is called photon efficacy. This is how energy efficient a fixture is producing PAR.

There are a myriad of metrics that influence plant growth in regards to LED lighting fixtures. This is whyLED Direct Horticulture efficacy it is important to understand the basics first. In summation PAR, PPF -> PPFD, and Efficiency are three of the most important factors and the fundamental basics of LED grow lights. Once we have a firm grasp on these we can take a look at a broader spectrum of LED grow lamp problems and solutions. As LED Direct Group expands its knowledge on the grow light fixtures and industry we will begin to sell grow lights but until then, stay tuned for more grow light info!

-Scott Yingling: LED Direct Group



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  • Albopepper.com. (2019). PAR LIGHT (Photosynthetically Active Radiation): Spectral Quality of Horticultural Lamps & LEDs -AlboPepper.com. [online] Available at: https://albopepper.com/PAR-light-spectral-quality-in-horticulture.php [Accessed 20 Feb. 2019].
  • Asensetek.com. (2019). YPFD (Yield Photon Flux Density) | AsenseTek Official. [online] Available at: https://www.asensetek.com/knowledge-ypfd-yield-photon-flux-density/ [Accessed 20 Feb. 2019].
  • DansReef.co.uk. (2019). Photosynthetic Photon Flux Density PPFD Photons falling on a surface – DansReef.co.uk. [online] Available at: https://www.dansreef.co.uk/2018/01/18/understanding-lighting-reef-tank/photosynthetic-photon-flux-density-ppfd-photons-falling-on-a-surface/ [Accessed 20 Feb. 2019].
  • Greenhouse Product News. (2019). Plant Lighting Efficiency and Efficacy: μmols per joule – Greenhouse Product News. [online] Available at: https://gpnmag.com/article/plant-lighting-efficiency-and-efficacy-%CE%BCmol%C2%B7j-%C2%B9/ [Accessed 20 Feb. 2019].