A paradigm shift is underway and is catching steam at an unprecedented pace. We’re talking hockey stick growth. The shift to LEDs from traditional lighting is in full bore beast mode. Gone are the stigmas and fears that have riddled the industry for decades and we are way past the point of validation by innovators and early adopters, pushing heavily into the mainstream with a wave of mass adoption.
Unfortunately there is still a lot to learn with LEDs. This problem is made even worse by the influx of non-horticulture industry companies and sales reps that are drinking from a fire hose in their efforts to learn about controlled environmental agriculture (CEA). Even in our own efforts to grow our team of Scyntists, it is overwhelming how many people I talk to that think they know lighting. It has been disappointing, to say the least, to hear the same old schtick around energy savings and lumens output as the key features. The fact is that plants are an organic matter that need insanely different things from its food source, light, than a building, landscape or theatrical environment. These two applications couldn’t be on more opposite sides of the spectrum.
For starters, light for humans is measured in Lumens. Whether we’re discussing office lighting, landscape illumination, off-roading or your flashlight, lumens are a critical metric to determine the quality of your lighting experience. We’ve just stumbled upon the first big lie. Lumens mean nothing to plants or any photosynthetically activated organism. When it comes to plants, we must shift the conversation to photosynthetic photon flux (PPF) which can be, albeit crudely, converted from lumens. Both lumens and PPF are a metric that measure the output of light (energy) from a fixture in all directions. Lumens are important to humans because it is based on the portion of the light spectrum that the human eye can see. PPF is based on the spectrum range that plants need to conduct photosynthesis. While there is some debate as to what the PPF spectrum for plants really is (the McCree curve has been the standard for almost 50 years), it is not our intention to dive into that debate here. Take away #1 is that horticulture applications of light require us to look at PPF, and not the lumen ratings.
PPF (or lumens for that matter) is a measure of the total output of light, in a certain spectrum, that a lighting fixture emanates in all directions, but says nothing about where that energy is going. The main reason for this has to do with intended purpose. When lighting a building it is the intention to spread the light everywhere so we, as humans, can see every surface; which usually involves flat surfaces and other geometrically shaped objects. Providing light for a plant is a different ballgame. This is where the 2nd lie comes in. In a controlled environment agriculture facility the last thing we want is to light the entire space, like walls, isles, ceilings or walkways. The only goal here is to get as much light as possible onto and down into the canopy. Of course, plant leaves aren’t flat boxes and growing styles usually preclude light from easily reaching the bottom levels of the canopy using traditional style light fixtures.
There is another metric that is relevant and (in our opinion) more important, but not always talked about. Photosynthetic photon flux density (PPFD) is a measure of the number of photons in the 400-700nm range (McCree curve) of the visible light spectrum that lands on a square meter of a flat surface per second. While there are challenges here because plants aren’t flat, it is the best metric we have to understand the amount of light actually reaching the plants. PPFD trumps PPF because plants don’t care about how much light a fixture emits, they are only concerned with how much of that light reaches their photoreceptors.
This is where knowing a little can be very dangerous when applying that knowledge to horticulture. When LED lighting companies teach and educate growers incorrectly, it leads to misinformation that ultimately ends in disappointment and potentially stifles the headway we have all made in bringing LED technology to the forefront. It is only too often that we hear from growers who have chosen a light based on it’s data sheet stated PPF. That’s like choosing a car based on how much horsepower it has, but forgetting to ask about all the other factors that determine speed, such as how much it weighs, how is it geared, what type of tires does it have, etc. Take away #2 is to always ask for a PPFD map showing the values across the canopy and at different levels below the canopy.
This leads us into another metric that is derived from PPF. Efficiency. In its simplest form, efficiency is calculated by taking the total PPF and dividing it by the watts a fixture is rated at. In horticulture, the current goal is to reach as close to an efficiency level of 3.0 µmols/s as possible. On the surface, this seems like a credible way to judge a lighting fixture. Technically, this rating does tell us how good of a job the fixture does at converting energy into light. Which is really important, right? Well, this is where the 3rd lie comes in. In reality, this lie is tied to the 2nd lie, or really is an extension of it. PPF and efficiency ratings really only tell us how much light is coming out of the fixture and how effectively it is accomplishing it. Take away #3 is that efficiency ratings don’t tell us how well a particular light will grow your plants.
The fallacy here has to do with the missing component of light delivery. Lights used in buildings, landscaping, etc. use a plethora of delivery tactics. Some of these include: filters, optics, reflectors, or other methodologies to harness the light and direct it in the emission patterns that suit the specific use case. When it comes to horticulture, most growers would love to have every plant in their facility getting the exact same amount of light. While that’s not physically possible, there are ways to ensure that we achieve a 95% or greater evenness across the canopy. Traditional light (HPS & CMH) utilized curved metal hoods that directed the light and spread it out. What’s strange is that most LEDs on the market have chosen not to use a hood, reflector or optics but instead either (1) use nothing or (2) spread out the LEDs so we end up with these 6-10 bar fixtures that look like you have a drop ceiling in your facility.
Light delivery is the most understated yet important topic when it comes to growing plants in a CEA environment. All those lumens, excuse me … PPF, must get harnessed and directed not only to the growing surface/canopy (measured in PPFD), but delivered in a way to penetrate deep and allow for growth down below the surface. This requires double duty and isn’t accomplished by simply spreading out the LEDs. This is where the 4th lie comes in. Light, especially from an LED, needs to be harnessed and focused in a way that is specific to its desired application. A proper hood or optic is scientifically designed to not only spread out the light but to push it out in a fashion that allows it to be delivered at multiple angles with the intention of being able to penetrate and reach the lower levels of the canopy. This topic is discussed in more detail in a previous article here. Take away #4 is that LED lights require a light delivery system that meets your facility’s needs.
Understanding the true facts behind how LEDs work is paramount to having a successful experience when switching over from traditional lighting. Misinformation is the bane to many aspects of our society and horticulture lighting is not left out of that mix. The momentum behind LEDs is not going away anytime soon. It is up to you, as the consumer, to demand metrics that are meaningful when you are making such an important and expensive decision as choosing what lights to go with. Set the bar high, cut through the hype and demand the truth!