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Post on - Aug 13 2020
Many LED lighting suppliers will say that full-spectrum LED grow lights are the best option for growing plants because they mimic the natural light from the sun. The argument goes:
Plants have grown under sunlight for millions of years. Why would we want to change what mother nature knows is best?”
Well, we want to let you know that there is no such thing as a full-spectrum LED grow light.
There, we said it.
But before we get a flood of messages from concerned growers wondering what all the confusion is about, let’s first uncover what full spectrum means. Then we’ll let you in on the truth about full-spectrum LED grow lights so you can make the best grow light choice for your facility..
Full-spectrum LED grow light is simply a marketing term that implies that your grow light closely resembles light from the sun. This marketing term comes from the concept of “full-spectrum light,” which in recent years has been used to refer to electromagnetic radiation from the UV to infrared wavebands.
Figure 1 – In recent years, full spectrum is a term that has been used to refer to light between the UV and infrared wavebands as seen in the graphic above.
The full-spectrum LED grow light is the newest evolution of an already confusing term. Originally, full-spectrum light described the only real full-spectrum light source, the sun.
Over time, the term began to take on other characteristics of sunlight. The commercial lighting industry began using the name “full-spectrum” to sell lights that produced a Color Rendering Index (CRI) over 90. Humans perceive colors more accurately under light sources with a CRI over 90, much like how we see colors in our natural world under daylight. This was a beneficial feature for human environments such as offices, outdoor spaces, and others.
With the advent of horticultural lighting, companies once again began to borrow the term. Only this time, they claimed that full-spectrum LEDs could reproduce the effects of sunlight for plants.
Thus, the full-spectrum LED grow light was born. Unfortunately, lighting for plants is not quite that simple.
There are many issues with the concept of full-spectrum LED grow lights. For starters, just because you name something, doesn’t make it true. This rhetoric may have made sense for lighting designers interested in selling lights so humans could see, but plants require light to feed, grow, and live.
There are three major problems when talking about full-spectrum grow lights:
1 Full-Spectrum Grow Lights Aren’t Optimized for Plants
2 Full-Spectrum Grow Lights Don’t Include the Full Solar Spectrum
3 Full-Spectrum Grow Lights Are Not Dynamic Like the Sun
We’ll briefly look at these problems with full-spectrum grow lights one-by-one, so you can understand how deep the roots of this problem run:
A major problem with many full spectrum LED grow lights is that they are designed to give the appearance of daylight without being custom-tailored for rigorous plant growth.
It’s the reason why we at BESTVA LED coined the phrase, “PAR is for plants and Lumens are for humans.” Not all wavelengths of light are optimal for photosynthesis. Plants photosynthesize electromagnetic radiation in the 400 to 700 nanometer range, known as Photosynthetically Active Radiation or PAR. So, plants don’t care how bright your light fixture appears to you.
Still, most full-spectrum lighting companies build fixtures with this visual appeal in mind.
When you hear that the diodes in your full spectrum grow light are 3,000k to 4,500k, or 5,000k+, this degree of Kelvin (K) refers to how “cool” or “warm” your light is in appearance
Our understanding of plant photobiology has come a long way. We understand much more about plants than to be using human lighting metrics to design our grow lights.
Our goal as growers is to improve the lighting characteristics most important for plant growth. This means not only getting enough PAR light, but also the right mix of light spectra, which brings us to problem #2.
In Figure 3 above, we see a standard 2800k full-spectrum LED curve. This LED has been optimized for its warm visual appeal by stacking most of its energy in the orange-to-red wavebands. This spectrum is optimized for the visual spectrum between 380 to 740 nanometers. Emphasis has also been placed on light around 555-nanometers because this is where our eyes are most sensitive
The thinking behind many full spectrum LED grow lights on the market is that by creating a spectral distribution similar to sunlight, your plants will grow well. A decent theory, except that full spectrum grow lights are not actually similar to the sun.
We can see below that the sun’s radiation includes much more than the visible or PAR wavebands.Sunlight itself is complex, and many scientists are still working to understand it today. You can see that sunlight also contains ultraviolet (UV) and infrared light (as well as x-rays, radio waves, and others, but we’ll leave those alone for now).
Although PAR is the most important light for photosynthesis, plants still respond to radiation outside of the PAR spectrum. For instance, UV light elicits protective compounds in plants similar to the way humans become tanned in the presence of UV.
Plants also use a type of infrared light called “far-red light” to induce a shade avoidance response, causing them to stretch and can induce early flowering.
To create a light source that elicits plant response the same way the sun does would be too costly and downright impossible given current grow light technology. Nor would you want to create such a grow light, which takes us to problem #3.
Not only would it be too costly to create an actual full spectrum LED grow light, but ifsuch a thing even existed, its performance would still not accurately reflect what’s happening in nature.
But before you rush and begin moving your grow room outdoors, let’s consider why plants don’t need the full spectrum of sunlight. For starters, plants don’t need UV or infrared light to live. Also, in a controlled environment, plants are given ideal conditions to grow in and often don’t need to compete with other species to live.
Plants only require light in the 400 to 700-nanometer range to photosynthesize. So, you’ll want to choose a grow light that produces your desired results, most often higher yields and better quality for your plants.
By now you must be wondering:
If I can’t mimic sunlight, then what light spectrum should I use?”. The answer is both simple and quite complex.
Plants only require PAR light for photosynthesis. So, if your grow light is optimized within the PAR spectrum, you’re going to get the most bang for your buck when it comes to minimizing electrical costs while maximizing plant health.
Beyond PAR, it’s important to choose a light spectrum that’s:
best for the environment you’re growing in (greenhouse or indoors)
tailored to your plant’s growth phase (propagation, vegetative, flowering, or finishing)
or specific to the cultivar being grown
It should be clear by now that there are no real standards around full spectrum LED grow lights. Full-spectrum is simply a term used to sell you a simple idea.
Although you cannot mimic sunlight, you can use light spectrum to your advantage.
Luckily, there are many grow lights available with designs intended to do just that. So, let’s uncover your options so you can pick the best grow light for your cultivation.