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With the increasing popularity of LED grow lights, manufacturers and distributors are innovating new ways to capture your attention. They like to lace genuine science with a healthy dose of marketing hype in hopes that you pause just long enough for them to dazzle you with the latest hyperbole. There are so many terms being thrown around, it can be difficult to dissect reality from marketing hype.

One of the common ways they try to get your attention is by talking about the light wavelength and spectrum used by their LED grow lights.

Here is a simple run-down of what is important and what isn’t to help your LED grow be all it can be.

LED Grow Light Spectrum

When discussing light, spectrum simply refers to a range of wavelengths of visible light in the entire electromagnetic spectrum. Aside from visible light, the electromagnetic spectrum includes energy (radiation) from radio & microwaves, infrared, ultraviolet, x-rays, and gamma rays. Incidentally, the plural for spectrum is spectra, not the often-seen spectrums.

In any case, grow lights are concerned primarily with the visible spectrum though, occasionally, utilize both infrared and ultra violet spectra as well.

LED Grow Light Wavelength

In terms of an LED grow lights (or any lights for that matter), the term wavelength refers to the distance between peaks and troughs in a wave. Light wavelengths behave similarly to waves in water and their peaks can be close together or far apart.

It is this trait that determines the color you see from red (long wavelength) to blue (short wavelength). Each shade of light along the visible spectrum can be measured in nanometers (nm) that range from 380nm to about 780nm, from blue/violet to red, respectively.

It is from within the visible light spectrum that plants derive all of the energy needed to conduct photosynthesis and grow. Taking advantage of how plants react to certain wavelengths of light is the basis behind the the development of LED grow lights.

How LED Grow Lights Promote Plant Growth

Even though HID lights have leanings toward a particular end of the light spectrum (blues for metal halide, yellow/red for high pressure sodium), they emit light in the full visible spectrum just the same way an everyday light bulb does. In general, plants respond in some fashion to all light, however, they get the most benefit from various blue and red wavelengths. Consequently, they get the least benefit from greens and yellows as most of it is reflected back.

Initially, LED manufacturers thought all that was needed was a single band of blue and a single band of red light – given at the right stage of growth – and you would have success. While this may have worked in limited testing on simple plants such as grass, it failed (or produced undesirable results) in more complex plants such as tomatoes and, of course, cannabis.

This did not stop many manufacturers from blasting out poorly designed models in the early days of LED grow lights, which is why this industry is still trying to separate itself from this bad reputation.

Necessary Bands & Wavelengths For LED Grow Lights

Early adopters of this technology saw plenty of promise and, fortunately for us, kept pushing the technology further. What they found was that initial models were at least partly right – they had the concept of red/blue light down but it lacked in delivery.

It was discovered that more wavelengths were needed in order to address the shortcomings of the first models. When looking at a PAR chart, you can see that there are distinct peaks along the visible light spectrum at which plants derive nearly all of their energy required for photosynthesis.

It is clear that red and blue are needed and, until I did more research, I thought that orange was needed as well. The fact is that just two wavelengths in the red band and two wavelengths in the blue band can provide over 95 percent of the light needed for all phases of plant growth.

Some manufacturers also deliver UV and/or infrared light bands in their products to enhance resin production and flowering.

Photosynthetic Pigments & Absorption Spectrum

There are six main photosynthetic pigments in higher plants that drive plant growth, flowering, and fruiting. Different pigments in the plant absorb light at various points of the visible light spectrum – both red and blue – for vegetative and flowering growth.

For example, let’s take the most common/abundant photosynthetic pigments in a plant, chlorophyll A and B. The absorption spectra for chlorophyll A is both at 400-450nm (violet to blue) and at 650-700nm (near-red to deep red) while chlorophyll B peaks at 450-500nm and 600-650nm. So, while red is essential to flowering, it is also necessary for vegging. It also happens to be absorbed less efficiently by plants, hence the increased need for red lighting during flowering.

Check out:

My previous understanding of the need for orange in LED grow lights was based on what I know now as flawed science from this Solar Oasis patent . . .

Their research and testing were flawed, which is where they came up with the 612nm (orange) and its importance to photosynthesis. While the reading is well within the absorption range for chlorophyll B, it is not at the peak of absorption. In their testing, they attributed growth to the 612nm while in fact, it was because of the 660nm they were also using (red). They also said that the orange excites carotenoids . . . which is just wrong as it peaks at around 439nm and 483nm as you can see here:

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 What’s Next For LED Grow Lights & Cannabis?

What we have now are LED grow lights that are optimized for full-cycle plant growth; from vegetative growth to flowering.

Keeping things simple, light from the blue end of the spectrum is necessary for vegetative growth – making for strong, healthy plants with thick foliage. In contrast, red light is necessary for flowering and fruiting – producing large, dense buds along all of the nodes that were created, in part, by the blue lights.

Remember though, it is not advisable to use single color LED grow lights (i.e. all blue for veg, all red for flowering) because you need a balance for the entire growth cycle.

While some companies are touting their full-spectrum and marketing 11+ band LED grow lights, others are opting to refine the current technology. It seems to me that the whole point behind LED grow lights is the efficiency and the fact that they are tuned-in to the precise wavelengths that are needed for photosynthesis.

After all, we already understand that full-spectrum light produced by HID bulbs is inefficient; then why are some companies promoting their “white light” or “full spectrum” LEDs? In addition, adding on excessive bands of LEDs also results in a less efficient light – seems to be a step backwards, not an innovation.

The exciting part is that the industry will continue to benefit from true innovation and research for years to come.

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