How Plants Use Light

We know that most plants need light to grow. The question is, how do they use light, and more importantly, how does the type of grow light that we use affect our plants’ general health and yield? 

A simple Google search will bring up a ton of conflicting information about the relationship between of light and plant growth. For the sake of clarifying all this information, we’ve gone to the experts and broken down how plants use light into three easy steps. 

While some of it may seem pretty technical, it’s actually pretty simple once you understand how plants use different types of light to thrive. Using today’s advanced technology, we can optimize this light to offer the perfect growing environment for happy, healthy plants and increased yields come harvest time. 

 STEP 1- CAPTURE 

 

WHY RED AND BLUE LIGHTS DON’T WORK 

One common misconception is that plants only capture or absorb red and blue light, while the rest of colors, like green and yellow, go unused by most plants.

To understand where this misconception comes from, you have to look into the past, to an experiment done in the 1970s. Scientists used chemicals to extract the chlorophyll of a plant, put it in a test tube, and measured the colors that it absorbed. A graph showing the wavelengths of light that chlorophyll absorbs shows peaks in the red and blue wavelengths, so you can see where that idea came from. 

This led to new designs of grow lights that only produced red and blue lights. Yet, growers using these lights were disappointed in the minimal yields that their plants were producing. In short, their plants weren’t exactly thriving, despite the research done. 

So what was wrong with the science experiment? 

THE FULL SPECTRUM IS NATURE’S M.O.

The truth is, plants need the full spectrum of light to perform at their best. Remember that our 1970s scientists only tested the chlorophyll extract- essentially a plant pulp. When you take the leaf as a whole unit (i.e. in its natural state) the leaf absorbs a lot more green and yellow light. A plant leaf has a specific structure made up of different elements. These elements work together to absorb the entire spectrum of light. When the structure is intact, the leaf absorbs a lot more green and yellow light. 

In reality, experimenting on the chlorophyll doesn’t give us an accurate measure of a plant’s needs. To yield exact results, you need to take the plant and analyze it in its natural form. 

Below, we’ll explain how the plant structure plays a pivotal role in light absorption. 

 THE POWER OF TRANSMITTANCE

Imagine an X-ray of a leaf taken from the side. You would see that the red and blue light barely penetrate the top layer of the leaf. Green and yellow light, on the other hand, trickles down through the entire leaf.

Because chlorophyll absorbs the red and blue light so well, it blocks that light from penetrating deeper into the leaf and the rest of the plant below. Green and yellow light has higher transmittance power, thus powering growth beneath the canopy of the plant. This is as important as the growth that occurs above the canopy. 

The takeaway: Transmittance is just as important as absorbance. 

What happens after they capture this light? This brings us to the next step, photosynthesis. 

STEP 2- PHOTOSYNTHESIS

The graph shown below, known as McCree’s P.A.R. graph, shows the rate of photosynthesis by color, as opposed to rate of photosynthesis by absorbance. As you can see, when you measure photosynthesis as nature intended, plants use the full spectrum of light, from 400 to 700 nanometers.

P.A.R. stands for “Photosynthetically Active Radiation”, and has become synonymous with the concept that plants use red and blue light for growth. 

After disappointing results from using red and blue LEDs, growers turned to white LEDs, in hopes of achieving better results. 

Now, remember that white LEDs were not designed for plants; rather, they were designed for humans to be able to see better (think dentist offices, surgical tables, etc.). The human eye picks up light in the green and yellow spectrum the best, which is why white LEDs focus on these colors of the spectrum.

Besides, the range of light that the human eye picks up is pretty limited, from 400 to 700 nanometers. However, while humans may not see outside this range, the colors outside this range are essential to the photosynthesis process that occurs in plants.

When Dr. McCree set up his experiment, he eliminated as many variables as possible, like any good scientist should. He set it up to test each color individually. 

How did he achieve this? 

Simply by putting a single leaf into each test chamber, and exposing it to one color at a time at low intensity, then measuring the rate of photosynthesis derived from that one color. He captured individual results at the same time.

Of course, in the real world, plants are exposed to all colors of the spectrum at once. This experiment, though, led us to understand why all colors of the spectrum are equally important in the process of photosynthesis.

INFRARED LIGHT 

So, what about infrared light? 

Another scientist named Dr. Emerson tested what happens when you expose a plant to two wavelengths at once- one in the red range, and one in the infrared range. What he found was that those two wavelengths worked together to increase photosynthesis. 

This extra boost of photosynthesis is called the Emerson effect, which works when any color of light in the P.A.R. Range (the graph above) is combined with infrared light. 

The Emerson effect is the product of two photosystems working together to maximize photosynthesis. 

Now, how do these two distinct photosystems work together? 

First, Photosystem II absorbs light below 600 Nanometers, which is red light. It uses that light to split an electron from water and send it to Photosystem I. Photosystem I then takes that electron and uses light above 700 Nanometers, (infrared light) to increase the rate of photosynthesis. 

 PHOTOSYNTHESIS IS LIKE A MUSCLE CAR

Here’s a handy analogy we at TGSC like to use to think about this process. Think about them as a high power V8 muscle car. Photosystem II is like the engine- if you don’t turn it on, the car won’t run. Photosystem I is like the supercharger- it turns on by itself, doesn’t do all that much, but with the engine turned on, it serves the purpose of boosting the power of the engine. 

Now that we’ve covered photosynthesis, it’s time to move on to our final step- how plants react to light in their environment. 

STEP 3- REACT

We often forget that in nature, plants are growing in all different types of lights and environments. They change the way they grow to produce optimal growth for themselves and maximize the light that is available to them. 

BALANCING BLUE LIGHT 

A great example of how plants react to light is to measure the amount of blue in the spectrum. Blue light is what plants use to sense whether they’re in the shade. Thinking back on our transmittance, remember that blue light doesn’t penetrate through the canopy.

So, if a plant isn’t getting enough blue light, it’ll grow upwards and become stretchy, searching for light. On the other hand, if the plant receives too much blue light, the plant will grow stunted, to avoid as much blue light as possible.  

As it turns out, there is an optimal amount of blue light in the spectrum for plants to grow at their best, so that the plant isn’t straining to find more light, or cowering away from too much light. 

In your average red and blue LED lights, there is a limited amount of green and yellow light, therefore stunting growth beneath the canopy. 

Also, the red and blue saturation at the tops of leaves can quickly lead to “light burn” or bleaching, with little to no growth beneath. Additionally, in some red and blue grow lights, the amount of blue is so high that it can lead to diminished growth, since the plant is using all its energy to avoid the high levels of blue light, instead of producing buds and flowers. 

A typical white LED spectrum, which covers the entire spectrum, reduces most of the issues that red and blue grow lights face. However, most white LED lights lack infrared light, which is critical to optimal plant growth. 

THE IMPORTANCE OF INFRARED 

Not only is infrared light important for Photosystems I and II, it also drives a host of other reactions in the plant. During vegetative growth, plants react to infrared light by growing larger. This includes bigger leaves, to capture more light, and stronger branching, especially beneath the canopy. 

Infrared light also increases the amount of bud and flower sites on the plant, and encourages the onset of flowering. 

Lastly, research shows that infrared light increases certain antioxidants in the plant, that translate to better aroma and flavor. 

Now that we know what kind of LEDs promote optimal growth, let’s take a look at the different types of lights available.

WIDE BAND LIGHT 

Wide band lights look a lot like a white light to the naked eye, when in reality they are creating colors in the red and infrared range, that humans can’t pick up. 

This wide band spectrum is designed for optimal plant growth. It has plenty of green, yellow, and infrared light, for optimal canopy penetration. The amount of blue light is balanced, to prevent plants from stretching or burning. Lastly, it has an abundance of red and infrared light to drive growth from seed all the way through flowering. 

This wide band light is the spectrum that we use in all our grow lights here at The Green Sunshine Company. We have spent years looking at scientific research and experimenting with different light types and plant types. The result? We have designed a beautiful grow light that will truly optimize plant growth, and transform your growing experience. 

We are passionate about science and giving growers what they need. Rooted in science and developed with passion and innovation, our Electric Sky wideband LED lights provide everything your plant needs to flourish. 

Comment below if you have any questions about lights, plants, and growing below!

3 thoughts on “How Plants Use Light

  1. Joe Duhaime Reply

    Good views of light how life evolved from plants. Darwin would have wanted to study photosynthesis, but it was not available for him in 1859.

  2. John Stone Reply

    Absolutely love this! Very specific and scientific yet in a language we can all understand. Ty
    No questions about it, My next light will be an Electric sky!! The cost?? Well did you just watch the video?? This “IS” the light of the future!! Fantastic!

  3. Shewane Reply

    Hi
    It is very informative video. Kindly,what is the best light use in plant tissues culture Lab in general? Some sources say 10000 kileven.

Leave a Reply

Your email address will not be published. Required fields are marked *