Can Green Light Benefit Plant Growth?

There’s a myth that Green Light cannot be useful for photosynthesis.

Even though this myth isn’t heard as often as in prior years, it’s still found commonplace in circles of people who tend to “know more than enough” about lighting conditions when it comes to advancing plants, but have never taken the time or effort to go in-depth within plant biology and horticulture to grasp a good understanding about how exactly photosynthesis works. 

This is common due to the reason that, in fact, not everything you read online tends to be true or backed up by science.

This leads to misinterpreted information and tends to lead people into spreading rumours. 

Greenlight can, in fact, be very useful to plants.

As stated factually and with definition, the waveband for photosynthetically active radiation or PAR is between 400 to 700nm.

Within this waveband, more specifically, in the middle of said waveband, green light can be found, which has a wavelength of around 500 to 600nm.

So the question remains if we have one-third of PAR that isn’t useful in photosynthesis, why would green light be included in the definition?

One of the key reasons why green light isn’t commonplace around plants is due to the fact that it isn’t absorbed by chlorophyll that well, even though it’s measurement is based on extracted and purified chlorophyll within a test tube or in vitro and not as an intact leaf or in vivo.

This is where the problems come and why misinformation can arise from.

There are other pigments besides chlorophyll that absorb light and can lead to more effective photosynthesis. 

These accessory pigments all feature different levels of absorption when it comes to spectra and some of them can in fact and do absorb green light.

As such, interpretations made from measurements in a test tube do not apply well to whole plants.

Another example and explanation people tend to go to when explaining the efficiency of green light, is the myth that plants reflect green light, which is why they appear green.

Even though this is a true fact, it tends to get overly exaggerated. 

When the light comes into contact with a leaf surface, it can be:

  • absorbed
  • used for photosynthesis
  • reflected off the leaf
  • transmitted through the leaf.

It has been proven that 85% of green light is absorbed, but only a small percentage of green light is reflected and transmitted.

However, the light that isn’t absorbed isn’t wasted either, it can also reflect the nearest leaves.

The “McCree Curve” has also been used in the past to justify the concept of green light’s efficiency when compared to blue or red light as a stimulant within photosynthesis. 

In short, this curve explains the relative quantum efficiency of photons that are found to be useful in photosynthesis. 

The data is based on instantaneous measurements and is done using low intensities of light, which means that this can also lead to people misinterpreting it, as plants are very good at adapting to their light environment, characteristics such as leaf size and thickness change to maximize the capture of photons.

A closer analysis of the curve shows us that the region which has the lowest level of quantum efficiency ranges from 470 to 490nm, which is a part of the blue light waveband, not the green one.

“Most plants appear green because their leaves reflect more green light than red or blue light.”

Greenlight can be useful than blue or red light in some situation, however, green light typically penetrates deeper into the leaves than the others.

When exposed to a higher intensity of blue and red light, chlorophylls and accessory pigments on the upper leaf surface tend to become more saturated and in turn, leave chlorophylls lower in the leaf not as saturated.

Through the addition of green light, protons have the ability to penetrate much deeper into the leaf and be used for photosynthesis. 

As such, green light can be useful under high-light intensities. 

One of the only credible justifications as to why you should grow plants without green light relates to the efficiency of a LED lighting texture.

Efficacy refers to the conversion of electricity into photosynthetic photons.

The red wavelength from LED Grow Lights is proven to have the highest levels of efficacy, with blue and white coming in close.

Green light does have low-efficiency values, as such, green light emitted from LED Grow Lights aren’t as common ground in commercial plant lighting applications as blue, red or white LEDs.

The most common and effective way to deliver green light to plants through the use of LEDs is through using white light.