How Different Colors of Light Affect Plant Growth

The growth of a plant might seem like a simple and straightforward process. The plant needs to be watered, the soil needs to have certain nutrients, and it needs to be in an environment where it receives light for a certain amount of time. Yet not many know how the latter can have a big impact in the development of a plant… until now.

In this post, I'll explain how different color lights affect plant growth, jumping into detail on the characteristics that light possess, and how you can use different colored LED grow lights to change the properties of plants and make plants grow faster.

What Exactly is Visible Light?

A crucial component in the growth of a plant besides water and oxygen, is sunlight. By receiving it, a plant is able to convert sunlight into edible food that it can use. This process is called photosynthesis. Water, oxygen, and sunlight make the holy trinity for plants.

Visible light as we perceive it behaves as a wave. As such, it displays different properties depending on its wavelength. For example, a source of light with a wavelength of around 650 nm will be detected as having a red color.

Full Spectrum Lighting Scale

Multiple studies have been conducted on how different colors of lights can have varying effects on the growth of a plant.

Thanks to the recent developments in LED (light emitting diode) grow light technology, specific light wavelengths can now be isolated in order to control the different physical properties that a plant displays as it develops throughout its life cycle. These properties include, but are not limited to, height, weight, color, and texture, as well as the chemical composure of the plant itself.

As a plant grows, you can use LED grow lights to manipulate these physical properties depending on the plant characteristics that you desire.

The Effects of Each Color of Light

In the following paragraphs, I explain what each light color does, and the effects that adding or removing them will have. But first, here is a quick summary, with extended information following:

  • Ultraviolet - No exposure produces better growth
  • Violet - Enhances the color, taste, and aroma of plants
  • Blue - Increases the growth rate of plants
  • Green - Enhances chlorophyll production and is used as a pigment for proper plant viewing
  • Yellow - Plants exhibit less growth compared to blue and red light
  • Red - When combined with blue light it yields more leaves and crops, depending on what is being grown
  • Far Red - Speeds up the Phytochrome conversion which reduces the time a plant takes to go into a night-time state. This allows the plant to produce a greater yield

Ultraviolet (200 nm to 380 nm)

Being exposed to UV light for a long period of time has harmful effects on humans. Likewise, exposure for a long time to this type of light will damage the plants that you are growing.

A study conducted demonstrated that plants raised without exposure to UV light exhibited enhanced growth.

Violet (380 nm to 445 nm)

On the other hand, studies have shown that when a plant receives visible violet light, the color, taste, and aroma of the plant are enhanced.

Additionally, the plant’s antioxidants are able to perform their functions more efficiently, which prevents the cells in the plant from being damaged.

Cannabis in purple light

Blue (450 nm to 495 nm)

Blue light has one of the largest effects on the development of a plant. Multiple studies have shown that exposing a plant to this color influences the formation of chlorophyll, which enables the plant to intake more energy from the sun. It also controls a plant’s cellular respiration and lessens water loss through evaporation during hot and dry conditions.

Blue light also has an effect on photosynthesis, and more exposure to this light can increase a plant’s growth and maturity rates. This process is called photomorphogenesis.

Overall, blue light has an influence over multiple functions in a plant’s life, and is a crucial color to have in your own grow room or grow box in order to ensure the most optimal growth.

Blue Light Absorb

Green (495 nm to 570 nm)

Most of the plants that we see around us possess a green color. This is due to the fact that they absorb all of the colors in the light spectrum (blue, red, violet, etc) but reflect the green one. As such, only the green light is bounced back to our eyes.

Even with the relatively low amount absorbed compared to the other colors, a study found that green light enhances the production of chlorophyll which helps with photosynthesis while giving the plants a greener color.

Overall, adding the green color to your plants does not have much effect in their life process compared to other light colors such as blue. Employing this type of light would be as a pigment for proper viewing of your plants in the grow room or grow box, but not necessary for the growth of the plant itself.

Yellow (570 nm to 590 nm)

Since yellow has a similar wavelength to green they both show similar properties in plants. A source from NASA indicates that yellow light does not contribute to photosynthesis since the wavelength of the light is reflected by the plant and is not absorbed.

Additionally, just like with green light, a study showed that when a plant was exposed to yellow light compared to blue and red, the growth of the plant tested was reduced.

Yellow Light Absorb

Red (620 nm to 720 nm)

Exposure to red light is another crucial factor which contributes to the optimal development of a plant.

Individually, red light won’t have a major effect on a plant, but when combined with blue light, it makes the plant yield better results when flowering.

A study which compared red light, blue light, and a mixture of both indicated that even though plants which grew under red light yielded more leaves than the ones grown under blue lights, the combination of both produced an amount of leaves which surpassed the plants who grew strictly under red light.

A similar case occurred during the growth of wheat where the crop yielded far better results when grown under a mixture of red and blue light, compared to strictly red light.

Far Red (720 nm to 1000 nm)

Even though little absorption occurs with this type of light, it plays an important role in plant germination and flowering. Red light and far red light go hand-in-hand in regards to the effects that they have on plants.

A regular plant has a phytochrome system (a light detection system) which regulates its growth, adjusting itself depending on the type of light that it is exposed to. In this system, there are two predominant forms of plant protein: its biologically inactive form (Pr), and its biologically active form (Pfr). When a plant perceives the red light, Pr transforms into Pfr, and if a plant receives the far-red light, it’s Pfr changes to Pr.

Pfr is important because it triggers plant growth, but it slowly reverts back to Pr over time when the plant is located in the dark. At the end of the day, a plant’s flowering and vegetative growth is directly influenced by the Pr to Pfr ratio.

An example on how the Far Red light properties can be used to your advantage to have a higher yield is seen in cannabis growth. During the day, this plant exhibits the most flowering, and during the night it ripens. Being a short day plant, it normally requires 12 hours of exposure to light, and 12 hours of darkness. Yet thanks to far-red light, it’s phytochrome conversion is sped up, making it go into a night state quicker and requiring less time in the darkness. This way, flowering can occur under a longer daylight period, which in turn produces a greater yield.

Red Light Absorb

So What is the Best Light Color for Plants?

Out of all the colors mentioned above, the most crucial ones in the development of your plant are red and blue. One source claims that for the most optimal growth of a plant, it is better to be exposed to 90% red light, and 10% blue light. Adding or removing the other light colors will vary the appearance and texture of the plant you are growing and will cause your plant to grow with the characteristics that you seek.

At Grobo, we developed our own LED grow light technology for a proprietary blend of the wavelengths best suited for plant growth. Additionally, through the use of the far red light we've incorporated, your plants produce a higher yield compared to being just grown under plain light.

 

Sources for further reading:
[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC550402/pdf/plntphys00407-0125.pdf
[2] http://www.lightinglab.fi/enlighten/publications/internetui_akvile.pdf
[3] http://cpl.usu.edu/files/publications/publication/pub__4116525.pdf
[4] http://www.nasa.gov/pdf/562188main_LS4_Light-Effects-Plant-Behavior_C1.pdf
[5] http://www.actahort.org/books/440/440_21.htm
[6] http://jxb.oxfordjournals.org/content/48/7/1407.abstract?ijkey=be0f09444b27ac23f5e36ab0b4505f1df5a6bd6f&keytype2=tf_ipsecsha
[7] https://www.boundless.com/biology/textbooks/boundless-biology-textbook/plant-form-and-physiology-30/plant-sensory-systems-and-responses-184/the-phytochrome-system-and-red-light-response-701-11926/
[8] http://www.mobot.org/jwcross/duckweed/phytochrome.htm
[9] http://www.cannagardening.ca/effect-of-red-and-far-red-light-on-flowering
[10] http://www.growweedeasy.com/phytochrome-manipulation-cannabis