Grow Light Green Light: What Green Photons Do for Plants
The short answer
Grow light green light is not wasted on plants. Michigan State University Extension says green is the least efficient visible color for photosynthesis, yet plants still use most of it. Green reaches deeper into a canopy than other colors and helps shape plant structure. A white or full spectrum LED gives you some green along with red and blue.
Do plants use green light?
They do. MSU Extension says green is the least efficient visible color for photosynthesis, but plants still use most of the green light that reaches them. University of Minnesota Extension describes the band plants use, called photosynthetically active radiation, as mostly red and blue light. Green still plays a part. See optimal lighting for growing indoors.
How does green light reach lower leaves?
MSU Extension notes green light can penetrate a canopy better than other wavebands. With better reach, lower leaves may go on photosynthesizing. It matters most in dense plantings where top leaves shade the rest. Learn more in grow lights for cannabis.
How does green light shape plants?
MSU Extension notes green light helps shape plant structure, while blue light holds stems shorter than green does. A white light that blends colors gives you some of each. Read about how plants use light in the process of light to energy in cannabis.
Green light basics
| Color | What it does | Source note |
|---|---|---|
| Green | Reaches deeper into a canopy | MSU Extension |
| Green | Shapes plant structure | MSU Extension |
| Blue | Holds stems short. Too much stunts growth | MSU and Missouri |
| Red and far red | Promote growth and tissue expansion | Missouri Extension |
| White | A blend that includes green | University of Minnesota |
Sources: Michigan State University Extension, University of Missouri Extension, University of Minnesota Extension.
How to: step by step
- Read the spectrum chart on your light.
- Find how much output falls in the green band.
- Check that lower leaves get some light.
- Watch for stretched stems, a sign of too little blue.
- Change only one light factor at a time.
- Log growth over a few weeks.
Troubleshooting
Lower leaves yellowing: shading. Space plants out.
Tall, stretched stems: little blue in the light. Add a fixture with more blue.
Weak growth: low total light, not color. Check intensity first, since Missouri Extension lists intensity as its own factor beside light quality.
Green is part of a balanced spectrum. Kind Seed Co readers starting cannabis seeds under lights can look for a white or full spectrum fixture that includes it.
Sources
- Green light: is it important for plant growth?, Michigan State University Extension
- Lighting for indoor plants and starting seeds, University of Minnesota Extension
- Controlled environment agriculture: understanding grow lights (G6987), University of Missouri Extension
FAQ
Are plants green because they reject green light?
Leaves look green to us, but that does not mean plants waste green light. Michigan State University Extension notes green light can pass deeper into a canopy than other colors, where lower leaves can still use it for photosynthesis. Plants use more of it than their color suggests.
Does green light drive photosynthesis?
Yes, it contributes. MSU Extension says green is the least efficient visible color for photosynthesis, but plants still use most of it. University of Minnesota Extension describes the light plants use as mostly red and blue, and green adds to that.
How much green should a grow light have?
There is no single figure in the Extension sources. For a home grower, a white or full spectrum LED supplies some green along with red and blue, which is a simple starting point.
Does green light affect plant shape?
It can. MSU Extension notes green light helps shape plant structure. It also says blue light suppresses stretching more than green light does, so plants under more blue stay shorter.
What does blue light do to plants?
University of Missouri Extension notes blue and ultraviolet light promote the buildup of some plant compounds, but too much blue light will stunt growth. MSU Extension notes blue light suppresses stretching more than green light does. A blend of colors avoids extremes.
