In plant lighting, red and blue light are often considered the most effective wavelengths because chlorophyll has strong absorption peaks in these regions. Green light, by comparison, is sometimes regarded as “unused light” that plants simply reflect.
However, green light behaves differently from red and blue light. Although it is not absorbed as strongly near the surface of a leaf, it can penetrate deeper into leaf tissue. For plants with thicker leaves, larger overall size, or dense canopies, this deeper penetration can improve light availability for chloroplasts deeper within the leaf and for leaves lower in the canopy.
Why Do Leaves Look Green?
When light reaches a leaf, some wavelengths are absorbed by pigments, some are reflected, and some pass through the leaf.
The green light reflected toward our eyes is what makes leaves appear green. But this does not mean that all green light is reflected. A significant portion enters the leaf and can be absorbed by chloroplasts at different depths within the tissue.
Red and blue light tend to be absorbed more strongly near the upper layers of a leaf, while green light can travel farther through the mesophyll tissue.
Green Light Can Drive Photosynthesis
Once green light is absorbed by chloroplasts, its energy can be transferred to the photosynthetic reaction centers, helping drive electron transport and photosynthesis. Green light can therefore contribute directly to carbon fixation—it is not a wavelength that plants are unable to use.
A study by Terashima and colleagues, published in Plant and Cell Physiology in April 2009, examined sunflower leaves and found that under moderate to strong white background light, adding green light could increase whole-leaf photosynthesis more effectively than adding red light. One important reason was the different way light was distributed within the leaf: green light penetrated deeper and enhanced photosynthesis in tissues that received less red and blue light.
When a plant has only a few leaves, canopy penetration is usually not a major concern. As the plant grows, however, leaves begin to overlap and shade one another. Upper leaves intercept much of the incoming light, leaving significantly less light available to leaves in the middle and lower parts of the canopy.
In this situation, green light can help redistribute light within the plant canopy. While the upper leaves may absorb a smaller proportion of the available light, more light can reach leaves deeper in the canopy. A more even distribution of light allows a greater proportion of the plant’s foliage to contribute to whole-plant carbon assimilation.
This effect is particularly relevant when:
- The plant has multiple layers of foliage;
- Leaves are large or densely arranged;
- The primary light source is positioned above the plant;
- Middle and lower leaves would otherwise receive relatively little light.
Green Light in Grow Lights
Full-spectrum grow lights designed for home use commonly contain white LEDs. These typically use blue LED chips combined with phosphor materials to produce a broader, continuous spectrum that already includes green wavelengths.
As a result, a full-spectrum grow light can provide plants with green light even when it does not contain dedicated green LED diodes.
A full-spectrum light source can provide several practical benefits:
- Increase usable light within deeper leaf tissue and inside the plant canopy;
- Improve light distribution among multiple layers of foliage;
- Produce more natural-looking leaf colors and a more comfortable visual environment in the home;
- Make it easier to observe yellowing, leaf spots, pest damage, and physical damage.
For indoor plant lighting, white light containing blue, green, and red wavelengths is well suited for long-term use. It supports plant growth while providing a more natural-looking environment for people. For thick-leaved plants, large plants, and dense canopies, green wavelengths can also help more chloroplasts and lower leaves participate in photosynthesis.
