How Does Green Light Affect Photosynthesis — and Is Green Light Good for Plants?
Plant and Green light Introduction
How does green light affect photosynthesis? We often focus on blue and red colors in grow lights because chlorophyll easily absorbs those wavelengths, as shown by the ubiquitous Chlorophyll Absorbance Curves (Figure 1). But what about green light?
People often overlook green light due to the big dip in its absorbance area (Figure 1). However, in this post, we will make a strong case for green light’s significant impact on indoor farming and explain why understanding how green light interacts with plants is essential for growers.
Fig 1 Chlorophyll Absorbance Chart
Is Green Light Good for Plants?
For many years, growers assumed that green light contributed very little to plant development because chlorophyll absorbs green wavelengths less efficiently than red or blue. This led to the misconception that green light is “wasted” on plants.
However, modern research shows the opposite: green light plays an important role in plant photosynthesis, particularly in dense canopies where blue and red light struggle to penetrate. Unlike shorter wavelengths that are absorbed at the leaf surface, green light reaches deeper tissue layers, providing additional photons for photosynthetic activity where they are most needed.
This deeper penetration makes green wavelengths especially beneficial for compact crops, leafy greens, or plants grown under high-density indoor farming setups. In practice, green light helps balance growth, improve visual quality, and enhance plant performance in ways traditional spectra cannot achieve.
How Does Green Light Affect Plant Growth?
Green light influences multiple aspects of plant growth, extending beyond photosynthesis alone. At the canopy level, green photons transmit through upper leaves and support photosynthesis in shaded leaves, improving whole-plant energy efficiency. At the physiological level, green light interacts with photoreceptors such as cryptochromes and phytochromes, influencing plant signaling, stem elongation, and leaf expansion.
This makes green wavelengths valuable for shaping biomass distribution and improving light-use efficiency under LED grow systems. In controlled environments, growers use green light to achieve a more balanced spectrum that supports both structural development and photosynthesis throughout the canopy. In short, green light helps plants grow more uniformly, especially in environments where traditional blue/red spectra alone may cause uneven or shallow penetration.
The McCree Curve Contradiction?
The most prevalent argument for green light’s efficacy is the McCree Curve graph (Figure 2). Keith McCree’s photosynthesis experiments, conducted in 1972, seem to contradict the traditional absorbance curves by showing a more significant photosynthetic contribution from green colors.
The McCree Curve does, in fact, accurately represent the efficacy of green light. Additionally, there is no contradiction with the Absorbance Curves – the two graphs measure different aspects of data. Here’s the explanation.
Fig 2 McCree Curve
Absorbance curve explained.
Traditional absorbance curve data comes from ground-up plant samples soaked in a solvent to separate the chlorophyll, which is then placed in a liquid solution.
Next, different colors of light pass through the liquid. A spectral device records the residual color characteristics of the transmitted light to determine how much of that light color the chlorophylls absorbed.
Researchers test different wavelengths of reds, blues, and greens, once for chlorophyll-a and once for chlorophyll-b. They record the data and use it to create the absorbance curves (Figure 1).
Fig 3 How Absorbance Curve data is accumulated.
McCree Curve explained.
The McCree experiments use whole solid leaves instead of ground-up plant components, which explains the differing data. In these experiments, leaves are placed in enclosed chambers and exposed to different light colors.
Researchers measure the increase in oxygen from photosynthetic respiration in the chamber to indicate how much photosynthesis occurred for each light color. At first, you might expect similar results to the traditional absorption curves, but another factor changes the game.
Fig 4 How McCree Curve data is accumulated
Leaf light absorbance
That factor is the thickness of the leaf tissue. Though visually flat, a leaf is quite thick in the microscopic world. The blue and red colors of light only penetrate the superficial layers of leaf tissue (Figure 5).
Fig 5 Leaf light absorbance (blue-left, red-right)
Broderson and Vogelmann (Functional Plant Biology 2010 37.403-412)
However, green light penetrates deeper and can even transmit through the leaf (Figure 6).
Even though chlorophyll absorbs a lower percentage of green light, green light has a better chance of contacting more chlorophyll deeper into the tissue. It’s a tradeoff – less chlorophyll absorbability but greater leaf penetration.
Fig 6 Leaf light absorbance (green-left, far-red-right)
Broderson and Vogelmann (Functional Plant Biology 2010 37.403-412)
Furthermore, a larger percentage of green light (and far-red) can transmit through the leaf and impact photosynthesis in lower branches, where blue and red light is limited to the top layer of leaves. This makes green light especially useful for dense, bushy plants like cannabis.
To demonstrate this, you can use a spectrometer or spectral PAR meter and take a light recording underneath a leaf – the resulting spectrum (Figure 7) will show a preponderance of green and far-red light (>700nm).
Figure 7 Spectrum of sunlight transmitting through a leaf.
Summary
The Chlorophyll Absorbance Curves suggest that green colors in grow lights have minimal impact – this might be misleading if you are trying to correlate it to photosynthesis.
In contrast, the McCree Curve data directly ties to photosynthesis and involves whole-leaf sampling. It introduces a new factor of light penetration into leaf tissue: green light better penetrates leaf tissue and transmits through to lower-layer leaves, increasing the contact rate between green photons and chlorophylls.
In summary, the McCree Curve strongly suggests that green colors in grow lights are significant – and there is substantial research data and empirical evidence to support this.
How PG200N Helps Growers Optimize Green Light for Better Photosynthesis
Green light plays a unique role in plant biology, but many growers struggle to measure it accurately. Most PAR meters only report total PPFD and cannot distinguish how much usable green light reaches the mid and lower canopy—where green wavelengths contribute most to photosynthesis.
The UPRtek PG200N Spectral PAR Meter solves this problem by offering precise, wavelength-specific measurement across the entire PAR range. This allows growers to:
- Quantify green light penetration through upper leaves
- Evaluate whether plant density is blocking blue/red while allowing green light transmission
- Compare lighting fixtures based on real spectrum output, not advertised charts
- Measure spectral changes over time due to diode aging or dirt accumulation
- Tailor lighting strategies to crop species that benefit strongly from green light
With IP66 protection, multi-mode measurement, spectrum logging, and optional UVA sensor integration, PG200N is engineered for precision indoor agriculture. It gives growers the spectral transparency they need to optimize photosynthesis—not just at the leaf surface, but throughout the entire canopy.
PG200N Spectral PAR Meter
Spectral PAR measurement gives farmers and researchers the advantages of expert lighting by helping them measure and tweak color parameters to improve the quality, timing, and quantity of their products.
Read On: PG200N Spectral PAR Meter
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- Green-light supplementation for enhanced lettuce growth under red- and blue-light-emitting diodes. | Kim, H.-H., Goins, G. D., Wheeler, R. M., & Sager, J. C. (2004).
- Don’t ignore the green light: Exploring diverse roles in plant processes. | Smith, H. L., McAusland, L., & Murchie, E. H. (2017).
- Green light drives leaf photosynthesis more efficiently than red light in strong white light: Revisiting the enigmatic question of why leaves are green. | Terashima, I., Fujita, T., Inoue, T., Chow, W. S., & Oguchi, R. (2009).
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UPRtek (est. 2010) is a manufacturer of portable, high-precision light measurement instruments; Handheld Spectrometers, PAR meters, Spectroradiometers, Light Calibration Solutions.
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