Chlorophylls are not the only photoreceptors that are responsible for photosynthesis - there are other types of photoreceptors such as carotenoids which also promote photosynthesis. Green light helps promote photosynthesis in chlorophylls very efficiently. Recent work has shown that green light is able to penetrate deeper into leaf surfaces to drive photosynthesis in chloroplast located towards the bottom surface of the leaf more efficiently than red light at high PPFD. As PPFD increases, light energy that is absorbed in the upper chloroplasts tends to be dissipated as heat, while penetrating green light increases photosynthesis by exciting chloroplasts located deep in the mesophyll (Terashima et. al., 2009). Green light also penetrates through leaf surfaces much better than red or blue light to reach the lower canopy, making green photons essentially as useful to plants for photosynthesis as red and blue photons. The relative quantum efficiency curve (Figure 2) shows how efficiently plants use wavelengths between 300 and 800 nm.
Figure 1 - Absorption Spectrum
Figure 2 - Action Spectrum
ADDING GREEN SPECTRUM
A study conducted on the growth of tomatoes indicated that including green light in the spectrum of light the plants were exposed to increased the mass of the plants, as well as the stem length, the total leaf area, and the overall yield of the plants. These studies show conclusively that plants exposed to green light will generally increase in mass and height, in addition to having a higher yield.
Photosynthesis is driven by PAR, and green light is included in the PAR range. When green light accompanies the red or blue light, studies have shown conclusively that plants have a higher photosynthetic rate than they have when it is just red and blue light alone.
This same study also demonstrated that green light has the effect of increasing the number of genes involved with photosynthesis, and significantly lowers the negative impact of prolonged exposure to light.
Green light induces physiological changes to plant morphogenesis; it makes leaves wider and encourages benign stomatal closing. NASA ran tests and found that a full spectrum of red-blue-green produced more dry mass of crop than purely red-blue, indicating green light’s ability to deliver yields. This was found to be because the plant was already saturated with red and blue light; therefore, a balance including green was more efficient in carbon fixation in photosynthesis