Green Light
Green Light
Green Light
Do plants use green light?
Absorption Spectrum vs Action Spectrum
Some suppliers reference the absorption spectrum of chlorophyll a & b (peaks in the blue and red regions of the EM spectrum) as the main reason for providing a purple spectrum for horticulture lighting:
Absorption rate in %
The Absorption spectrum of Photosynthesis
If this makes sense, as chlorophyll drives photosynthesis, how is the absorption spectrum of chlorophyll measured?
If the absorption spectrum of chlorophyll directly correlates to photosynthesis and plant growth, what happens if you only target a sole pigment and neglect other pigments responsible for plant growth and development? Let's see:
ACTION SPECTRUM
The action spectrum of photosynthesis is fundamental in defining the range of Photosynthetically Active Radiation (PAR). Until recently, it was not known how varying wave lengths of light influenced photosynthesis and plant growth.
Then researchers utilized filters to create monochromatic wavebands to determine the influence of light spectra on photosynthesis of single leaves using an assimilation chamber. The picture below shows that plants do utilize green light for photosynthesis, quite efficiently.
The Action spectrum of Photosynthesis
How to explain the difference between the absorption spectrum and the action spectrum if chlorophyll is responsible for photosynthesis?
Chlorophylls are not the only photoreceptors that are responsible for photosynthesis. Carotenoids are other types of antenna photoreceptors that also promote photosynthesis.
If only narrow band red/blue LEDs are used in lighting conditions, then these pigments are not able to optimize their light harvesting capabilities.
As PPFD increases, light energy absorbed in the upper chloroplasts tends to be dissipated as heat, while research has shown that penetrating green light increases photosynthesis by exciting chloroplasts located deep in the leaf.
Also, green light penetrates through leaf surfaces much better than red or blue light to reach the lower canopy, which is extremely important in dense canopy production techniques which are common in controlled environment agriculture.
CONCLUSION
If a horticulture lighting system is delivering a spectrum which neglects photoreceptors that absorb light in the 500-600 nm green region, the growing environment is not optimized.