While it shows there is very little absorption of green light (500-600 nm) in extracted chlorophyll molecules, as the integrity of the leaf increases to the whole leaf, we see more and more absorption in the green region. Gorton’s Biological Action Spectra, 2010, and modified from Moss & Loomis, 1952, shows the light absorption spectra of isolated pigments, disrupted chloroplasts, intact chloroplasts, and whole leaves from spinach (Spinacia oleracea), a plant leaf in which all of the pigments remain bound to their specific proteins. This phenomenon explains why wavebands, rather than a single wavelength, are absorbed. Additionally, pigments are always bound to proteins, which shifts their absorption spectrum. In fact, in living systems, pigments never exist alone, and each pigment has a specific absorption spectrum. Carotenoids (accessory pigments) also play a role in light absorption and energy transfer to the photosystems, and they absorb light in the blue and green regions. But relying on the absorption spectra of isolated pigments, as opposed to living plants, is not a very sound foundation for LED selection. Since the absorption spectra of chlorophyll a and b extracts have been found to lie in the blue and red regions, some LED grow light companies, at least previously, claimed that living plants do not use green light. To complicate matters, the solvent in which chlorophyll is extracted also affects the absorption spectrum. So, which regions of the spectrum do plants absorb? This is different for extracted chlorophyll molecules, whole chloroplasts (where the chlorophyll resides), and plant leaves. This depends on the cellular and molecular make-up of the plant and therefore differs depending on species. The light absorption spectrum defines the range of electromagnetic radiation plants absorb. Before we go into more detail, let’s start by defining the absorption and action spectra:Ībsorption Spectrum: Describes the wavelengths that are absorbed or the light that is harvested.Īction Spectrum: Describes the wavelengths that actually drive photosynthesis. To address this, the roles of the light absorption spectrum, the light action spectrum, and how they relate to photosynthesis need to be understood. There is much discussion about light colors and whether green light should be included in the spectra applied to crops. The higher transmission and reflection of green light by plants also means that green can better penetrate the plant canopy and reach lower leaves. Plants appear green to us because they reflect and transmit slightly more green light than they do blue or red, and the human eye is more sensitive to green light. When the light touches a leaf, it can be absorbed by, reflected from, or transmitted through to other leaves. Light has a complex relationship with plants. This decision was made based on the light used by plants. From the beginning, Heliospectra has always included green light in grow lights.
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