I’ve been trying different searches but everything I find just says “sunlight”. Since sunlight consists of multiple parts such as UV, Infrared and the normal visible spectrum, I’m curious which part is actually responsible for photosynthesis to occur? On that note, depending on what part of the light, would it still grow with an LED, black light, etc.?
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Awesome, so if I’m reading that right UV can contribute to growth, and IR doesn’t contribute much at all. The blue and red end of the visible spectrum encourages growth, however it can pretty much occur at any visible wavelength, just not as efficient as the bands listed on the image.
Blue and red are the biggest drivers for photosynthesis, but other wavelengths have effects on the plants as well. For example, far red light (infrared) has a huge influence on flowering and stem elongation in many plants. They really rely on light for a lot of cues for regulation.
Edit: words
That chart is a good starting point, but it doesn’t tell the whole story. It only shows the absorption spectrum for Chlorophyll A, which is a key pigment for photosynthesis in all plant species, but there is also Chlorophyll B, and there are numerous other so called accessory pigments (beta carotinoids are the most common examples), that can work in conjunction with chlorophyll in a photosystem to collect light of different wavelengths. Algae in particular show a greater diversity of accessory pigments. They have evolved use light at different depths below the water surface, where it reaches them with a different spectrum, because water itself absorbs part of it. Have a look at red algae and brown algae, for example.
So if you want to grow algae in a controlled environment, you should do some research about the particular absorption preferences of the species you’d like to grow.
Interestingly that chart basically says “light visible to humans”
Plants use visible light for photosynthesis. Visible light ranges from low blue to far-red light and is described as the wavelengths between 380 nm and 750 nm. The region between 400 nm and 700 nm is what plants primarily use to drive photosynthesis and is typically referred to as Photosynthetically Active Radiation (PAR). Plant biologists quantify PAR using the number of photons in the 400-700 nm range received by a surface for a specified amount of time, or the Photosynthetic Photon Flux Density (PPFD) in the units μmol/s.
During photosynthesis, plants take in carbon dioxide (CO2) and water (H2O) from the air and soil. Within the plant cell, the water is oxidized, meaning it loses electrons, while the carbon dioxide is reduced, meaning it gains electrons. This transforms the water into oxygen and the carbon dioxide into glucose. The plant then releases the oxygen back into the air, and stores energy within the glucose molecules.
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