Understanding the light spectrum and wavelengths is crucial for optimizing plant growth. Using the right wavelengths promote plant growth and development.
Photosynthetically Active Radiation (PAR)
To drive photosynthesis, only certain wavelengths of light are used. Plants have pigments that can absorb wavelengths of the “photosynthetically active radiation”(PAR) spectrum, which are 400-700 nm (nano meters).
PAR is the part of the radiation from the sun or artificial lighting (in this case plant grow lights) that the plant can really use for photosynthesis.
Energy of light wavelengths matters
Energy of light wavelengths matters
This light spectrum of 400-700 nm, nearly corresponds with the spectrum that we can see with our human eyes (380 to 700 nm). This spectrum is also called the visible light spectrum. The light at 400 nm can be described as violet and at 700 nm “far red”.
A photon (which can be explained as a light particle which carries a certain amount of energy) of a shorter wavelength than 400 nm (such as UV light), carries too much energy for the plant to be able to use it for photosynthesis.
A surplus of energy carried by a photon can damage cells and plant tissues. Most of the high energy photons found in sunlight are filtered out by our atmosphere. Photons at longer wavelengths (>700 nm) do not participate in driving photosynthesis in plants, because they do not carry enough energy to allow photosynthesis to take place. A rule of thumb: the longer a wavelength, the less energy it has.
Measuring light for plants
The PAR light can be measured in W/m2 (energy of the total radiation) or in µmol/m2/s. Often, in horticulture, µmol/m2/s is more often used. Because this value tells you the amount of light received, by plants. 1 mol = 6.03*10^23 photons. A major advantage of using µmol/m²/s, is that it provides a standardized and consistent way to measure light intensity, regardless of the specific wavelengths (colours) of light being considered.
1% more light = 1% more yield
Besides using the energy of light to drive photosynthesis, plants need light to regulate their internal metabolism, development, direction of growth and creation of certain compounds. For many greenhouse crops, there is a linear relationship between the amount of light intercepted by the leafs and dry mass (plant biomass) production. In fruit vegetable crops (such as tomatoes and cucumber), 1% additional light results in an increase of 0.7-1% in harvestable yield! Supplemental lighting in greenhouses is therefore unmissable in many situations.
Effect of Light on Plant Per Wavelength Range (nm)
Different wavelengths of light have different effects on the plant.
Based on the research results of Gupta and Jatothu (2013), Singh et al. (2015) and Tian et al. (2014), Ahmed and his colleagues (2020) have summarized the effect of light on plant development and growth per wavelength. Additional information on plant physiological effects per wavelength has been added to this table:
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