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HomeNewsAnalysis of the Effect of Full Spectrum Grow Lights on Plant Photosynthesis

Analysis of the Effect of Full Spectrum Grow Lights on Plant Photosynthesis

2020-05-09
The sensitivity of Plant Grow Lights to the spectrum is different from the human eye. The most sensitive spectrum of the human eye is 555nm, which is between yellow-green light. It has poor sensitivity to the blue and red regions. Plants are not. They are most sensitive to the red light spectrum and less sensitive to green light, but the difference in sensitivity is not as wide as the human eye. The most sensitive area of plants to the spectrum is 400-700nm. This spectrum is usually called the effective energy region of photosynthesis. About 45% of the energy of sunlight lies in this spectrum. Therefore, if an artificial light source is used to supplement the amount of light, the spectral distribution of the light source should also be close to this range.

The photon energy emitted by the light source varies with wavelength. For example, the energy at a wavelength of 400nm (blue light) is 1.75 times the energy at 700nm (red light). But for photosynthesis, the effect of the two wavelengths is the same. The excess energy in the blue spectrum that cannot be used for photosynthesis is converted into heat. In other words, the rate of plant photosynthesis is determined by the number of photons that the plant can absorb in 400-700 nm, and is not related to the number of photons sent by each spectrum. But the general knowledge of the general people think that the color of light affects the rate of photosynthesis. Plants differ in their sensitivity to all spectra. This reason comes from the special absorption of pigments in the leaves. Among them, chlorophyll is best known. But chlorophyll is not the only useful pigment for photosynthesis. Other pigments are also involved in photosynthesis, so the photosynthesis efficiency cannot only consider the absorption spectrum of chlorophyll.

The difference in photosynthesis paths is also not related to color. Light energy is absorbed by chlorophyll and carotene in the leaves. Energy is converted from two types of photosynthetic systems to glucose and oxygen with fixed moisture and carbon dioxide. This process uses all visible light spectrum, so the effect of light sources of various colors on photosynthesis is almost the same.

Some researchers believe that the orange-red light part has the greatest photosynthesis ability. However, this does not mean that the plant should be cultivated on such a monochromatic light source. For plant morphology development and leaf color, plants should receive a variety of balanced light sources. Blue light source (400-500nm) is very important for plant differentiation and stomatal regulation. If there is not enough blue light, the proportion of far-red light is too much, the stem will grow excessively, and it is easy to cause yellowing of the leaves. The ratio of the energy of the red light spectrum (655 ~ 665nm) to the energy of the far red light spectrum (725 ~ 735nm) is between 1.0 and 1.2, and the plant development will be positive. But each plant has different sensitivities to these spectral ratios.

In the greenhouse, high-pressure sodium lamps are often used as artificial light sources. Taking the Philips Master SON-TPIA lamp source as an example, it has the highest energy in the orange-red spectrum region. However, the energy of far-infrared light is not high, so the ratio of red / far red energy is greater than 2.0. However, because there is still natural sunlight in the greenhouse, the plants are not shortened. (If this light source is used in the growth box, it may have an effect.)

Under natural sunlight, blue light energy accounts for 20%. For artificial light sources, such a high ratio is not required. For normally developing plants, most plants only need 6% blue light energy in the range of 400-700nm. In natural sunlight, there is already enough blue light energy. Therefore, the artificial light source does not need to supplement more blue light spectrum. However, when the natural light source is insufficient (such as winter), the artificial light source needs to increase the blue light energy, otherwise the blue light source will become a limiting factor for plant growth. However, if the light source improvement method is not used, there are still other methods to remedy the problem of insufficient light source. For example, temperature regulation or application of growth hormones.
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