Light is a key environmental factor for plant growth and development and agricultural production. In the light spectrum, only some wavelengths of light are absorbed by plants for photosynthesis. Photosynthesis refers to the process in which plants containing chloroplasts, under the irradiation of visible light, undergo light reaction and carbon-fixation reaction, use photosynthetic pigments, convert carbon dioxide and water into organic matter, and release oxygen. There is also an energy conversion process that converts light energy into chemical energy in organic matter.
The complex mixed light in sunlight, arranged through different wavelengths, is the spectrum of sunlight, and the spectrum of sunlight can be called the full spectrum. It can be divided into visible light and invisible light. The wavelength of visible light is 400-760nm. After scattering, it is divided into 7 colors: red, orange, yellow, green, blue, violet and indigo. When concentrated, it becomes white light. Invisible light is divided into two types: infrared light, which is located in the area outside the red light, with a wavelength greater than 760 nm, up to 1mm; ultraviolet light, which is located in the area outside the violet light, with a wavelength of 100-400 nm.
Visible light, as the name suggests, is the electromagnetic spectrum that is visible to the human eye. The visible spectrum has no precise range. The wavelength range that the human eye can perceive is generally 400 nm to 760 nm, and some people can perceive the range from 310 nm to 1100 nm. The different wavelengths of visible light are seen as the colors of the rainbow, and each wavelength range corresponds to one color. Experiments have shown that different wavelengths of light have different effects on plant growth.
1）Blue light(445-500 nm)
Blue light with shorter wavelengths can provide energy and catalysis for chemical reactions in photosynthesis, while inhibiting plant elongation and promoting cell differentiation. Blue light is one of the necessary conditions for plants to thrive.
2）Red light (R, 620-700 nm)
The wavelength of red light is longer, which mainly provides power for plant photosynthesis, which is conducive to plant photosynthesis and chlorophyll formation, and is conducive to the growth of stems and promotes plant flowering.
3）Green light(G, 500-580 nm)
Green light has always been a controversial light quality, and some scholars believe that it can inhibit plant growth, cause plants to dwarf, and reduce vegetable yields. However, there are also many studies on the positive effect of green light on vegetables. A low proportion of green light can promote the growth of lettuce; adding 24% of green light on the basis of red and blue light can promote the growth of lettuce.
There are two main types of invisible light that affect plants less: ultraviolet and infrared.
UV radiation is a form of radiation. Sunlight is the main source of UV radiation, which produces three main types of UV light:
- UVA: 315-400nm
- UVB: 280-315nm
- UVC: 100-280nm
UV rays are harmful to most plants. Far-ultraviolet rays with wavelengths less than 280nm can kill plants immediately. But there are studies showing that the right amount of UV light can be beneficial for growing marijuana. UVA and UVB can increase the production of THC, CBD and terpenes in cannabis plants.
Infrared has a very long wavelength and very little energy. Infrared wavelengths are invisible to the human eye and can only be felt as heat.
Infrared radiation is divided into the following three bands:
- Near Infrared: 760 and 1400 nm
- Mid-IR: 1400 and 3000 nm
- Far infrared: 3000 nm and 1 mm
Research has shown that combining blue and red light with far-red light can increase the rate of photosynthesis. This is called the Emerson effect. The only known receptors that are sensitive to far-red wavelengths are protein phytochromes. Plants use phytochromes to regulate when to transition from a vegetative state to a flowering state.
As people's research on artificial light technology becomes more and more mature, light is no longer a limiting condition for greenhouse cultivation. When we know what light affects plant growth, we can add light to plants to make them grow better. This is also the significance of our exploration of light.