Illumination is a key environmental factor for plant growth and agricultural production. Photosynthesis is the main receptor for the transformation of inorganic and organic substances on the earth. The wavelength in the range of 300mm to 800mm can be absorbed by green plant chlorophyll or photoreceptors. Worldwide, before the 1970s, people’s understanding of the effective light quality types of plant photosynthesis and the photosynthesis efficiency of light quality types was at a standstill because there were only electric light sources emitting continuous spectra, and there was a lack of research methods to understand the spectral needs of plants Whether it is selective or not, it is generally believed that plants can only complete their life cycle under continuous spectrum artificial light or sunlight.
1. Red and blue lights of plant growth lights are the basis of artificial light cultivation
Since the 1960s, the invention of red LEDs has provided tools for the study of plant light quality biology. The discovery of blue light in the 1990s promoted the study of light quality biology. Studies have confirmed that different light qualities in the photosynthetically active radiation spectrum are not equally important to plant photosynthesis and morphogenesis, among which red light and blue light are the most important to plant photosynthesis, and the relative quantum efficiency of plant photosynthesis is higher. The difference in light quality efficiency of plant growth lamps provides a preliminary scientific basis for determining artificial light cultivation plants centered on red light and blue light quality.
The combination of red and blue light can replace the continuous spectrum for artificial light plant cultivation. This conclusion has universal application value for horticultural crop cultivation. Therefore, the spectral requirements of plants are selective, discontinuous and substitutable, which provides biological theoretical support for artificial light cultivation in protected horticulture. Its significance lies in the simplification of artificial cultivation from continuous spectrum to red and blue composite light quality, which provides a basis for the research and development of LED light sources and plant growth lights for facility gardening, simplifies lamp design, and reduces manufacturing costs.
At present, a consensus has been reached on the light quality requirements and efficiency of plants, that is, the types of light quality necessary for plants are discontinuous and selective. Red light and blue light are necessary for plants to grow and develop normally and complete their life cycle. Other visible light qualities Species and far-red light are beneficial light qualities. However, in order to achieve the special goals of plant growth and yield quality, sometimes it is necessary to add some special light quality components on the basis of red and blue combined light, which can be called beneficial light quality, including other visible light qualities other than red and blue, UV and remote Red light etc.
2. There are two ways to improve the efficiency of plant growth lights
Plant growth supplementary light in modern facility agriculture or plants planted with full artificial light consume a lot of lighting power. Excessive light radiation or light radiation that cannot be used by plants will cause energy waste, thereby reducing the efficiency of the lighting system.
First, determine the spectral response curve of plant species and varieties, the ratio of red and blue light requirements, as well as the required total amount of light and photoperiod; second, provide artificial light lighting systems according to the plant light environment requirements. As a nutrient in the process of plant growth, light should not only ensure the healthy growth of plants, but also save lighting energy consumption to the greatest extent and improve the efficiency of the plant growth lamp lighting system. In fact, the energy of photons of visible light is inversely proportional to the wavelength. Light with different light quality (wavelength range) has significantly different physiological effects, including different effects on plant morphology, structure, photosynthesis and organ growth and development. The dry matter production of plants is the total result of these effects, and the size of plant dry weight is the most important and convincing index reflecting the positive and negative effects of light quality.