LED plant factory fill lighting method

The life activities of plants are inseparable from light. Light is the only energy source for plant photosynthesis. The periodic changes of light intensity, light quality (spectrum) and light have a profound impact on the growth and development of crops. Among them, light intensity affects the photosynthesis of plants has the greatest impact.

LED plant factory fill lighting method

The intensity of light can change the shape of crops, such as flowering, length of internodes, thickness of stems and size and thickness of leaves. Plants' requirements for light intensity can be divided into light-loving, medium-light-loving, and low-light-tolerant plants. Vegetables are mostly light-loving plants, and their light compensation point and light saturation point are relatively high. In artificial light plant factories, the relevant requirements of crops on light intensity are an important basis for selecting artificial light sources. Understanding the light requirements of different plants is important for designing artificial light sources, it is extremely necessary to improve the production performance of the system.

Artificial fill light is to increase the light intensity in the target area or prolong the light time by installing a fill light system to meet the needs of plants for light. Generally speaking, a supplementary light system includes a supplementary light device, a circuit and a control system thereof. The fill light source mainly includes several common types such as incandescent lamps, fluorescent lamps, metal halide lamps, high pressure sodium lamps and LEDs. Due to the low electro-optical efficiency and low photosynthetic energy efficiency of incandescent lamps, they have been eliminated by the market, so this article does not make a detailed analysis.

Fluorescent lamps are a type of low-pressure gas discharge lamps. The glass tube is filled with mercury vapor or inert gas, the inner wall of the tube is coated with fluorescent powder, and the light color varies with the fluorescent material coated in the tube. Fluorescent lamps have good spectral performance, high luminous efficiency, low power, longer lifespan (12000h) compared to incandescent lamps, and relatively low cost. Due to the low heat generation of fluorescent lamps, they can be illuminated close to plants and are suitable for three-dimensional cultivation, but the spectral layout of fluorescent lamps is unreasonable. The Japanese adv-agri company has also developed a new type of supplementary light source, HEFL. HEFL actually belongs to the category of fluorescent lamps. It is a general term for cold cathode fluorescent lamps (CCFL) and external electrode fluorescent lamps (EEFL). The HEFL lamp is extremely thin, with a diameter of only about 4mm, and the length can be adjusted from 450mm to 1200mm according to the needs of cultivation, which is an improved version of conventional fluorescent lamps.

Metal halide lamp is a high-intensity discharge lamp formed by adding various metal halides (tin bromide, sodium iodide, etc.) to the discharge tube on the basis of high-pressure mercury lamp, which can excite different elements to produce different wavelengths. Halogen lamps have high luminous efficiency, high power, good light color, long life and large spectrum. However, because the luminous efficiency is lower than that of high-pressure sodium lamps and the lifespan is shorter than that of high-pressure sodium lamps, it is currently only used in a few plant factories.

High-pressure sodium lamps are a type of high-pressure gas discharge lamps. A high-pressure sodium lamp is a high-efficiency lamp in which a discharge tube is filled with high-pressure sodium vapor and a small amount of xenon (Xe) and mercury lamp metal halides are added. Due to the high electro-optical conversion efficiency and low manufacturing cost of high-pressure sodium lamps, high-pressure sodium lamps are currently the most widely used in the application of supplementary light in agricultural facilities. . On the other hand, the spectral components emitted by high-pressure sodium lamps are mainly concentrated in the yellow-orange light band, lacking the red and blue spectrums necessary for plant growth.

As a new generation of light sources, light-emitting diodes (LEDs) have many advantages such as higher electro-optical conversion efficiency, adjustable spectrum, and high photosynthetic efficiency. Compared with ordinary fluorescent lamps and other supplementary light sources, LEDs have the advantages of energy saving, environmental protection, long life, monochromatic light, and cold light sources. With the further improvement of the electro-optical efficiency of LEDs and the reduction in the cost of scale effects, LEDs will become the mainstream equipment for light supplementation in agricultural facilities.

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