As an important physical environmental factor, light plays a key role in plant growth and metabolism. "One of the main characteristics of plant plants is full artificial light source and intelligent control of the light environment" has become a general consensus in the industry.
Plants' need for light
Light is the only source of energy for plant photosynthesis. Light intensity, light quality (spectrum) and periodic changes of light have a profound impact on the growth and development of crops, among which light intensity has the greatest impact on plant photosynthesis.
Light intensity can change crop morphology, such as flowering, internode length, stem thickness and leaf size and thickness. The light intensity requirements of plants can be divided into photophilia, photophilia and photophilia. Most vegetables belong to light-loving plants, and their light compensation point and light saturation point are relatively high. Relevant requirements of crops on light intensity in artificial light plant factories are an important basis for selecting artificial light source. Understanding the light demand of different plants is very necessary for designing artificial light source and improving the production performance of the system.
The relationship between plant photosynthesis and photophagy and day length (or photoperiod) is known as plant peripherality. Photoperiodicity is closely related to light hours, which refers to the time when crops are exposed to light. Different crops need a certain number of light hours to complete the photoperiod before flowering and fruiting. According to the different photoperiod, it can be divided into long sunshine crops, such as cabbage, which need more than 12 ~ 14h of light hours at a certain stage of their growth. Short sunshine crops, such as Onions and soybeans, need less than 12 to 14 hours of sunlight; Medium sunshine crops, such as cucumbers, tomatoes and peppers, can bloom and bear fruit under longer or shorter sunshine.
Among the three elements of environment, illumination intensity is an important basis for selecting artificial light source. Currently, there are many ways to describe illumination intensity, including the following three.
(1) Illumination refers to the surface density of light flux (light flux per unit area) received on the illuminated plane (lx).
(2) PAR of photosynthetic effective irradiance, unit: W/m2.
(3) photosynthetic effective quantum flux density PPFD or PPF refers to the number of photons of photosynthetic effective radiation arriving or passing through per unit time and area, unit: mumol/(m2·s). Mainly refers to the light intensity of 400 ~ 700nm which is directly related to photosynthesis. It is also the most commonly used light intensity index in the field of plant production.
Analysis of light source of typical supplementary light system
Fluorescent lamp belongs to the type of low pressure gas discharge lamp. The glass tube is filled with mercury vapor or inert gas, and the inner wall of the tube is coated with fluorescent powder. The light color varies with the different fluorescent materials coated in the tube. Fluorescent lamps have good spectral performance, high luminous efficiency, low power, long service life (12000h) compared with incandescent lamps, and relatively low cost. Because fluorescent lamp oneself calorific value is lesser, can carry illume of plant of close to, apply to stereo culture, but fluorescent lamp spectral layout is unreasonable, the method that compares commonly used on the world is to add reflective cover, increase the effective illuminant composition of crop of cultivated area as far as possible.
Based on the high pressure mercury lamp, the metal halide lamp is a kind of high intensity discharge lamp which can stimulate different elements to produce different wavelengths by adding various metal halides (tin bromide, sodium iodide, etc.) in the discharge tube. Halogen lamp has high luminous efficiency, high power, good color, long life and large spectrum. However, because the luminous efficiency is lower than the high pressure sodium lamp, and the service life is shorter than the high pressure sodium lamp, it is only used in a few plant plants.
High - pressure sodium lamp belongs to high - pressure discharge lamp type. High pressure sodium lamp is a high efficiency lamp in which high pressure sodium vapor is filled in a discharge tube and a small amount of metal halide of xenon (Xe) and mercury is added. High pressure sodium lamp has high electro-optic conversion efficiency and low manufacturing cost at the same time, so the application of high pressure sodium lamp in filling light of agricultural facilities is the most extensive. On the other hand, the spectrum components emitted by high pressure sodium lamp are mainly concentrated in the yellow and orange light band, lacking the red and blue spectrum necessary for plant growth.
Light-emitting diode (LED), as a new generation of light source, has many advantages such as higher electro-optical conversion efficiency, adjustable spectrum and high photosynthetic efficiency. LED can emit the single color light needed by the growth of plants. Compared with ordinary fluorescent lamps and other supplementary light sources, LED has the advantages of energy saving, environmental protection, long life, single color light and cold light source. With the further improvement of LED's electro-optical efficiency and the reduction of cost caused by scale effect, LED will become the mainstream equipment to supplement light in agricultural facilities.
Portable light supplement device
The intensity of light is closely related to the growth of crops. Three-dimensional cultivation is often adopted in plant plants. However, due to the limitation of the structure of cultivation framework, the uneven distribution of light and temperature between layers will affect the yield of crops, and the harvest time is not synchronized.
Design idea of typical crop light supplement system
It is easy to see from the design of the mobile light-supplement device that the light-supplement system of plant factories is designed with the light intensity, light quality and photoperiod parameters of different crop growth periods and the special means of terminal regulation as the core content of the design, which relies on the intelligent control system to implement and achieve the ultimate goal of energy saving and high yield. At present, the design and construction of light supplement for leaf vegetables have been gradually mature.