Do you know that plant growth is selective for spectrum?

LED semiconductor lighting network information in the existing facilities, the light source in agriculture is difficult to meet the needs of plant growth, thus giving birth to a new market for agricultural lighting. This market is very hot, but for the sake of agricultural lighting, I am afraid that few people can say clearly.

It is better to start from the environment of plant growth, most of the plants we see are mostly grown in daylight, so some people think of it, simulating the full spectrum of sunlight, giving plants a stable growth environment, this idea is correct. However, plant growth does not require a spectrum of all bands.

Plants are selective to the spectrum. Plant photosynthesis absorbs about 60% of the light energy in the visible light spectrum (380~760nm), including red orange light with a wavelength of 610~720nm (wavelength of 660nm) and 400~510nm. The blue-violet light (with a peak of 450 nm) is the absorption peak region, and these two bands become the "light fertilizer" of the plant. Plants absorb less yellow-green light from 510 to 610 nm. Therefore, the development of these two bands as the main artificial light source will improve the plant's light energy utilization efficiency.

(Experimental method: the acetone extract of chlorophyll is placed between the light source and the prism. After the light passes through the chlorophyll extract and the prism, a visible spectrum is formed behind, and the absorbed spectral region will appear black or black. The absorption spectrum of chlorophyll can be obtained.

As we all know, light is one of the most important environmental factors for plant growth and development. There are two kinds of mechanisms affecting plant growth and development and yield quality, one is photosynthesis; the other is light form.

First, photosynthesis is the basis for the formation of plant biomass and yield. 95% of the plant's dry matter is derived from carbohydrates produced by photosynthesis. Plants have complex reactions to light conditions, including light response, light inhibition, light adaptation, and vaginal response. In the full-color spectrum of the sun, only part of the light in the band is absorbed by plants to produce photosynthesis, and the leaf morphology of plants and the physiological responses of plants affect photosynthesis.

Second, light morphogenesis refers to the process by which light acts as an environmental signal on plants, regulating plant growth, differentiation, and development. Receptors that sense light are rarely present in plant cells, but are sensitive to changes in the external light environment. For example, the red light field of 600~700nm promotes the germination of lettuce seeds, while the 720~740nm far red light field inhibits the germination of lettuce seeds.

(plant leaf structure)

(plant cell structure and chloroplast internal structure diagram)

(Photograph of photosynthesis in chloroplast)

This is to mention another concept - "photosynthetic pigments". Leaves are the main organs of plant photosynthesis, chloroplasts are the most important organelles for photosynthesis, and pigments that absorb light energy in photosynthesis reactions are called photosynthetic pigments. There are three main types: chlorophyll, carotenoids and algae. Bilirubin. Higher plants contain the first two classes, and phycobiliproteins are only found in algae. Among them, chlorophyll is most known. But chlorophyll is not the only pigment that is useful for photosynthesis. Other pigments are also involved in photosynthesis, so photosynthesis efficiency cannot be based solely on the absorption spectrum of chlorophyll.

(Curve 1, chlorophyll a; curve 2, chlorophyll a; curve 3, chlorophyll b; curve 4, phycobilicil; curve 5, beta-carotenoid.)

(chlorophyll a effective spectrum)

(chlorophyll b effective spectrum)

(Carotene effective spectrum)

(chlorophyll f effective spectrum)

(Specific use of photosynthetic pigments on spectra: Note: in the book " LED Light Sources and Their Horticultural Applications" by Liu Wenke, Yang Qichang, etc.)

The selective absorption of light waves by different photosynthetic pigments in plants is an adaptation of the ecological environment formed by plants in the long-term evolution, which enables plants to use photosynthesis with various wavelengths of light.

Photosynthesis is also associated with photosynthetically active radiation that strikes the surface of the leaves, which is effective visible light for plant photosynthesis. Usually, 8 to 10 photons are required for a photosynthesis. Therefore, the optical quantum flux density PPFD (unit: μmol/m2/s) is used to evaluate the effective radiant energy of photosynthesis to achieve the effect of actual photobiological effects. Widely introduced.

The proportions of red and blue light suitable for different plants are different, and the appropriate lighting formulas are different at different growth stages. The spectrum of traditional light sources is not controllable, and LEDs can emit monochromatic light required for plant growth. Monochromatic light combines to form the spectrum required for plant photosynthesis and morphogenesis. However, to achieve the regulation of the light radiation environment, it is necessary to accurately measure the optical parameters of the light environment to meet the growth requirements of the corresponding plants.

It is worth mentioning that the most sensitive spectrum of the human eye is 555 nm, which is yellow-green light, and is less sensitive to the blue region and the red region. As mentioned above, plants are not the most sensitive to the red spectrum and less sensitive to yellow-green light, but the difference in sensitivity is not as disparate as the human eye. That is to say, the response characteristics of plants and human eyes to the spectrum are different.

(Ideal photon sensor and typical plant spectral response curve)

The spectral characteristics of the remote PLA-20 plant lighting analyzer are consistent with the spectral response characteristics of the plant, which can accurately determine the absorption spectrum, red/blue ratio and PPFD parameters of the photosynthetic pigment. It can be widely used in on-site monitoring of light radiation in plant growth, such as plant factories, soilless culture, greenhouses, and plant growth chambers.

(Parameters measurable by the PLA-20 plant lighting analyzer, the red part is the parameter set for the plant lighting)

Main Specifications

Wavelength range: 380nm ~ 800nm

Wavelength accuracy: ±0.5nm

Illuminance measurement range: 10lx ~ 200klx

Illumination accuracy: ±4%

Spectral measurement of a plant lamp