1.1The sun is the source of all living things. The planet we live in is so vibrant that it comes from the sun. The sun we see is the visible part of the solar electromagnetic radiation. When the vibration is transmitted, the vibration is transmitted at the speed of light. The physical phenomenon, the relationship between electromagnetic radiation and visible light is shown in Figure .
1. Need to understand some basic concepts: frequency is the number of repetitions of waves per unit time, the unit of frequency is Hertz (Hz), the wavelength is the distance between two adjacent peaks (or troughs), the wavelength is in meters, the speed of light = wavelength × Frequency, period vs. frequency: frequency × period = 1, period and wavelength indicate the same position, but the period represents the time required to complete one wavelength, and the unit of the period is second.
When the wavelength of the vibration wave propagating at the speed of light is from 1 km to 10 picometers, we are familiar with radio waves, mobile communication, microwaves transmitted by television, military radar, medical X-rays, gamma rays, etc., all of which are different wavelengths. Solar radiation is only part of it at applications that travel at the speed of light.
In the visible range, the human eye observes that different colors of light are visually presented. The light of these colors is mixed together, which is the white light we usually see. The white light is expressed by the color temperature, as shown in Figure 1 of 2000K-9000K.
The range of solar radiation that we can test on the Earth’s surface ranges from 280nm to 2500nm. Solar radiation below 280nm and wavelengths greater than 2500nm is observed on the ground due to the strong absorption of ozone, water vapor and other atmospheric molecules in the Earth’s atmosphere. Not enough. When the wavelength is in the range of 400nm-750nm, the human eye can feel the light emitted by these wavelengths. We call it visible light. The solar radiation is mainly concentrated in the visible part. The solar radiation plays an important role in the life evolution of all living things on the earth. Scientists use spectroscopy to analyze electromagnetic radiation and visible light. We study that sunlight, artificial light sources, and light absorbed by plants are inseparable from the spectrum.
Figure 2 IEC60904-9 Solar electromagnetic radiation spectrum
The solar spectrum in Figure 2 has a wavelength range of 280 nm to 1100 nm. We divide the spectrum of this range into several parts.
1.1.Ultraviolet: The wavelength is from 280 nm to 400 nm.
1.1.2 Visible light: wavelength from 400 nm to 750 nm.
1.1.3 Infrared: The wavelength is from 750 nm to 1100 nm.
In terms of agricultural planting, we study the application of wavelengths from 300nm to 1100nm. The solar radiation spectrum of Figure 2 has a reference role in studying the solar radiation effects on plants. When studying plant photosynthesis, we usually study wavelengths from This range is from 400nm to 700nm.
The color segment of Figure 2 corresponds to the visual color of different ranges of radiation wavelengths. The sunlight is composed of different colors of light. The visible part of sunlight is mainly composed of red, green and blue light. Green light and blue light are called three basic light colors, and artificial light sources are also white light mixed with these three basic light colors.
In the visible range, the most sensitive light of the human eye (that is, the light we feel the brightest) is yellow light (peak is 555 nm), and the most insensitive light of the human eye is blue light. When the sky appears rainbow, we often see yellow, red and green, and the blue color is a small part. as the picture shows.
The most sensitive light and the least sensitive light of the human eye are determined by the visual function of the human eye. It does not mean the amount of light radiated by the light. The energy carried by the blue light is greater than the yellow light, but the human eye feels the brightest for the yellow light. When artificial radiation is provided to plants, the photosynthesis effect of plants cannot be judged by the light and darkness of the light perceived by the human eye.
The light we see by the human eye is felt by the columnar cells and cone cells inside the human eye. The light seen by the human eye is derived by the visual function, while the light that the plant “sees” needs to be irradiated with electromagnetic radiation. measure. Because plants can not only “see” visible light from 400nm to 750nm, plants can “see” invisible light, such as ultraviolet light and infrared light. This is very important, and it is not suitable for plant artificial light source products to develop using the concept of photometry.
1.2 Photosynthesis of plants.
Plants are the only creatures that can convert solar energy into mass. The photosynthesis of plants is the foundation of all life on earth. Plants not only provide humans with the oxygen necessary for survival, but also provide food and energy to human beings. At present, there are more than 300,000 species of plants known.
Plants are the only creatures in all living things that can convert solar radiation energy into organic matter. They are the basic organisms that humans and other animals depend on for survival.
The process by which plants convert solar radiant energy into organic matter is called plant photosynthesis. Specifically, photosynthesis refers to the conversion of carbon dioxide (or hydrogen sulphide) and water into light by plants, algae and certain bacteria through photosynthetic pigments. Organic matter, and release the biochemical process of oxygen (or hydrogen), Figure 3 is the theoretical basis of plant photosynthesis。
Plants are energy-transformed by photosynthetic pigments, including chlorophyll a, chlorophyll b, and carotenoids. According to the law of conservation of energy, plants convert light energy into organic matter during photosynthesis.
The photosynthesis of plants requires carbon dioxide and water to complete. When photosynthesis, plants absorb carbon dioxide and water, release oxygen and produce organic matter. The chloroplasts in plant leaves are the places where photosynthesis is used by green plants.
The photosynthesis of plants only occurs in chloroplasts. Figure 4 shows the structure of plant leaves as seen from a high power microscope. The green particles in the figure are chloroplasts, and the leaves of plants have a large number of chloroplasts. The chloroplasts are the photosynthesis sites of plants. .
Green leaf tissue structure
The chloroplasts of most plants mainly contain chlorophyll (chlorophyll a and chlorophyll b), β-carotenoids (carotene and lutein), and photosensitin (Pfr, Pr). These pigments are involved in photosynthesis. Figure 5 shows the absorption and reflection of light by chloroplasts. Chlorophyll a and chlorophyll b mainly absorb blue-violet light and red light. Carotenoids mainly absorb blue-violet light. Photosensins mainly absorb red light and far-infrared light. Green plants have the most chlorophyll content, and chlorophyll absorbs less green light, and most of the green light is reflected, so the chloroplast appears green. The main component of the leaf tissue of plants is the chloroplast, so the leaves of the plants are also green.
Green plants only absorb red and blue light in the sun. The reason we see plants is green is because plants reflect green light, leaving only red and blue light for photosynthesis. Red light and blue After the color light is mixed, a purple light is formed.
1.3 Physiological effects of various wavelengths of radiation on plants。
Effects on plant physiology
Little effect on morphology and physiological processes
Less chlorophyll absorption, affecting photoperiod effect
Chlorophyll and carrots have the highest absorption ratio and have a great influence on photosynthesis.
The absorption of chlorophyll is small, and most of it is reflected.
Chlorophyll a and b absorption have significant effects on photosynthesis and photoperiod effects
The main absorption of phytochrome, affecting flowering and seed germination
Convert to heat
1.4 Absorption spectra of plant pigments under solar radiation
We study the photosynthesis of plants based on the study of the absorption of solar radiation by plant pigments to reveal the basic principles of plant photosynthesis. The absorption spectrum of plant pigments is shown in Figure 6.
The main range of effective spectrum of plant pigment photosynthesis is 300nm-800nm. The most abundant chlorophyll in pigments mainly absorbs red and blue light and a small part of ultraviolet light. Chlorophyll absorbs less green light, and other pigments do not absorb green light. The unabsorbed green light is reflected by the plant and passes through the blade to the back of the blade. Studies have shown that green light can be scattered and absorbed inside the blade, while passing through the blade to the back of the blade to provide chlorophyll for photosynthesis, pigment to sunlight The absorption spectrum has a peak, and the absorption peak only means that the energy required for solar radiation is the most, not the complete absorption. The reason why we see the appearance and texture of the green leaves is because red light and blue light are also reflected, otherwise the human eye can not clearly see the leaves.
Photosynthetic absorption spectrum of pigment
It can be seen from Fig. 6 that chlorophyll a and chlorophyll b have two peaks for absorption of sunlight, one occurring between 430 nm and 450 nm, and the other peak occurring between 620 nm and 660 nm, and β-carotene absorption. Between 440 nm and 500 nm, the photosensitizer absorption peaks are 380 nm, 660 nm, and 730 nm.
By analyzing the absorption spectrum of plant pigments, we can use plants with the same wavelength as solar radiation to radiate plants to achieve the same photosynthesis effect as sunlight, which is the basic idea of plant lights.
Plant light (we call artificial radiation source PARS) is the same as the physical principle of solar radiation in radiation. There is no difference. The absorption of electromagnetic radiation by plants is only the requirement of electromagnetic radiation of a specific wavelength. Plants cannot distinguish between these wavelengths. Whether electromagnetic radiation is from solar electromagnetic radiation or artificial electromagnetic radiation source, therefore, there is no variation of photosynthesis of plant light on plants. Unlike transgenic plants, plant lamps have the same physical and chemical effects as solar radiation. Compared with solar radiation, the only difference is that the spectral shape of the plant lamp cannot be as small as the peak value of the solar radiation. Since the absorption spectrum of the pigment is concentrated only on several peaks, at this point, the LED plant light can be used for plant photosynthesis. The effect is more effective, of course, plant lights are to increase planting costs.
We define plant lights called plant artificial radiation sources PARS (Plant Artificial Radiation Sources). Plant photosynthesis is only to receive photons of electromagnetic radiation of different wavelengths, instead of providing illumination to plants. The effective photosynthetic PPFD value of plants is plant photosynthesis. The unit of measurement, using photometric unit illumination value (LUX) to express plant photosynthesis will cause users to apply errors in plant cultivation. When the plant artificial radiation source is added with invisible radiation, the value of LUX tends to zero, but the plant However, the photons of these invisible radiation can be absorbed normally; when the wavelength of the radiation source is in the visible range (400-700 nm), it can be called a plant lamp, but it needs to be labeled with PPF or PPFD.
1.5 Process of artificial radiation source of plants
From the technical literature of global agricultural science, early scientists have studied some physical and chemical phenomena of plants and light, including: sunlight and plant growth, solar radiation and plant photosynthesis, artificial light sources and plants. Photosynthetic efficiency, etc. The comparative system research originated from the US military and NASA NASA. In order to study the long-term survival of astronauts in space, the Kennedy Space Center (KSC) proposed “crop production of advanced life support systems”. This pilot project, in this field, scientists have made many fruitful technical studies on plant cultivation in artificial environments, and Figure 7 is NASA’s plant research.
NASA’s plant research
Early planting using artificial radiation sources is an illumination source, such as incandescent lamps, high-pressure sodium lamps, metal halide lamps, and fluorescent lamps. These artificial light sources also have certain effects in plant cultivation. However, these light sources have a common disadvantage, that is, The loss of electricity is large, the heat is large, and the weight of plants produced per watt of electricity is low.
Comparison of various artificial light sources for plant growth:
Lack of blue ligh
Lack of blue ligh
Lack of red light
With the development of lighting technology, a product called semiconductor solid-state lighting (SSL) is increasingly used in the field of lighting. It has been found that many inherent characteristics of LEDs have a good effect on plant photosynthesis. The decline in LED costs, LED plant artificial radiation sources have achieved unprecedented development in agricultural planting, scientists around the world are committed to the application of LED in modern agricultural production, plant plant concept continues to impact traditional agricultural planting technology.
2．LED and LED plant lights introduction
2.1． What is LED
LED is the abbreviation of Light Emitting Diode, which belongs to semiconductor device. In 1962, LED was applied. Before 1993, LED was only red, green and yellow. It was mainly used as indicator light. LEDs have achieved industrial production, and four-element red LEDs and blue LEDs have been gradually developed in plant cultivation. LED applications are called solid state lighting in the field of lighting, and LED applications are called planting in plants. Artificial Plant Radiation Sources (PARS), LED for planting has the following characteristics:
1）Artificial radiation sources with different wavelength combinations can be fabricated
2）The conversion efficiency of electric power to radiation power is high.
3）LED is a cold light source, and the emitted light has no heat radiation.
4）Single-sided illumination, the highest utilization rate of light radiation
5）The output of the radiation can be adjusted by the drive current
6）Low radiation attenuation rate, average life of more than 30,000 hours
7）Low power consumption and low planting costs
8）Can be driven by low voltage DC for digital scale control
9）Easy access to solar and wind power systems
10）LED device production process will not cause environmental pollution
11）High product cost, large initial investment
2.2 LED spectrum for plant photosynthesis
For the development of plant lights, we are based on the system of solar radiation and plant photosynthesis. Therefore, it is necessary to start from the spectral analysis of LEDs for LED light sources. Figure 8 is a spectrum of wavelengths commonly used for LED plant lights. In the spectrum of each wavelength, the waveform is single smooth, no other clutter, and the wave morphology is close to the peak wavelength form of plant photosynthesis, which can provide a combination of multiple bands.
Figure 8 Spectrogram of LEDs of various wavelengths
According to the characteristics of the absorption spectrum of different plants, the LEDs of different wavelengths are combined in proportion to form a multi-band artificial radiation source. The combination of wavelength and the amount of radiation are related to plant varieties, and the radiation energy of LEDs of different wavelengths It is related to the radiation characteristics of the LED itself. The radiation efficiency of the LED is related to the quality of the packaging factory. It requires a professional instrument for physical analysis to determine the ratio combination. Figure 9 is a comparison of the spectrum of the LED plant lamp. As can be seen from the figure, the LED plant The spectrum of the lamp is close to that of the plant pigment absorption spectrum, but the LED plant lamp can’t imitate the pigment absorption spectrum. It needs to refer to the Mokley curve and scientific experiments. Please refer《McCree research and action curve》
Figure 9 LED plant lamp and pigment spectrum for relationship
2.3 Some technical requirements for LED plant lights
The key technology for LED plant lights is structural heat dissipation and secondary optical design. For other aspects, please refer to the article “LED Plant Light Spectrum”. Here, just introduce the technical support of our design plant lights.