The LED grow light is an artificial light source that uses LED as the luminous body to meet the lighting conditions of plant photosynthesis. It has many types, belonging to the third generation of plant fill light.
In the absence of sunlight, this kind of lamp can play the role of sunlight, so that plants can grow normally or better.
This kind of lamp has the functions of strengthening roots, regulating flower period and color, promoting fruit ripening and coloring, as well as improving taste and quality.
What is grow light?
The grow light is a kind of electric light to help plants grow. The grow light either provides a spectrum similar to that of the sun, or a spectrum more suited to the needs of the plant. Grow lights simulate outdoor conditions by varying its color, temperature and spectral output, as well as the intensity of the light. We can adjust the spectral range, luminous efficiency and color temperature of the grow light, depending on the type of cultivated plant, the growth stage (e.g, germination/vegetative or flowering/fruiting period), and the photoperiod required by the plant.
What is LED light?
LED lamp or LED bulb is an electric light source that uses a light-emitting diode to emit light. The most efficient commercial LED lamp has an efficiency of 200 lumens per watt (LM / W). The service life of commercial LED lamps is many times longer than that of incandescent lamps.
The LED lamp needs an electronic LED driver circuit to work through the main power line. The loss of the circuit means that the efficiency of the LED lamp is lower than that of the LED chip. The driver circuit may require special functions compatible with incandescent dimmers. Generally speaking, the current waveform contains a certain degree of distortion, which depends on the lamp technology.
The LED market is expected to grow from US $2 billion in early 2014 to US $25 billion in 2023.
The LED lights up immediately without preheating delay. Frequent switching does not reduce life expectancy like fluorescent lamps. During the service life of the LED, the light output gradually decreases (see the “efficiency reduction” section).
Some LED lamps are direct substitutes for incandescent or fluorescent lamps. LED lights can use multiple LED packages to improve light diffusion, heat dissipation, and overall cost. The text on the retail LED packaging can be displayed with light output in lumens, power consumption in watts, color temperature in Kelvin, or a color description, such as “warm white”, “cool white” or “daylight”.
Working principle of LED grow light
Light is a necessary factor in plant growth. Without light, plants cannot survive. Controlling plant growth through air conditioning is an important means of horticulture. LED grow light is more efficient and more effective. LED grow light provides an efficient light source for plants, promotes the photosynthesis of plants, shortens the flowering time of plants, speeds up the growth of plants, and provides the yield of plants. It is an important component to realize the intelligent development of agricultural modernization.
Requirements for plant light
The duration, quantity, and quality of light regulate the development and growth of plants. Generally speaking, If a plant can’t get enough light, it can’t get enough photosynthesis, nutrition, and it can’t grow normally. As the pigment decreases, it begins to hide from light. Plants that do not receive the right light quality may show physiological differences compared to the same plants grown under the best light conditions.
In the past, the quantity and quality of plant lights were technically limited. Metal halide lamps and high-pressure sodium lamps are still common auxiliary light sources because of their own advantages, especially for greenhouse and some single light source operations. The older LED grow light only consists of blue and red LEDs because they convert electrical energy into the efficiency of photons and the efficiency of driving photosynthesis. As LEDs become cheaper and more efficient, interest in light quality has risen in plant science.
a. Photosynthetically active radiation (PAR)
The photon weighting curve is used to convert PPFD to YPF; The energy weighting curve is used to weight the par in watts or joules.
Lumens and lux are photometric units of light intensity, and they serve to measure the light intensity perceived by the human eye.
The spectral level of light measured by lumen is similar to but different from that used for photosynthesis. The spectral range of solar radiation from 400 to 700 nm is the corresponding spectral range of photosynthesis. Plants can use this range of spectrum for photosynthesis, and the light in this range is also photosynthetically active radiation or par for short. Therefore, when measuring the amount of light that plants can use for photosynthesis, botanists usually measure the amount of par that plants receive.
The irradiance of PAR can be expressed as energy flux (w / m2), which is related to the energy balance of photosynthetic organisms. Botanists usually use the number of photons or photosynthetic photon flux density in the range of 400-700nm per unit area received in a given time to quantify par, because photosynthesis is a quantum process, and the amount of energy obtained by the chemical reaction of photosynthesis depends more on the number of photons than the energy contained in photons. This is usually measured using mol m-2 s-1, but the value associated with plant growth is the daylight integral (DLI), with PPFD integral over 24 hours.
Most plant species will grow well at DLI of 5-15 mol m-2 D-1. Light tolerant species can easily handle 30-50 mol m -2 day -1, and shade-tolerant species can grow at DLI values of 1-3 mol m -2 day -1.
b. Amount of light
The amount of light is the amount of light that plants need to grow best every day. Historically, the amount of light was expressed in units of WM-2, lumen, or lux. Although these units can be used for energy calculations of W M -2 or human illumination (lumens and Lux), plant scientists now prefer to use the μ photosynthetic photon flux density (PPFD) measured in mol m-2s-1. PPFD is an efficient measurement method, which can accurately measure the number of photons per square meter per second impacting the surface, so as to infer the direct cooperation between photons and plants.
DLI or Solar integration is also an effective way to measure the amount of light. DLI considers the PPFD and the total hours of plant exposure to the PPFD to obtain the total photon amount per day in mol m-2 D-1. Assuming PPFD is a constant, the formula for converting PPFD to DLI is as follows:
DLI (mol m-2 d-1 ) =0.0036 * PPFD ( μ Mol m -2 s-1) * illumination time
Generally speaking, the light requirement of specific crops is larger for the crops that bear fruit and bloom, but less for the crops that keep nutrition. We generally consider green leafy vegetables such as lettuce, spinach, and kale as low light crops, requiring DLI of 12 to 17 mol m-2 D-1. Tomato, cucumber, and pepper need 20-30 mol m -2 D-1. Marijuana is one of the most demanding plants for light, which needs up to 40 mol m-2 D-1 DLI.
c. Light quality
Light quality is the spectral distribution, and the light quality that affects plant growth refers to the spectral distribution that affects plant growth. We typically measure the absorption spectra of free chlorophyll b (red) and a (blue) in solvent. According to the specific pigment-protein interaction, the interaction spectrum of the chlorophyll molecule changes slightly.
Different wavelengths of light have different colors; 700-750 nm is far red, 600-700 nm is red, 500-600 nm is green, 400-500 nm is blue, and 320-400 nm is UVA. Light quality can also be expressed as their peak irradiance, such as 660 nm red and 450 nm blue, or sometimes as a ratio, such as a 2:3 blue to red ratio. Plants can sense the spectrum through some special light-sensitive substances, such as zein, phytochrome, cryptochrome, and phototropism. Each light-sensitive substance has a different sensitivity to different light. Photomorphogenesis is a kind of light-mediated reaction of the plant to the spectrum. Spectrum can send different signals to plants, and plants will give different feedback according to these signals, which can affect the metabolism of plants, the growth state of plants, such as flowering and germination, and the growth speed of plants.
Photoperiod is the dark period and light period that plants need. The change of photoperiod can trigger flowering. Therefore, it is necessary to set the on or off time of the light. Set the optimal switching time according to the species and preferences of plants, because some plants like long nights and short days, while some plants like short nights and long days, and some plants like the same length of day and night.
Photoperiod is an important factor in plant growth and development, and we must pay attention to it. However, The time of darkness can affect the plant’s judgment of the length of the day. Generally speaking, “short sunshine” refers to sunshine with a Photoperiod of no more than 12 hours“ “Long sunshine” refers to sunshine with a Photoperiod of not less than 14 hours. Long-day plants are those that bloom only when the photoperiod is greater than the critical duration. Short-day plants are those that bloom when the length of the day is less than the critical duration. Daytime neutral plants are those that bloom regardless of photoperiod.
Plants flowering in response to photoperiod may have facultative or specific responses. Facultative response means that regardless of the photoperiod, the plant will eventually bloom, but if it grows under a specific photoperiod, the flowering rate will be faster. Specific response means that plants can only bloom under a specific photoperiod.
Features of LED grow light
In addition to energy-saving and environmental protection, LED has many characteristics different from other light sources. It is the fourth generation lighting source. Due to the rich wavelength spectrum, the light emitted by LED is consistent with the spectral range of plant light morphogenesis and photosynthesis, so LED is particularly suitable for plant cultivation.
By refracting the spectrum, the refraction angle of different wavelengths of light is different. In this way, we can obtain pure monochromatic light and composite spectrum as required, and can concentrate the light of specific wavelength to evenly irradiate crops. By controlling the change of grow light to regulate the germination, growth, and Fruiting of crops, it can also control the rising trend and nutrients of crops. The LED grow light can be used in a multi-layer three-dimensional combined culture system to realize the miniaturization of production space and low heat load. In addition, the strong durability and low power of LED grow lights reduce operating costs. Because of these remarkable characteristics, LEDs are very suitable for plant cultivation, such as seedling raising, plant tissue culture, facility horticulture, and even aerospace ecological life protection system.
Application of LED grow light
a. It can work as supplementary illumination for plant photosynthesis when the sunshine amount is small or the sunshine time is short.
b. As the induced illumination of plant photoperiod and light morphogenesis.
- LED grow light as the induced illumination of light morphogenesis and plant photoperiod
The specific wavelength of LED will affect the blooming time, duration, and the number of flowers. Some wavelengths of LED can adjust the length of the flowering period and pedicel, some wavelengths can reduce the number of flowers, and some wavelengths can increase the number of flowers and buds. The flowering and growth status of plants can be regulated by LED, which is conducive to the production and marketing of flowers and crops.
- Research on the application of LED grow light in the aerospace ecosystem
In order to solve the long-term life support problem of spaceflight, the establishment of a controlled ecological life support system is a key link, in which the cultivation of higher plants is an important part, and light is one of the key factors.
The space environment is different from the general indoor environment. The selection of light sources for space plant cultivation is more strict and harsh. The lights must be safe and reliable, without environmental pollution, small size, lightweight, long life, high-efficiency, and the output light wavelength is suitable for plant photosynthesis and morphogenesis. Compared with other light sources, LED can convert light energy into photosynthetically active radiation; In addition, LED has the characteristics of light weight, small size, long life, and so on, which has attracted a lot of attention in the field of aerospace plant cultivation. The results show that these characteristics of LED lighting make it the most suitable light source for space plant cultivation. Maybe in the near future, we will establish our own ecological circulation system through LED cultivation technology in space and on the moon.
- LED grow light as supplementary lighting for plant photosynthesis
The traditional light source produces too much heat. If the seat auxiliary light source wastes energy, it will increase the cost, and too high a temperature is not conducive to the growth of crops. Relatively speaking, the heat generated by LED is relatively small. If combined with the hydroponic system, the air can be used, and excessive heat and water can be removed. Because the light source generated by LED is similar to the spectrum of photosynthesis, electric energy can be converted into effective photosynthetic radiation, and finally into bioenergy. The results show that the photosynthetic rate and growth rate of lettuce will increase by more than 20% by using LED lighting. It is feasible to use LEDs in plant factories.
Compared with the ordinary metal halide lamp, the stems and leaves of Capsicum annum and Perilla fruit scenes grown under the specific wavelength LED changed significantly, and the photosynthetic rate increased with the increase of light density. Composite wavelength LED can increase the number of stomata of Salvia multirrhiza and marigold.
The results show that, compared with other light sources, the full spectrum LED light source can significantly improve the growth rate of lettuce, spinach, and radish. It can make beet biomass maximum, beet element accumulation in hairy root is the most significant, and produce the highest sugar and starch accumulation in the hairy root.
With the extensive development of the modern agricultural industry, the LED grow light is undoubtedly an opportunity to regenerate these enterprises. However, despite the bright prospects of plant grow light, the development of plant factories is still facing some “bottlenecks”. For example, if the initial investment is too large, an artificial light plant factory with a daily output of 1000 lettuce plants generally needs a relatively high initial investment. Even if the government subsidizes 30%, it usually takes two years to make a profit. In addition, the planting technology in the era of factory agriculture has yet to be mature, and the related quality control and logistics sales mode are still in the exploration phase.