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In about 12,000 years of human agricultural history, we can be sure that soon humans learned that the amount of sunlight received by plants has a direct effect on their characteristics and growth.
Almost after the invention of the electric light bulb in the 1860s, humans began to use artificial light to help promote plant growth. 1
Electric lighting can fill the gap when natural sunlight is insufficient, for example, in a cloudy day in a greenhouse or in winter. Appropriate lamps can also achieve large-scale indoor planting.
Artificial lighting provides opportunities to grow crops under many conditions that were previously impossible to achieve by providing light energy.
Photosynthesis is a key process to make the earth livable. Plants (including some bacteria and algae) absorb nutrients and water (H2O) from the soil, absorb carbon dioxide (CO2) from the air, and then use the energy (photons) in the sun to convert these components into glucose, which is the necessary sugar to sustain humans And animal life.
During this process, plants release oxygen (O2) back into the air to make it breathable.
Photosynthesis is the process by which plants use sunlight to produce glucose. Glucose is an important foundation of the earth's food chain. (Image source: National Geographic)
However, plants respond differently to different wavelengths of light energy. The visible spectrum of sunlight extends from deep purple at one end to red at the other end (wavelengths are about 380 nm-750 nm).
For decades, scientists have known that photosynthesis is optimized by red wavelengths, especially around 660 nm. (Plants look green in our eyes because they are best at absorbing red light for photosynthesis, while mainly reflecting green light.)
For root strength during germination, plants need, among other things, light waves in the blue part of the spectrum. Far red, almost invisible beyond the red, promoting larger branches, leaves and flowering. 2
With the development of different lighting technologies, research on agricultural lighting applications and plant responses continues.
From carbon arc lamps and incandescent lamps in the early 1900s, to the development of mercury lamps and fluorescent lamps in the 1930s, to today’s latest color-tunable LEDs, growers, researchers, and farmers are looking for artificial light that can provide "similar sunlight". light source. "It's light, and it's also energy-efficient and reasonably priced.
In the past few decades, some technologies have become commonplace in horticultural lighting applications. These lamps are called high intensity discharge (HID) lamps and provide higher lumens per watt than earlier technologies.
However, they also generate a lot of radiant heat, which does not contribute to photosynthesis, so they lose some efficiency.
In addition, they are not spectrally optimized for plant growth, but they are sufficient for many general applications. HID lamps include metal halides, mercury vapor, ceramic metal halides, conversion bulbs, and high-pressure sodium lamps.
Each horticultural lighting application specific situation has a wide range of requirements, just as various plants may have different requirements for water, nutrients, and light. Broadly speaking, they can be divided into supplementary lighting, photoperiod lighting and single light source lighting. 3
Providing medium-intensity lighting on cloudy days and night to promote plant growth and quality is called supplementary lighting. For example, this method is used for crops that require a lot of light, such as tomatoes grown in greenhouses on dark days in winter.
Currently, the most common light source in these environments is a high-pressure sodium lamp.
Many ornamental crops (such as crops used for landscaping) regulate their flowering according to the alternation of day and night.
Photoperiod lighting provides low-intensity light to simulate light-dark cycles to encourage these plants to bloom when needed. It can promote plant height, but does not promote photosynthesis, so it does not promote plant growth.
It is becoming more and more common to grow some crops in a completely indoor environment rather than in a greenhouse.
For example, vertical farms are becoming increasingly popular in high-density agricultural operations. Indoor growers are increasingly turning to LEDs because artificial light is now the only energy source that offers many advantages for horticultural applications.
The main lighting applications and characteristics used in the production of horticultural crops: photoperiod lighting, supplementary lighting and single-source lighting. Image source: source
The earliest LED was invented for the first time in 1962, with relatively low brightness, only red. Since then, developers have been able to make rainbow-colored LEDs, including high-intensity white LEDs, by using a range of methods and materials.
These newer LED products provide better efficiency and performance, and can have a variety of spectral characteristics. They allow precise adjustment of lighting schemes to different color spectrums and produce specific lighting properties to promote plant development.
Due to the additional advantages of LEDs such as low heat radiation, low power consumption and durability, LEDs have begun to become the preferred horticultural lighting solution for more and more applications.
LED has created a new technology platform for researchers and designers, bringing more choices to growers.
LED technology is driving important conversations around spectrum, energy efficiency, and advanced control systems; it can improve crop performance and business functions. 4 In fact, by 2027.5, global growers’ LED lamp shipments are expected to grow at an average annual rate of 32%.
The emerging practice of vertical agriculture stacks multi-layer plant trays indoors and uses optimized LED lighting to promote the growth cycle. The technology can maximize crop yields in the available footprint in areas where land is scarce or expensive, such as urban areas. Image source: Radiant Vision Systems
The ability to precisely control color tone and output is one of the exciting aspects of LEDs for gardeners. This is the correlated color temperature (CCT) and spectral power distribution (SPD) of the LED.
A new light "recipe" agricultural discipline has been discovered. With advances in LED technology, light formulations, determining lighting hours, plant photon intensity, and color mixing, fine-tuning can be made for each crop and even each stage of crop life. 6
Plant light, photosynthesis rate and growth morphology (that is, the growth of plant roots, stems, leaves and fruits) optimize two key elements. Both of these elements depend on the number of incident photons and the wavelength of light absorbed by the plant structure.
Human-centered light sources are usually characterized by indicators such as illuminance, lumens, and luminous flux, because these terms help quantify how the human eye perceives the light emitted by the light source.
Use a set of different indicators to characterize horticultural lighting-how plants "perceive" and respond to light:
The photosynthetic active area (PAR) of light is 400 nm-700 nm. PAR contains light waves that plants can use for photosynthesis. Image source: BIOS lighting
In the four stages of plant growth: germination, vegetation, flowering and fruiting, lighting formulas can be used to optimize activities. Different light wavelengths are absorbed by light pigments that promote and control growth.
Different light formulas (wavelength and intensity combinations) can be used to:
Examples of how to use different light formulations to change plant growth and characteristics. Image source: source
Different plants respond differently to various combinations of light, and each plant responds differently to light at different stages of its growth.
Taking into account spectral factors, PPFD, beam angle, DLI, etc., custom calculations can be used to establish correct lighting recipes for various crops to achieve specific results in each unique setting.
It is necessary to carefully consider how each LED bulb or fixture used fits into a complete agricultural lighting plan.
Radiant provides a variety of integrated solutions for the R&D and production line testing of the intensity, brightness, illuminance, dominant wavelength and CCT of various light sources to help LED lighting design engineers and manufacturers measure and verify the output of lighting components.
The compact goniometer system measures light as an angle factor, and is used in conjunction with application software and imaging technology in the R&D environment to provide fast, economical and comprehensive data for 3D light modeling.
Radiant's system allows lighting engineers to optimize their product designs and easily generate standard output files, including IES, EULUMDAT or Radiant Source Model™ (RSM) formats.
Their ProMetric® imaging colorimeter and photometer solutions ensure real-time product quality and consistency on the production line, increase manufacturing yield and optimize the efficiency of the light measurement process.
With the increasing popularity of LED lighting, the trend of using LEDs to transform agricultural lighting systems, and the global horticultural lighting market’s forecast of a compound annual growth rate of 21.4% by 2025, 7 it can be said with certainty that the use of LEDs in agricultural applications will continue to "root" germination". "
Made of materials originally created by Anne Corning of Radiant Vision Systems.
This information is derived from materials provided by Radiant Vision Systems and has been reviewed and adapted.
For more information on this source, please visit Radiant Vision Systems.
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