Miraculous technological invention in terms of LEDs has revolutionized almost every field like lighting, electronics, sensing, medical/health sector, agriculture, animal husbandry, horticulture and their applications are still expanding to various other sectors. With the desired technological growth of mankind, its basic life needs like agriculture, horticulture and animal husbandry also need to be strengthened and progressed. Therefore, the uses of LED lights for the benefits in these sectors are also being explored.
In this article, I will briefly present the role LED lights are playing in the horticulture sector. While growing plants like perennials, fruits and herbs outside is a great pastime, but sometimes climates are not ideal for year-round survival. Growing with LED lights is a project many people can tackle without years of experience or horticulture knowledge. Every green plant requires adequate light for photosynthesis. The amount of light a plant needs will vary. Common houseplants typically flourish with a bit of natural sunlight, while fruiting plants, like tomatoes and cucumbers, generally require more light. LED grow lights are often used to produce the best results for indoor gardening because they give off very little heat compared to fluorescent grow lights or high pressure sodium varieties. Many LED lights designed for indoor growing also allow selecting a specific range of light that’s ideal for plants in their current state. This gives users greater control over indoor growing and will generally yield better results.
Role of lighting
Human have long back realized the importance of sunlight, water and air along with the availability of a fertile soil and enough care towards growth and characteristics of plants. As soon electric light bulbs were invented in the 1860s, people started applying artificial light to help promote plant growth. Electrical lighting can fill the gap when there is a shortage of natural sunlight, for example, in a greenhouse on overcast days or during the winter. The right light fixtures can also enable indoor growing on a large scale. By supplying light energy, artificial illumination has opened the opportunity to grow crops under many conditions that were not previously possible.
All light is not created equally, however, where plant growth is concerned. The visible spectrum of sunlight extends from deep violet at one end to red at the other (wavelengths of approximately 380 nm – 750 nm), and plants respond differently to light energy at various wavelengths. For decades, scientists have known that photosynthesis is optimized by red wavelengths, particularly around 660 nm. Plants also need light waves in the blue portion of the spectrum for root strength during germination, among other benefits. A barely visible range beyond red, known as far red, promotes larger leaves, branching, and flowering.
Development of Horticultural Lighting
For the last several decades, a handful of technologies have become common in horticultural lighting applications. Called High Intensity Discharge (HID) lights, these fixtures offer higher lumen-per-watt intensity than earlier technologies. However, they also typically produce significant radiant heat, which does not contribute to photosynthesis, thus losing some efficiency. They also are not spectrally optimized for plant growth but are sufficient for multiple general applications. HID lights include mercury vapour, metal halide, ceramic metal halide, high pressure sodium and conversion bulbs. Just as the nutrient, water, and light needs of various types of plants can differ, the specifics of each horticultural lighting application present a wide range of requirements. In broad terms, they can be categorized into photoperiodic lighting, supplemental lighting, and sole-source lighting situations.
LEDs in Horticulture
First invented in 1962, the earliest LEDs offered relatively low brightness and came in just one colour: red. Since then, developers have been able to create LEDs in a rainbow of colours, including high-intensity white LEDs, using a variety of materials and methods. These newer LED products offer improved performance and efficiency and can have a wide range of spectral properties. They are enabling lighting schemes that are precisely tuned to different colour spectra and that produce specific lighting attributes that enhance plant development.
With the additional advantages of low power consumption, low thermal radiation, and durability, LEDs have started to become the horticultural lighting solution of choice for an increasing number of applications. One of the exciting aspect of LEDs to horticulturalists is the ability to precisely control the hue and output – the Correlated Colour Temperature (CCT) and Spectral Power Distribution (SPD) – of LEDs. With advances in LED technology, light recipes-determining the number of hours illuminated, the intensity of photons directed at plants and the mix of colours – can be finely tuned to each crop and even to each stage in a crop’s life. Plant lighting is designed to optimize two key elements: photosynthesis rates and growth morphology. Both of these elements depend on the number of incident photons and the wavelengths of light that are absorbed by plant structures. Lighting recipes can be used to optimize activity during the four stages of plant growth: germination, vegetation, flowering, and fruiting. Different light wavelengths are absorbed by photopigments that control and promote growth. Different light recipes (wavelength and intensity combinations) can be used to achieve more biomass, shorten the growth cycle, enhance the taste or colour of produce, and achieve optimal plant size. LED grow lights for the horticultural industry are powerful LED fixtures, meaning they have the intensity and colour spectrum required to stimulate plant growth. This corresponds perfectly with the photosynthetic action spectrum, thus matching the light composition that plants benefit the most from. Thus, offering low energy usage, low heat, and colour optimized for growth, LED lights are the most efficient, effective, and customer-friendly way to grow plants at home than growing with fluorescent lights or incandescent lights.
Horticultural research has established that radiation at some relatively narrow spectral bands can optimize chlorophyll absorption in plants that in turn drives the photosynthesis process critical to plant growth. Both packaged LED manufacturers and makers of Solid-State Lighting (SSL) finished products are moving to capture a slice of what is a rapidly growing marketplace. Meanwhile, researchers continue to work to understand how other wavelengths might further boost productivity in greenhouses and indoor commercial plant farms. The mix of LED types in horticulture will continue to evolve. Manufactures of LEDs are offering monochromatic orange, yellow, and green LEDs along with phosphor-converted white LEDs with which researchers are experimenting. In recent years, research on Light Emitting Diodes (LEDs) has highlighted their great potential as a lighting system for plant growth, development and metabolism control. The suitability of LED devices for plant cultivation has turned the technology into a main component in controlled or closed plant-growing environments, experiencing an extremely fast development of horticulture LED metrics. In reality, the potential for LED-lighting sales in horticulture is impossible to predict, especially with research uncovering new ways to use SSL to increase productivity.
Choosing lights for plants
LED lights for growing come in a range of types and colours depending on particular needs. Many indoor growers rotate their grow lights for indoor plants based on the current state of their plants. Here’s a quick guide based on the different stages of growth:
- Violet/blue lights typically come in a nanometer range of 400 and 530. This encourages the early stages of photosynthesis.
- Green light in the 500 to 620 range is ideal for plants with thick growth cover, as it can penetrate top foliage for better light retention.
- Red light in the 600 to 730 range promotes flowering for later stage plants.
- Far red light in the 700 to 740 range is often used to speed the process of flowering.
- Mixing light colours and nanometer ranges is often recommended for certain plants.
- Providing different lighting conditions for different plants will be beneficial.
In general, LED lights for growing are placed directly over or just to the side of plants as they sprout. Sometimes an array of lights is used for a more complex setup. The user controls the light type, on/off time and the colour of the light based on the growth stage of the plant. Some of the best practices while using LED lights are as:
- Aim to place LED grow lights 6 to 12 inches from plants. This will give plants the right amount of light without overheating them.
- Turn lights off about eight hours per day because as a general rule of thumb, LED lights can be used about 12-16 hours each day for growing.
- Try to change light configuration as moving of lights or increasing or reducing the amount of time they’re on can create a dramatic difference in overall growth.
- Take time to understand the response of plants growing to LED lights.
- Using LED grow lights for plants can seem complex at the start but in many ways, it’s a simple process that’s easy to follow and understand.
- LEDs are generally the best bet since they don’t put off too much heat.
- LED plant grow lights are an ideal option to do it indoors.
- LED grow light system can be easily scaled up to accommodate more plants.
Bottlenecks of technology
LEDs provide many advantages as plant lighting, but there are difficulties that are slowing their implementation for horticultural applications. The primary difficulty is cost as plant lighting applications require a large number of individual high-output LED devices and the integration of these devices into a controllable lighting system. The technical impediment to using LEDs for horticultural lighting is the low light output of some current LEDs in wavebands of interest to horticulturists. Although many wavelengths are available, only a limited number are available in very high output configurations. Further, it is needed to make the standardization of horticultural processes around installation as well as for creating luminaries. Research is required with regards to the other functions that can be built into plants themselves, such as form and taste. Hence, there is still so much to discover and look forward to in the application of horticultural lighting.
Suggested reading resources
- https://www.radiantvisionsystems.com/blog/leds-are-growing-horticultural-lighting-applications (May 2021)
- Applications and Advances in LEDs for Horticulture and Crop Production (August 2019), In book: Ultraviolet LED Technology for Food Applications, Publisher: Academic Press by Akvile Virsile, et.al., DOI: 10.1016/B978-0-12-817794-5.00003-0
- https://www.ledsmagazine.com/horticultural-lighting/vegetables-floriculture/article/16695961/led-technology-serves-rapidly-growing-horticultural-market-magazine (March 2015)
- https://encyclopedia.pub/2800-LED Lighting Systems for Horticulture
- file:///C:/Users/SLIET/Downloads/ANO003a_E_Advantages_of_LED_Lightingin_Horticultural_Applications%20(1).pdf (2018)
- https://journals.ashs.org/hortsci/view/journals/hortsci/43/7/article-p1947.xml- LED Lighting in Horticulture by Robert C. Morrow, DOI: https://doi.org/10.21273/HORTSCI.43.7.1947 (Dec. 2008)
- https://apps.osramos.com/horticulture/Content/AN133_LEDs%20for%20horticultural%20lighting%20applications.pdf- LEDs for horticultural lighting applications.
Dr. S. S. VERMA is a Professor in the Department of Physics, Sant Longowal Institute of Engineering and Technology (Deemed to be a University), Longowal, Distt.-Sangrur (Punjab)-148 106.