En-route to the high-rise farm with LEDs
Safa Demir, Rutronik
The world is facing two major challenges - rising population and climate change - which if no appropriate solutions are found, will result in food shortages. One outstanding response to the challenge is vertical agriculture in the horticultural sector.
With the latest LED technology, which emits very little heat, light sources can be provided close to the cultivated plants without burning them. This enables multi-level cultivation. Compared with conventional farms or standard greenhouses, space and water are used much more efficiently with vertical agriculture, and what’s more it can take place in urban areas. It also is of interest to high-demand commercial plant cultivation such as cannabis for medical use. The efficiency and reliability of the lighting plays a crucial role in all these fields.
Optimum photosynthesis with the appropriate light spectrum
To optimally promote the plants’ photosynthesis in artificial light the correct combination from a wide wavelength spectrum is required. Only wavelengths of 450 nm, 660 nm, 730 nm and some green light in 520 to 550 nm affect photosynthesis. Depending on the phase - whether the plants are at the germination, vegetative or fertilisation stage - a different light composition is ideal. This is particularly the case in a vertical agriculture facility where no natural sunlight is present. Moreover the wavelengths must be adapted to the purpose of the cultivation. This is dependent on whether the plants need to grow quickly or slowly, whether the flowers are the focus or whether particularly large or abundant fruit is required.
When applied individually many color spectra do not contain a particularly high proportion of photosynthesising light waves. But when combined in the correct proportions with other wavelengths, the rate of photosynthesis goes up. The mixing proportion must relate to the wavelengths found in natural light during the day. For example, as evening draws in, the optimum wavelength is 730 nm (far red) to prepare the plants for their night-time rest, while 450 nm (deep blue) and 660 nm (hyper red) are required for photosynthesis. Different compositions of the light spectrum can be achieved simply by varying the number of LEDs in the relevant wavelengths, without changing the design of the PCB or the luminaries. However, a controller is required to be able to accurately control the LEDs, altering the mix ratio as the day goes on.
LEDs for efficient horticulture lighting
There is a wide variety of LEDs of many different wavelengths that can be combined, as necessary, to assemble an individual horticulture board.
High power LEDs give maximum brightness. The Oslon product range by Osram comprises high-power LEDs with varying illumination angles (80°, 120° and 150°) and a wide selection of color spectra. Osram has developed, particularly for use in the horticulture lighting sector, the Oslon-SSL-Color LEDs in wavelengths of 450 nm (deep blue), 660 nm (hyper red) and 730 nm (far red) along with the Oslon Square in wavelengths 450 nm (deep blue) and 660 nm (hyper red). The SSL range also provides color spectra such as blue, true green and red for special light combinations. The Oslon Square, with its beam angle of 120° achieves an efficiency of up to 3,779 mmol/J, while the Oslon SSL product range even achieves 3,91 mmol/J.
Rutronik also offers a wide portfolio of mid-power LEDs. They are not as bright as the high-power version, but for that, are less expensive. That means they are of interest for consumer applications. The efficiency values are sufficient to promote photosynthesis corresponding to the needs. The Duris-S5 series by Osram and the 2835 and 3030 packages by Everlight are suitable mid-power components. The Duris S5 series is also suitable for domestic use horticultural applications. The compact Duris S5 purple LED provides a space-saving combination of the photosynthesising 450 and 650 nm wavelengths.
In addition to the LEDs providing visible light, there are also components from Stanley, emitting ultra-violet wavelengths in UV-B (280-315 nm) and UV-A (315-400 nm). They kill germs and thus extend storage time. In addition, they can improve the taste and color of the fruit.
Increased efficiency with the correct power solutions
Once the optimal LEDs have been selected for the application in question, the next thing is to tune the LED drivers. Because there are large numbers of LEDs on the horticulture boards, efficient energy supply is required. The Osram OT FIT 380/230-400/1A4, with its wide voltage range of 200 to 400 V and large breadth of current intensity from 400 to 1400 mA allows flexible layout of the board design, and good variety in the number of LEDs. It also has an NFC adjustable current intensity and optimised surge and burst capability at 4 kV.
If the LEDs are also fitted with a secondary optic, the color spectrum and the illumination angle of the light can be better controlled. Depending on the density of the LEDs the light can be focused or scattered. This achieves different light intensities to deal with the specific needs of the particular plants. Ledil, for one, has a good range of lenses with various illumination characteristics. They are compatible with many of the standard LED packages, such as the Oslon range.
LATEST issue 4/2020
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