Svenja Mahler, Rutronik
The market for light-emitting diodes (LEDs) has been experiencing continuous growth for several years. The reasons for this include, for instance, the low costs of the LEDs, whose energy efficiency and capabilities, brightness, and color scheme can be adapted individually to the respective requirements. In addition, drivers enable a simple method, usually via plug&play, for targeted control of the LEDs.
Today, more than half of the world’s population lives in cities, and this trend looks set to continue. When it comes to providing people in so-called mega cities with a sufficient amount of healthy food, conventional methods of agriculture will soon reach their limits. A possible solution is horticulture lighting.
Horticulture lighting refers to the illumination of plants with artificial light to achieve both faster and targeted growth; specifically aimed, for example, at bud development and fruit ripening. Light stimulates photosynthesis and is thus decisive for plant growth. However, the light must provide the correct spectral range. Different wavelengths are important for the growth, shape, development, and blossoming of the plant. For instance, if red LEDs with a wavelength of 660 nm are used for tomatoes, it has a positive effect on the harvest, especially on the number of fruit. Conversely, exposing cucumbers to blue light with 455 nm slows down growth, while a blue wavelength of 470 nm results in a greater leaf area and fresh and dry shoot biomass.
The time period during which the plants are exposed to light is also significant for horticulture lighting. The "natural daytime" can thus be extended with the aid of artificial light and results in stronger growth and increased bud development.
Furthermore, there is a range of options for arranging the lights to the plants. The standard method is "top lighting" where the LEDs hang above the plants. Due to the low heat development of LEDs, the distance between the light source and the plant can be kept to a minimum. And the racks can thus contain a greater number of levels. Moreover, LEDs also enable "inter-lighting". In this case, the lights are positioned in between the plants, which, compared to "top lighting", helps to reduce shading. This ensures that smaller plants are exposed to sufficient light, too.
Thanks to new LED technologies, it is possible to maximize plant exposure to the precise wavelength that promotes photosynthesis and optimum growth. Additionally, being able to influence the exposure period and benefiting from a flexible arrangement of the LEDs are strong arguments in favor of the use of LED lighting for plant growth. In the sector of horticulture lighting, the OSLON-SSL product range from OSRAM Opto Semiconductors offers an extensive portfolio of high-performance LEDs with low thermal resistivity. The robust ceramic package is ideal for the conditions inside greenhouses. The OSLON-SSL-Colors family is available in eight colors, ranging from 450 nm (deep blue) to 730 nm (far red), which represent the most reliable wavelengths in terms of plant growth. Everlight Electronics also provides customers with a wide range of products for the horticulture lighting sector and is therefore an ideal addition to Rutronik’s portfolio.
However, each LED has to be supplied with the respective energy. Infineon Technologies is a technology leader in the field of power management and offers an extensive selection of analog and digital LED drivers, microcontrollers, MOSFETs, and Dimming ICs for horticulture lighting solutions. The portfolio of Infineon Technologies addresses all the standard topologies for single string 100 W, and multi-string applications.
Controller for monochrome LEDs
Infineon’s configurable XDPL8105 digital, single-stage flyback controller provides a perfect solution for controlling the Oslon-SSL-Color family, especially when controlling uni-color LEDs below 100 W. Figure 1 shows an example of the circuit diagram for the XDPL8105 in single-stage flyback CC topology. The XDPL8105 is a digital AC/DC converter with flyback function that enables isolated dimming from 0 to 10 V. Yet another advantage is intelligent thermal management.
The CDM10V driver can be individually configured once, thus resulting in a plethora of versatile applications. Infineon delivers pre-configured components, but configuration can also be performed by each customer individually. The main benefits of the CDM10V are the programming option, the reduced space as a result of the 6-pin SOT package, and the dimming function (0-10 V).
Figure 1. Circuit diagram for the XDPL8105 in single-stage flyback CC topology.
Precise control of multicolor LEDs
If plants are exposed to light from multi-colored LED strips, it requires precise control to ensure the light is provided at the correct wavelength. To achieve this goal, suppliers such as Infineon or Diodes supply an array of solutions.
One example is the ICL5101 AC-DC LED driver IC from Infineon in combination with the 700 V/800 V CoolMOS™ P7. This PFC+LLC solution offers, above all, advantages due to very low THD (Total Harmonic Distortion) over a wide load range (Figure 2).
Figure 2. PFC+LLC solution circuit diagram.
Infineon’s ILD6150 DC-DC LED driver, in conjunction with the XMC1300 microcontroller, complements this multi-string solution by supporting, among other things, connectivity, e.g. via DALI and DMX, as well as the integration of sensory equipment. Furthermore, the XMC1300 supports automatic exponential dimming and linear intensity changes and ensures brightness and color transitions appear natural to the human eye. Further, the automatic brightness control enables flicker-free dimming, also for a dimming level of below 0.1%.
From a financial perspective, the use of LEDs offers various advantages compared to conventional lighting options. For a start, LEDs do not burn out like traditional light bulbs but simply experience minimum lumen depreciation over time. While light bulbs are liable to fail on average after just one year, top grade LEDs can now be operated for more than 50 000 hours (depending on the type of application). The increased lifetime additionally ensures high reliability. Further, energy can be saved through effective and efficient control. Horticulture lighting looks set to grow in the coming years thanks to new LED technologies and intelligent control units.
Rutronik recognized this trend at an early stage and already offers a wide range of products that can be used for horticulture lighting. Heatsinks, connectors, cables, MOSFETs, diodes, and microcontrollers are just a few examples from Rutronik’s extensive portfolio.
LATEST issue 3/2019