Light stimulates photosynthesis and is thus essential to growth. But the light must provide the correct spectral range. There are also other factors that affect plant growth:
- Wavelength: The various wavelengths of horticultural plants allow the growth, form, development and blooms of the plants to be controlled. If tomato plants are lit with red LEDs at a wavelength of 660nm, they bear more fruit. Exposing cucumbers to blue light at 455nm slows down growth, while a blue wavelength of 470nm results in a greater leaf area, producing fresh and dry biomass.
- Light period: Prolonging natural daylight using artificial light from a horticultural lamp allows plants to grow better and blossom more.
- Arrangement of the lamps: "Toplighting", where the lamps are positioned above plants, has been especially common to date. Because an LED emits little heat, the light source can be positioned very closely over the plant, allowing a plant rack to support many more levels. Horticultural LED lamps can even be positioned between plants ("interlighting") to largely prevent shadows and ensure that smaller plants also get enough light.
New LED technologies enable precise control of wavelengths and lighting times, allowing plants to experience optimum growth and the harvest to be improved. OSRAM Opto Semiconductors offers powerful LEDs with low thermal resistance specially for horticultural lighting in the form of the OSLON SSL family. The robust ceramic package is ideal for the horticultural lighting conditions inside greenhouses. The OSLON SSL Colors family, available in eight colors in a range from 450nm (deep blue) to 730nm (far red), hosts the most reliable wavelengths for plant growth. Everlight Electronics also offers a broad selection of LEDs for horticultural lighting.
Power Supplies for LEDs
Of course, all LEDs need to be supplied with power, and developers will find numerous analog and digital LED drivers, microcontrollers, MOSFETs and dimming ICs for horticultural lighting thanks to Infineon Technologies. They can be used for any standard topology in single-string applications below and above 100W and in multi-string applications.
Controllers for multi-colored LEDs
Exposing plants to light from multi-colored LED strips requires precise control to ensure the light is provided at the correct wavelength. This can be achieved for instance using the AC/DC LED driver IC ICL5101 combined with the 700V/800V CoolMOS™ P7, both from Infineon. This solution, a combination of PFC (Power Factor Correction) and LLC (Light Emitting Diode), is distinguished in particular by its very low THD (Total Harmonic Distortion) across a broad load range.
Such a multi-string solution makes for an optimized general horticultural lighting solution thanks to the DC/DC LED driver ILD6150 combined with the XMC1300 microcontroller (both Infineon). The microcontroller enables connectivity, for instance using DALI or DMX, and the integration of sensors. Furthermore, it supports automatic exponential dimming and linear intensity changes, ensuring that brightness and color transitions appear smooth and natural to the human eye. Further, the automatic brightness control enables flicker-free dimming, even at a dimming level of below 0.1%.
Controllers for single-colored LEDs
The single-stage flyback controller XDPL8105 from Infineon is ideal for controlling single-colored LEDs under 100W. The digital AC/DC converter with flyback function enables isolated dimming from 0-10V and offers smart heat management. The image shows an example circuit diagram for the configurable controller in a single-stage flyback CC topology.
The CDM10V driver from Infineon is especially versatile, as it uniquely offers many configuration possibilities for horticultural lighting. Users have the choice of using the driver in pre-configured form or configuring it themselves. The driver also offers excellent programmability and dimmability (0-10V), and requires little space with its 6-pin SOT package.
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