Vertical farming should capitalize on full-spectrum LEDs

The LED industry can make an immediate impact through the sectors which it serves, including solid-state lighting (SSL) across many applications. One example with enormous potential for reduced carbon emissions through reduced energy consumption is within agriculture, where LEDs are ideally constructed to provide light in vertical farms. Vertical farming is an extremely sustainable food production method, important as industrialization and climate change continue to reduce soil fertility and shrink available land for conventional farming.

One effective strategy in LED cultivation has been to select the optimal spectra for a specific crop or cultivar - wavelengths that offer both high quality and energy efficiency. Photosynthetic responses from various plants are generally similar in terms of considering quantum yield, while a morphological response is more species and cultivar-specific.

Studies show red light and blue light tend to fit with the absorption peak of chlorophylls involved in photosynthesis. Red radiation is best for driving photosynthesis based on quantum yield. However, blue light nurtures the vegetative and flowering stages of plant growth.

Until now, these functions have made for a conventionally narrow horticulture spectrum by simply employing a combination of blue and red lights - an approach widely used in Europe.

While the use of red, blue (and to an extent, green) light is common to encourage growth, Samsung trials of different LED types showed surprising results when using white-based, full-spectrum LED light to grow common leafy green vegetables and herbs.

As part of an experiment, researchers grew lettuce and basil in four separate containers, each featuring different light conditions. Three of the containers used white-LED-based full spectra, and one used narrow spectra by employing only blue and red LEDs. The photoperiod of all the treatments was 16 hours per day and photosynthetic photon flux density (PPFD) was set at 160 μmol⋅m2/s.

The results of the individual growth chambers showed that the broad-spectra treatments clearly outperformed narrow ones, implying the addition of other colors, like green and yellow, or full-spectrum lights, produce a stronger yield than dual-colored blue and red lights. Moreover, the testing showed that green light reaches the bottom layer of leaves and branches due to its high transmittance, while also contributing to signaling information that reverses the defense mechanism of UV blue light.

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