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The importance of using the full spectra of LEDs for horticultural lighting

Back in 2018, the vertical farming market exceeded the $3 billion mark for the first time — and according to industry experts it’s likely to grow at a compound annual growth rate of 27% between 2019 and 2026.

This is clearly great news for our planet as we look to more efficient ways to grow crops and the food that we need to sustain human life. Now, though, the LED world needs to support this shift towards sustainability as efficiently and as effectively as possible.

The purpose of using LEDs as artificial lighting is to stimulate plant growth and nurture development. But different spectral engineering wavelengths produced by LED lighting have a differing effect on both of these outcomes for different crops. Therefore, an effective strategy to date has been to select the best spectra for a specific crop or cultivar — one that offers both high quality and energy efficiency. Photosynthetic responses from various plants are generally similar, at least when considering quantum yield, while a morphological response seems to be more species- and cultivar-specific.

But what spectral ranges tend to work best?

Experimenting with light

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

As part of an experiment, Samsung grew lettuce and basil in four separate containers, each containing different light conditions — three of which used white LED-based full spectra, while one used with narrow spectra using only blue and red LEDs. Photoperiod of all the treatments was 16 hours/day and PPFD was set at 160 μmol*m2/s.

The results then showed that the broad spectra treatments clearly outperform narrow ones, implying the addition of other colours, like green and yellow, or ‘full-spectrum’ lights, produce a stronger yield than dual-coloured blue and red lights. Moreover, the testing showed that green light can reach the bottom layer of leaves and branches due to its high transmittance, while also contributing to signalling information that reverses the defence mechanism of UV blue light.

Selecting the right colour

Summarising the conclusions of the study: red light (630–660 nm) is essential for the growth of stems and the expansion of leaves; blue light (400–520 nm) needs to be carefully mixed with light in other spectra (otherwise overexposure may stunt growth of certain plants); green light (500–600 nm) penetrates through thick top canopies to support the leaves in the lower canopy; and far red light (720–740 nm) also passes through dense upper canopies to support the growth of leaves located lower on the plants. In addition, exposure to IR light reduces the time a plant needs to flower.

Achieving this range of light is almost impossible through purely natural methods. Therefore, Samsung has built two options for horticulturists looking to drive their vertical farming efforts forwards.

The first option available is a white-based full spectrum of LEDs, which delivers strong plant growth across the board, while suiting a broad range of applications. The second option is a white+single wavelength combination, which is beneficial for several plant species grown for specified purposes. In combination, Samsung’s LEDs for horticulture move well beyond existing standards with the highest efficacy of 2.74 μmol/J, a dramatically extended non-yellowing lifetime, and better PPFD uniformity.

To find out more about Samsung’s horticulture LEDs, visit our horticulture page