LEDs provide spectral output control for horticultural applications

As we all know, LED lighting has revolutionized the way indoor grow facilities operate, mainly due to the flexibility of LEDs to provide spectral output with extremely low heat generation. The American Society of Agricultural and Biological Engineers (ASABE) recently released ANSI/ASABE S642 SEP2018, Recommended Methods For Measurement And Testing Of LED Products For Plant Growth And Development )", the second in a series of three standards focusing on the performance of LED lighting products for horticultural applications.

LEDs provide spectral output control for horticultural applications

The new standard defines test methods for LED products with optical radiation emission in the range of 280-800nm?(while the visible light spectrum is in the range of about 390-700nm).

"Using LED lighting for horticultural applications has been one of our most interesting projects over the past two decades," said Scott Cedarquist, director of standards and technology at ASABE.

Not surprisingly, the terminology used in horticultural lighting is plant-centric, here are some of the more widely used terms:

Photosynthetically Active Radiation (PAR) - The spectral range of solar radiation available to plants during photosynthesis. It is traditionally thought to be in the range of 400nm to 700nm, but recent research has shown that wavelengths up to 740nm can also affect plant growth and development.

Photosynthetic Photon Flux (PPF) - The number of photosynthetically active photons per second produced by a lighting system, similar to luminous flux (lumens), measured in micromoles per second (Nol/s).

Photosynthetic Photon Flux Density (PPFD) - The number of photosynthetically effective photons hitting a surface per unit time per unit area, similar to illuminance (lux), in ol/m s.

The focus of horticultural lighting is the photons that are delivered, because it is they that initiate photosynthesis and other processes in plant development by exciting electrons. LED products for horticultural applications differ from LED products for general lighting in several important ways, the first being that the spectral output of these products is generally broader. This is useful since different plants respond to different parts of the spectrum.

Industrial and academic research has proven that each plant has a specific "light recipe" that allows it to grow more crops in less time. The recipe defines changes in the spectrum to optimize each stage of the plant's life cycle and improve desired plant properties, such as increasing vegetable flavor or hemp potency.

LED lighting products also have special features that not only provide a precise output spectrum, but can also be "tuned" to the optimum spectrum for different plant life cycle stages.

In order to solve the problem of excessive temperature in some growing environments, active cooling, although not universal, is another important feature of LED horticultural lighting products. Active cooling is mainly achieved by fans, but water cooling systems are also used. A waterproof enclosure is also a consideration, especially in installations where the LEDs are mounted close to the plants, such as vertical farms.

When it comes to vertical farms, LED lighting products are widely adopted because they generate much less heat than traditional lighting. LED lights can be scattered near plants without causing damage, which allows facility managers to maximize available space. In addition to the large-scale operations shown here, vertical farming is also gaining popularity in urban areas. In these areas, abandoned buildings have been converted into plant-growing places to produce fresh produce at a lower cost.

Note that the article so far has not mentioned the main reason for the widespread use of LED lighting in general lighting, namely energy saving. Because for grow facility managers, the primary purpose of this move is yield. For a high-value crop like cannabis - which undoubtedly was the first industry to embrace LED lighting - energy costs are negligible compared to the revenue gains from higher yields and shorter life cycles. Even for more traditional crops, such as leafy greens and flowers, reducing energy costs is no more compelling than producing more crops in less time.

The adoption of LED lighting for horticultural applications is growing rapidly and will lead to a major shift in the way food is grown in the future. So when you're shopping for blackberries at the grocery store next winter, think about whether your rare item was grown indoors with LED lighting.

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