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LED lighting challenges in Horticulture

Aug 23, 2019

LED lighting challenges in Horticulture

Of course, there are challenges in any emerging technology, and there are challenges in LED-based horticultural lighting. At present, the experience of solid-state lighting technology is still very shallow. Even horticultural scientists who have been engaged in many years are still studying the “light formula” of plants. Some of these new “formulas” are not feasible at present.

 

Asian lighting manufacturers are often positioned as affordable but low-end products, and many low-end products on the market lack relevant certifications such as UL ratings, as well as LM-79 luminaire reports and LM-80 LED reports. Many growers tried to deploy LED lighting early, but felt frustrated by the poor performance of the luminaire, so high-pressure sodium lamps are still the gold standard in the industry.

 

Of course, there are many high quality LED grow lighting products on the market. However, horticultural and floral growers still need better metrics related to the application. For example, the American Society of Agricultural and Biological Engineers (ASABE) Agricultural Lighting Committee began to develop standardized metrics in 2015. This work is considering metrics related to the PAR (Photosynthetically Active Radiation) spectrum. The PAR range is usually defined as the spectral band of 400-700 nm, where photons actively drive photosynthesis. Common metrics associated with PAR include photosynthetic photon flux (PPF) and photosynthetic photon flux density (PPFD).

 

Recipe and metrics

The “recipe” and metrics are intertwined because the grower needs metrics to identify whether the plant luminaire provides intensity and spectral power distribution (SPD), which includes the “recipe”.

 

Early research focused on the relationship of chlorophyll absorption to spectral power, as chlorophyll is the key to the photosynthesis process. Laboratory studies have shown that the energy peaks in the blue and red spectra match the absorption peaks, while the green energy shows no absorption. Early research led to an oversupply of pink or purple light fixtures on the market.

However, current thinking has focused on illumination that provides peak energy in the blue and red spectrum, but at the same time emits a broad spectrum of illumination like sunlight.

 

 White light is very important

Using only red and blue LED growth lights is quite outdated. When you see a product with this spectrum, it is based on older science and is often misunderstood. The reason people choose blue and red is because these wavelength peaks are consistent with the absorption curves of chlorophyll a and b separated in the test tube. We know today that all wavelengths of light in the PAR range are useful for driving photosynthesis. There is no doubt that the spectrum is important, but it is related to plant morphology such as size and shape.

 

We can influence the height and flowering of plants by changing the spectrum. Some growers constantly adjust the light intensity and SPD because plants do have something similar to the circadian rhythm, and most plants have unique rhythms and "formulation" requirements.

 

The main red and blue combination may be relatively good for leafy vegetables such as lettuce. But he also said that for flowering plants, including tomatoes, the intensity is stronger than the special spectrum, 90% of the energy in the high-pressure sodium lamp is in the yellow area, and the lumens in the flowering plant horticultural lamps (lm), lux (lx) And efficacy may be more accurate than PAR-centric metrics.

 

Experts use 90% phosphor-converted white LEDs in their luminaires, with the rest being red or far-red LEDs, and white LED-based blue illumination provides all the blue energy needed for optimal production.