Commercial growers experiment with lighting setups ever since affordable fluorescent tubes hit the market in the 1950s. It turned out there are no silver bullets, but cold fluorescent lamps are great for germination, seedlings and graft healing. It also turned out that almost monochromatic, Low Pressure Sodium (LPS) light sources have very limited applicability, despite their high luminous efficacy.
The High Pressure Sodium (HPS) lamps proved to be game changer later on. Manufacturers kept improving this technology by changing pressure dynamics and mixing different gases into the ceramic tube, reaching high PAR efficacy and a spectrum balanced towards the green colour. Growers, on the other hand, like mixing HPS fixtures with plasma lamps (LEP), as it can complement the spectrum in the blue and UV region, which is beneficial for young plants. It's still a practice today at some high-value speciality crops.
Colour (red/blue/fr) LEDs are narrow-band, almost monochromatic emitters, just like LPS technology was. What's the difference then? The available spectrum and the ability to fine-tune.
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LEDs allow us to produce light effectively (more photons per energy) at spectrum where it's utilized at high efficacy (the plant does more photosynthesis for the same amount of photons).
The common sense suggests that it's probably not the best idea to lit something with blue/red light that was evolved to be lit by natural white. Actually, it's more complex than that. On one hand, it's true: there are several studies and results supporting this idea. On the other hand, in a greenhouse environment there's always some natural light, and even small amount of green component is enough to grow healthy plants. It's a game of economy: we can create monochromatic light more efficiently today than full-spectrum white.
That's the main reason why indoor growers prefer white LEDs, while greenhouse/polytunnel growers can use the more effective purple ones.
Most of today's LED fixtures offer a fixed, crop-specific light spectrum, fine-tuned for a specific use-case. There are major differences in what a potted rose needs to develop long shoots and small buds than than a creamy lettuce cultivar needs to grow soft tissues.
You can however change the spectrum midways, adding an other layer of control.
Basil Example By applying gradual changes, you can grow an initially small, but wide basil plant, and add biomass later on. Weeks before harvesting we change the spectrum again which activates more flavour. Meanwhile a special lighting schedule is applied to inhibit reproductive processes, which tend to lower the levels of tasty oils.
We manufacture LED-based fixtures that can create every reasonable spectrum by combining blue, white, red and far red diodes. These components are carefully mixed in order to support a wide variety of uses, like seed production or flowering. The system was designed with efficacy in mind, while remaining as cost-effective as possible.
As you see, this field is under active research nowadays worldwide, but many results are kept in-house. We and our research partners are actively investigating different uses today as well.
Contact us if you're interested in further details and opportunities in this field!