Grow lights with adjustable far-red LEDs
“Of course, the high energy prices were a significant reason for the switch to full LED,” explains owner Hein van Wordragen. “What made the difference as far as I was concerned though, was the research by WUR into controlling elongation and response times with far-red light.” According to the results, chrysanthemum stem length can be properly regulated with full LED by providing subsequent end-of-day lighting with 30 minutes of 20 μmol/m²/s far-red light. This research puts an end to the fear amongst chrysanthemum growers that use of full LED might result in too short flower stems in the winter. Another benefit of using far-red in this way is a potential reduction in the cultivation period by a few days and less shoot growth at the base of the plant.
“I had every confidence in the research carried out by WUR and eventually got in touch with Signify,” says Van Wordragen. “They then suggested the Philips GreenPower LED toplighting force dynamic with adjustable far-red light.” Leontiene van Genuchten, Plant Specialist at Signify, explains: “We have already previously trialed adjustable far-red, but at the time it was mainly about the growth rate instead of elongation. This is also because there were still a lot of hybrid lighting systems at the time, where elongation was not an issue.
Meanwhile, further research by WUR has demonstrated that subsequent lighting with far-red also has positive effects on crop elongation when illuminated for shorter periods and using only 10 or even 5 μmol/m²/s far-red. Furthermore, the practical application at Van Wordragen next winter will yield a lot of new information and insights. “We are all going to learn a great deal,” says Van Wordragen. “The results are highly encouraging so far.” Signify has also been closely involved. Van Genuchten: “Every week we harvest a small section to see how long the stems are. If you then compare this against the amount of far-red applied and the use of plant growth regulators, it is very enlightening. We want to identify when you need far-red in particular and when you might still be able to decrease this; if you use energy, it needs to serve a purpose after all.”