Far-red boosts tomato yields, but requires more energy

The lighting industry continues cranking out the educational messages about the benefits of using tunable LEDs to grow crops. In one of the latest examples, a Signify study showed that extended supplemental doses of far-red wavelengths increased yields of one tomato variety by 16%.

Beware, however, that it takes more energy to emit far-red than it does to support other spectra. 

So growers should anticipate a noticeable upward spike in electricity bills should they apply far-red in the optimal yield dosage, which in the study was 16 hours a day alongside the same duration of LED lighting in the more visible part of the spectrum known as PAR (photosynthetically active radiation).

The trial took place in a greenhouse, where natural light also contributed. While keeping the PAR constant at 16 hours, Signify and its two research partners fiddled with far-red durations, with the biggest yields coming from daily 16-hour applications.

“The best result was a 16% increase in yield; however, major differences between varieties make the outcome uncertain for growers,” a Signify spokesperson said. The 16% applied to one variety. The company did not publicly reveal which one, and did not respond to LEDs Magazine in time for this story. It also did not state the light levels.

“The next step is to focus on the ratio between far-red and PAR light to find the ideal balance between growing optimization and energy efficiency,” said Erik Stappers, plant specialist with Signify’s Philips Horticulture LED Solutions, in a press release announcing the far-red findings.

The question of energy consumption is an important one, because the current high price of electricity has led to a slump in the sale of horticultural lighting products. Even though LEDs are energy efficient compared to conventional lighting, they still represent an energy bill that does not exist when there is no artificial lighting.

Lighting vendors like Signify’s Philips’ group and its Fluence operation have used the downturn to ramp up the messaging that in the long run, LED lighting can go a long way to establishing global and sustainable food security, both in greenhouses as supplemental lighting and indoors as the only source of light.

In the many permutations of horticultural LED lighting, there are methods that minimize energy consumption. For example, earlier this year Signify pointed out that growers should curtail white light.

Horticultural lighting has been shown to sometimes improve crop quality as well as yields. In the case of Signify and the far-red nurtured tomatoes, the sweetness improved in all durations of far-red, not just for the 16-hour daily crops.

Whatever the light levels were that Signify applied, it will now experiment with varying those.

“The question now is the level at which the use of far-red becomes advantageous in relation to the extra energy consumption,” Signify noted in the announcement. “If a relatively low percentage of far-red light produces additional yield, then the researchers expect it may become appealing.”

Signify studied the far-red lighting in partnership with Holland’s Wageningen University and with Nunhems, a horticultural group within German chemical giant BASF.

MARK HALPER is a contributing editor for LEDs Magazine, and an energy, technology, and business journalist ([email protected]).

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