Research

Kyle Banas, Nursery Manager/Head Grower

Pizzo Native Plant Nursery Leland, Ill.

We have used HPS and LED but only for photoperiod extension and supplemental light. We have seen the best results when using them to extend day lengths which helps with germination of some wetland and prairie species, namely carex species.  

Duke Stockslager, owner

Stockslager’s Greenhouse & Garden Center New Lebanon, Ohio

One of the biggest successes is the [LED] lighting that we’ve put into [our propagation houses]. We saw such a tremendous change from the HPS lamps and the metal halide to these. We knew that [HPS and metal halide] were just taking the energy and running the meter, so we knew we could do better. We did not anticipate the time savings that we would get on cuttings [with LEDs]. We used to be happy with 15 to 18 days on rooting a geranium cutting, and we’re down to [10 days].

Based on this year’s results, more growers are measuring light in general, as well as daily light integral (DLI), in their operations. This year, 8% fewer growers said they don’t measure light levels, and more growers are using micromoles (up 4%) and lumens (up 11%), both at 21%. Ten percent more growers selected “Often” for DLI measurement while 10% fewer said they never measure DLI.

Professor and Greenhouse Management columnist Christopher J. Currey spoke with us recently about the importance of light measurement. “You need both instantaneous measurements, micromoles per meter squared per second (µmol·m-2·s-1), as well as cumulative measurements, DLI,” he says. Each measurement has its own benefits and can serve growers in different ways. For example, instantaneous light readings are useful for daily lighting decisions. “If you have a retractable shade cloth, light intensity is going to help tell you when to draw that cloth over the plants on a sunny day, or when to leave the plants uncovered if it’s a rainy day,” Currey says. Or growers can set an environmental control to automatically turn off lights when the ambient light reaches the desired light intensity, and turn them back on when levels dip below a set point.

Knowing the DLI levels in the greenhouse is also vital for longer-term decisions, Currey says. “DLI is good for knowing in general how much photosynthetic light you’re getting,” he says. “It’s also good for making seasonal lighting decisions: when [to] paint whitewash on our greenhouse, when we should turn our lights off and keep them off, when we should apply permanent shade cloths, when we should start to turn our lights back on again, etc.”

For more on the topic, you can read Currey’s April 2018 Production Pointers column, “Photosynthetic light: instantaneous vs. cumulative measurements,” at bit.ly/2xYdHKc

Lloyd Traven, Owner

Peace Tree Farm Kintnersville, Pa.

We’re not measuring light levels other than outdoors; we are not physically measuring inside the greenhouse. We have an Argus environmental control system that triggers all the light systems on and off, based on the light level and the rate of change of the light level [outdoors].

Jessica Marlowe, Propagation tech

Hoffman Nursery Rougemont, N.C.

We have a light meter and use the data from it to improve our production. We took sample readings in our older structures and then started monitoring light levels in the first section of our new greenhouse when it was finished. Some crops were growing slowly in the new section. Measuring the light allowed us to compare older and newer houses and figure out that light was the difference. We moved crops with lower light requirements (Carex) to that section to take advantage of the conditions. We also wanted to know if the new greenhouses could serve as overflow space for seedling propagation. Monitoring the light levels let us know where the best spots would be.

Fluorescent and metal halide use in floriculture and edible production is about the same as it was in 2016. In HPS usage, 7% fewer growers are using these lights for 100% of their operation; however, there was an increase of 11% in the 50-99% range. This may be because of growers who are slowly transitioning parts of their greenhouse to other types of lighting, such as LEDs. Neither metal halide nor incandescent lights are widely used, with 80% of growers saying they don’t use them, respectively.

The biggest change we see in the LED category is an 11% increase in those growing 50-99% of their crops using LED lights; we also see a 5% increase in those using LEDs for 1-49% of their crops. Those who say they’re not using LEDs at all dropped 19%, to 42% total.

Lloyd Traven, Owner

Peace Tree Farm Kintnersville, Pa.

[LED] technology has exploded, and amazingly, we jumped on that bandwagon. The main purpose for the lights was growing basil and for propagating. … We feel that [LED lighting] will revolutionize the way we grow here. It certainly is revolutionizing the way we propagate. I think that it’s not suitable for all growers. … But if you are a propagator, I can’t imagine how you do it without.

We are definitely cutting time off of our propagation cycle. We are greatly increasing the quality of what we put out. Our propagation business is almost triple this year [compared to] what it was. And we’re getting really good germination and really good uniformity.

Our basil [plants are] just so uniform [too]. It’s amazing, and that’s what we need. We supply Wegmans twice a week and they want the same plant every time. I am that rare wholesale greenhouse that has cash flow 52 weeks a year.

Jacob Stockslager, Grower

Stockslager’s Greenhouse & Garden Center, New Lebanon, Ohio

When we were under the metal halide and HPS [in our propagation house], the heat coming off of them would stress our cuttings. ... With the LEDs, they’re getting the light concentration they need, but the stress of the heat isn’t there. … That is another great benefit from these lights. 

Christopher J. Currey

Iowa State University

Increased popularity [of LEDs] could be attributed to potentially both the photosynthetic LED fixtures as well as the flowering lamp LEDs that are replacing incandescents and pie plates.

Duke Stockslager, owner

Stockslager’s Greenhouse & Garden Center, New Lebanon, Ohio

As the cost comes down on these LED full-spectrum fixtures, [we] would love to see them in the entire range. What that does for us growing in February, March, mid-April, [is controlling] that crop, and [having] a much finer crop ready for sale [in May]. We’re seeing the benefits of that and the day will come when I’m certain we will have [LED] lighting throughout the range. 

Jessica Marlowe, Propagation tech

Hoffman Nursery, Rougemont, N.C.

We just recently started trialing lighting in our seedling crop propagation area. The lights are LED fixtures from two different manufacturers. The manufacturers are working with us to set up a series of evaluations, but we are just getting started. We began with seedling propagation because it’s a smaller, more controlled environment, and we can see results more quickly with the short turnover. We thought the seedlings might dry out under the fixtures, but so far that’s not the case. Initially, we’re focusing on the effects of day length. We hope for better germination rates, increased vigor, and reduced elongation. First impressions are that the seedlings under lights are darker green and stockier. However, it’s still early in the process, so it’s too soon to come to any conclusions. We hope to move on to trial other aspects of the lighting, like wavelength and timing of application.

Conclusion

The data from the 2018 State of Lighting Report research supports what we’ve been informally seeing and hearing throughout the industry — growers are increasingly interested in learning about lighting their horticultural crops, whether they grow flowers or food. There is a continuing shift from incandescent, fluorescent and metal halide fixtures to high-efficiency HPS and LED lights as more research supports the benefits of the latter two. We’re looking forward to seeing how these trends evolve over the coming years.