Limits of dimming lights in phalaenopsis reached

Research into robust sensors for measuring light use
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Limits of dimming lights in phalaenopsis reached

Intensive lighting in winter is common in Phalaenopsis growing. A long-running Dutch research project is seeking to answer the question of whether less lighting could be used at that time of year. The trials in the first three years revealed that turning the lights up or down could cut electricity bills by as much as 30% without loss of quality or production. The results from the fourth trial year, with practical trials at Ter Laak Orchids, show that the limit has been reached in terms of quality – at least in the top segment.

The trials run in 2014-2016 by the specialist Dutch research companies Plant Lighting and Plant Dynamics, with support from growers, delivered some surprising insights. One of these was that timing is more important than the light sum in the vegetative and generative phases. They also discovered that a long day of 16 hours produces more CO2 uptake than a day of 11½ hours. Dimming the lights at the beginning and end of the lighting period seems to be possible without loss of production or quality. That generates electricity savings of more than 30%.

Dimming in cooling phase

Based on these results, two follow-on studies were run in the winter of 2016/2017. The first took place in climate chambers equipped with daylight simulators and SON-T lights from Plant Lighting in Bunnik, the Netherlands. In these chambers, the dimming treatment, which can cut electricity usage by up to 30%, was also applied in the cooling phase for the first time. In another room, the plants were lit in line with the biorhythm, starting at 05:00 instead of 01:00. This can save as much as 43% in electricity because it makes better use of free daylight.

Researcher Sander Hogewoning explains: “The CO2 uptake was the same in all three treatments. Yet something caught our eye: CO2 uptake ended relatively late: it didn’t stop until 2½ hours after the lights went on. So the plant rhythm is not always the same, and we have no idea why that is. This indicates that it is important to keep on taking measurements with sensors, otherwise you are taking a risk. We also noticed that the plants were a week behind in the treatments with dimmed light. That can be explained by the fact that the plant temperature was 0.5°C lower on average because the SON-T lamps were used less. In practice, you would compensate for that by turning up the heat. Although the percentage of double spiked plants was just as high, the percentage of branched ones was lower. With these treatments, you’re reaching the limits in terms of quality.”

Practical trials

The limits were explored and found in the second trial as well. This study took place in the Ter Laak Orchids trial greenhouses in Wateringen in the west of the Netherlands, in both the vegetative and cooling stages. The generative stage took place in the production greenhouse. The researchers and growers chose four varieties for the trials: Sacramento, Donau, Jewel and Las Palmas. Martin van Dijk of Ter Laak: “We grow more than 100 varieties here, so we wanted to know what effect a different lighting regime would have on different varieties. The quality and the number of double spikes must remain the same. That’s essential for us.”

In the one 80 m² trial greenhouse, the plants were lit for the usual 16 hours. The plants in the other trial greenhouse were also lit for 16 hours but with the dimming treatment used in the previous trial. The only difference was that the start was delayed until 03:00 in order to make better use of the daylight. To check the quality, the root weight and above-ground weight were measured three times. At the end of the generative stage, the researchers counted the number of double spikes and the number of flowers.

The same or marginally lower

The results? The quality of the plants was the same or marginally lower. With the dimming treatment, the roots in three of the four varieties were lighter than in the control treatment, although the weight of the leaves and flowers was comparable. The number of flower buds was also the same.
Another indicator of quality is the percentage of multiple spikes. With the dimming treatment, only Jewel showed significantly lower results by the end of the generative stage. The percentage was slightly lower in the other two varieties but not to a statistically significant extent. The differences are not massive, but they do show that the limits of dimming were reached in this trial as well.

Hogewoning: “My conclusion after these trials is that dimming saves a lot of electricity and produces the same or slightly lower quality. We advise growers in the top segment not to push the boundaries when looking for savings but to stop a little way from the limit. However, the quality differences are small. Growers with fewer lamps will find that switching the lights on later saves them money. By making better use of free daylight, they will reach their light sum more easily at the time of day that is most important for the plants. And finally, bear in mind that any differences in quality are very much magnified because we are simulating winter for 30 weeks of cultivation. In reality it’s not always December.”

Different choices

With the benefit of hindsight, the growers involved are making various choices depending on the capacity of lamps, but also depending on whether they have a CHP plant or have to buy in electricity, which is expensive. At Ter Laak Orchids they are biding their time. Van Dijk: “With the results of the study and the experience we gained last year, we are waiting to see what the results of next year’s sensor study will be. This winter we plan to turn the lights up and down incrementally, but starting at 01:00 as normal.”

Honselersdijk-based Levoplant has been switching the lights on later since last year. Cultivation manager Erwin van Vliet, a long-standing member of the supervisory committee: “We used to start at 01:00 and we would stop suddenly at 16:00, sometimes even earlier. Now we start at 04:00 in October and finish at 19:00. In November and December we start at 03:00 in order to achieve our light sum. We also turn the lights up and dim them incrementally. That works very well for us because it makes the climate in the greenhouse more uniform. An additional advantage last year was that we had less of an issue with premature spiking. The quality is every bit as good as before.”

Developing knowledge

Are these insights resulting in energy savings? Van Vliet: “We are not saving as much as in the study. We are lighting for longer, although we are saving energy by dimming. Before the study, the trend was heading towards 100% lighting for 16 hours. But we now know that really isn’t necessary. So we need to continue to develop our knowledge – by working together.”

The Pot Orchid Growers Cooperative this year invested in the development of robust, affordable sensors to provide ongoing information on the plants’ light usage. Van Dijk and Ter Laak are certainly convinced of the benefits. “We are installing a wireless network in the new Daylight Greenhouse we are building to allow for the use of wireless sensors in the future.”

Summary

The fourth year of the research into lighting Phalaenopsis in winter has confirmed the previous years’ results. The orchid needs a long day, but that can be achieved by gradually turning up and dimming the lights in the vegetative, cooling and generative stages. Switching on the lights later saves more electricity. The quality of the plants in the dimming treatments is the same or marginally lower. The limits of the savings thus seem to have been reached.

Text: Karin van Hoogstraten. Images: LD Photography.

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