An Adaptive Control Approach for Light-emitting Diode Lights Can Reduce the Energy Costs of Supplemental Lighting in Greenhouses

in HortScience

Supplemental lighting in greenhouses is often needed for year-round production of high-quality crops. However, the electricity needed for supplemental lighting can account for a substantial part of overall production costs. Our objective was to develop more efficient control methods for supplemental lighting, taking advantage of the dimmability of light-emitting diode (LED) grow lights. We compared 14 hours per day of full power supplemental LED lighting to two other treatments: 1) turning the LEDs on, at full power, only when the ambient photosynthetic photon flux (PPF) dropped below a specific threshold, and 2) adjusting the duty cycle of the LEDs so that the LED lights provided only enough supplemental PPF to reach a preset threshold PPF. This threshold PPF was adjusted daily from 50 to 250 μmol·m−2·s−1. Turning the LED lights on at full power and off based on a PPF threshold was not practical since this at times resulted in the lights going on and off frequently. Adjusting the duty cycle of the LED lights based on PPF measurements underneath the light bar provided excellent control of PPF, with 5-minute averages typically being within 0.2 μmol·m−2·s−1 of the threshold PPF. Continuously adjusting the duty cycle of the LED lights reduced electricity use by 20% to 92%, depending on the PPF threshold and daily light integral (DLI) from sunlight. Simulations based on net photosynthesis (An) − PPF response curves indicated that there are large differences among species in how efficiently supplemental PPF stimulates An. When there is little or no sunlight, An of Heuchera americana is expected to increase more than that of Campanula portenschlagiana when a low level of supplemental light is provided. Conversely, when ambient PPF >200 μmol·m−2·s−1, supplemental lighting will have little impact on An of H. americana, but can still results in significant increases in An of C. portenschlagiana (1.7 to 6.1 μmol·m−2·s−1 as supplemental PPF increases from 50 to 250 μmol·m−2·s−1). Adjusting the duty cycle of the LEDs based on PPF levels assures that supplemental light is provided when plants can use that supplemental light most efficiently. Implementing automated duty cycle control of LED grow lights is simple and low cost. This approach can increase the cost effectiveness of supplemental lighting, because of the associated energy savings.

Contributor Notes

We thank the Fred C. Gloeckner Foundation, the American Floral Endowment, the Georgia Centers of Innovation, and the Georgia Research Alliance for financial support for this research.

This work also was supported by the USDA National Institute of Food and Agriculture, Hatch project 1011550.

Corresponding author. E-mail: mvanier@uga.edu.

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    Diagram of the adapative lighting control system. A datalogger and control system uses a quantum sensor to measure the photosynthetic photon flux (PPF) underneath the LED light. Based on the measured PPF, the datalogger adjusts a 0 to 5 V-DC signal that is sent to a duty cycle (or pulse width modulation) control board. If the measured PPF is lower than the programmed PPF threshold, the duty cycle (fraction of time the LED light is energized during a very short on/off cycle) is increased and vice versa.

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    Representative data of the performance of the adaptive light-emitted diode (LED) light control system. The system controls the duty cycle of the LED light in such a way that the LED grow light provides just enough light so that the combined photosynthetic photon flux (PPF) from the sun and LED light reaches the PPF threshold. Data shown are for the highest and lowest PPF threshold on days with relatively low and high daily light integrals (DLI, in mol·m−2·d−1). Note that the LED light bar could only provide a PPF of ≈225 μmol·m−2·s−1. Therefore, the 250 μmol·m−2·s−1 PPF threshold was not reached when the PPF from sunlight was below 25 μmol·m−2·s−1.

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    The relationship between the duty cycle of the light-emitted diode (LED) light and the photosynthetic photon flux (PPF) provided by sunlight (left). The duty cycle was adjusted every second so that the LED light bar provided just enough supplemental light to assure that the total amount of PPF underneath the light bar reached the threshold level. Each data point is the average of 300 measurements collected over 5-min intervals. Using data points with duty cycles from 0.05 to 0.95: Duty cycle = 0.0250 − (0.00457 × PPFsun) + (0.00407 × PPFthreshold), R2 = 0.99.

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    The average duty cycle of light-emitted diode (LED) lights over a 14-h photoperiod as a function of the daily light integral from sunlight (DLIsun) on that day. Two different approaches to lighting control were tested. Pulse width modulation (PWM) control (top) refers to adjustments made in the duty cycle of the LEDs to provide just enough light to reach the threshold photosynthetic photon flux (PPF). With PPF control, the LEDs are turned on at full power every time the PPF from sunlight drops below the threshold PPF. Regression lines were derived from the following equations: for PWM control, Duty cycle = −0.0604 + 0.00378 × threshold PPF − 0.000184 × DLIsun × threshold PPF, R2 = 0.99; for PPF control: Duty cycle = 0.512 + 0.00553 × threshold PPF − 0.0000120 × threshold PPF2 − 0.0529 × DLIsun (R2 = 0.98).

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    The daily light integral measured underneath light-emitted diode (LED) light bars that were controlled in one of three ways: 1) 14-hr of supplemental light with the LEDs on at full power (DLI14hr), 2) LEDs were turned on at full power whenever the photosynthetic photon flux (PPF) from sunlight dropped below the threshold PPF (DLIPPF), and 3) pulse-width modulation control in which the duty cycle of the LED bar was adjusted every second to provide just enough supplemental light to reach the threshold PPF (DLIPWM). Numbers in the lower right corner of the graphs indicate the threshold PPF (in μmol·m−2·s−1). Lines shown were calculated using the multiple regression equation (upper right).

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    Photosynthesis (An)–light response curve for Heuchera americana ‘Dale’s Strain’ grown at an average daily light integral of 7.8 mol·m−2·d−1 and ambient CO2 (data from Garland et al., 2012) and Campanula portenschlagiana ‘Blue Get Mee’ grown under long days and elevated CO2 (600 μmol·mol−1; Kjaer et al., 2011). Regression curves: H. americana An = −0.24 + 10.4 × (1-e−0.011 × PPF), C. portenschlagiana An = −0.91 + 24.6 × (1-e−0.026 × PPF), R2 >0.98 for both species. These curves were used to estimate the increase in An of both species that can be achieved by providing supplemental light in the presence of different amounts of photosynthetic photon flux (PPF) provided by sunlight.

Article References

  • AlbrightL.D.BothA.J.ChiuA.J.2000Controlling greenhouse light to a consistent daily integralTrans. ASAE43421431

  • BotG.P.A.2001Developments in indoor sustainable plant production with emphasis on energy savingComput. Electron. Agr.30151165

  • BourgetC.M.2008An introduction to light-emitting diodesHortScience4319441946

  • ClausenA.Maersk-MoellerH.M.Corfixen SoerensenJ.JoergensenB.N.KjaerK.H.OttosenC.O.2015Integrating commercial greenhouses in the smart grid with demand response based control of supplemental lighting p. 199–213. In: Intl. Conf. Ind. Technol. Mgt. Sci. (ITMS 2015)

  • Demmig-AdamsB.CohuC.M.MullerO.AdamsW.W.2012Modulation of photosynthetic energy conversion efficiency in nature: From seconds to seasonsPhotosynth. Res.1137588

    • Search Google Scholar
    • Export Citation
  • GarlandK.F.BurnettS.E.DayM.E.van IerselM.W.2012Influence of substrate water content and daily light integral on photosynthesis, water use efficiency, and morphology of Heuchera americanaJ. Amer. Soc. Hort. Sci.1375767

    • Search Google Scholar
    • Export Citation
  • GómezC.MorrowR.C.BourgetC.M.MassaG.D.MitchellC.A.2013Comparison of intracanopy light-emitting diode towers and overhead high-pressure sodium lamps for supplemental lighting of greenhouse-grown tomatoesHortTechnology239398

    • Search Google Scholar
    • Export Citation
  • GotoE.2012Plant production in a closed plant factory with artificial lightingActa Hort.9563749

  • HeuvelinkE.P.ChallaH.1989Dynamic optimization of artificial lighting in greenhousesActa Hort.260401412

  • JensenM.H.MalterA.J.1995Protected agriculture: A global review. World Bank technical paper; no. WTP 253. The World Bank Washington DC

  • KjaerK.H.OttosenC.O.JørgensenB.N.2011Cost-efficient light control for production of two campanula speciesSci. Hort.129825831

  • KorczynskiP.C.LoganJ.FaustJ.E.2002Mapping monthly distribution of daily light integrals across the contiguous United StatesHortTechnology121216

    • Search Google Scholar
    • Export Citation
  • LiuW.2012Light environment management for artificial protected horticultureAgrotechnology1 doi: 10.4172/2168-9881.1000101

  • MorrowR.C.2008LED lighting in horticultureHortScience4319471950

  • NelsonJ.A.BugbeeB.2014Economic analysis of greenhouse lighting: Light emitting diodes vs. high intensity discharge fixturesPLoS One9e99010

    • Search Google Scholar
    • Export Citation
  • NelsonP.V.2003Greenhouse operation and management. 6th ed. Prentice Hall Upper Saddle River NJ

  • NemaliK.S.van IerselM.W.2004Acclimation of wax begonia to light intensity: Changes in photosynthesis, respiration, and chlorophyll concentrationJ. Amer. Soc. Hort. Sci.129745751

    • Search Google Scholar
    • Export Citation
  • OuzounisT.RosenqvistE.OttosenC.-O.2015Spectral effects of artificial light on plant physiology and secondary metabolism: A reviewHortScience5011281135

    • Search Google Scholar
    • Export Citation
  • PimputkarS.SpeckJ.S.DenBaarsS.P.NakamuraS.2009Prospects for LED lightingNat. Photonics3180182

  • PLOS ONE2016New LED fixtures from Philips with efficacies of 1.9 to 2.46 micromol per joule. 9 Sept. 2016. <http://journals.plos.org/plosone/article/comment?id=info%3Adoi/10.1371/annotation/a162bf97-4868-40b9-86c0-f390c2aac055>.

  • StutteG.W.2015Commercial transition to LEDs: A pathway to high-value productsHortScience5012971300

  • TennessenD.J.BulaR.J.SharkeyT.D.1995Efficiency of photosynthesis in continuous and pulsed light emitting diode irradiationPhotosynth. Res.44261269

    • Search Google Scholar
    • Export Citation
  • U.S. Department of Agriculture National Agricultural Statistics Service20142012 Census of agriculture. United States summary and state data

  • Utah State University2016NCERA-101 Instrument package. 9 Sept. 2016. <https://cpl.usu.edu/htm/ncera-101-package>.

  • van IerselM.W.ChappellM.Lea-CoxJ.D.2013Sensors for improved efficiency of irrigation in greenhouse and nursery productionHortTechnology23723735

    • Search Google Scholar
    • Export Citation
  • VoxG.TeitelM.PardossiA.MinutoA.TinivellaF.SchettiniE.2010Sustainable greenhouse systems p. 1–80. In: A. Salazar and I. Rios (eds.). Sustainable agriculture: Technology planning and management. Nova NY

  • WallaceC.BothA.J.2016Evaluating operating characteristics of light sources for horticultural applicationsActa Hort.1134435444

  • WoodsM.WarrenA.S.1988Glass houses: A history of greenhouses orangeries and conservatories. Rizzoli NY

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