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On the Technical Performance Characteristics of Horticultural Lamps

On the Technical Performance Characteristics of Horticultural Lamps Article On the Technical Performance Characteristics of Horticultural Lamps 1 2, Timothy J. Shelford and Arend-Jan Both * School of Integrative Plant Science, Horticulture Section, Cornell University, Ithaca, NY 14853, USA; tjs47@cornell.edu Department of Environmental Sciences, Rutgers University, New Brunswick, NJ 08901, USA * Correspondence: both@sebs.rutgers.edu Abstract: Recent advances in light emitting diode (LED) technology have provided exciting oppor- tunities for plant lighting applications, and it is expected that LED lighting will soon overtake the still common use of high-intensity discharge (HID) lighting technology. Because LED lighting offers novel capabilities, extensive research is needed to identify optimal lighting practices for the large number of crops grown by commercial greenhouse growers. Plant scientists and growers facing decisions about plant lighting systems do not always have sufficient information about lamp per- formance characteristics. In this paper, we reported on various technical performance characteristics for 18 lamp types commonly used for plant production, and compared these characteristics with the characteristics of sunlight. The results showed a substantial range of performance characteristics, highlighting the importance of a careful assessment before selecting a light source for horticultural Citation: Shelford, T.J.; Both, A.-J. applications. The data presented in this paper can be used to assess the suitability of a specific light On the Technical Performance source for a particular horticultural application. Characteristics of Horticultural Lamps. AgriEngineering 2021, 3, Keywords: controlled environment agriculture; crop production; efficacy; extended 716–727. https://doi.org/10.3390/ agriengineering3040046 photosynthetically active radiation; spectrum; supplemental lighting Academic Editors: Francesco Marinello and Lin Wei 1. Introduction Received: 27 June 2021 The rapid improvements in light emitting diode (LED) technology over the last three Accepted: 23 September 2021 decades have resulted in a host of intriguing opportunities for plant lighting applications Published: 28 September 2021 [1,2]. Before that, high-intensity discharge (HID) lighting systems were used as the most practical and cost effective option for commercial growers. As a result, the industry accu- Publisher’s Note: MDPI stays neu- mulated a lot of knowledge about how best to use HID lighting. However, LED technol- tral with regard to jurisdictional claims in published maps and institu- ogy has several advantages, e.g., flexibility in spectral output, higher electric conversion tional affiliations. efficiency, and little radiant heat production. However, since LED fixtures for horticul- tural applications are still more expensive than comparable HID fixtures, the latter, and particularly high-pressure sodium (HPS) fixtures, are still the most dominant light source for plant lighting applications. Nevertheless, the expectation is that the use of LED light- Copyright: © 2021 by the authors. Li- ing systems will overtake the use of HID lighting systems in the near future. censee MDPI, Basel, Switzerland. With the advances in LED technology come new opportunities to investigate plant This article is an open access article responses to a host of lighting conditions that were previously difficult or impossible to distributed under the terms and con- study (e.g., light dimming, diurnal or seasonal changes in light spectrum, placing high- ditions of the Creative Commons At- intensity light sources close to or inside the plant canopy). Not surprisingly, the scientific tribution (CC BY) license (http://crea- community has embraced LED technology and is investigating new ways to elucidate tivecommons.org/licenses/by/4.0/). plant physiological responses (e.g., [3,4]) as well as economic benefits from potentially cheaper production practices (e.g., [5,6]). Promising results have been reported, but it will take some time before optimum lighting strategies have been worked out for the large variety of crops grown in greenhouses and indoor production facilities (e.g., [7,8]). Note AgriEngineering 2021, 3, 716–727. https://doi.org/10.3390/agriengineering3040046 www.mdpi.com/journal/agriengineering AgriEngineering 2021, 3, 716–727 717 that our study focused on the technical performance characteristics of lamps, and did not include any plant production trials. Previous reporting by our research group [9–11] discussed the operating characteris- tics of select plant lighting sources, as well as how best to measure and report key technical metrics of light sources used for horticultural applications. The purpose of this paper was to present performance characteristics of the most commonly used light sources so that their differences in performance characteristics can be used to make better informed deci- sions about the most suitable light source for a particular plant production application. Several of the light sources evaluated as part of this study are no longer manufac- tured (e.g., Illumitex and Lumigrow), or the specific models evaluated have been replaced by updated or new models. This issue is an important consideration for growers evaluat- ing and selecting lighting systems and illustrates the importance of having meaningful technical data that can be used for comparisons. Instead of providing data on the latest light sources, the focus of this study was to provide performance metrics for the purpose of comparisons. Our laboratory is not a certified testing facility, nor does it have the ca- pacity to test every lamp available in the market place. Instead, our test results attempted to fill knowledge gaps that may exist with end users of horticultural lighting technologies. 2. Materials and Methods 2.1. Light Sources A variety of electric light sources commonly used for horticultural applications were evaluated. These sources included nine different LED lamps, three fluorescent lamps, three HPS lamps, a low-pressure sodium (LPS) lamp, a metal halide (MH) lamp, and a ceramic MH lamp (Table 1). While rarely used for horticultural applications, the LPS lamp was included because it has one of the highest luminous efficacy (lumen/W) values (based on lamp bulb wattage, not on fixture wattage that includes the power draw by the ballast), and has occasionally been reported on in the scientific literature when the performance of different lamp types was discussed (e.g., [12]). In addition to these electric sources, data describing sunlight were included for comparison. A scan of solar radiation was per- formed on a clear day close to the summer solstice at around solar noon (June 25, 2015 in New Brunswick, NJ, USA). 2.2. Measurement Equipment Light measurements were conducted in a 2-m diameter integrating sphere (Model LMS-760, Labsphere, North Sutton, NH, USA) connected to a spectroradiometer (Model CDS 2100, Labsphere, North Sutton, NH, USA) with a fiber-optic cable. The electric power used to operate the lamps or fixtures was conditioned using a programmable alternating current (AC) power source (Model 6460, Chroma, Foothill Ranch, CA, USA) and meas- ured with a digital power meter (Model 66202, Chroma, Foothill Ranch, CA, USA). The electric power measured represents the “wall plug” or total power used by the lamp or fixture and includes any power drawn by a ballast, driver, or cooling fan. Additional light measurements were conducted in a 3 by 4 m darkroom equipped with a spectroradiometer (Model PS-300, Apogee Instruments, Logan, UT, USA). The ver- tical distance between the bottom of the lamp bulb (or transparent cover in the case of some LED fixtures) and the sensor head was maintained at 61 cm. All measurements re- ported in this paper were measured directly below the center of the lamp bulb(s) or fix- ture. 2.3. Environmental Conditions All lamp testing was performed at temperatures ranging between 20 and 25 °C, and relative humidity conditions ranging between 30% and 50%. The temperature inside the integrating sphere was maintained by closing the integrating sphere for only a short pe- riod of time (less than 20 s) during data collection. Immediately after data collection, the AgriEngineering 2021, 3, 716–727 718 integrating sphere was opened again, allowing the inside temperature to return to labor- atory conditions. 2.4. Calibration All measurement equipment was calibrated according to manufacturer specifications and recommended frequency. When recommended, equipment was returned periodically to the manufacturer for recalibration. 2.5. Definitions and Calculations Photosynthetically active radiation (PAR) was measured across the 400–700 nm waveband, while giving equal weight to each of the photons across that waveband. An equivalent measurement is the photosynthetic photon flux density (PPFD). Both have the units µmol/(m s). The photosynthetic photon flux (PPF) covers the same waveband, but has units of µmol/s [13]. The extended photosynthetically active radiation (ePAR) waveband was proposed by [14,15] and covers the 400–750 nm waveband. Note that a similar acronym (EPAR) was proposed by [16], who used the 290–850 nm waveband to define the term extended PAR. Using the concept of ePAR, the extended photosynthetic photon flux (ePPF) can be used to calculate the extended efficacy (ePPF divided by the electric power consumption) for a light source. The yield photon flux (YPF) was calculated according to the definition used by [17]. It covers the 360 to 760 nm waveband and weighs each photon according to the relative quantum efficiency curve [18,19]. The phytochrome photoequilibrium (PPE) was calculated according to the method described in [19], and covers the 300 to 800 nm waveband. An equivalent term for this parameter is the phytochrome photostationary state (PSS). The calculation involves the spectral composition of light before it interacts with plant tissue. Note that [20] proposed to modify the calculation of the PPE so as to account for spectral distortions that occur as light interacts with leaf tissue. The far-red (FR) fraction was calculated using an equation proposed by [21]: FR frac- tion = FR/(R + FR), with FR defined as the photon flux across the 730 ± 10 nm waveband, and red (R) as the photon flux across the 655 ± 10 nm waveband. 3. Results Figures 1 and 2 show the normalized spectral output across the 300–800 nm wave- band for the various lamps evaluated. Figure 3 shows the normalized spectral output across the 300–800 nm waveband for sunlight. The normalization was carried out by di- viding all the spectral output values by the largest spectral output value across the 300– 800 nm waveband. In Table 1, the various light sources evaluated are identified. Table 2 through 5 show the measurement values from the tests performed in the integrating sphere and the darkroom, as well as the measurement results from the solar scan. AgriEngineering 2021, 3, 716–727 719 Figure 1. Normalized spectral output across the 300–800 nm waveband for nine different light sources. Original data measured as photon flux density with a spectroradiometer (Model PS-300, Apogee Instruments, Logan, UT, USA) in the units µmol/(m s) per nm. Horizontal axes: wavelength in nm, vertical axes: normalized spectral output (unitless). AgriEngineering 2021, 3, 716–727 720 Figure 2. Normalized spectral output across the 300–800 nm waveband for nine different LED fixtures. Original data measured as photon flux density with a spectroradiometer (Model PS-300, Apogee Instruments, Logan, UT, USA) in the units µmol/(m s) per nm. Horizontal axes: wavelength in nm, vertical axes: normalized spectral output (unitless). AgriEngineering 2021, 3, 716–727 721 1.0 0.8 0.6 0.4 0.2 0.0 300 400 500 600 700 800 Wavelength (nm) Figure 3. Normalized photon flux for solar radiation measured on a clear day near the summer solstice and around solar noon (25 June 2015 in New Brunswick, NJ, USA). Original data measured as photon flux density with a spectroradiometer (Model PS-300, Apogee Instruments, Logan, UT, USA) in the units µmol/(m s) per nm. Total photosynthetically active radiation (400–700 nm): 1894 µmol/(m s). Table 1. Light sources evaluated. No. Manufacturer and Model Type Code GE Warm White 3000 K (electronic ballast, in- 1 Fluorescent, bare twin tubes, F32T8 FWW stant start) GE Cool White 4100 K (electronic ballast, in- Fluorescent, bare twin tubes, F32T8 FCW stant start) GE Daylight 6500 K (electronic ballast, instant 3 Fluorescent, bare twin tubes, F32T8 FDL start) Osram SOX (magnetic ballast) LPS (90 W, bare bayonet bulb, horizontal) LPS 5 Sun Systems LEC 315 (Ceramic Metal Halide) CMH (315 W, mogul Elite Agro bulb, vertical) CMH MH (400 W, bare mogul GLBULBM400 bulb, hori- 6 iPower (electronic ballast) MH zontal) Gavita Pro 600e SE (electronic ballast) HPS (600 W, mogul bulb, horizontal) HPS-600 8 Gavita Pro 750e DE (electronic ballast) HPS (750 W, double ended bulb, horizontal) HPS-750 HPS (1000 W, double ended Agrosun bulb, hori- 9 PARSource (electronic ballast) HPS-1000 zontal) 10 Fluence VYPR X Plus LED (passively cooled, white) LED-PCW1 11 GE Arize Element L1000 LED (passively cooled, magenta) LED-PCM Philips GreenPower LED Toplight LED (passively cooled, magenta, low blue) LED-PCMLB 13 Valoya Model R150 NS1 LED (passively cooled, white) LED-PCW2 LED (fan cooled; operated at 100% red, 100% blue, LED- 14 Heliospectra LX602 G and 100% white output) FCRBW1 Illumitex PowerHarvest 10 Series Wide LED (fan cooled; F1 Spectrum) LED-FCM1 LED (fan cooled; operated at 100% red, 100% blue, LED- 16 Lumigrow Pro 650e and 100% white output) FCRBW2 Normalized photon flux (-) AgriEngineering 2021, 3, 716–727 722 17 Osram Zelion HL300 Grow Light LED (fan cooled, magenta) LED-FCM2 LED (water cooled, magenta, operated with a wa- Lemnis Oreon Grow Light 2.1 LED-WCM ter flow rate of 7.6 Lpm) Sunlight Solar noon, near summer solstice SUN Table 2. Measurement results from tests conducted in the integrating sphere. CCT = Correlated color temperature, CRI = Color rendering index, Ra = International standard for color rendering index (unitless), PPF = Photosynthetic photon flux. PPF Lumi- Radiant Volt Current Power Power CCT CRI (µmol/s) No. Code nous Flux Watt (400– (VAC) (Amp) (Electric Watt) Factor (-) (K) (Ra) (400–700 (lm) 700 nm) nm) 1 FWW 120.0 0.8 56.7 0.58 4182 2980 85 11.3 53.0 FCW 120.0 0.8 55.9 0.58 4039 3975 82 11.3 51.6 3 FDL 120.0 0.8 56.2 0.58 3930 6462 83 12.4 54.5 4 LPS 120.0 1.3 154.3 0.98 12,238 1785 −43 23.5 115.9 CMH 277.0 1.2 339.4 0.99 29,508 2965 91 110.6 535.0 6 MH 120.0 3.7 441.8 1.00 28,990 5713 69 91.2 402.2 7 HPS-600 120.0 5.3 635.8 1.00 72,097 1922 36 193.6 968.8 HPS-750 208.1 4.3 888.5 0.99 95,598 2027 50 277.4 1395.4 9 HPS-1000 120.0 9.0 1076.7 1.00 121,425 1965 41 341.9 1714.1 10 LED-PCW1 120.0 4.3 513.8 0.99 64,773 5464 91 224.7 1036.0 LED-PCM 119.9 5.2 617.3 1.00 16,328 1000 −44 307.6 1635.2 12 LED-PCMLB 208.0 1.0 215.7 1.00 4906 1064 −83 98.3 515.9 13 LED-PCW2 120.0 1.1 133.3 1.00 12,480 4949 80 41.0 191.4 LED-FCRBW1 120.0 5.3 622.9 0.99 19,060 22,000 −6 152.7 749.0 15 LED-FCM1 120.0 4.3 510.4 1.00 8429 22,000 −282 175.7 873.7 16 LED-FCRBW2 120.0 4.8 566.3 0.99 10,660 22,000 −72 153.2 764.3 LED-FCM2 120.0 3.2 381.0 0.99 9016 1184 −3 135.4 704.5 18 LED-WCM 120.0 5.2 617.8 0.99 15,284 1000 −20 241.6 1282.3 SUN - - - - - 6500 100 - - 4. Discussion For this study, we evaluated single lamps or fixtures as the representative of a par- ticular lamp type. We did not inform the manufacturers we were performing our tests, so we have no reason to believe that the specific lamps or fixtures we tested were selected for atypical performance. Nevertheless, it is not possible to draw conclusions about the typical performance of the lamps or fixtures we tested. The purpose of our tests was not to call out specific manufacturers about their products, but rather show the range of per- formance characteristics among light sources commonly used for horticultural applica- tions. Additionally, since LED technology is developing rapidly, it is likely that the infor- mation on LED lamps presented here will be outdated in a few years. The spectral output of the various lamps we evaluated were measured with spectro- radiometers with calibrated detection ranges of approximately 300–1000 nm. As a result, little infrared (heat) radiation was detected. It is well known that some lamps (e.g., HID lamps) produce substantial amounts of infrared radiation, and this can be an important consideration when deciding on which lighting system is most appropriate for a particu- lar installation. An approximation for the amount of infrared radiation produced by each lamp is the difference between the electric power consumed by the lamp and the radiant AgriEngineering 2021, 3, 716–727 723 energy delivered (Table 2), but such an approximation neglects any passive or forced con- vective heat losses. However, any amount of radiant or convective energy produced by a lamp will eventually be converted into heat (first law of thermodynamics). The scientific literature contains little information about the independent testing of a variety of lamp types used for horticultural applications. An exception is the report pub- lished by [22], who conducted an electrical and photometric evaluation of ten LED lamps, two HPS lamps, and one MH lamp. However, [22] contains only partial information about the spectral distribution across the 280–800 nm waveband. The electrical metrics reported in Table 2 (volt, current, power, and power factor) can be used to assess the power requirements and performance characteristics of specific lamp types. Lamps operated with electronic ballasts (fluorescent, and HID lamps) or drivers (LED lamps) often can be operated at several different supply voltages. The higher the voltage used, the lower the current draw and this feature can be used to save on installa- tion costs because smaller diameter wires can be used when the current draw is lower. The power factor indicates how much of the supplied power is used to do useful work. A value of 1 indicates that 100% of the supplied power performs useful work (i.e., operates the lamp), while lower numbers indicate that some percentage of the supplied power is lost (i.e., does not perform useful work). Table 2 also reports on three performance characteristics that describe some of the visual aspects of light (lumen output, correlated color temperature, and color rendering index). These characteristics are not particularly useful for horticultural applications, but do allow for comparisons with light sources that are used for human vision applications (e.g., residential and commercial lighting). In addition, the color rendering index provides some insight into how easy it is to observe leaf color when the leaves are lit with a partic- ular light source. This can be important when growers want to observe discolorations due to plant nutritional issues or damage due to insects or plant diseases. Table 3 shows the lamp efficacy values that were calculated from the measurements performed in the integrating sphere. Efficacy data is one of the key performance metrics that are used to evaluate lamp performance. The numbers we report are not always as high as those reported by the manufacturers. There could be several reasons for this, but since our sample size was only one, it is not possible to determine which number is correct. Nevertheless, since our tests were performed using the same procedures and equipment, the relative differences among the various lamp types can be used for comparisons. Table 3 also reports on performance characteristics that involve visible light. As men- tioned before, assessing visible light for horticultural applications is not very useful, but the performance characteristics involving visible light that are included in Table 3 can be used to compare our measurements with those reported in the literature (e.g., [12]). Table 4 reports on several additional light parameters that are used by plant scientists to further qualify the light environment for plant production. These parameters include the yield photon flux (YPF), the ratio of the YPF and the photosynthetic photon flux (PPF), the phytochrome photoequilibrium (PPE), and three different ways to assess the amount of far-red that is present in the produced light spectrum. In each of these three different approaches, the definition (i.e., its waveband) of far-red light is different. Other definitions of far-red light have also been used, but the point here is to show that these different def- initions can lead to quite different calculation results. It is common for researchers to identify the blue, green, and red wavebands by the 400–500 nm, 500–600 nm, and 600–700 nm ranges, respectively. However, this practice double-counts the radiation output at 500 and 600 nm. Therefore, we used non-overlap- ping wavebands to report the radiation output across the various wavelength ranges (Ta- ble 5). As this paper demonstrated, careful measurement of lamp characteristics is neces- sary so that sufficient information can be reported. Only reports with sufficient infor- mation will enable the repeatability of plant lighting research. Detailed reports will also help commercial growers make more informed decisions about plant lighting options. The AgriEngineering 2021, 3, 716–727 724 range of performance characteristics disclosed in this paper highlight the importance of lamp selection for a particular horticultural application. In a perfect world, performance characteristics would be made available by lamp manufacturers, but that is not always the case, or the information is incomplete. Researchers and growers are encouraged to ask manufacturers for detailed information about the lighting products they are considering. Table 3. Values derived from the measurements conducted in the integrating sphere. Values for sunlight in italics from [23], and in bold from [12]. PPF = Photosynthetic photon flux (400–700 nm), ePPF = Extended photosynthetic photon flux (400–750 nm), Wr = radiant Watt, We = electric Watt. PPF per Radi- Luminous Ef- PPF ePPF Lux per ant Watt No. Code Efficacy Efficacy ficacy µmol/(m s) (µmol/s per (µmol/J) (µmol/J) (lm/We) of PAR Wr) FWW 0.94 0.96 4.71 73.8 78.9 2 FCW 0.92 0.94 4.59 72.2 78.3 3 FDL 0.97 0.97 4.41 69.9 72.1 LPS 0.75 0.76 4.92 79.3 105.6 5 CMH 1.58 1.70 4.84 86.9 55.2 6 MH 0.91 0.93 4.41 65.6 72.1 HPS-600 1.52 1.62 5.00 113.4 74.4 8 HPS-750 1.57 1.71 5.03 107.6 68.5 9 HPS-1000 1.59 1.71 5.01 112.8 70.8 LED-PCW1 2.02 2.09 4.61 126.1 62.5 11 LED-PCM 2.65 2.65 5.32 26.5 10.0 12 LED-PCMLB 2.39 2.40 5.25 22.7 9.5 LED-PCW2 1.44 1.50 4.67 93.7 65.2 14 LED-FCRBW1 1.20 1.21 4.90 30.6 25.4 15 LED-FCM1 1.71 1.72 4.97 16.5 9.6 LED-FCRBW2 1.35 1.36 4.99 18.8 13.9 17 LED-FCM2 1.85 1.85 5.20 23.7 12.8 18 LED-WCM 2.08 2.08 5.31 24.7 11.9 SUN 2.08 - 4.57 107 * 54 * Unit: lm/Wr. Table 4. Values derived from measurements conducted in the dark room with a spectroradiometer (Model PS-300, Apogee Instruments, Logan, UT, USA), except for the values for sunlight which were obtained from an outdoor spectral scan using the same spectroradiometer. YPF = Yield photon flux, PPF = Photosynthetic photon flux, PPE = Phytochrome photoequi- librium. YPF/PPF (300– R:FR wide (600– R:FR Narrow (655– YPF (300– 800)/ (400–700) PPE (300– 699)/(700–800) 665)/(725–735) [Wave- No. Code FR Fraction 800 nm) [Wave-Lengths 800 nm) [Wave-Lengths Lengths in nm] in nm] in nm] 1 FWW 18.0 0.92 0.85 8.4 5.3 0.14 FCW 17.3 0.89 0.84 9.5 5.8 0.13 3 FDL 17.0 0.85 0.82 10.1 6.4 0.12 4 LPS 14.5 0.98 0.84 1.0 1.3 0.45 CMH 542.9 0.91 0.82 3.7 2.4 0.26 6 MH 47.1 0.90 0.82 2.7 1.6 0.37 AgriEngineering 2021, 3, 716–727 725 7 HPS-600 439.6 0.96 0.85 5.3 3.0 0.23 HPS-750 706.0 0.95 0.83 4.2 2.8 0.25 9 HPS-1000 967.3 0.95 0.83 4.0 2.8 0.25 10 LED-PCW1 514.9 0.87 0.85 13.4 12.6 0.08 LED-PCM 1215.4 0.92 0.88 14,019 ∞ 0.00 12 LED-PCMLB 284.9 0.90 0.87 45.8 109.6 0.01 13 LED-PCW2 161.2 0.88 0.83 6.3 7.2 0.14 LED-FCRBW1 575.2 0.88 0.87 38.1 111.3 0.01 15 LED-FCM1 1703.5 0.88 0.87 74.9 265.4 0.01 16 LED-FCRBW2 396.0 0.87 0.86 29.4 69.9 0.02 LED-FCM2 336.3 0.91 0.88 66.3 226.3 0.01 18 LED-WCM 152.6 0.92 0.88 90.1 299.3 0.00 SUN 1696.1 0.90 0.72 1.1 1.1 0.47 Table 5. Light distribution ratios as a percentage of the photon flux density across the 280–800 nm waveband as measured with a spectroradiometer (Model PS-300, Apogee Instruments, Logan, UT, USA). The values were calculated from meas- urements conducted in the dark room, except for the values for sunlight which were obtained from an outdoor spectral scan. UV = Ultraviolet, PAR = Photosynthetically active radiation, ePAR = Extended photosynthetically active radiation. Photon Flux UV-A Green Red Far-red PAR ePAR Density UV-B (280–314 Blue (400– No. Code (315–399 (500–599 (600– (700–800 (400–700 (400–750 µmol/(m s) nm) 499 nm) nm) nm) 699 nm) nm) nm) nm) (280–800 nm) FWW 20.9 0.2% 1.6% 15.3% 38.5% 40.0% 4.4% 93.8% 97.8% 2 FCW 20.5 0.2% 1.4% 22.2% 41.2% 31.7% 3.3% 95.1% 98.1% 3 FDL 20.6 0.1% 0.6% 33.0% 41.5% 22.5% 2.2% 97.1% 99.0% LPS 17.5 0.4% 1.7% 2.0% 68.8% 13.8% 13.3% 84.6% 87.1% 5 CMH 690.8 0.03% 1.1% 13.1% 28.4% 45.2% 12.2% 86.8% 93.7% 6 MH 64.5 0.05% 2.0% 22.7% 48.2% 19.7% 7.3% 90.7% 93.8% HPS-600 506.8 0.04% 0.4% 3.2% 40.4% 47.0% 8.9% 90.7% 96.1% 8 HPS-750 847.6 0.01% 0.2% 3.4% 32.7% 51.3% 12.4% 87.5% 94.9% 9 HPS-1000 1167.3 0.04% 0.3% 3.6% 32.1% 51.2% 12.7% 87.0% 94.2% LED- 611.0 0.03% 0.2% 23.8% 38.4% 35.0% 2.6% 97.2% 99.3% PCW1 11 LED- PCM 1327.2 0.00% 0.00% 6.0% 0.0% 94.0% 0.0% 100% 100% LED- 324.3 0.02% 0.1% 5.3% 0.4% 92.2% 2.0% 98.0% 99.6% PCMLB LED- 13 195.4 0.04% 0.3% 18.0% 39.9% 36.0% 5.7% 94.0% 98.3% PCW2 LED- 14 666.1 0.04% 0.2% 23.2% 13.1% 61.9% 1.6% 98.2% 99.4% FCRBW1 LED- 15 1951.4 0.03% 0.2% 24.7% 0.5% 73.6% 1.0% 98.8% 99.6% FCM1 LED- 16 464.9 0.05% 0.2% 26.1% 5.8% 65.7% 2.2% 97.6% 99.3% FCRBW2 LED- 17 375.1 0.00% 0.1% 12.0% 2.7% 84.0% 1.3% 98.7% 99.6% FCM2 18 LED-WCM 167.3 0.01% 0.1% 8.0% 0.5% 90.4% 1.0% 98.9% 99.7% SUN 2658.4 0.1% 5.5% 20.4% 25.2% 25.5% 23.2% 71.2% 83.1% AgriEngineering 2021, 3, 716–727 726 5. Conclusions • Every light source tested had unique performance characteristics, including their spectral outputs. • The PPF efficacy of a light source is but one performance characteristic that should be considered. • A spectroradiometer is needed in order to assess the spectral output of a light source. • Changing the definition of PAR will make it more difficult to compare published results that used the current definition for PAR (400–700 nm) with results published based on the extended definition for PAR (ePAR, 400–750 nm). • The sooner the scientific community can agree on definitions that describe key per- formance characteristics (e.g., waveband ranges, photosynthetically active radiation), the less confusion there will be when these performance characteristics are used to make plant lighting decisions. • Due to the rapidly improving LED technology, it is critically important to have a consistent system for measuring and reporting lamp characteristics. • Due to the challenges involved, commercial growers are encouraged to experiment with new light sources on a small growing area, before deciding to scale up to large production areas. Author Contributions: Conceptualization, A.-J.B.; methodology, T.J.S. and A.-J.B.; data collection and analysis, T.J.S. and A.-J.B.; data curation, T.J.S. and A.-J.B.; writing—original draft preparation, A.-J.B.; writing—review and editing, T.J.S. and A.-J.B.; visualization, A.-J.B.; supervision, A.-J.B.; project administration, A.-J.B.; funding acquisition, A.-J.B. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the New York State Energy Research and Development Au- thority (Greenhouse Lighting and Systems Engineering–GLASE–project) and the New Jersey Agri- cultural Experiment Station. Data Availability Statement: Original measurement data available on request from the authors. Acknowledgments: The authors gratefully acknowledge the help they received from Claude Wal- lace who conducted several of the lamp evaluation tests. Conflicts of Interest: The authors declare no conflict of interest. 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Economic analysis of greenhouse lighting: Light emitting diodes vs. high intensity discharge fixtures. PLoS ONE 2014, 9, e99010, https://doi.org/10.1371/journal.pone.0099010. 6. Katzin, D.; Marcelis, L.F.M.; van Mourik, S. Energy savings in greenhouses by transition from high-pressure sodium to LED lighting. Appl. Energy 2021, 281, 116019, https://doi.org/10.1016/j.apenergy.2020.116019. 7. Lopez, R.; Runkle, E.S. (Eds.) Light Management in Controlled Environments; Meister Media: Willoughby, OH, USA, 2017; 180p. 8. Mickens, M.A.; Skoog, E.J.; Reese, L.E.; Barnwell, P.L.; Spencer, L.E.; Massa, G.D.; Wheeler, R.M. A strategic approach for in- vestigating light recipes for ‘Outredgeous’ red romaine lettuce using white and monochromatic LEDs. Life Sci. Space Res. 2018, 19, 53–62. 9. Wallace, C.; Both, A.J. Evaluating operating characteristics of light sources for horticultural applications. Acta Hortic. 2016, 1134, 435–444. 10. Both, A.J.; Bugbee, B.; Kubota, C.; Lopez, R.G.; Mitchell, C.; Runkle, E.S.; Wallace, C. Proposed product label for electric lamps used in the plant sciences. Hort. Technol. 2017, 27, 544–549. AgriEngineering 2021, 3, 716–727 727 11. Shelford, T.; Wallace, C.; Both, A.J. Calculating and reporting key light ratios for plant research. Acta Hortic. 2020, 1296, 559–566. 12. Thimijan, R.W.; Heins, R.D. Photometric, radiometric, and quantum light units of measure: A review of procedures for inter- conversion. HortScience 1983, 18, 818–822. 13. ANSI/ASABE Standard S640. Quantities and Units of Electromagnetic Radiation for Plants (Photosynthetic Organisms); American Society for Agricultural and Biological Engineers: St. Joseph, MI, USA, 2017. 14. Zhen, S.; Bugbee, B. Far-red photons have equivalent efficiency to traditional photosynthetic photons: Implications for redefin- ing photosynthetically active radiation. Plant Cell Environ. 2020, 43, 1259–1272. 15. Zhen, S.; van Iersel, M.; Bugbee, B. Why far-red photons should be included in the definition of photosynthetic photons and the measurement of horticultural fixture efficacy. Front. Plant Sci. 2021, 12, 693445, doi:10.3389/fpls.2021.693445. 16. Pazuki, A.; Aflaki, F.; Pessarakli, M.; Gurel, E.; Gurel, S. Plant responses to extended photosynthetically active radiation (EPAR). Adv. Plants Agric. Res. 2017, 7, 00260. 17. Barnes, C.; Tibbitts, T.; Sager, J.; Deitzer, G.; Bubenheim, D.; Koener, G.; Bugbee, B. Accuracy of quantum sensors measuring yield photon flux and photosynthetic photon flux. HortScience 1993, 28, 1197–1200. 18. McCree, K.J. The action spectrum, absorptance and quantum yield of photosynthesis in crop plants. Agric. Meteorol. 1972, 9, 191–216. 19. Sager, J.C.; Smith, W.O.; Edwards, J.L.; Cyr, K.L. Photosynthetic efficiency and phytochrome photoequilibria determination using spectral data. Transact. ASAE 1988, 31, 1882–1889. 20. Kusuma, P.; Bugbee, B. Improving the predictive value of phytochrome photoequilibrium: Consideration of spectral distortion within a leaf. Front. Plant Sci. 2021, 12, 596943, doi:10.3389/fpls.2021.596943. 21. Kusuma, P.; Bugbee, B. Far-red fraction: An improved metric for characterizing phytochrome effects on morphology. J. Am. Soc. Hortic. Sci. 2021, 146, 3–13. 22. Radetsky, L.C. LED and HID Horticultural Luminaire Testing Report; Lighting Research Center, Rensselaer Polytechnic Institute: Troy, NY, USA, 2018; 80p. 23. Ting, K.C.; Giacomelli, G.A. Availability of solar photosynthetically active radiation. Transact. ASAE 1987, 30, 1453–1457. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png AgriEngineering Multidisciplinary Digital Publishing Institute

On the Technical Performance Characteristics of Horticultural Lamps

AgriEngineering , Volume 3 (4) – Sep 28, 2021

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Article On the Technical Performance Characteristics of Horticultural Lamps 1 2, Timothy J. Shelford and Arend-Jan Both * School of Integrative Plant Science, Horticulture Section, Cornell University, Ithaca, NY 14853, USA; tjs47@cornell.edu Department of Environmental Sciences, Rutgers University, New Brunswick, NJ 08901, USA * Correspondence: both@sebs.rutgers.edu Abstract: Recent advances in light emitting diode (LED) technology have provided exciting oppor- tunities for plant lighting applications, and it is expected that LED lighting will soon overtake the still common use of high-intensity discharge (HID) lighting technology. Because LED lighting offers novel capabilities, extensive research is needed to identify optimal lighting practices for the large number of crops grown by commercial greenhouse growers. Plant scientists and growers facing decisions about plant lighting systems do not always have sufficient information about lamp per- formance characteristics. In this paper, we reported on various technical performance characteristics for 18 lamp types commonly used for plant production, and compared these characteristics with the characteristics of sunlight. The results showed a substantial range of performance characteristics, highlighting the importance of a careful assessment before selecting a light source for horticultural Citation: Shelford, T.J.; Both, A.-J. applications. The data presented in this paper can be used to assess the suitability of a specific light On the Technical Performance source for a particular horticultural application. Characteristics of Horticultural Lamps. AgriEngineering 2021, 3, Keywords: controlled environment agriculture; crop production; efficacy; extended 716–727. https://doi.org/10.3390/ agriengineering3040046 photosynthetically active radiation; spectrum; supplemental lighting Academic Editors: Francesco Marinello and Lin Wei 1. Introduction Received: 27 June 2021 The rapid improvements in light emitting diode (LED) technology over the last three Accepted: 23 September 2021 decades have resulted in a host of intriguing opportunities for plant lighting applications Published: 28 September 2021 [1,2]. Before that, high-intensity discharge (HID) lighting systems were used as the most practical and cost effective option for commercial growers. As a result, the industry accu- Publisher’s Note: MDPI stays neu- mulated a lot of knowledge about how best to use HID lighting. However, LED technol- tral with regard to jurisdictional claims in published maps and institu- ogy has several advantages, e.g., flexibility in spectral output, higher electric conversion tional affiliations. efficiency, and little radiant heat production. However, since LED fixtures for horticul- tural applications are still more expensive than comparable HID fixtures, the latter, and particularly high-pressure sodium (HPS) fixtures, are still the most dominant light source for plant lighting applications. Nevertheless, the expectation is that the use of LED light- Copyright: © 2021 by the authors. Li- ing systems will overtake the use of HID lighting systems in the near future. censee MDPI, Basel, Switzerland. With the advances in LED technology come new opportunities to investigate plant This article is an open access article responses to a host of lighting conditions that were previously difficult or impossible to distributed under the terms and con- study (e.g., light dimming, diurnal or seasonal changes in light spectrum, placing high- ditions of the Creative Commons At- intensity light sources close to or inside the plant canopy). Not surprisingly, the scientific tribution (CC BY) license (http://crea- community has embraced LED technology and is investigating new ways to elucidate tivecommons.org/licenses/by/4.0/). plant physiological responses (e.g., [3,4]) as well as economic benefits from potentially cheaper production practices (e.g., [5,6]). Promising results have been reported, but it will take some time before optimum lighting strategies have been worked out for the large variety of crops grown in greenhouses and indoor production facilities (e.g., [7,8]). Note AgriEngineering 2021, 3, 716–727. https://doi.org/10.3390/agriengineering3040046 www.mdpi.com/journal/agriengineering AgriEngineering 2021, 3, 716–727 717 that our study focused on the technical performance characteristics of lamps, and did not include any plant production trials. Previous reporting by our research group [9–11] discussed the operating characteris- tics of select plant lighting sources, as well as how best to measure and report key technical metrics of light sources used for horticultural applications. The purpose of this paper was to present performance characteristics of the most commonly used light sources so that their differences in performance characteristics can be used to make better informed deci- sions about the most suitable light source for a particular plant production application. Several of the light sources evaluated as part of this study are no longer manufac- tured (e.g., Illumitex and Lumigrow), or the specific models evaluated have been replaced by updated or new models. This issue is an important consideration for growers evaluat- ing and selecting lighting systems and illustrates the importance of having meaningful technical data that can be used for comparisons. Instead of providing data on the latest light sources, the focus of this study was to provide performance metrics for the purpose of comparisons. Our laboratory is not a certified testing facility, nor does it have the ca- pacity to test every lamp available in the market place. Instead, our test results attempted to fill knowledge gaps that may exist with end users of horticultural lighting technologies. 2. Materials and Methods 2.1. Light Sources A variety of electric light sources commonly used for horticultural applications were evaluated. These sources included nine different LED lamps, three fluorescent lamps, three HPS lamps, a low-pressure sodium (LPS) lamp, a metal halide (MH) lamp, and a ceramic MH lamp (Table 1). While rarely used for horticultural applications, the LPS lamp was included because it has one of the highest luminous efficacy (lumen/W) values (based on lamp bulb wattage, not on fixture wattage that includes the power draw by the ballast), and has occasionally been reported on in the scientific literature when the performance of different lamp types was discussed (e.g., [12]). In addition to these electric sources, data describing sunlight were included for comparison. A scan of solar radiation was per- formed on a clear day close to the summer solstice at around solar noon (June 25, 2015 in New Brunswick, NJ, USA). 2.2. Measurement Equipment Light measurements were conducted in a 2-m diameter integrating sphere (Model LMS-760, Labsphere, North Sutton, NH, USA) connected to a spectroradiometer (Model CDS 2100, Labsphere, North Sutton, NH, USA) with a fiber-optic cable. The electric power used to operate the lamps or fixtures was conditioned using a programmable alternating current (AC) power source (Model 6460, Chroma, Foothill Ranch, CA, USA) and meas- ured with a digital power meter (Model 66202, Chroma, Foothill Ranch, CA, USA). The electric power measured represents the “wall plug” or total power used by the lamp or fixture and includes any power drawn by a ballast, driver, or cooling fan. Additional light measurements were conducted in a 3 by 4 m darkroom equipped with a spectroradiometer (Model PS-300, Apogee Instruments, Logan, UT, USA). The ver- tical distance between the bottom of the lamp bulb (or transparent cover in the case of some LED fixtures) and the sensor head was maintained at 61 cm. All measurements re- ported in this paper were measured directly below the center of the lamp bulb(s) or fix- ture. 2.3. Environmental Conditions All lamp testing was performed at temperatures ranging between 20 and 25 °C, and relative humidity conditions ranging between 30% and 50%. The temperature inside the integrating sphere was maintained by closing the integrating sphere for only a short pe- riod of time (less than 20 s) during data collection. Immediately after data collection, the AgriEngineering 2021, 3, 716–727 718 integrating sphere was opened again, allowing the inside temperature to return to labor- atory conditions. 2.4. Calibration All measurement equipment was calibrated according to manufacturer specifications and recommended frequency. When recommended, equipment was returned periodically to the manufacturer for recalibration. 2.5. Definitions and Calculations Photosynthetically active radiation (PAR) was measured across the 400–700 nm waveband, while giving equal weight to each of the photons across that waveband. An equivalent measurement is the photosynthetic photon flux density (PPFD). Both have the units µmol/(m s). The photosynthetic photon flux (PPF) covers the same waveband, but has units of µmol/s [13]. The extended photosynthetically active radiation (ePAR) waveband was proposed by [14,15] and covers the 400–750 nm waveband. Note that a similar acronym (EPAR) was proposed by [16], who used the 290–850 nm waveband to define the term extended PAR. Using the concept of ePAR, the extended photosynthetic photon flux (ePPF) can be used to calculate the extended efficacy (ePPF divided by the electric power consumption) for a light source. The yield photon flux (YPF) was calculated according to the definition used by [17]. It covers the 360 to 760 nm waveband and weighs each photon according to the relative quantum efficiency curve [18,19]. The phytochrome photoequilibrium (PPE) was calculated according to the method described in [19], and covers the 300 to 800 nm waveband. An equivalent term for this parameter is the phytochrome photostationary state (PSS). The calculation involves the spectral composition of light before it interacts with plant tissue. Note that [20] proposed to modify the calculation of the PPE so as to account for spectral distortions that occur as light interacts with leaf tissue. The far-red (FR) fraction was calculated using an equation proposed by [21]: FR frac- tion = FR/(R + FR), with FR defined as the photon flux across the 730 ± 10 nm waveband, and red (R) as the photon flux across the 655 ± 10 nm waveband. 3. Results Figures 1 and 2 show the normalized spectral output across the 300–800 nm wave- band for the various lamps evaluated. Figure 3 shows the normalized spectral output across the 300–800 nm waveband for sunlight. The normalization was carried out by di- viding all the spectral output values by the largest spectral output value across the 300– 800 nm waveband. In Table 1, the various light sources evaluated are identified. Table 2 through 5 show the measurement values from the tests performed in the integrating sphere and the darkroom, as well as the measurement results from the solar scan. AgriEngineering 2021, 3, 716–727 719 Figure 1. Normalized spectral output across the 300–800 nm waveband for nine different light sources. Original data measured as photon flux density with a spectroradiometer (Model PS-300, Apogee Instruments, Logan, UT, USA) in the units µmol/(m s) per nm. Horizontal axes: wavelength in nm, vertical axes: normalized spectral output (unitless). AgriEngineering 2021, 3, 716–727 720 Figure 2. Normalized spectral output across the 300–800 nm waveband for nine different LED fixtures. Original data measured as photon flux density with a spectroradiometer (Model PS-300, Apogee Instruments, Logan, UT, USA) in the units µmol/(m s) per nm. Horizontal axes: wavelength in nm, vertical axes: normalized spectral output (unitless). AgriEngineering 2021, 3, 716–727 721 1.0 0.8 0.6 0.4 0.2 0.0 300 400 500 600 700 800 Wavelength (nm) Figure 3. Normalized photon flux for solar radiation measured on a clear day near the summer solstice and around solar noon (25 June 2015 in New Brunswick, NJ, USA). Original data measured as photon flux density with a spectroradiometer (Model PS-300, Apogee Instruments, Logan, UT, USA) in the units µmol/(m s) per nm. Total photosynthetically active radiation (400–700 nm): 1894 µmol/(m s). Table 1. Light sources evaluated. No. Manufacturer and Model Type Code GE Warm White 3000 K (electronic ballast, in- 1 Fluorescent, bare twin tubes, F32T8 FWW stant start) GE Cool White 4100 K (electronic ballast, in- Fluorescent, bare twin tubes, F32T8 FCW stant start) GE Daylight 6500 K (electronic ballast, instant 3 Fluorescent, bare twin tubes, F32T8 FDL start) Osram SOX (magnetic ballast) LPS (90 W, bare bayonet bulb, horizontal) LPS 5 Sun Systems LEC 315 (Ceramic Metal Halide) CMH (315 W, mogul Elite Agro bulb, vertical) CMH MH (400 W, bare mogul GLBULBM400 bulb, hori- 6 iPower (electronic ballast) MH zontal) Gavita Pro 600e SE (electronic ballast) HPS (600 W, mogul bulb, horizontal) HPS-600 8 Gavita Pro 750e DE (electronic ballast) HPS (750 W, double ended bulb, horizontal) HPS-750 HPS (1000 W, double ended Agrosun bulb, hori- 9 PARSource (electronic ballast) HPS-1000 zontal) 10 Fluence VYPR X Plus LED (passively cooled, white) LED-PCW1 11 GE Arize Element L1000 LED (passively cooled, magenta) LED-PCM Philips GreenPower LED Toplight LED (passively cooled, magenta, low blue) LED-PCMLB 13 Valoya Model R150 NS1 LED (passively cooled, white) LED-PCW2 LED (fan cooled; operated at 100% red, 100% blue, LED- 14 Heliospectra LX602 G and 100% white output) FCRBW1 Illumitex PowerHarvest 10 Series Wide LED (fan cooled; F1 Spectrum) LED-FCM1 LED (fan cooled; operated at 100% red, 100% blue, LED- 16 Lumigrow Pro 650e and 100% white output) FCRBW2 Normalized photon flux (-) AgriEngineering 2021, 3, 716–727 722 17 Osram Zelion HL300 Grow Light LED (fan cooled, magenta) LED-FCM2 LED (water cooled, magenta, operated with a wa- Lemnis Oreon Grow Light 2.1 LED-WCM ter flow rate of 7.6 Lpm) Sunlight Solar noon, near summer solstice SUN Table 2. Measurement results from tests conducted in the integrating sphere. CCT = Correlated color temperature, CRI = Color rendering index, Ra = International standard for color rendering index (unitless), PPF = Photosynthetic photon flux. PPF Lumi- Radiant Volt Current Power Power CCT CRI (µmol/s) No. Code nous Flux Watt (400– (VAC) (Amp) (Electric Watt) Factor (-) (K) (Ra) (400–700 (lm) 700 nm) nm) 1 FWW 120.0 0.8 56.7 0.58 4182 2980 85 11.3 53.0 FCW 120.0 0.8 55.9 0.58 4039 3975 82 11.3 51.6 3 FDL 120.0 0.8 56.2 0.58 3930 6462 83 12.4 54.5 4 LPS 120.0 1.3 154.3 0.98 12,238 1785 −43 23.5 115.9 CMH 277.0 1.2 339.4 0.99 29,508 2965 91 110.6 535.0 6 MH 120.0 3.7 441.8 1.00 28,990 5713 69 91.2 402.2 7 HPS-600 120.0 5.3 635.8 1.00 72,097 1922 36 193.6 968.8 HPS-750 208.1 4.3 888.5 0.99 95,598 2027 50 277.4 1395.4 9 HPS-1000 120.0 9.0 1076.7 1.00 121,425 1965 41 341.9 1714.1 10 LED-PCW1 120.0 4.3 513.8 0.99 64,773 5464 91 224.7 1036.0 LED-PCM 119.9 5.2 617.3 1.00 16,328 1000 −44 307.6 1635.2 12 LED-PCMLB 208.0 1.0 215.7 1.00 4906 1064 −83 98.3 515.9 13 LED-PCW2 120.0 1.1 133.3 1.00 12,480 4949 80 41.0 191.4 LED-FCRBW1 120.0 5.3 622.9 0.99 19,060 22,000 −6 152.7 749.0 15 LED-FCM1 120.0 4.3 510.4 1.00 8429 22,000 −282 175.7 873.7 16 LED-FCRBW2 120.0 4.8 566.3 0.99 10,660 22,000 −72 153.2 764.3 LED-FCM2 120.0 3.2 381.0 0.99 9016 1184 −3 135.4 704.5 18 LED-WCM 120.0 5.2 617.8 0.99 15,284 1000 −20 241.6 1282.3 SUN - - - - - 6500 100 - - 4. Discussion For this study, we evaluated single lamps or fixtures as the representative of a par- ticular lamp type. We did not inform the manufacturers we were performing our tests, so we have no reason to believe that the specific lamps or fixtures we tested were selected for atypical performance. Nevertheless, it is not possible to draw conclusions about the typical performance of the lamps or fixtures we tested. The purpose of our tests was not to call out specific manufacturers about their products, but rather show the range of per- formance characteristics among light sources commonly used for horticultural applica- tions. Additionally, since LED technology is developing rapidly, it is likely that the infor- mation on LED lamps presented here will be outdated in a few years. The spectral output of the various lamps we evaluated were measured with spectro- radiometers with calibrated detection ranges of approximately 300–1000 nm. As a result, little infrared (heat) radiation was detected. It is well known that some lamps (e.g., HID lamps) produce substantial amounts of infrared radiation, and this can be an important consideration when deciding on which lighting system is most appropriate for a particu- lar installation. An approximation for the amount of infrared radiation produced by each lamp is the difference between the electric power consumed by the lamp and the radiant AgriEngineering 2021, 3, 716–727 723 energy delivered (Table 2), but such an approximation neglects any passive or forced con- vective heat losses. However, any amount of radiant or convective energy produced by a lamp will eventually be converted into heat (first law of thermodynamics). The scientific literature contains little information about the independent testing of a variety of lamp types used for horticultural applications. An exception is the report pub- lished by [22], who conducted an electrical and photometric evaluation of ten LED lamps, two HPS lamps, and one MH lamp. However, [22] contains only partial information about the spectral distribution across the 280–800 nm waveband. The electrical metrics reported in Table 2 (volt, current, power, and power factor) can be used to assess the power requirements and performance characteristics of specific lamp types. Lamps operated with electronic ballasts (fluorescent, and HID lamps) or drivers (LED lamps) often can be operated at several different supply voltages. The higher the voltage used, the lower the current draw and this feature can be used to save on installa- tion costs because smaller diameter wires can be used when the current draw is lower. The power factor indicates how much of the supplied power is used to do useful work. A value of 1 indicates that 100% of the supplied power performs useful work (i.e., operates the lamp), while lower numbers indicate that some percentage of the supplied power is lost (i.e., does not perform useful work). Table 2 also reports on three performance characteristics that describe some of the visual aspects of light (lumen output, correlated color temperature, and color rendering index). These characteristics are not particularly useful for horticultural applications, but do allow for comparisons with light sources that are used for human vision applications (e.g., residential and commercial lighting). In addition, the color rendering index provides some insight into how easy it is to observe leaf color when the leaves are lit with a partic- ular light source. This can be important when growers want to observe discolorations due to plant nutritional issues or damage due to insects or plant diseases. Table 3 shows the lamp efficacy values that were calculated from the measurements performed in the integrating sphere. Efficacy data is one of the key performance metrics that are used to evaluate lamp performance. The numbers we report are not always as high as those reported by the manufacturers. There could be several reasons for this, but since our sample size was only one, it is not possible to determine which number is correct. Nevertheless, since our tests were performed using the same procedures and equipment, the relative differences among the various lamp types can be used for comparisons. Table 3 also reports on performance characteristics that involve visible light. As men- tioned before, assessing visible light for horticultural applications is not very useful, but the performance characteristics involving visible light that are included in Table 3 can be used to compare our measurements with those reported in the literature (e.g., [12]). Table 4 reports on several additional light parameters that are used by plant scientists to further qualify the light environment for plant production. These parameters include the yield photon flux (YPF), the ratio of the YPF and the photosynthetic photon flux (PPF), the phytochrome photoequilibrium (PPE), and three different ways to assess the amount of far-red that is present in the produced light spectrum. In each of these three different approaches, the definition (i.e., its waveband) of far-red light is different. Other definitions of far-red light have also been used, but the point here is to show that these different def- initions can lead to quite different calculation results. It is common for researchers to identify the blue, green, and red wavebands by the 400–500 nm, 500–600 nm, and 600–700 nm ranges, respectively. However, this practice double-counts the radiation output at 500 and 600 nm. Therefore, we used non-overlap- ping wavebands to report the radiation output across the various wavelength ranges (Ta- ble 5). As this paper demonstrated, careful measurement of lamp characteristics is neces- sary so that sufficient information can be reported. Only reports with sufficient infor- mation will enable the repeatability of plant lighting research. Detailed reports will also help commercial growers make more informed decisions about plant lighting options. The AgriEngineering 2021, 3, 716–727 724 range of performance characteristics disclosed in this paper highlight the importance of lamp selection for a particular horticultural application. In a perfect world, performance characteristics would be made available by lamp manufacturers, but that is not always the case, or the information is incomplete. Researchers and growers are encouraged to ask manufacturers for detailed information about the lighting products they are considering. Table 3. Values derived from the measurements conducted in the integrating sphere. Values for sunlight in italics from [23], and in bold from [12]. PPF = Photosynthetic photon flux (400–700 nm), ePPF = Extended photosynthetic photon flux (400–750 nm), Wr = radiant Watt, We = electric Watt. PPF per Radi- Luminous Ef- PPF ePPF Lux per ant Watt No. Code Efficacy Efficacy ficacy µmol/(m s) (µmol/s per (µmol/J) (µmol/J) (lm/We) of PAR Wr) FWW 0.94 0.96 4.71 73.8 78.9 2 FCW 0.92 0.94 4.59 72.2 78.3 3 FDL 0.97 0.97 4.41 69.9 72.1 LPS 0.75 0.76 4.92 79.3 105.6 5 CMH 1.58 1.70 4.84 86.9 55.2 6 MH 0.91 0.93 4.41 65.6 72.1 HPS-600 1.52 1.62 5.00 113.4 74.4 8 HPS-750 1.57 1.71 5.03 107.6 68.5 9 HPS-1000 1.59 1.71 5.01 112.8 70.8 LED-PCW1 2.02 2.09 4.61 126.1 62.5 11 LED-PCM 2.65 2.65 5.32 26.5 10.0 12 LED-PCMLB 2.39 2.40 5.25 22.7 9.5 LED-PCW2 1.44 1.50 4.67 93.7 65.2 14 LED-FCRBW1 1.20 1.21 4.90 30.6 25.4 15 LED-FCM1 1.71 1.72 4.97 16.5 9.6 LED-FCRBW2 1.35 1.36 4.99 18.8 13.9 17 LED-FCM2 1.85 1.85 5.20 23.7 12.8 18 LED-WCM 2.08 2.08 5.31 24.7 11.9 SUN 2.08 - 4.57 107 * 54 * Unit: lm/Wr. Table 4. Values derived from measurements conducted in the dark room with a spectroradiometer (Model PS-300, Apogee Instruments, Logan, UT, USA), except for the values for sunlight which were obtained from an outdoor spectral scan using the same spectroradiometer. YPF = Yield photon flux, PPF = Photosynthetic photon flux, PPE = Phytochrome photoequi- librium. YPF/PPF (300– R:FR wide (600– R:FR Narrow (655– YPF (300– 800)/ (400–700) PPE (300– 699)/(700–800) 665)/(725–735) [Wave- No. Code FR Fraction 800 nm) [Wave-Lengths 800 nm) [Wave-Lengths Lengths in nm] in nm] in nm] 1 FWW 18.0 0.92 0.85 8.4 5.3 0.14 FCW 17.3 0.89 0.84 9.5 5.8 0.13 3 FDL 17.0 0.85 0.82 10.1 6.4 0.12 4 LPS 14.5 0.98 0.84 1.0 1.3 0.45 CMH 542.9 0.91 0.82 3.7 2.4 0.26 6 MH 47.1 0.90 0.82 2.7 1.6 0.37 AgriEngineering 2021, 3, 716–727 725 7 HPS-600 439.6 0.96 0.85 5.3 3.0 0.23 HPS-750 706.0 0.95 0.83 4.2 2.8 0.25 9 HPS-1000 967.3 0.95 0.83 4.0 2.8 0.25 10 LED-PCW1 514.9 0.87 0.85 13.4 12.6 0.08 LED-PCM 1215.4 0.92 0.88 14,019 ∞ 0.00 12 LED-PCMLB 284.9 0.90 0.87 45.8 109.6 0.01 13 LED-PCW2 161.2 0.88 0.83 6.3 7.2 0.14 LED-FCRBW1 575.2 0.88 0.87 38.1 111.3 0.01 15 LED-FCM1 1703.5 0.88 0.87 74.9 265.4 0.01 16 LED-FCRBW2 396.0 0.87 0.86 29.4 69.9 0.02 LED-FCM2 336.3 0.91 0.88 66.3 226.3 0.01 18 LED-WCM 152.6 0.92 0.88 90.1 299.3 0.00 SUN 1696.1 0.90 0.72 1.1 1.1 0.47 Table 5. Light distribution ratios as a percentage of the photon flux density across the 280–800 nm waveband as measured with a spectroradiometer (Model PS-300, Apogee Instruments, Logan, UT, USA). The values were calculated from meas- urements conducted in the dark room, except for the values for sunlight which were obtained from an outdoor spectral scan. UV = Ultraviolet, PAR = Photosynthetically active radiation, ePAR = Extended photosynthetically active radiation. Photon Flux UV-A Green Red Far-red PAR ePAR Density UV-B (280–314 Blue (400– No. Code (315–399 (500–599 (600– (700–800 (400–700 (400–750 µmol/(m s) nm) 499 nm) nm) nm) 699 nm) nm) nm) nm) (280–800 nm) FWW 20.9 0.2% 1.6% 15.3% 38.5% 40.0% 4.4% 93.8% 97.8% 2 FCW 20.5 0.2% 1.4% 22.2% 41.2% 31.7% 3.3% 95.1% 98.1% 3 FDL 20.6 0.1% 0.6% 33.0% 41.5% 22.5% 2.2% 97.1% 99.0% LPS 17.5 0.4% 1.7% 2.0% 68.8% 13.8% 13.3% 84.6% 87.1% 5 CMH 690.8 0.03% 1.1% 13.1% 28.4% 45.2% 12.2% 86.8% 93.7% 6 MH 64.5 0.05% 2.0% 22.7% 48.2% 19.7% 7.3% 90.7% 93.8% HPS-600 506.8 0.04% 0.4% 3.2% 40.4% 47.0% 8.9% 90.7% 96.1% 8 HPS-750 847.6 0.01% 0.2% 3.4% 32.7% 51.3% 12.4% 87.5% 94.9% 9 HPS-1000 1167.3 0.04% 0.3% 3.6% 32.1% 51.2% 12.7% 87.0% 94.2% LED- 611.0 0.03% 0.2% 23.8% 38.4% 35.0% 2.6% 97.2% 99.3% PCW1 11 LED- PCM 1327.2 0.00% 0.00% 6.0% 0.0% 94.0% 0.0% 100% 100% LED- 324.3 0.02% 0.1% 5.3% 0.4% 92.2% 2.0% 98.0% 99.6% PCMLB LED- 13 195.4 0.04% 0.3% 18.0% 39.9% 36.0% 5.7% 94.0% 98.3% PCW2 LED- 14 666.1 0.04% 0.2% 23.2% 13.1% 61.9% 1.6% 98.2% 99.4% FCRBW1 LED- 15 1951.4 0.03% 0.2% 24.7% 0.5% 73.6% 1.0% 98.8% 99.6% FCM1 LED- 16 464.9 0.05% 0.2% 26.1% 5.8% 65.7% 2.2% 97.6% 99.3% FCRBW2 LED- 17 375.1 0.00% 0.1% 12.0% 2.7% 84.0% 1.3% 98.7% 99.6% FCM2 18 LED-WCM 167.3 0.01% 0.1% 8.0% 0.5% 90.4% 1.0% 98.9% 99.7% SUN 2658.4 0.1% 5.5% 20.4% 25.2% 25.5% 23.2% 71.2% 83.1% AgriEngineering 2021, 3, 716–727 726 5. Conclusions • Every light source tested had unique performance characteristics, including their spectral outputs. • The PPF efficacy of a light source is but one performance characteristic that should be considered. • A spectroradiometer is needed in order to assess the spectral output of a light source. • Changing the definition of PAR will make it more difficult to compare published results that used the current definition for PAR (400–700 nm) with results published based on the extended definition for PAR (ePAR, 400–750 nm). • The sooner the scientific community can agree on definitions that describe key per- formance characteristics (e.g., waveband ranges, photosynthetically active radiation), the less confusion there will be when these performance characteristics are used to make plant lighting decisions. • Due to the rapidly improving LED technology, it is critically important to have a consistent system for measuring and reporting lamp characteristics. • Due to the challenges involved, commercial growers are encouraged to experiment with new light sources on a small growing area, before deciding to scale up to large production areas. Author Contributions: Conceptualization, A.-J.B.; methodology, T.J.S. and A.-J.B.; data collection and analysis, T.J.S. and A.-J.B.; data curation, T.J.S. and A.-J.B.; writing—original draft preparation, A.-J.B.; writing—review and editing, T.J.S. and A.-J.B.; visualization, A.-J.B.; supervision, A.-J.B.; project administration, A.-J.B.; funding acquisition, A.-J.B. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the New York State Energy Research and Development Au- thority (Greenhouse Lighting and Systems Engineering–GLASE–project) and the New Jersey Agri- cultural Experiment Station. Data Availability Statement: Original measurement data available on request from the authors. Acknowledgments: The authors gratefully acknowledge the help they received from Claude Wal- lace who conducted several of the lamp evaluation tests. Conflicts of Interest: The authors declare no conflict of interest. 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Journal

AgriEngineeringMultidisciplinary Digital Publishing Institute

Published: Sep 28, 2021

Keywords: controlled environment agriculture; crop production; efficacy; extended photosynthetically active radiation; spectrum; supplemental lighting

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