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Wesley C. Randall and Roberto G. Lopez

under HPS lamps ( Table 1 ). High-pressure sodium lamps are rated to be 25% to 30% efficient at converting electrical energy to light; the other 70% to 75% is radiated as heat energy ( Spaargaren, 2001 ). Celosia is the only species considered cold

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Celina Gómez, Robert C. Morrow, C. Michael Bourget, Gioia D. Massa, and Cary A. Mitchell

supplemental photosynthetic light to sustain steady supplies of high-quality produce during the off-season. Most greenhouse growers who use supplemental lighting rely on overhead high-pressure sodium lamps because of their capability to deliver adequate

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Brian R. Poel and Erik S. Runkle

flowering of Celosia, Impatiens, Salvia, Tagetes , and Viola HortScience 40 1336 1339 Randall, W.C. Lopez, R.G. 2014 Comparisons of supplemental lighting from high-pressure sodium lamps and light-emitting diodes during bedding plant seedling production

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Joshua K. Craver, Jennifer K. Boldt, and Roberto G. Lopez

. 43 421 431 Cosgrove, D.J. 1981 Rapid suppression of growth by blue light Plant Physiol. 67 584 590 Currey, C.J. Lopez, R.G. 2013 Cuttings of Impatiens, Pelargonium , and Petunia propagated under light-emitting diodes and high-pressure sodium lamps

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Wesley C. Randall and Roberto G. Lopez

overhead SL ( Oh et al., 2010 ; Randall and Lopez, 2014 ; Sherrard, 2003 ). High-intensity discharge lamps, such as HPS and metal halide lamps, have traditionally been used for SL to increase greenhouse DLI. High-pressure sodium lamps have long been the

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Theo J. Blom and Brian D. Piott

Four freesia cultivars were exposed to 24 hour·day-1 high-pressure sodium (HPS) lighting during various stages of their development. Upon emergence, freesia plants were exposed to the following four lighting treatments: 1) ambient; 2) ambient until shoot length was 5 to 8 cm followed by HPS lighting until flowering; 3) HPS lighting until shoot length was 5 to 8 cm followed by ambient lighting; and 4) continuous HPS lighting. Supplemental HPS lighting was provided at 37 μmol·m-2·s-1 at plant level in a glasshouse. Continuous lighting or lighting during flower development hastened flowering but reduced the number of flowering stems per corm, as well as stem length and weight. Lighting during the vegetative and flower initiation periods produced minor effects. The main benefit of supplemental lighting was found in total corm weight.

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David L. Bubenheim, Raman Sargis, and David Wilson

Electronic dimming of high intensity discharge lamps offers control of photosynthetic photon flux (PPF) but is often characterized as causing significant spectral changes. Growth chambers with 400 W metal halide (MH) and high pressure sodium (HPS) lamps were equipped with a dimmer system using silicon controlled rectifiers (SCR) as high speed switches. Phase control operation turned the line power off for some period of the AC cycle. At full power the electrical input to HPS and MH lamps was 480 W (RMS) and could be decreased to 267 W and 428 W, respectively, before the arc was extinguished. Concomitant with this decrease in input power, PPF decreased by 60% in HPS and 50% in MH. The HPS lamp has characteristic spectral peaks at 589 and 595 nm. As power to the HPS lamps was decreased the 589 nm peak remained constant while the 595 nm peak decreased, equalling the 589 nm peak at 345 W input, and was almost absent at 270 W input. The MH lamp has a broader spectral output but also has a peak at 589 nm and another, smaller peak, at 545 nm. As input power to the MH lamps decreased the 589 nm peak diminished to equal the 545 nm peak. As input power approached 428 W the 589 nm peak shifted to 570 nm. While a spectral change was observed as input power was decreased in both MH and HPS lamps, the phytochrome equilibrium ratio (Pfr/Ptot) remain unchanged for both lamp types.

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David L. Bubenheim, Raman Sargis, and David Wilson

Electronic dimming of high-intensity discharge lamps offers control of photosynthetic photon flux (PPF) but is often characterized as causing significant spectral changes. Growth chambers with 400-W metal halide (MH) and high-pressure sodium (HPS) lamps were equipped with a dimmer system using silicon-controlled rectifiers (SCR) as high-speed switches. Phase control operation turned the line power off for some period of the alternating current cycle. At full power, the electrical input to HPS and MH lamps was 480 W (root mean squared) and could be decreased to 267 W and 428 W, respectively, before the arc was extinguished. Concomitant with this decrease in input power, PPF decreased by 60% in HPS and 50% in MH. The HPS lamp has characteristic spectral peaks at 589 and 595 nm. As power to the HPS lamps was decreased, the 589-nm peak remained constant while the 595-nm peak decreased, equaling the 589-nm peak at 345-W input, and the 589-nm peak was almost absent at 270-W input. The MH lamp has a broader spectral output but also has a peak at 589 nm and another smaller peak at 545 nm. As input power to the MH lamps decreased, the peak at 589 diminished to equal the 545-nm peak. As input power approached 428 W, the 589-nm peak shifted to 570 nm. While the spectrum changed as input power was decreased in the MH and HPS lamps, the phytochrome equilibrium ratio (Pfr: Ptot) remains unchanged for both lamp types.

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Matthew G. Blanchard and Erik S. Runkle

A technology for long-day (LD) lighting was evaluated for commercial production of ornamentals using a stationary high-pressure sodium (HPS) lamp with an oscillating aluminum parabolic reflector (rotating HPS lamp). We performed an experiment with four LD species (Campanula carpatica Jacq., Coreopsis grandiflora Hogg ex Sweet, Petunia ×hybrida Vilm.-Andr., and Rudbeckia hirta L.) to compare the efficacy of a rotating HPS lamp in promoting flowering with night-interruption (NI) lighting using incandescent (INC) lamps. Seedlings were grown under natural short-day (SD) photoperiods (12 h or less) and NI treatments were delivered from a 600-W rotating HPS lamp mounted at one gable end of the greenhouse or from INC lamps that were illuminated continuously for 4 h or cyclically for 6 min every 30 min for 4 h. Plants were grown at lateral distances of 1, 4, 7, 10, or 13 m from the rotating HPS lamp, which provided a maximum photosynthetic photon flux of 25.4 μmol·m−2·s−1 (at 1 m) to 0.3 μmol·m−2·s−1 (at 13 m). Control plants were grown under an uninterrupted 15-h skotoperiod. Within 16 weeks, 80% or greater of the plants within each species that received NI lighting had a macroscopic visible flower bud or inflorescence, whereas all species but Petunia ×hybrida remained vegetative under the SD. Flowering of all species grown at 13 m from the rotating HPS lamp was delayed by 14 to 31 d compared with those under continuous INC. The weekly operational costs to provide NI lighting to a 139-m2 greenhouse with one 600-W rotating HPS lamp or a standard cyclic INC lamp installation was estimated to be 80% to 83% lower compared with INC lighting for the entire 4-h NI. These results indicate that a rotating HPS lamp can be used to efficiently deliver LD lighting, but flowering time was delayed and flower number reduced in some species when the maximum NI light intensity was less than 2.4 μmol·m−2·s−1.

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Christopher J. Currey and Roberto G. Lopez

Increasing photosynthetic daily light integral (DLI) by supplementing with high-pressure sodium (HPS) lamps during propagation has been shown to enhance photosynthesis and biomass accumulation of cuttings. The development of high-intensity light-emitting diodes (LEDs) is a promising technology with potential as a greenhouse supplemental lighting source. Our objective was to quantify the impact of narrow spectra supplemental lighting from LEDs on growth, morphology, and gas exchange of cuttings compared with traditional HPS supplemental lighting. Cuttings of Impatiens hawkeri W. Bull ‘Celebrette Frost’, Pelargonium ×hortorum L.H. Bailey ‘Designer Bright Red’, and Petunia ×hybrida Vilm. ‘Suncatcher Midnight Blue’ were received from a commercial propagator and propagated in a glass-glazed greenhouse at 23 °C air and substrate temperature set points. After callusing (≈5 mol·m−2·d−1 for 7 days), cuttings were placed under 70 μmol·m−2·s−1 delivered from HPS lamps or LED arrays with varying proportions (%) of red:blue light (100:0, 85:15, or 70:30). After 14 days under supplemental lighting treatments, growth, morphology, and gas exchange of rooted cuttings were measured. There were no significant differences among Impatiens and Pelargonium cuttings grown under different supplemental light sources. However, compared with cuttings propagated under HPS lamps, stem length of Petunia cuttings grown under 100:0 red:blue LEDs was 11% shorter, whereas leaf dry mass, root dry mass, root mass ratios, and root:shoot ratio of cuttings grown under 70:30 red:blue LEDs were 15%, 36%, 17%, and 24% higher, respectively. Supplemental light source had minimal impact on plants after transplant. Our data suggest that LEDs are suitable replacements for HPS lamps as supplemental light sources during cutting propagation.