Economic Analysis of Greenhouse Lighting: Light Emitting Diodes vs. High Intensity Discharge Fixtures

Abstract

Lighting technologies for plant growth are improving rapidly, providing numerous options for supplemental lighting in greenhouses. Here we report the photosynthetic (400–700 nm) photon efficiency and photon distribution pattern of two double-ended HPS fixtures, five mogul-base HPS fixtures, ten LED fixtures, three ceramic metal halide fixtures, and two fluorescent fixtures. The two most efficient LED and the two most efficient double-ended HPS fixtures had nearly identical efficiencies at 1.66 to 1.70 micromoles per joule. These four fixtures represent a dramatic improvement over the 1.02 micromoles per joule efficiency of the mogul-base HPS fixtures that are in common use. The best ceramic metal halide and fluorescent fixtures had efficiencies of 1.46 and 0.95 micromoles per joule, respectively. We also calculated the initial capital cost of fixtures per photon delivered and determined that LED fixtures cost five to ten times more than HPS fixtures. The five-year electric plus fixture cost per mole of photons is thus 2.3 times higher for LED fixtures, due to high capital costs. Compared to electric costs, our analysis indicates that the long-term maintenance costs are small for both technologies. If widely spaced benches are a necessary part of a production system, the unique ability of LED fixtures to efficiently focus photons on specific areas can be used to improve the photon capture by plant canopies. Our analysis demonstrates, however, that the cost per photon delivered is higher in these systems, regardless of fixture category. The lowest lighting system costs are realized when an efficient fixture is coupled with effective canopy photon capture.

The Impact of Spectral Composition of White LEDs on Spinach (Spinacia oleracea) Growth and Development

“…and is not useful for evaluating the efficiency of lighting for plant growth: they proposed to evaluate energy conversion in plants with a new unit, the photon efficiency (μmol/J). The photon efficiency for the Cold LED is aligned with the value shown in [32] where an efficiency of 1.52 μmol/J was calculated for the cool white LED.…”

“…Both the efficiency for human light perception (lumen/watt) and plant growth (micromoles of photosynthetic photons per joule of energy input) are shown. Nelson and Bugbee [32] highlighted that luminous efficiency (lm/W) is a unit linked to the visual system The artificial lighting was provided with non-dimmed LED devices measuring 60 cm × 60 cm and containing four luminous strips shaded by a diffusive glass: this typology of luminaries has been selected for their small form factor, which allows to get the required uniformity of flux distribution and to reduce shadows. The cold source has 30 LEDs embedded in the luminous strips while in the warm one 42 LEDs are included.…”

“…Both the efficiency for human light perception (lumen/watt) and plant growth (micromoles of photosynthetic photons per joule of energy input) are shown. Nelson and Bugbee [32] highlighted that luminous efficiency (lm/W) is a unit linked to the visual system and is not useful for evaluating the efficiency of lighting for plant growth: they proposed to evaluate energy conversion in plants with a new unit, the photon efficiency (µmol/J). The photon efficiency for the Cold LED is aligned with the value shown in [32] where an efficiency of 1.52 µmol/J was calculated for the cool white LED.…”

Toward an optimal spectral quality for plant growth and development: the importance of radiation capture

“…Nelson and Bugbee (2014) reported the photosynthetic (400-700 nm) photon efficiency and photon distribution pattern of multiple models of fixtures from four lighting technologies. The most efficient LED and HPS fixtures had nearly identical efficiencies at 1.66 to 1.70 micromoles per joule.…”

“…At the same time, the more traditional high pressure sodium (HPS) technology has improved in efficiency by as much as 60% (Nelson and Bugbee, 2014). The thermal properties of fixtures can change experimental outcomes, and alter heating and cooling costs.…”