1. Introduction
Electric lamps, such as fluorescent lamps, are widely used to supplement sunlight (supplemental lighting) and day-length extension (photoperiodic lighting) for the production of horticultural crops in greenhouses. Recent advances in light-emitting diode (LED) technology now provide the horticultural industry with multiple lighting options. However, to our knowledge, almost all of the previous studies of artificial lights focused only on the evaluation of effectiveness and energy saving of the different kinds of lamps, including horticultural light emitting diode (H-LED) lights used for horticultural applications [
1,
2,
3,
4,
5,
6,
7,
8]. These studies neglected to examine the influence of artificial lighting sources on the environment associated with four environmental categories: air/climate, water, soil and resources. However, reduced environmental impact is one of the major selling points of artificial lighting sources and an in-depth environmental impact study is initiated in our study. Life cycle assessment (LCA) was used because it is an approach well-suited for comparing the environmental impacts of the traditional lighting sources with H-LED lighting. It provides an excellent methodology to answer the question “Is the proposed H-LED light better for the environment than the traditional light?”. To respond to this question, a case study on the environmental impacts of compact fluorescent lamps (CFL) and H-LED lights for night break of chrysanthemum cultivation was carried out.
Chrysanthemum is one of the most important cut flowers and has the highest consumption in the world. As a short-day plant (SDP), wild type chrysanthemum flowers in autumn under natural conditions. In other words, chrysanthemum flowers when night length exceeds a critical dark period. By interrupting the dark period by a brief light treatment through “night break” (NB), flowering in SDPs is prevented. This method of farming helps chrysanthemum flowers bloom on specific days with bulky flowers, beautiful petals, while being able to be sold at higher prices. Previously, in order to inhibit early flowering, for example from autumn to winter, chrysanthemum growers applied NB lighting by using incandescent (INC) bulbs. However, the use of incandescent bulbs prevents flowering and consumes a lot of electricity because of its very low electrical to light energy transformation efficiency. Currently, to save energy, flower planters have shifted to using compact fluorescent lamps (CFLs).
Da Lat City (Vietnam) has approximately 2500 ha for the cultivation of various types of daisies and chrysanthemums. Every year, the gardeners use 20–25 W CFLs for lighting at an average density rate of 1000 CFLs/ha, at a frequency of about 4–6 lighting hours per night, 35 nights per harvest and 4 harvests per year. Therefore, the total power consumption across the region is about 29–47 million kilowatt hours per year with a monetary value of electricity at about VND 35–66 billion per year, equivalent to about USD 1.5–2.8 million per year (assuming the 2019 electricity price and the Vietnam dong (VND)/USD exchange rate are ≈ VND 1200/kWh, and ≈23,000, respectively). Therefore, many farmers who produce chrysanthemum cuttings in greenhouses in Da Lat City and surrounding areas, have boldly replaced the compact lamp lighting systems with H-LED lighting. The test results from using 5 W–10 W H-LED lights on some acreage of Da Lat chrysanthemum farms shows that the chrysanthemum absorbs the light, which controls flowering well, saving up to half the energy costs compared to the use of 20–25 W compact fluorescent light.
As seen in
Figure 1, the nonilluminated chrysanthemum bed flowered well after 40 days and was harvested after 68 days of growth. Meanwhile, the illuminated chrysanthemum bed did not flower after 40 days and was harvested only after 100 days of growing. In addition, the height of the chrysanthemum plants when illuminated was superior to that when it was not illuminated. Compared to the case using CFL lamps, the height of chrysanthemum plants and the flower dimensions were higher and larger when illuminated by H-LED lights.
3. Results and Discussion
Table 3 below presents the environmental impacts associated with air and climate for each of the lamp types. Within each of the impact indicators, the values presented are comparable between the different lamp types because the lighting service was normalized to represent 234,000 μmol/s-h for the H-LED lamp.
For global warming potential (GWP), the CFL had CO2-equivalent emissions, with 1534 kg of emissions associated with the functional unit of 234,000 μmol/s-h of light. The H-LED lamps were better, offering only 147.4 kg of CO2-equivalent emissions.
For acidification potential (AP), the trend was similar. The CFL caused the most impact, with 8.33 kg of sulfur dioxide-equivalent emissions for 234,000 μmol/s-h of light. The H-LED lamps offered only 0.82 kg of sulfur dioxide, greatly reducing the acidification potential.
Photochemical oxidation potential (POCP) leads to urban smog and the emissions of this air pollutant was the most severe with the CFLs. These lamps emitted approximately 55.42 g of ozone for the functional unit of light output meanwhile the H-LED lamps only emitted approximately 6.12 g.
For the stratospheric ozone depletion potential (ODP), the CFLs and H-LED lamp emitted 14 mg and 2 mg of CFC-11-eq., respectively.
For human toxicity potential (HTP), the impact for the functional unit of light output was 241.31 kg of 1.4-DCB-eq. for CFLs and 30.18 kg of 1.4-DCB-eq. for the H-LED lamps.
Table 4 presents the environmental impacts associated with water-related indicators for each of the lamp types, normalized for 234,000 μmol/s-h of light output.
For fresh water aquatic eco-toxicity potential (FAETP), the CFL’s impact was more than 10 times higher than the impact of H-LED with over three times the impact. The units for this environmental indicator were reported in equivalent kilograms of “1.4-DCB” which is 1.4-Di-ChloroBenzene, a known carcinogen.
For marine aquatic eco-toxicity potential (MAETP), the trend was similar. The CFL had the most impact, with 124.37 kg of 1.4-DiChloroBenzene equivalent emissions for 234,000 μmol/s-h of light. The H-LED lamp offered a reduction of only 11.9% over the CFL, with less than 14.75 kg, greatly reducing this environmental damage potential.
Eutrophication potential (EP) is the last indicator of water-related impacts, and measures the impact in terms of kilograms of phosphate equivalents that could cause excessive algal growth in waterways, reducing oxygen in the water and damaging the ecosystem. The CFL emitted approximately 2.29 kg of phosphate equivalents over the 234,000 μmol/s-h lighting service functional unit. The H-LED lamp was approximately 11.3% less than that with 0.26 kg.
Table 5 presents the environmental impacts associated with soil-related indicators for each of the three lamp types, normalized for 234,000 μmol/s-h of light output.
Land use (LU) is a measure of impact on both the area involved and the number of years over which that impact occurs. The land use equivalent for CFL providing 234,000 μmol/s-h of lighting service was 25.17 square meters per year. The H-LED lamps reduced it further still, to only 2.57 square meters. These levels were 10 times less compared to the CFL.
For ecosystem damage potential (EDP), the trend was similar. The CFL had the most impact, with 18.9 points of ecosystem damage potential over the functional unit. The H-LED offered a 1.9 point, i.e., 89.7%, reduction over the CFL, greatly reducing the ecosystem damage potential.
Terrestrial eco-toxicity potential (TAETP) was measured in the 1.4-dichlorobenzene equivalents. The CFL was found to cause the release of 156 g equivalents of this carcinogen. Compared to this impact, the H-LED offered a reduction of 88.8%, lessening the impact to only 17.5 g-eq.
Table 6 presents the four resource-related environmental indicators that were assessed for each of the three lamp types, normalized for 240,000 μmol/s-h of light output.
For the first of the resource-related environmental impacts, abiotic resource depletion potential (ARD), the CFL had the most impact, with 8.76 kg of antimony equivalents. The H-LED offered 0.85 kg, less than 10 times that of CFL.
For nonhazardous waste landfill (NHWL), the trend was similar. The CFL had the most impact, with 40.14 kg of nonhazardous waste equivalents for the functional unit of 234,000 μmol/s-h of light. The H-LED offered 6.55 kg, a reduction of 83.7% over CFL, which was a large impact reduction for this metric
For radioactive waste landfill (RWL), the proportions of the reduction were nearly identical to that of the abiotic resource depletion potential. The CFL generated 49.06 g of radioactive waste landfill equivalents, where the H-LED lamp offered 90% savings at just 5 g of radioactive waste landfill generated for the same light output.
For hazardous waste landfill (HWL), the trend was similar but not exactly the same. The CFL still had the most impact, with 27.38 g of hazardous waste landfill generated. The H-LED lamp had a lower impact, with 4.24 g, or 84.5%, reduction.
As can be seen from
Table 3,
Table 4,
Table 5 and
Table 6, the energy-in-use was the dominant LCA stage in terms of environmental impacts for both types of lamps. In addition, in comparison with CFL, H-LED used in horticulture offered much less environmental impact, even compared with white LED used for human lighting in previous publications [
9,
10,
11,
12], and for high power LED lights used in greenhouse crop production [
14]. In the future, improvements in H-LED manufacturing technology will improve efficacy and reduce costs, lowering environmental impacts in almost all respects than any of the competing products on a life cycle basis, even before accounting for the energy consumed in use.