Light-emitting Diode Fixtures Research Articles

Sole-source Lighting of Lettuce that Increased Yield Had No Negative Effect on Postharvest Longevity

The effects of sole-source lighting on the growth and yield of hydroponically grown lettuce have been extensively studied, but research of postharvest performance is limited. We grew frill-leaf lettuce (Lactuca sativa) ‘Green Incised’ and ‘Hydroponic Green Sweet Crisp’ hydroponically in an indoor vertical research farm under daily light integrals (DLIs) of 12 or 18 mol⋅m−2⋅d−1 and the following three ratios of blue (B; 400–499 nm) and red (R; 600–699 nm) light from light-emitting diode fixtures: B5:R95, B20:R80, and B35:R65. We postulated that biomass accumulation would increase with the DLI and decrease with the B light fraction, and that postharvest longevity would increase with the DLI and the B light fraction. As expected, shoot fresh weight, leaf length and width, leaf number, and relative chlorophyll content (SPAD; ‘Green Incised’ only) decreased as the proportion of B light increased from 5% to 35%. Decreasing the DLI from 18 to 12 mol⋅m−2⋅d−1 reduced the shoot fresh weight and leaf number of both cultivars. Leaves of ‘Green Incised’ were up to 27% wider under B5:R95 and 60% longer under B5:R95 at 12 mol⋅m−2⋅d−1 than those under treatments with a higher DLI or more B light. The shoot fresh weight of ‘Hydroponic Green Sweet Crisp’ was greatest when grown under B5:R95 at 18 mol⋅m−2⋅d−1 and decreased as B light increased or DLI decreased. At the time of harvest, leaves of each cultivar and treatment were placed in clamshells and stored at 7 °C in darkness and evaluated for decay. ‘Green Incised’ that grew under B35:R65 and a DLI of 18 mol⋅m−2⋅d−1 had the shortest storage life, with 9.5 d and 11.4 d for replications 1 and 2, respectively, which were ∼2.5 to 4.0 d and 1.4 to 3.6 d earlier, respectively, than the storage life of lettuce grown under other treatments. In contrast, ‘Hydroponic Green Sweet Crisp’ was not influenced by light quality or DLI and had a storage life of 12.6 to 13.3 d and 13.5 to 14.3 d for replications 1 and 2, respectively. Therefore, a B light fraction between 5% and 20% and a DLI of 18 mol⋅m−2⋅d−1 produced high-yielding frill-leaf lettuce with a relatively long storage life.

Energy-saving strategies to convert existing campus to smart campus: a conservative method analysis

Energy consumption has wide applications in the construction industry. The pattern of energy demand depends on the nature of energy usage in accordance with time. Prominence is given to meet the demand without forfeiture of energy. This paper focuses on the importance of developing a smart campus and energy management. In the present study, a prominent engineering institute located in Karnataka, India, is considered for analysis. The approaches considered here are installing solar roof panels and replacing existing electrical fixtures with light-emitting diode (LED) fixtures. The cost and energy consumption analysis before and after the application of these methods will give a strong image of how energy and money can be saved and are useful for society. The initial investment may slightly be high but the payback period is quite early. Results of the study indicate that the initial investment required for solar panel installation and replacement of existing electrical fixtures with LED fixtures for interiors and corridors at the institution has proved worthwhile by various investment criteria used in the project. The study implicates a positive step towards energy-saving strategies, a revolutionary change in the energy sector and the development of the country.

Spectral composition of light-emitting diodes impacts aquatic and terrestrial invertebrate communities with potential implications for cross-ecosystem subsidies.

Resource exchanges in the form of invertebrate fluxes are a key component of aquatic-terrestrial habitat coupling, but this interface is susceptible to human activities, including the imposition of artificial light at night. To better understand the effects of spectral composition of light-emitting diodes (LEDs)-a technology that is rapidly supplanting other lighting types-on emergent aquatic insects and terrestrial insects, we experimentally added LED fixtures that emit different light spectra to the littoral zone and adjacent riparian habitat of a pond. We installed four replicate LED treatments of different wavelengths (410, 530 and 630 nm), neutral white (4000 k) and a dark control, and sampled invertebrates in both terrestrial and over-water littoral traps. Invertebrate communities differed among light treatments and between habitats, as did total insect biomass and mean individual insect size. Proportional allochthonous biomass was greater in the riparian habitat and among some light treatments, demonstrating an asymmetrical effect of differently coloured LEDs on aquatic-terrestrial resource exchanges. Overall, our findings demonstrate that variation in wavelength from LEDs may impact the flux of resources between systems, as well as the communities of insects that are attracted to particular spectra of LED lighting, with probable implications for consumers. This article is part of the theme issue 'Light pollution in complex ecological systems'.

Protection of Dark-Sky Areas in the United States Through Development and Implementation of Warm-Light LED Fixtures

The light-emitting-diode (LED) revolution has drastically decreased the quality of the United States’ night sky. LEDs are brighter than the sodium doublet lighting fixtures they are replacing, causing an increase in light pollution. Emerging technology promises to replace high-color-temperature LED lighting with lower-color-temperature lighting that reduces light pollution. High-color-temperature, or “cool-lighting” causes unnecessary amounts of light pollution that decreases humanity's connection with the cosmos through stargazing. Policy implementations can increase public awareness of how LEDs affect light pollution through research grants and tax incentive structures. The federal government can directly decrease the United States’ luminous footprint by funding research on warm-light LED development , regulating LED lighting on federal projects to only use low-color-temperature LED fixtures and offering incentives to communities to reduce their light pollution through the tax code.

Recent Progress in Visible Light Positioning and Communication Systems

In this paper, we report the recent progress in visible light positioning and communication systems using light-emitting diodes (LEDs). Due to the wide deployment of LEDs for indoor illumination, visible light positioning (VLP) and visible light communication (VLC) using existing LEDs fixtures have attracted great attention in recent years. Here, we review our recent works on visible light positioning and communication, including image sensor-based VLP, photodetector-based VLP, integrated VLC and VLP (VLCP) systems, and heterogeneous radio frequency (RF) and VLC (RF/VLC) systems.

Supplemental Lighting Quality Influences Time to Flower and Finished Quality of Three Long-Day Specialty Cut Flowers

Year-round demand for locally sourced specialty cut flowers continues to increase. However, due to low radiation intensities and temperatures, growers in northern latitudes must utilize greenhouses, but limited production information detailing manipulation of the radiation environment exists. Therefore, our objective is to quantify the influence of supplemental lighting (SL) quality on time to flower and harvest and stem quality of three long-day specialty cut flowers. Godetia ‘Grace Rose Pink’ (Clarkia amoena), snapdragon ‘Potomac Royal’ (Antirrhinum majus), and stock ‘Iron Rose’ (Matthiola incana) plugs are transplanted into bulb crates and placed in one of six greenhouse compartments with SL providing a total photon flux density of 120 µmol·m−2·s−1 from 0700 to 1900 HR. After four weeks, SL is extended to provide a 16 h photoperiod to induce flowering. SL treatments are provided by either high-pressure sodium (HPS) fixtures or various light-emitting diode (LED) fixtures. Treatments are defined by their 100 nm wavebands of blue (B; 400–500 nm), green (G; 500–600 nm), red (R; 600–700 nm), and far-red (FR; 700–800 nm) radiation (photon flux density in μmol·m−2·s−1) as B7G60R44FR9 (HPS120), B20G50R45FR5, B20R85FR15, B30G25R65, B120, or R120. Time to harvest (TTH) is up to 14, 15, and 10 d slower under R120 SL for godetia, snapdragon, and stock, respectively, compared to the quickest treatments (HPS120, B120, and B20R85FR15 SL). However, R120 SL produces cut flowers up to 18% longer than those grown under the quickest treatments. Both broad-spectrum LED fixtures slightly delay TTH compared to the quickest treatments. Stem caliper is not commercially different between treatments for godetia or snapdragon, although stems are up to 14% thinner for stock grown under B120 SL compared to the other treatments. Flower petal color is not commercially different between SL treatments. We recommend utilizing a SL fixture providing a spectrum similar to B20R85FR15 SL or B20G50R45FR5, as they elicit desirable crop responses with minimal developmental, quality, and visibility tradeoffs. While HPS lamps perform similarly to the recommended fixtures, we recommend utilizing LEDs for their higher photon efficacy and potential energy savings.

Radiation Intensity and Quality Affect Indoor Acclimation of Blueberry Transplants

The objectives were to characterize and compare shrinkage (i.e., transplant loss) and growth of tissue-cultured blueberry (Vaccinium corymbosum) transplants acclimated in greenhouses or indoors under 1) different photosynthetic photon flux densities (PPFDs) (Expt. 1); or 2) spectral changes over time using broad-spectrum white (W; 400 to 700 nm) light-emitting diodes (LEDs) without or with red or far-red (FR) radiation (Expt. 2). In Expt. 1, ‘Emerald’ and ‘Snowchaser’ transplants were acclimated for 8 weeks under PPFDs of 35, 70, 105, or 140 ± 5 µmol·m‒2·s‒1 provided by W LED fixtures for 20 h·d−1. In another treatment, PPFD was increased over time by moving transplants from treatment compartments providing 70 to 140 µmol·m‒2·s‒1 at the end of week 4. Transplants were also acclimated in either a research or a commercial greenhouse (RGH or CGH, respectively). Shrinkage was unaffected by PPFD, but all transplants acclimated indoors had lower shrinkage (≤4%) than those in the greenhouse (15% and 17% in RGH and CGH, respectively), and generally produced more shoot and root biomass, regardless of PPFD. Growth responses to increasing PPFD were linear in most cases, although treatment effects after finishing were generally not significant among PPFD treatments. In Expt. 2, ‘Emerald’ transplants were acclimated for 8 weeks under constant W, W + red (WR), or W + FR (WFR) radiation, all of which provided a PPFD of 70 ± 2 μmol·m−2·s−1 for 20 h·d−1. At the end of week 4, a group of transplants from WR and WFR were moved to treatment compartments with W (WRW or WFRW, respectively) or from W to a research greenhouse (WGH), where another group of transplants were also acclimated for 8 weeks (GH). Shrinkage of transplants acclimated indoors was also low in Expt. 2, ranging from 1% to 4%. In contrast, shrinkage of transplants acclimated in GH or under WGH was 37% or 14%, respectively. Growth of indoor-acclimated transplants was generally greater than that in GH or under WGH. Although growth responses were generally similar indoors, plants acclimated under WFR had a higher root dry mass (DM) and longer roots compared with GH and WGH.

Effects of achromatic and chromatic lights on pupillary response, endocrinology, activity, and milk production in dairy cows.

Artificial light can be used as a management tool to increase milk yield in dairy production. However, little is known about how cows respond to the spectral composition of light. The aim of this study was to investigate how dairy cows respond to artificial achromatic and chromatic lights. A tie-stall barn equipped with light-emitting diode (LED) light fixtures was used to create the controlled experimental light environments. Two experiments were conducted, both using dairy cows of Swedish Red and light mixtures with red, blue or white light. In experiment I, the response to light of increasing intensity on pupil size was evaluated in five pregnant non-lactating cows. In experiment II 16h of achromatic and chromatic daylight in combination with dim, achromatic night light, was tested on pregnant lactating cows during five weeks to observe long term effects on milk production, activity and circadian rhythms. Particular focus was given to possible carry over effects of blue light during the day on activity at night since this has been demonstrated in humans. Increasing intensity of white and blue light affected pupil size (P<0.001), but there was no effect on pupil size with increased intensity of red light. Milk yield was maintained throughout experiment II, and plasma melatonin was higher during dim night light than in daylight for all treatments (P<0.001). In conclusion, our results show that LED fixtures emitting red light driving the ipRGCs indirectly via ML-cones, blue light stimulating both S-cones and ipRGCs directly and a mixture of wavelengths (white light) exert similar effects on milk yield and activity in tied-up dairy cows. This suggests that the spectral composition of LED lighting in a barn is secondary to duration and intensity.

Fault-Tolerant LED Lighting Systems Featuring Minimal Loss of Luminous Flux

The adoption of lighting systems based on light-emitting diode (LED) technologies gains further significance as these technologies become mature, particularly within the context of homes and offices. LED technologies are well known for the superior reliability standards and extended lifetime. Unfortunately, power electronic technologies used to drive LED lighting systems are unable to reach identical levels of longevity. Particularly, active semiconductors pose one of the major hurdles to the full exploitation of the LEDs lifetime. This article proposes a fault-tolerant LED driver, derived from the single-inductor multiple-output (SIMO) topology, which combines the benefits of fault tolerance, multiple and independent fixture control, and full dimming range, on a single LED driver. Two alternative reconfiguration strategies ensure, whenever feasible, that none of the LED fixtures suffer significant depreciation of luminous flux during the postfault driver operation. Simulation and experimental results demonstrate the effectiveness of the proposed fault-tolerant LED driver.

Energy-Efficient Supplemental LED Lighting Control for a Proof-of-Concept Greenhouse System

In this paper, a multiple-input multiple-output control system integrated with daylight harvesting is presented as a proof-of-concept system for energy-efficient greenhouse lighting. The control objective is to regulate the intensity of dimmable multispectrum light-emitting diode (LED) fixtures for achieving desired spectral irradiance levels and color ratios while utilizing the natural sunlight as much as possible. To ensure stability and improved dynamic performance, a Smith predictor is utilized to compensate for the delay introduced into the system by the communication hardware. A stability analysis of the closed-loop system is presented considering system delay and modeling uncertainties. The proposed control system was experimentally tested in a grow-tent environment consisting of dimmable halogen lights that emulate daylight variation, multispectrum dimmable LED fixtures, and low-cost light sensors. The results indicate that about 30% energy savings can be achieved by using the proposed automated lighting control system.

Spectral Quality of Light Can Affect Energy Consumption and Energy-use Efficiency of Electrical Lighting in Indoor Lettuce Farming

High energy-use cost for electric lighting is one of the major issues challenging sustainability of the indoor lettuce-farming industry. Thus, maximizing electrical energy-use efficiency (EUE, g·KWh−1), defined as the ratio of dry matter production (g) to electrical energy consumption (EEC, KWh−1), is crucial during indoor production. Light-emitting diodes (LEDs) are energy efficient and highly suitable for indoor farms. Research on optimal spectral quality of LEDs for lettuce growth is extensive; however, there is limited research examining LED spectral quality effects on EEC and EUE. Photon efficiency, defined as the ratio of light output to electrical energy input (PE, µmol·J−1), generally is used for selection of LED fixtures. Because PE does not account for differences in emitted light spectrum, it is not clear whether light-fixture selection based on PE can maximize EUE in lettuce production. This study comprised two experiments. In Expt. 1, we used four “phosphor-converted” commercial LEDs with different light intensities and spectra to model the effect of light spectral quality on lettuce shoot dry weight (SDW), EEC, and EUE. We also evaluated relations between EUE vs. PE and EUE vs. PER (PE based on red light) for indoor lettuce production. Results indicated that light spectral quality affected SDW, EEC, and EUE in lettuce production. Fitted models indicated that EEC increased linearly with increasing percentage of red-light output and was unaffected by other spectral colors or ratios. However, EUE increased in a curvilinear fashion with an increasing ratio of red to blue (R:B) light and reached a maximum at a ratio of 4.47. Similar to EUE, SDW also responded in a curvilinear fashion to R:B. Results also indicated that EUE correlated poorly with PE but linearly to PER. In Expt. 2, we grew three lettuce varieties under two commercial LED fixtures. They had similar levels of PE but different percentages of red, R:B, and PER values. Regardless of the variety, fixtures with greater percentages of red, R:B, and PER significantly increased EUE. We conclude that red-light quality is an important determinant of EUE and growers should select fixtures based on R:B and high PER in indoor lettuce farming.

Manipulating growth, color, and taste attributes of fresh cut lettuce by greenhouse supplemental lighting

Supplemental lighting (SL) is often used in greenhouse lettuce production to increase yield when the solar daily light integral is low. High-pressure sodium (HPS) fixtures are traditionally used to deliver SL, but light-emitting diodes (LEDs) have become a feasible, more energy-efficient replacement. Red light (R; 600–700 nm) and blue light (B; 400–500 nm) are especially effective in promoting photosynthesis and increasing crop growth, whereas far-red (FR; 700–800 nm) radiation has the potential to increase yield by promoting leaf expansion. We performed three greenhouse experiments with HPS or LED fixtures to determine the effects of SL on lettuce growth, coloration, and sensory attributes. We grew lettuce at 20 °C without or with SL from HPS or R + B LEDs with a 16-h photoperiod (Expts. 1 and 2). In Expt. 3, we grew plants without or with HPS SL without or with R + FR photoperiodic lighting at the end of the day during the growing (first) stage, SL from R + B or B LEDs during the finishing (second) stage, or both. SL enhanced lettuce growth and yield by 32%–104% regardless of light quality. Four hours of end-of-day R + FR lighting at 2 to 5 μmol m−2·s−1 had few effects on lettuce growth or quality attributes. Compared with lettuce with no SL, lettuce provided with R + B LED SL for 7 d before harvest was 27% darker, 76%–82% redder, and 39%–55% less yellowish. Consumers tended to prefer lettuce grown under natural daylight more than plants grown with SL, and judged it to be less bitter, to be sweeter, and to have a more likable aftertaste. We conclude that providing different types of greenhouse SL at different growing stages can improve lettuce growth and coloration but that consumers could prefer taste attributes less.

LED lighting affects the composition and biological activity of Cannabis sativa secondary metabolites

Growth conditions are expected to alter the relative and absolute content of the hundreds of phytochemicals produced by Cannabis sativa L.; some of these possess biological activity on the human body. However, relatively little information exists regarding the effects of different light regimes on the composition of C. sativa secondary metabolites and thus on their biological activity. In this study, we investigated how light quality influences the production and final content of secondary metabolites, as well as their bioactive properties. Toward these, plant growth and blooming were carried out at different illumination conditions, utilizing light-emitting diode (LED) fixtures vs. conventional fluorescent and high-pressure sodium (HPS) lamps as controls. Inflorescences were sampled at different time points along the blooming; extract compositions were analyzed by HPLC and GC/MS, and the biological activity of the extracted material was assessed using cell viability assays. We found that growth and blooming under LED illumination considerably changed shoot architecture and inflorescence mass. Moreover, the content of cannabinoids, terpenes, and alkanes were altered in the inflorescences of LED-grown plants during the flowering period as well as in the harvested flowers. In particular, significantly higher quantities of cannabigerolic acid accumulated in the inflorescences that flowered under LED fixtures, with a cannabigerolic acid to Δ9-tetrahydrocannabinolic acid (CBGA:THCA) ratio of 1:2 as opposed to 1:16 when grown under HPS. Notably, the cytotoxic activities of extracts derived from plants grown under the different illumination regimes were different, with extracts from LED-grown plants possessing higher cytotoxicity along the flowering stage. Our results thus indicate that the transition to indoor growth of C. sativa under LED lighting, which can have significant impacts on cannabinoid and terpene content, and also on the bioactive properties of the plant extracts, should proceed with thorough consideration.

Comparison of Supplemental Lighting Provided by High-pressure Sodium Lamps or Light-emitting Diodes for the Propagation and Finishing of Bedding Plants in a Commercial Greenhouse

High-quality young plant production in northern latitudes requires supplemental lighting (SL) to achieve a recommended daily light integral (DLI) of 10 to 12 mol·m−2·d−1. High-pressure sodium (HPS) lamps have been the industry standard for providing SL in greenhouses. However, high-intensity light-emitting diode (LED) fixtures providing blue, white, red, and/or far-red radiation have recently emerged as a possible alternative to HPS lamps for greenhouse SL. Therefore, the objectives of this study were to 1) quantify the morphology and nutrient concentration of common and specialty bedding plant seedlings grown under no SL, or SL from HPS lamps or LED fixtures; and 2) determine whether SL source during propagation or finishing influences finished plant quality or flowering. The experiment was conducted at a commercial greenhouse in West Lafayette, IN. Seeds of New Guinea impatiens (Impatiens hawkeri ‘Divine Blue Pearl’), French marigold (Tagetes patula ‘Bonanza Deep Orange’), gerbera (Gerbera jamesonii ‘Terracotta’), petunia (Petunia ×hybrida ‘Single Dreams White’), ornamental millet (Pennisetum glaucum ‘Jester’), pepper (Capsicum annuum ‘Hot Long Red Thin Cayenne’), and zinnia (Zinnia elegans ‘Zahara Fire’) were sown in 128-cell trays. On germination, trays were placed in a double-poly greenhouse under a 16-hour photoperiod of ambient solar radiation and photoperiodic lighting from compact fluorescent lamps providing a photosynthetic photon flux density (PPFD) of 2 µmol·m−2·s−1 (ambient conditions) or SL from either HPS lamps or LED fixtures providing a PPFD of 70 µmol·m−2·s−1. After propagation, seedlings were transplanted and finished under SL provided by the same HPS lamps or LED fixtures in a separate greenhouse environment. Overall, seedlings produced under SL were of greater quality [larger stem caliper, increased number of nodes, lower leaf area ratio (LAR), and greater dry mass accumulation] than those produced under no SL. However, seedlings produced under HPS or LED SL were comparable in quality. Although nutrient concentrations were greatest under ambient conditions, select macro- and micronutrient concentrations also were greater under HPS compared with LED SL. SL source during propagation and finishing had little effect on flowering and finished plant quality. Although these results indicate little difference in plant quality based on SL source, they further confirm the benefits gained from using SL for bedding plant production. In addition, with both SL sources producing a similar finished product, growers can prioritize other factors related to SL installations such as energy savings, fixture price, and fixture lifespan.

Effect of two different commercially available white light LED fixtures on broiler hatchability and chick quality

ABSTRACT1. The objective of this study was to evaluate the effect of two different spectra of white light on hatchability and chick quality of broiler chickens.2. A total of 8424 Ross 708 broiler eggs were divided over three light exposure treatments during incubation: No light (DARK), a light emitting diode (LED) light with high levels of blue light (BLUE), or a LED light with high levels of red light (RED). Hatchability, embryo mortality and chick quality were assessed at hatch.3. DARK had a higher percentage of chicks with unhealed navels (21.1 ± 1.3%) and fewer overall chicks with no defects (77.0 ± 1.2%) compared to both the BLUE (9.9 ± 0.9% and 88.4 ± 1.1%) and RED treatments (7.7 ± 0.8% and 90.2 ± 1.0%).4. Both the BLUE (80.9 ± 1.0%) and RED treatments (82.9 ± 1.4%) had higher hatchability of fertile eggs than the DARK treatment (76.0 ± 2.2%).5. These results indicate that either of these LED fixtures could be used to improve hatchability and chick quality in broiler chickens. Utilising these types of lightings in commercial hatcheries will improve the efficiency via increased hatchability and quality of the chicks hatched.

Seedling Growth Is Similar under Supplemental Greenhouse Lighting from High-pressure Sodium Lamps or Light-emitting Diodes

Light-emitting diodes (LEDs) have the potential to replace high-pressure sodium (HPS) lamps as the main delivery method of supplemental lighting (SL) in greenhouses. However, few studies have compared growth under the different lamp types. We grew seedlings of geranium (Pelargonium ×hortorum), pepper (Capsicum annuum), petunia (Petunia ×hybrida), snapdragon (Antirrhinum majus), and tomato (Solanum lycopersicum) at 20 °C under six lighting treatments: five that delivered a photosynthetic photon flux density (PPFD) of 90 μmol·m−2·s−1 from HPS lamps (HPS90) or LEDs [four treatments composed of blue (B, 400–500 nm), red (R, 600–700 nm), or white LEDs] and one that delivered 10 μmol·m−2·s−1 from HPS lamps (HPS10), which served as a control with matching photoperiod. Lamps operated for 16 h·d−1 for 14 to 40 days, depending on cultivar and season. The LED treatments defined by their percentages of B, green (G, 500–600 nm), and R light were B10R90, B20R80, B10G5R85, and B15G5R80, whereas the HPS treatments emitted B6G61R33. Seedlings of each cultivar grown under the 90 μmol·m−2·s−1 SL treatments had similar dry shoot weights and all except pepper had a similar plant height, leaf area, and leaf number. After transplant to a common environment, geranium ‘Ringo Deep Scarlet’ and petunia ‘Single Dreams White’ grown under HPS90 flowered 3 days earlier than those grown under HPS10, but flowering time was not different from that in LED treatments. There were no consistent differences in morphology or subsequent flowering among seedlings grown under HPS90 and LED SL treatments. The inclusion of white light in the LED treatments played an insignificant role in growth and development when applied as SL with the background ambient light. The LED fixtures in this study consumed substantially less electricity than the HPS lamps while providing the same PPFD, and seedlings produced were of similar quality, making LEDs a suitable technology option for greenhouse SL delivery.

Single Stage–Single Switch High Power Factor Long Lifetime AC-DC Driver for High-power White Light-emitting Diodes in Streetlight Applications

To achieve the main advantages of individual high-power white light-emitting diodes, light-emitting diode drivers should feature a high power factor, high efficiency, and a long lifetime. In streetlight applications, due to the inconvenience in reaching out to light-emitting diode fixtures for replacing out-of-order drivers, the durability (long lifetime) of drivers plays an important part in designing lighting products. In this article, a new integrated, single-stage single-switch AC-DC driver for high-power white light-emitting diodes featuring high efficiency, a high power factor, and a long lifetime for streetlight applications is proposed. The single power switch of the proposed driver operates in a non-floating manner without a need for any snubber circuits due to proper inherent operation, which makes the driver simple and reliable. To verify accurate operation of the driver as well as validate the analysis and design procedure discussed herein, a 35-watt light-emitting diode fixture is first simulated in PSIM software (PowerSIM Inc., USA), and then a laboratory prototype is implemented. Simulation and experimental results verify proper performance, high input power factor, and validity of the analysis and the design procedure adopted in the process.

A Plug-and-Play Realization of Decentralized Feedback Control for Smart Lighting Systems

This paper proposes decentralized feedback controllers with plug-and-play capability for a class of smart lighting systems. In these systems, each light fixture has a spectrally tunable light source and a multichannel color sensor, and no communication is required between fixtures. Further, the light transport in the illuminated space is diagonally dominant, i.e., the light sensed by each sensor is primarily from the source in the same fixture. The controller design problems are formulated and solved for two cases of decentralized setpoint tracking and decentralized quadratic optimal control (with tracking error and energy penalty). For the decentralized setpoint tracking problem, a mechanism is proposed to automatically determine the feedback gains using individual sensor measurements in a plug-and-play fashion without the knowledge of the light transport model of the illuminated space. For the decentralized quadratic optimal control, the design problem is approximated with a series of local optimization problems, which are solved in a decentralized manner using individual sensor measurements. A suboptimality bound for the solution of the approximated problem compared with the global optimum is obtained. The performance of the suggested controllers in terms of achievement of a desired setpoint and daylight harvesting for energy saving is validated and evaluated based on typical lighting parameters in a room-scale experimental testbed with light-emitting diode fixtures and color sensors.

Analysis on energy efficiency and optimality of LED and photovoltaic based street lighting system

This study evaluates the optimality and energy efficiency of Light Emitting Diode (LED) and Photovoltaic based street lighting systems as a part of energy conservation. This evaluation is based on the detailed review carried out through a country wide street lamp survey. Since LEDs are becoming increasingly competitive due to their rapidly increasing efficiencies and decreasing cost, this research assessed the LED fixtures which have the capability of achieving 50% to 70% energy saving potential compared to the existing established technologies based street lamps available in the country. As a case study, illumination levels were examined at two neighboring traffic junctions in the Capital City, from Bambalapitiya junction to Kollupitiya junction. Two kinds of measurements were taken and average luminance levels were analysed for all measured points in the traffic lanes. It was found that same lighting performance could be achieved by replacing 250W HPS (High Pressure Sodium) by 150W HPS and further it was verified the same results while having 62% energy saving by replacing 250WHPS lamps with 111W LED through a simulation with Lighting Reality TM software. This change would easily meet the minimum recommended level of 7.5 Lux and average luminance of 0.5 cd/m 2 as per British Standards. Even though solar powered street lighting systems need high capital outlay, it will be one of the most appropriate energy solutions for a country like Sri Lanka. Incentive program development by the government may further encourage LED street lamp and solar powered system development adoptions. This study also recommends that any such incentive program should include performance standards that consider warranty, efficacy and other important criteria as the next steps. ENGINEER, Vol. 48, No.01, pp. 11-20, 2015

Occupancy distribution estimation for smart light delivery with perturbation-modulated light sensing

The advent of modern light-emitting diode (LED) techniques enables us to develop novel lighting systems with numerous previously unavailable features. Specifically, by using the fixtures for both illumination and to interrogate the space, source-to-sensor communication becomes possible at very low cost. In this paper, we present a novel framework to estimate the occupancy distribution in an indoor space using color-controllable LED fixtures (the same fixtures providing the illumination, simultaneously) and sparsely distributed non-imaging color sensors. By modulating randomly generated perturbation patterns onto the drive signals of the LED fixtures and measuring the changes in the color sensor responses, we are able to recover a light transport model for the room. Two approaches are proposed to estimate the spatial distribution of the occupancy, based on a light blockage model and a light reflection model, respectively. These two approaches, which can be combined, can faithfully reveal the occupancy scenario of the indoor space, while preserving the privacy of its occupants. An occupancy-sensitive lighting system can be designed based on this technique.