Combination Of Light-emitting Diodes Research Articles

The effect of light emitting diode (LED) spectrum and light duration on growth and yield of Brassica sinensis L. grown on floating raft hydroponic system

Recent technology in agriculture allows vegetable cultivation in controlled environment by utilizing energy derived from an artificial lighting. Light Emitting Diodes (LED) is a source of artificial light which produce light with the wavelength ranged from ultraviolet - 100 nm to infrared - 3,000 nm. Under natural or artificial lighting condition, plants require energy for photosynthesis from light between 380 nm to 700 nm. In this study we examined the use of two types of 45-watt LED (red and blue – C1, full spectrum – C2) with three different light durations (12 h – D1, 16 h – D2, and 18 h – D3) on the growth and yield performance of brassica under hydroponic technique. Research result showed that full spectrum LED provided better performance in plant height, leaves number and width, fresh yield, root length, and biomass in all combinations with light duration as compared to red and blue LED. The combination of full spectrum LEDs with a duration of 16 h showed the best fresh yield (3.96 kg m-2) followed by 18 h (3.57 kg m-2) and 12 h (3.22 kg m-2). Although the highest production was resulted from the combination of full spectrum LED and 16 h light duration, the most efficient in electric energy utilization was showed in the combination of full spectrum LED and 12 h light duration. All in all, we concluded that the use of full spectrum LED in combination with 16 h light duration feasible to be implemented in brassica cultivation under controlled environment.

Growth responses of tomato plants to different wavelength ratios of amber, red, and blue light

The differential effects of light quality and quantity are under scrutiny so that energy-efficient plant production may be optimized. This study aimed to determine the combined effects of amber (595 nm), red (635 nm), and blue (445 nm) wavelengths at different light intensities on tomato plant growth. Plants were treated for 12 days with combined light-emitting diode (LED) wavelengths, at a photosynthetic photon flux density (PPFD) ranging from 232 to 1660 μmol m−2s−1 with a 16 h d−1 photoperiod. Mean fresh mass of tomato plants treated with amber-red light (AR) was 22% greater than plants treated with blue-amber (BA) light and 67% greater than blue-red (BR) light. Plants treated with BA exhibited 36% greater fresh mass than plants treated with BR light. Mean dry mass of plants treated with AR light was 30% greater compared to BR light, and the dry mass of plants treated with BA and BR was statistically similar. Plants grown under BR had 28% and 35% smaller leaf area compared with those grown under BA and AR, respectively. Mean height of the plants treated with AR increased by 24 and 52% compared to plants grown under BA and BR lights, respectively. Maximum stem diameter was observed at 1000 μmol m−2s−1 for AR and BA, and 1200 μmol m−2s−1 for BR. Specific leaf area (SLA) decreased with the increase of PPFD levels up to 1000 μmol m−2s−1 for all the light treatments. A PPFD above 1000 μmol m−2s−1 showed an increase in SLA for plants cultivated with AR and AB. SLA for plants treated with RB was stable above 1000 μmol m−2s−1 PPFD levels. Plants treated with BR light had 25 and 38% higher chlorophyll content compared to plants treated with BA and AR light, respectively. Maximum yield and chlorophyll content data indicate that using Chl content to correlate full plant photosynthetic and growth potential is inappropriate. Findings suggest that a high percentage of amber light (>75%) in a full-spectrum LED regimen may augment controlled environment crop production.

Efficacy of 405 nm Light-Emitting Diode Illumination and Citral Used Alone and in Combination for Inactivation of Vibrio parahaemolyticus on Shrimp

Vibrio parahaemolyticus is a widely distributed pathogen, which is frequently the lead cause of infections related to seafood consumption. The objective of the present study was to investigate the antimicrobial effect of the combination of 405 nm light-emitting diode (LED) and citral on V. parahaemolyticus. The antimicrobial effect of LED illumination and citral was evaluated on V. parahaemolyticus not only in phosphate-buffered saline (PBS) but also on shrimp. Quality changes of shrimp were determined by sensory evaluation. Changes in bacteria cell membrane morphology, cell membrane permeability, cell lipid oxidation level, and DNA degradation were examined to provide insights into the antimicrobial mechanism. The combination of LED treatments and citral had better antimicrobial effects than either treatment alone. LED combined with 0.1 mg/mL of citral effectively reduced V. parahaemolyticus from 6.5 log CFU/mL to below the detection limit in PBS. Combined treatment caused a 3.5 log reduction of the pathogen on shrimp within 20 min and a 6 log reduction within 2 h without significant changes in the sensory score. Furthermore, combined LED and citral treatment affected V. parahaemolyticus cellular morphology and outer membrane integrity. The profile of the comet assay and DNA fragmentation analysis revealed that combination treatment did not cause a breakdown of bacterial genomic DNA. In conclusion, LED may act synergistically with citral. They have the potential to be developed as novel microbial intervention strategies.

Low Concentration of Anti-Auxin and Anti-Fungal Agent Accelerates the PLB Regeneration of Dendrobium okinawense under Green LED.

Dendrobium okinawense is an endangered epiphytic orchid, and there has been no scientific report so far on its propagation. Protocorm is a mass of cells, and protocorm-like bodies (PLBs) are lookalike protocorms produced by vegetative explants in vitro. Regeneration of PLBs is a widely used technique for orchid micropropagation. We used different light-emitting diodes (LEDs) for the PLB regeneration of D. okinawense. The number of PLBs and fresh weight were increased by 81.1% and 80.8%, respectively, under green LED over the white fluorescent (WF) light. We added different concentrations of PCIB (p-Chlorophenoxyisobutyric acid, an anti-auxin) and HMI (3-Hydroxy-5-methyl isoxazole, an anti-fungal agent) in culture media. The number of PLBs was increased in media having 0.01 mg/L of PCIB (35.9%) compared to control (no PCIB), whereas 19.3% increased in media having 0.01 mL/L of HMI compared to control (no HMI). Green LED in combination with 0.01 mg/L of PCIB significantly increased the number of PLBs (69.0%) compared to the WF–without PCIB combination. In LEDs-PCIB and LED-HMI combinations, HMI did not show better PLBs regeneration compared with PCIB. The results suggested that a combination of low concentrations of PCIB and green LED have the potential to accelerate PLB regeneration of D. okinawense.

Efficacy of 405-nm LED illumination and citral used alone and in combination for the inactivation of Cronobacter sakazakii in reconstituted powdered infant formula

Cronobacter sakazakii, a foodborne opportunistic pathogen, mainly affects neonates and infants, with mortality rates of 26.9%. Most outbreaks arise from powdered infant formula (PIF). The aim of this study was to investigate the efficacy and mechanism of 405-nm light-emitting diode (LED) and citral treatment used in combination against C. sakazakii in reconstituted PIF. LED-illumination combined with citral showed better antimicrobial effects than either treatment alone. In reconstituted PIF, the abundance of C. sakazakii cells was reduced by 6.5 log 10 CFU/mL following combined LED and 9 µL/mL citral treatment for 90 min compared with untreated controls, respectively. Combined LED and 6 µL/mL citral treatment destroyed C. sakazakii cellular morphology and membrane integrity, prolonged the recovery time of sublethally-injured cells, and induced lipid peroxidation. Besides, LED treatment decreased the amount of lipid peroxidation caused by citral treatment alone. Neither LED illumination nor citral treatment resulted in breakdown of C. sakazakii genomic DNA. Because of its safe, environmentally-friendly, economical, and high-performance characteristics, the combination of LED-illumination and citral treatment has the potential to be developed into a strategy to control C. sakazakii contamination in stored and reconstituted PIF.

The LED wavelength, lighting intensity, feather coverage, and novelty inclusion in turkey hens

Light-emitting diodes (LED) have been gaining acceptance in agriculture applications as alternatives to incandescent light sources. Daylength intensity and spectral wavelength are important in poultry production and also, in some cases, serve as the only mean of light in some facilities. Therefore, Large White turkey hens of the same strain were reared to market weights using two different housing facilities in combination with different LED light treatments. Each treatment within the environmentally controlled facility (ECF) consisted of four replicate rooms, 16 rooms total in the facility. LED bulbs consisted of 5,000 Kelvin (K) or 2,700K LED in conjunction with a high or low foot-candle (FC) intensity level. Daylength was fixed at 14L:10D. Additionally, birds were reared in a natural curtain-sided facility (6 replicate pens) with exposure to natural light with a 75W incandescent bulb to maintain daylength consistency with the ECF. Performance parameters were measured at 0, 5th, 9th, and 12th week (wk) of age. Serum triiodothyronine (T3) and right eye measurements were taken at the 5th and 9th wk of age. Feather coverage was assessed at the 9th and 12th wk old as indicators of bird wellbeing. Novelty interactions for visual or nutritional items were recorded at 7th wk old. Spectral output within the same Kelvin temperature was significantly altered during dimming to achieve intensity levels. There were mixed performance results; however, cumulatively, birds reared under LED lighting, regardless of LED type or intensity level, had consistently increased body weight. Bird wellbeing was altered under 5,000K LED in combination with 2 FC as measured by a significant elongation of the anterior-posterior distance. However, the same effect was not measured in the 5,000K, 10 FC treatment, or in the 2,700K treatments, regardless of FC measurement. There were no differences among treatments for T3, feather coverage, or latency to approach or interact with novel items. When LED lights are used in environmentally controlled facilities, coupled with novelty interactions, birds maintained and excelled in performance parameters when compared to birds reared with natural light and ventilation conditions.

Application of blue light-emitting diode in combination with antimicrobials or photosensitizers to inactivate Escherichia coli O157:H7 on fresh-cut apples and cherry tomatoes

The aim of this study was to investigate the antibacterial effect of blue light-emitting diode (blue-LED; 460–470 nm) combined with various chemicals at inactivating Escherichia coli O157:H7 on the surface of agar media and fresh produce. Fresh-cut apples and cherry tomatoes were immersed in antimicrobials (1 % ascorbic acid, 0.025 % carvacrol, and 0.125 % citric acid) or photosensitizers (0.0078 % curcumin and 0.0078 % riboflavin) on the inactivation of E. coli O157:H7 during illumination for 5 d at 4 °C. When carvacrol was combined with blue-LED, there was a higher reduction in E. coli O157:H7 populations compared with treatment with blue-LED, an antimicrobial, or a photosensitizer alone. In particular, among the chemicals tested, the populations of E. coli O157:H7 on cherry tomatoes was reduced below detectable level (<1.48 log10 CFU/g) when treated with the combination of carvacrol or ascorbic acid and blue LED after storage of 5 d, without causing color deterioration. BI values were significantly reduced by the combined treatment of carvacrol (38.30), citric acid (37.67) or ascorbic acid (39.85) with blue LED for 5 d when compared to control (59.36). These results indicates that blue-LED in combination with antimicrobials or photosensitizers, may be applied to extend the shelf-life of fresh-cut fruits and vegetables during distribution without causing color deterioration.

Anti-Early Stage of Bacterial Recolonization Effect of Curcuma longa Extract as Photodynamic Adjunctive Treatment.

Objective To evaluate the amount of Fusobacterium nucleatum (F. nucleatum) and Prevotella intermedia (P. intermedia) on subgingival recolonized plaque after mechanical debridement and photodynamic treatment by using blue light-emitting diodes (LEDs) in combination with topical Curcuma longa gel extract. Methods A total of 12 subjects with stage III grade B periodontitis were recruited for the study. Maxillary posterior teeth with periodontal pocket >4 mm were selected. These teeth were examined for periodontal clinical data at baseline and at 1, 2, 4, and 6 weeks after treatment. All remaining teeth were treated by scaling and root planing (SRP). Then, the teeth were bilaterally divided using randomized split-mouth design with and without photodynamic adjunctive therapy (PDT). Samples of the subgingival microbiota were obtained in each visit. All samples were analyzed by multicolor TaqMan real-time polymerase chain reaction (PCR) for the presence of target bacteria. Results Throughout the six-week follow-up, long-term improvement of probing depth and bleeding on probing was revealed on the PDT group. The number of subgingival F. nucleatum and P. intermedia also significantly reduced, compared to the baseline. There was a statistically significant recolonization in F. nucleatum and P. intermedia number after 2 and 4 weeks of conventional SRP, respectively. Our quantitative PCR method showed no significant recolonization of those subgingival bacteria on PDT sites throughout the 6-week study duration. Conclusion The results showed that adjunctive photodynamic treatment by using blue LEDs in combination with topical Curcuma longa gel extract was effective to alter the recolonization patterns of F. nucleatum and P. intermedia after conventional debridement.

Synergistic effects of blue light-emitting diodes in combination with antimicrobials against Escherichia coli O157:H7 and their mode of action

This study was conducted to evaluate the antibacterial effect of 460–470 nm light-emitting diodes illumination (460/470 LED) combined with various antimicrobials at inactivating Escherichia coli O157:H7 and identify the antibacterial mechanisms. When carvacrol, thymol, citric acid, malic acid, citrus fruit extract, 3% NaCl, or 5% NaCl was combined with 460/470 LED, there was a higher reduction in E. coli O157:H7 compared to 460/470 LED treatment or antimicrobials alone at 4 °C. Particularly, a marked synergistic effect (>8.74 log10 CFU/ml) was observed when 460/470 LED was combined with carvacrol, malic acid, citrus fruit extract, or 3% NaCl. Levels of intracellular ROS and lipid peroxidation of E. coli O157:H7 were higher in the combination of 460/470 LED and antimicrobials compared to individual treatments. Moreover, the combination treatment increased depolarization of the cell membrane leading to membrane damage as well as the loss of DNA integrity. Thus, adding antimicrobial treatment to 460/470 LED could improve its efficacy against pathogenic bacteria such as E. coli O157:H7.

Efficacy of LED-enhanced blue sticky traps combined with the synthetic lure Lurem-TR for trapping of western flower thrips (Frankliniella occidentalis)

Pest monitoring is an important tool for successful integrated pest management programmes. Blue sticky traps are important for monitoring western flower thrips, Frankliniella occidentalis, in greenhouses. However, blue sticky traps have three major weak points: (1) efficacy depends on reflection of light, which varies in intensity with fluctuating light conditions (season, diurnal rhythmic pattern), (2) they reflect broad wavelength pattern not optimally matching with maximum sensitivity of WFT photoreceptors, and (3) they offer no olfactory cues which are important for thrips orientation. This study explored the most attractive wavelength range for WFT using broad range of narrow-bandwidth light-emitting diodes (LEDs) in order to improve the attractiveness of blue sticky traps. Subsequently, trapping efficacy of the most attractive blue LED in combination with blue sticky trap and addition of an attractive lure (Lurem-TR) was evaluated in flight cages under greenhouse conditions. Release-capture studies revealed that LEDs with peak emission of 445 nm were clearly more effective than conventional blue sticky traps. In choice experiments, up to 2.7-fold and in no-choice experiment up to 2.1-fold more WFT were captured by LED-blue sticky traps compared to conventional reflecting blue sticky traps. Lurem-TR improved the performance of blue sticky traps and LED-blue sticky traps 2.3-fold and 2.0-fold, respectively, as compared to those without Lurem-TR. The addition of LEDs and kairomone lure to blue sticky traps seems promising for improving WFT trapping, specifically at low population densities especially during early infestation. However, these results should be further validated under more complex, large field conditions.

Hermitian symmetry free optical-single-carrier frequency division multiple access for visible light communication

Optical-orthogonal frequency division multiplexing (O-OFDM) is an effective scheme for visible light communications (VLC), offering a candid extension to multiple access (MA) scenarios, i.e., O-OFDMA. However, O-OFDMA exhibits high peak-to-average power ratio (PAPR), which exacerbates the non-linear distortions from the light emitting diode (LED). To overcome high PAPR while sustaining MA, optical-single-carrier frequency-division multiple access (O-SCFDMA) is used. For both O-OFDMA and O-SCFDMA, Hermitian symmetry (HS) constraint is imposed in frequency-domain (FD) to obtain a real-valued time-domain (TD) signal for intensity modulation-direct detection (IM-DD) implementation of VLC. Howbeit, HS results in an increase of PAPR for O-SCFDMA. In this regard, we propose HS free (HSF) O-SCFDMA (HSFO-SCFDMA). We compare HSFO-SCFDMA with several approaches in key parameters, such as, bit error rate (BER), optical power penalty, PAPR, quantization, electrical power efficiency and system complexity. BER performance and optical power penalty is evaluated considering multipath VLC channel and taking into account the bandwidth limitation of LED in combination with its optimized driver. It is illustrated that HSFO-SCFDMA outperforms other alternatives.

Antibacterial effect of 460 nm light-emitting diode in combination with riboflavin against Listeria monocytogenes on smoked salmon

This study investigated the antibacterial effect of a 460 nm light emitting diode (LED) in combination with riboflavin on the inactivation of Listeria monocytogenes on smoked salmon. The influence of irradiance and temperature on this inactivation was examined. Smoked salmon fillets, surface-inoculated with a 4-strain cocktail of L. monocytogenes and topically administered with 25, 50 and 100 μM riboflavin, were illuminated by 460 nm LEDs at three different irradiances (15, 31 and 58 mW/cm2) and two temperatures (4 and 12 °C). Three conceptually different mathematical models - log-linear, modified Weibull and reduced Baranyi were used to fit the inactivation curves. The color of smoked salmon was also monitored during the illumination. A dosage of 2.4 kJ/cm2 LED illumination in combination with riboflavin caused 0.7–1.2 log CFU//cm2 reductions of L. monocytogenes at all irradiances and temperatures. Three-way ANOVA showed that all the three variables significantly influenced the inactivation of L. monocytogenes (P < 0.05). Significant interaction was observed between concentration and irradiance at 12 °C. Mathematical modeling suggested that the Weibull as well as the Baranyi model best fitted the inactivation curve and thus the Weibull model was subsequently used to compute the dose required for the first log reduction (δ). In most cases, the combination of LEDs and riboflavin was more effective than either treatment alone. The results of this study demonstrate the potential of 460 nm LEDs aided by riboflavin to minimize the risk of L. monocytogenes associated with smoked salmon during storage at food establishments.

Antibacterial effect of 405 ± 5 nm light emitting diode illumination against Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella on the surface of fresh-cut mango and its influence on fruit quality

To investigate a potential of 405±5nm light emitting diode (LED) as a novel technology for food preservation, the antibacterial effect of 405±5nm LED on Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella spp. on the surface of fresh-cut mango and its influence on fruit quality were evaluated at different storage temperatures. LED-illumination inactivated 1.0–1.6 logCFU/cm2 of populations at 4 and 10°C for 36–48h (total dose, 2.6–3.5kJ/cm2) regardless of bacterial species, while those on non-illuminated mange remained unchanged or slightly increased during storage. At 20°C for 24h (total dose, 1.7kJ/cm2), non-illuminated E. coli O157:H7 and Salmonella gradually grew, whereas LED-illumination reduced 1.2 log of Salmonella and inhibited the growth of E. coli O157:H7. Unlike these, non-illuminated L. monocytogenes cells rapidly increased to 7.3 log, while illuminated cells reached 4.6 log, revealing that LED-illumination delayed their growth. There were no significant (P>0.05) differences in color, antioxidant capacity, ascorbic acid, β-carotene, and flavonoid between non-illuminated and illuminated cut mangoes, regardless of storage temperature. These results suggest that 405±5nm LEDs in combination with chilling temperatures could be applied to preserve fresh-cut fruits without deterioration of physicochemical quality of fruits at food establishments, minimizing the risk of foodborne disease.

Metallic nanostructures for efficient LED lighting.

Light-emitting diodes (LEDs) are driving a shift toward energy-efficient illumination. Nonetheless, modifying the emission intensities, colors and directionalities of LEDs in specific ways remains a challenge often tackled by incorporating secondary optical components. Metallic nanostructures supporting plasmonic resonances are an interesting alternative to this approach due to their strong light–matter interaction, which facilitates control over light emission without requiring external secondary optical components. This review discusses new methods that enhance the efficiencies of LEDs using nanostructured metals. This is an emerging field that incorporates physics, materials science, device technology and industry. First, we provide a general overview of state-of-the-art LED lighting, discussing the main characteristics required of both quantum wells and color converters to efficiently generate white light. Then, we discuss the main challenges in this field as well as the potential of metallic nanostructures to circumvent them. We review several of the most relevant demonstrations of LEDs in combination with metallic nanostructures, which have resulted in light-emitting devices with improved performance. We also highlight a few recent studies in applied plasmonics that, although exploratory and eminently fundamental, may lead to new solutions in illumination.

Tetraphenylpyrazine-Based Luminogens with Aggregation-Enhanced Emission Characteristics: Preparation and Property

The research on aggregation-induced emission (AIE) has been a hot topic in the fields of photo-physics and luminescent materials. Design and synthesis of new AIE-active luminogens (AIEgens) will further promote the development of this area. Based on our developed new AIEgen of tetraphenylpyrazine (TPP), in this paper, we further enriched its family by covalently attaching thiophene unit on TPP core, and prepared three AIEgens of TPP-T, TPP-2T and T-TPP-T. Their structure-property relationship was studied in detail. The results showed that TPP-T, TPP-2T and T-TPP-T feature the aggregation-enhanced emission (AEE) characteristics. Their powders emit at 418, 437 and 436 nm with absolute fluorescence quantum yields of 26.8, 29.0 and 30.9%, respectively, which makes them promising to be used as emitting layer in fabrication of organic light-emitting diodes in combination with their excellent thermal stability.

Phosphors by Design: Approaches Toward the Development of Advanced Luminescent Materials

1Replacing inefficient incandescent light bulbs with energy-efficient light emitting diode (LED) technology is one of the best opportunities to dramatically reduce energy use due to their outstanding efficiency. 2 LED lights have additional advantages of longer lifetimes compared to incandescent bulbs, they are compact in physical size, and they are composed of environmentally benign materials, unlike compact fluorescent bulbs that contain toxic heavy metals. This has led to the use of LEDs in a range of applications from indicator lights to display backlighting; yet, to truly impact global energy use, their use is necessary in homes as general white luminaries. There are three principle strategies for creating a useful broad spectrum white light from a monochromatic LED. 3,4 One employs multiple LEDs, e.g., red, green, and blue, in a single device, as illustrated in Fig. 1a. Although viable, the low efficiency and shorter lifetime of green LEDs along with the need for complex circuitry prevents the current widespread use of these devices. Another solution uses a UV (or near-UV) LED in combination with three (red, green, and blue) inorganic phosphors (Fig. 1b). Here, the narrow LED emission is completely converted to longer wavelengths by three rareearth substituted inorganic phosphors that when blended in the correct ratios produces white light. The third, and industry standard approach, is to generate white light by using rare-earth substituted (usually Ce 3+

적색, 초록, 청색 및 혼합광 LED 조사의 식중독균 저해 효과

The antimicrobial properties of Light-Emitting Diode (LED) are an area of increasing interest. The aim of this study was to evaluate the bactericidal effects of blue (peak at 456 nm), green (peak at 518 nm), red (peak at 654 nm) and blue-green combined (blue 456 nm : green 558 nm = 69:31) LED irradiation to pathogenic bacteria. For this, LED equipment providing power density of <TEX>$10mW/cm^2$</TEX> was installed and plates were exposed to 0.9 or <TEX>$3.0mW/cm^2$</TEX> to irradiate bacteria with 3.2 to <TEX>$259.2mW/cm^2$</TEX> of energy density. As a result, blue and combined LED have shown bactericidal effects on Escherichia coli KCTC 1467 and Listeria monocytogenes ATCC 19115 after irradiation of <TEX>$3.0mW/cm^2$</TEX> for 2 and 4 hr, respectively. Staphylococcus aureus KCTC 1916 was inhibited at 518 nm green LED irradiation. However, red LED irradiation showed no inhibitory effect to the other tested strains. Light technology that utilizes the bactericidal properties of blue (at 456 nm) and blue-green(blue 456 nm : green 558 nm = 69:31) combined LED may have potential applications in the food industry sector.

Comparison of the efficiency of titanium(IV) and iron(III) oxide nanoparticles as mediators in suppression of bacterial growth by radiation of a blue (405 nm) light-emitting diode

The effect of blue (405 nm) radiation of a light-emitting diode in combination with titanium(IV) and iron(III) oxide nanoparticles on S. aureus 209 P, S. simulans, and D. hominis bacteria is studied. It is shown that, upon irradiation of bacteria by blue (405 nm) light, Fe2O3 nanoparticles have a stronger (by 5–30%) antibacterial effect than TiO2 nanoparticles.

Antibacterial effect of light emitting diodes of visible wavelengths on selected foodborne pathogens at different illumination temperatures

The antibacterial effect of light emitting diodes (LEDs) in the visible region (461, 521 and 642nm) of the electromagnetic spectrum was investigated on Escherichia coli O157:H7, Salmonella typhimurium, Listeria monocytogenes and Staphylococcus aureus. The irradiances of the 461, 521 and 642nm LEDs were 22.1, 16 and 25.4mW/cm2, respectively. Bacterial cultures suspended in tryptic soy broth were illuminated by 10-watt LEDs at a distance of 4.5cm for 7.5h at 20, 15 and 10°C. Regardless of the bacterial strains, bacterial inactivation was observed with the range of 4.6–5.2logCFU/ml at 10 and 15°C after illumination with the 461nm LED, while illumination with the 521nm LED resulted in only 1.0–2.0 log reductions after 7.5h. On the other hand, no antibacterial effect was observed using the 642nm LED treatment. The photodynamic inactivation by 461 and 521nm LEDs was found to be greater at the set temperatures of 10 and 15°C than at 20°C. The D-values for the four bacterial strains at 10 and 15°C after the illumination of 461nm LED ranged from 1.29 to 1.74h, indicating that there was no significant difference in the susceptibility of the bacterial strains to the LED illumination between 10 and 15°C, except for L. monocytogenes. Regardless of the illumination temperature, sublethal injury was observed in all bacterial strains during illumination with the 461 and the 521nm LED and the percentage of injured cells increased as the treatment time increased. Thus, the results show that the antibacterial effect of the LEDs was highly dependent on the wavelength and the illumination temperature. This study suggests the potential of 461 and 521nm LEDs in combination with chilling to be used as a novel food preservation technology.

A batch LED reactor for the photocatalytic degradation of phenol

Photocatalytic degradation of phenol by titanium dioxide illuminated by one light emitting diode (LED) in a batch photocatalytic reactor is reported in this paper. The effect of catalyst loading, catalyst type, phenol–hydrogen peroxide ratio, pH, initial phenol concentration and irradiance by applying pulse width modulation (PWM) was studied. The effect of the beam width on photocatalytic degradation of phenol is also included in this paper as is the use of different type of reflectors outside the reactor. With both an LED beam width of 120° and optimal chemical conditions of 10ppm phenol concentration with a hydrogen peroxide–phenol molar ratio of 100 and pH of 4.8, a degradation rate of 42% was achieved after 4h. Decreasing the beam width to 40° raised degradation to 87%.In order to study the irradiance distribution and its effect on the reactor performance, experiments were conducted incorporating various catalysts loading, reactor heights and beam widths. The irradiance was measured for different amount of catalyst loading ranging from 0.17 to 1.8gL−1at different reactor heights. The results are compared with optimal catalyst loading measurement to assess the correlation between phenol degradation and irradiance distribution. The UV LED in combination with titanium dioxide is appropriate for water treatment to degrade organic pollutants at low concentration.