Light Intensity Of Light-emitting Diodes Research Articles

Effectiveness of laser pulsed irradiation for antimicrobial photodynamic therapy

The aim of this study was to compare two types of light irradiation devices for antimicrobial photodynamic therapy (aPDT). A 660-nm light-emitting diode (LED) and a 665-nm laser diode (LD) were used for light irradiation, and 0.1 mg/L TONS 504, a cationic chlorin derivative, was used as the photosensitizer. We evaluated the light attenuation along the vertical and horizontal directions, temperature rise following light irradiation, and aPDT efficacy against Staphylococcus aureus under different conditions: TONS 504 only, light irradiation only, and TONS 504 with either LED (30 J/cm2) or LD light irradiation (continuous: 30 J/cm2; pulsed: 20 J/cm2 at 2/3 duty cycle, 10 J/cm2 at 1/3 duty cycle). Both LED and LD light intensities were inversely proportional to the square of the vertical distance from the irradiated area. Along the horizontal distance from the nadir of the light source, the LED light intensity attenuated according to the cosine quadrature law, while the LD light intensity did not attenuate within the measurable range. Following light irradiation, the temperature rise increased as the TONS 504 concentration increased in the order of pulsed LD < continuous LD < LED irradiation. aPDT with light irradiation only or TONS 504 only had no antimicrobial effect, while aPDT with TONS 504 under continuous or pulsed LD light irradiation provided approximately 3 log reduction at 30 J/cm2 and 20 J/cm2 and approximately 2 log reduction at 10 J/cm2. TONS 504-aPDT under pulsed LD light irradiation provided anti-microbial effect without significant temperature rise.

Photoluminescence measurement of ruby excited by duty ratio-controlled pulse light-emitting diodes (LED) light source.

Photoluminescence (PL) spectra from ruby were obtained using a highly stable LED light source, employing pulse width modulation technique for excitation. The temporal variation in PL intensity caused by the increasing temperature of the LED used for excitation can be mitigated by adjusting the duty ratio (%) of the pulsed LED light to below 10% for cooling the LED. Stable PL spectra measurements were achieved with a duty ratio of less than 10% using a duty ratio-controlled pulsed LED light source, as temperature fluctuations in LED light intensity are minimized at duty ratios less than 10%. Furthermore, fluctuations in the measured PL intensity were diminished by setting the frequency of the pulsed LED light source to greater than 1kHz. This method enables more reliable, cost-effective, and stable PL measurements for material characterization in semiconductors, photonics, and nanotechnology.

Study on Smart Street Light (SSL) using Ultra Narrowband (UNB) Technology: a case study of Malaysia Power Utility

Street light is important to road user and residential area to improve visibility and creating safer road by preventing traffic accidents and also by reducing crime. However, present practice for street lighting management largely remains a challenge. Smart Street Lighting (SSL) system is a system where the street lighting system adds up with communication technology producing a real time monitoring system. Smart Street Lighting (SSL) is known to gain high value creation through maintenance savings and improvement of the environmental impact for Malaysia. Tenaga Nasional Berhad (TNB) through its research arm, TNB Research (TNBR) has recently carried a feasibility study on the compatibility of SSL system using Ultra Narrowband (UNB) technology on the energy efficient and better light intensity of light-emitting diode (LED) lighting technology street light. The SSL systems have been deployed on a small scale, tested and monitored at selected areas. This paper discussed the technical performance such as functionality and compatibility that have been assessed in the study.

Kajian Penggunaan LED pada Pertumbuhan Tanaman Kailan dengan Sistem Hidroponik Dalam Ruangan

The use of LED (Light Emitting Diode) in indoor hydroponic systems can optimize the process of photosynthesis in plants. This can be a replacement of sunlight during plant growth. This study aims to examine the treatment of LED light intensity and duration of irradiation on the vegetative growth of kailan (Brassica oleracea var. alboglabra L) in indoor hydroponic systems. This experimental study consisted of 5 treatments: exposure to white (A1) and blue (A2) LED lights, exposure time of 16 hours (B1) and 20 hours (B2) and sunlight (K0) as a control in a greenhouse. Treatment with LED lights placed in the growth chamber. Treatment consisted of 4 replicates with a total of 20 plants. The results showed that the white LED light intensity and 20 hours of irradiation time were better than other treatments including plant height, stem diameter, leaf width, leaf length, number of leaves, fresh weight, root weight and water efficiency.

Effect of 450 nm Visible Blue Light from Light-Emitting Diode on Escherichia coli O157:H7 in Agar Gels: Optimizing the Lighting Array and Quantitative Microbial Exposure Assessment

Visible blue light emitting diodes (LED) have been studied to inactivate Escherichia coli (E. coli) O157:H7 in agar gels. The LED array was optimized to attain uniform light illumination, and the light intensity distribution was visualized through optical simulation. The uniformity of LED light intensity was assessed, and the evenly spaced array showed the best uniformity with a Petri factor of 0.99. Microbial populations in agar gels prepared with and without a dye were analyzed after light irradiation. Each segment of the gels with different heights was taken to measure microbial reduction, and the results indicated that optical properties, such as opaqueness, played an important role in microbial reduction. The agar gel without and with a dye showed a maximum reduction of &lt;3.4 and &lt;2.1 log CFU/g, respectively. An exposure assessment for E. coli O157:H7 was conducted based on the assumption for the agar gel product after LED illumination. The probability results indicated that a risk (&gt;5 log CFU/g) existed mainly in the bottom layer of the sample, despite the average contamination being &lt;5 log CFU/g. This study provides a suitable approach for designing the LED photoinactivation process and subsequent exposure assessment to avoid risk.

Different LED light intensity and quality change perennial ryegrass (Lolium perenne L.) physiological and growth responses and water and energy consumption.

Light intensity and spectral composition highly affect plant physiology, growth, and development. According to growing conditions, each species and/or cultivar has an optimum light intensity to drive photosynthesis, and different light spectra trigger photosynthetic responses and regulate plant development differently. For the maintenance of natural sports pitches, namely professional football competitions, turf quality is a key condition. Due to the architecture of most football stadiums, the lawns receive low intensities of natural light, so supplementary artificial lighting above the turf is required. The use of light-emitting diodes (LEDs) can have a higher cost-benefit ratio than traditional high-pressure sodium lamps. The continuous emission spectrum, combined with high spectral selectivity and adjustable optical power, can be used to optimize plant growth and development. Thus, perennial ryegrass (Lolium perenne L.) plants, commonly used for lawns, were primarily grown at three different intensities (200, 300, and 400 μmol m-2 s-1) of cool white light. Despite the higher water and energy consumption, 400 μmol m-2 s-1 maximizes the plant's efficiency, with higher photosynthetic rates and foliar pigment concentration, and more foliar soluble sugars and aboveground biomass accumulation. Then, it was evaluated the perennial ryegrass (Double and Capri cultivars) response to different spectral compositions [100% cool white (W), 80% Red:20% Blue (R80:B20), 90% Red:10% Blue (R90:B10), and 65% Red:15% Green:20% Blue (R65:G15:B20)] at 400 μmol m-2 s-1. Both cultivars exhibited similar responses to light treatments. In general, W contributed to the better photosynthetic performance and R90:B10 to the worst one. Water consumption and aboveground biomass were equal in all light treatments. R80:B20 allows energy savings of 24.3% in relation to the W treatment, showing a good compromise between physiological performance and energy consumption.

Effect of White LED Light on the Growth of Apple Seedlings in Controlled Environment System

Plant growth in a controlled environment system is highly dependent on the availability of light. The light-emitting diode (LED) is capable of providing the needed quality and quantity of light for the plant. The purpose of this study was to determine the effect of white LED light intensity on the growth of in vitro propagated apple (M-9) seedlings in a controlled environment system. Seedlings were grown for 30 days under five different white LED light intensities: 100–500 (L1), 250–500 (L2), 500–500 (L3), 250–250 (L4), and 100–100 (L5). Our findings indicate that seedlings treated with L3 grew substantially taller than seedlings treated with L1, L2, or L5. The number of leaves, stem diameter, shoot fresh weight, root fresh weight, and shoot dry weight of L3 treated seedlings were considerably greater than those growing in other treatments. Furthermore, root length, root dry weight, chlorophyll content, and photosynthesis rate were considerably increased in the L3 treatment group compared to the L5 treatment group. However, there was no significant difference in the stomatal conductance or transpiration rate of apple seedlings between the light treatments. Moreover, a positive correlation was seen between stomatal conductance and transpiration rate. These results suggest that light intensity PPFD 500-500 were favorable for the initial growth of in vitro propagated apple seedlings.

Water, land, and energy use efficiencies and financial evaluation of air conditioner cooled greenhouses based on field experiments

High temperature and humidity can be controlled in greenhouses by using mechanical refrigeration cooling system such as air conditioner (AC) in warm and humid regions. This study aims to evaluate the techno-financial aspects of the AC-cooled greenhouse as compared to the evaporative cooled (EV-cooled) greenhouse in winter and summer seasons. Two quonset single-span prototype greenhouses were built in the Agriculture Experiment Station of Sultan Qaboos University, Oman, with dimensions of 6.0 m long and 3.0 m wide. The AC-cooled greenhouse was covered by a rockwool insulated polyethylene plastic sheet and light emitting diodes (LED) lights were used as a source of light, while the EV-cooled greenhouse was covered by a transparent polyethylene sheet and sunlight was used as light source. Three cultivars of high-value lettuce were grown for experimentation. To evaluate the technical efficiency of greenhouse performance, we conducted measures on land use efficiency (LUE), water use efficiency (WUE), gross water use efficiency (GWUE) and energy use efficiency (EUE). Financial analysis was conducted to compare the profitability of both greenhouses. The results showed that the LUE in winter were 10.10 and 14.50 kg/m2 for the AC- and EV-cooled greenhouses, respectively. However, the values reduced near to 6.80 kg/m2 in both greenhouses in summer. The WUE of the AC-cooled greenhouse was higher than that of the EV-cooled greenhouse by 3.8% in winter and 26.8% in summer. The GWUE was used to measure the total yield to the total greenhouse water consumption including irrigation and cooling water; it was higher in the AC-cooled greenhouse than in the EV-cooled greenhouse in both summer and winter seasons by almost 98.0%–99.4%. The EUE in the EV-cooled greenhouse was higher in both seasons. Financial analysis showed that in winter, gross return, net return and benefit-to-cost ratio were better in the EV-cooled greenhouse, while in summer, those were higher in the AC-cooled greenhouse. The values of internal rate of return in the AC- and EV-cooled greenhouses were 63.4% and 129.3%, respectively. In both greenhouses, lettuce investment was highly sensitive to changes in price, yield and energy cost. The financial performance of the AC-cooled greenhouse in summer was better than that of the EV-cooled greenhouse and the pattern was opposite in winter. Finally, more studies on the optimum LED light intensity for any particular crop have to be conducted over different growing seasons in order to enhance the yield quantity and quality of crop.

Wavelengths of LED light affect the growth and cannabidiol content in Cannabis sativa L

Given the special pharmacological value of cannabidiol (CBD), industrial hemp (hemp) has become a real “hot” crop. Though indoor farming of hemp has been widely used, the effects of red and blue light-emitting diode (LED) acting as supplementary light on the CBD synthesis in hemp remains unclear. Herein, a pot experiment with six treatments [CK, high-pressure sodium as light source, (R:B (ratio of red light to blue light) 9.30:1, PPFD (photosynthetic photon flux density) 191); LED1 (R:B 9.20:1; PPFD 129); LED2 (R:B 1.61:1; PPFD 540); LED3 (R:B 6.47:1; PPFD 28.2); LED4 (R:B 7.15:1; PPFD 41.7); LED5 (R:B 16.8:1; PPFD 252)] was carried out to study the effects of LED light quality on the growth and cannabinoid synthesis of hemp. Results showed that LED2 and LED5 could well maintain hemp growth compared with CK in terms of plant height, stem diameter, and leaf numbers. Compared with CK, the treatment of LED1, LED4, and LED3 significantly decreased the aboveground biomass, while LED2 and LED5 notably improved the aboveground biomass with an increment of 15.2 % and 55.1 %; the biomass of hemp flowers for LED2 and LED5 was markedly increased compared with that for CK with increments of 238 % and 61.5 %, respectively, but the other LED light treatments significantly reduced the flowers yield; LED2 could significantly increase the CBD content of both leaves (1.81 %) and flowers (5.83 %) compared to CK (leaves 1.38 %, flowers 4.27 %) while LED5 only notably increased the CBD content of leaves; among the LED treatments, the theoretic CBD yield for a per plant of LED2 and LED5 was 26.8 % and 9.0 % higher than that of CK. In conclusion, different red and blue LED light intensity ratios would dramatically influence the growth and cannabinoid synthesis of hemp, LED2 and LED5 can be good choices for indoor farming of hemp targeted for higher CBD yield.

Improvement of light intensity and efficiency of n-ZnO/NiO/p-GaN heterojunction-based white light emitting diodes using micro-/nanolens array

Our study proposes a technique to enhance light extraction efficiency of light emitting diodes (LEDs) by incorporating various micro-/nanolens arrays (MNLAs) on the substrate layer, which in turn increases the external quantum efficiency (EQE) of the LEDs. To simulate the LEDs, we utilized the finite difference time domain method. To achieve a white LED, we inserted a thin layer of NiO at the interface between the n-type ZnO and the p-type GaN. The basic n-ZnO/NiO/p-GaN heterojunction-based LED exhibited an EQE of 10.99% where the effective refractive index of the LED structure was 1.48. The EQE was further increased by engraving various planoconvex or planoconcave MNLA on the top surface of the substrate layer. A maximum EQE of 12.4% was achieved for convex-1 type (lens height of 0.5 μm and radius of 0.4 μm) elliptical lens engraved LED where the effective refractive index was 1.4. In addition, the peak electroluminescence (EL) light intensity of convex-1 lens-based LED was twice than the light intensity observed in basic LED. Because of excellent EL spectrum and significant amount of light throughout the visible spectrum, the proposed convex-1 structure-based LED can be considered as a prospective candidate for white LED.

Design and Application of Daylight-Based Lighting Controller on LED Luminaire

This paper proposes a control circuit for Light Emitting Diode (LED) luminaire based on the amount of daylight. This system uses both natural daylight and artificial light from a luminaire to reach the desired illuminance on a working plane. The control circuit operates by receiving an illuminance value from a light sensor and comparing it with a set value in the microcontroller before limiting the light intensity of LED by sending a control Pulse Width Modulation (PWM) signal to the LED driver. In the experimental setup, the controller and a physical model of a working space were built in order to field test the LED daylight control circuit. Electrical characteristics such as voltage, current, and power were measured with a power meter. Illumination characteristics in terms of illuminance on a working plane were determined using a lux meter. The results from actual field tests revealed that this LED control circuit was able to reduce the power consumption of the lighting system while keeping the illuminance on the working plane at the standard value. Both simulation results and the actual experiment of the control circuit proved that it could be used to improve the energy efficiency of both newly installed and retrofitted lighting systems.

Performance of Light Sources for Plants under Altered Gravity Conditions in Parabolic Airplane Flights

Performances of light sources, a halogen lamp, a fluorescent lamp and light emitting diodes (LEDs), commonly used for plant culture were examined under altered gravity conditions created during parabolic airplane flights. The surface temperatures of the light sources, irradiances, photosynthetic photon flux densities (PPFDs) and spectral distributions of radiation from the light sources were measured at the gravity levels of 0.01, 1.0 and 1.8 G for 20 s each during parabolic airplane flights. As a result, the surface temperature of the halogen lamp bulb increased most rapidly and the irradiance increased most remarkably among the three light sources at 0.01 G. On the contrary, the surface temperatures and light intensities of LEDs were most stable followed by the florescent lamp with gravity change. These characteristics of LEDs would be suitable for plant experiments and plant culture in space. Keyword(s): LED, light, microgravity, wavelength

Effects of Colored Light on Growth and Nutritional Composition of Tilapia, and Biofloc as a Food Source

Light stimulation and biofloc technology can be combined to improve the efficiency and sustainability of tilapia production. A 73-day pilot experiment was conducted to investigate the effect of colored light on growth rates and nutritional composition of the Nile tilapia fingerlings (Oreochromis niloticus) in biofloc systems. The effect of colored light on the nutritional composition of bioflocs as a food source for fish was measured. Three groups were illuminated in addition to natural sunlight with colored light using RGB light emitting diodes (LEDs) with peak wavelengths (λ) of 627.27 nm for red (R), 513.33 nm for green (G), and 451.67 nm for blue (B) light. LED light intensity was constant (0.832 mW / cm 2 ), and had an 18-h photoperiod of light per day throughout the study. The control group was illuminated only with natural sunlight (natural). Tilapia had an average initial weight of 0.242 g. There was a significant effect of colored light on tilapia growth and composition. The R group showed the best growth rate, highest survival, and highest lipid content. The B group showed homogeneous growth with the lowest growth rate and lipid content, but the highest protein level. On the other hand, the biofloc composition was influenced by the green light in the highest content of lipids, protein, and nitrogen-free extract.

Growth and glucosinolate profiles of a common Asian green leafy vegetable, Brassica rapa subsp. chinensis var. parachinensis (choy sum), under LED lighting

Technological advancements in light-emitting diode (LED) technology have led to the production, under controlled indoor conditions, of value-added crops that are high in nutritional or nutraceutical contents. In this study, the growth and glucosinolate (GSL) profiles of a common Asian vegetable, Brassica rapa subsp. chinensis var. parachinensis (choy sum or cai xin) were determined under LED lighting. The growth of choy sum was influenced by both the LED light intensity and spectrum, with plants grown under 160 μmol m−2 s−1 red-blue light (160RB) producing the highest shoot biomass (∼100–300 % increment in adult plants). GSL content was found to vary across growth stages regardless of LED treatment. Total GSLs per gram fresh weight were four times higher in one-leafed seedlings than in adult plants. A shift from a high proportion of aliphatic GSLs in one-leafed seedlings to indolic and aromatic GSLs in three-leafed seedlings and adult plants was attributed to an increase in the proportion of glucobrassicin and/or 4-hydroxy-glucobrassicin, and gluconasturtiin which are known to have anti-cancer properties. Our results will be useful for the production of GSL-enhanced vegetables through urban farming.

Effects of LED Light Color and Intensity on Feather Pecking and Fear Responses of Layer Breeders in Natural Mating Colony Cages.

Simple SummaryCommercial breeder farms are moving forward using colony cages due to high efficiency, low energy input, clean production, and as a result of the rising public concerns with respect to the welfare of hens in conventional cages. Compared with conventional cages, layer breeders in colony cage are the parent-stock of laying hens and are confined together with roosters. However, the use of colony cages is still in a preliminary stage due to behavioral issues such as feather pecking (FP) and cannibalism. These behaviors can cause poor health, poor welfare, and economic problems. It is necessary to identify effective and proximal management practices to alleviate the damage that is caused by FP and cannibalism in such colony cage systems. This study aims to mitigate the problems of FP and cannibalism by utilizing light environment regulation. Results of this study indicates that red light and low light intensity could effectively alleviate FP and cannibalism during the laying period. Such knowledge might help to understand FP behavior and stress susceptibility of hens in this system and will provide a basis for the optimization of the cage equipment and the regulation of light environment.Natural mating colony cages for layer breeders have become commonplace for layer breeders in China. However, feather pecking (FP) and cannibalism are prominent in this system. The objective of this study was to investigate the effects of four light-emitting diode (LED) light colors (white: WL, red: RL, yellow-orange: YO, blue-green: BG) with two light intensities for each color, on FP, plumage condition, cannibalism, fear, and stress. A total of 32 identical cages were used for the eight treatments (four replicates for each treatment). For both light intensities, hens in RL had a lowest frequency of severe FP, whereas hens in WL had the highest frequency of severe FP. Hens in RL and BG had better plumage conditions than in WL and YO. Compared with RL and BG treatments, hens treated with WL and YO had a significantly longer tonic immobility (TI) duration. Hens treated with RL had a higher concentration of 5-hydroxytryptamine (5-HT), a lower concentration of corticosterone (CORT), and a lower heterophil to lymphocyte ratio than WL and YO. Furthermore, RL could significantly reduce mortality from cannibalism. Overall, hens treated with RL and low light intensity showed a lower frequency of severe FP, less damaged plumage, were less fearful, had lower physiological indicators of stress, and had reduced mortality from cannibalism. Transforming the light color to red or dimming the light could be regarded as an effective method to reduce the risk of FP and alleviate the fear responses of layer breeders.

Optical System for Led Luminaire

Lighting devices are an important element of a large number of technical systems, including road, living, industrial lighting, lighting systems of vehicles. It is known that the light instrument must fulfill two basic lighting tasks: to redistribute the light source of light source in the right way and to limit its dazzling effect. The introduction of light-emitting diodes (LEDs) for lighting necessitated a completely new quality in the construction of luminaires. The different production technology required new methods and designing tools. It also challenged designers with new problems to solve. LEDs are light sources emitting in one hemisphere, which requires a special approach to designing an LED lighting unit. However, for the illumination of premises with high spans or streets, roads such a light distribution is not suitable. For luminaires with solid-state light sources, other materials and new technology must be used; moreover, light distribution needs to be formed using different methods.&#x0D; This paper presents the design process of a LED luminaire from concept to implementation, exemplified by road lighting, and describes the methods and procedures used by the designer. Also, technological problems influencing the quality of the above lighting are addressed. Optical systems for LEDs are considered. The peculiarities of the use of secondary optical elements in the form of lenses for purpose of obtaining different diagrams of the spatial distribution of light intensity of light-emitting diodes are analyzed. Features and problems of calculation of secondary optical systems are considered. Massive collimators do not have to be elements that focus a narrow beam of light. They are able to form a beam in accordance with any accepted distribution that is appropriate for a given application. They are also able to form a beam in a specific way that is required for outdoor lighting luminaires. The stages of a project for designing a road luminaire require the application of the knowledge and experience gained in various research projects. The design methods described in this paper have been developed designing activity and are also to be used successfully in lighting production.&#x0D;

Retinal damage after exposure to white light emitting diode lights at different intensities in Sprague-Dawley rats

Background: The usage of the light emitting diode (LED) has been increasingly applied in the illumination setting and electronic equipment. However, the effect of LED lights on the retina remains unclear. In this study, we observed and analyzed the impact of white LED lights at different intensities on the function and morphology of rat retinas. Methods: Thirty-six Sprague-Dawley rats weighing 150–180 g were randomly divided into six groups (n=6 in each group) including a normal control (NC) group, 4 white LED groups at different light intensities (4,000, 6,000, 7,000, and 10,000 lux), and an ultraviolet B (UVB) lighting group (302 nm, 1,000 µw/cm 2 ). After 24 hours of continuous illumination, full-field flash electroretinogram (FERG) and pathological examination were performed in each group. Results: As revealed by FERG, the impairment of retinal function gradually worsened with the increase of LED light intensity. In contrast, the UVB group had the most severe retinal function impairment. Particularly, the functional damage of rod cells and inner nuclear layer cells was the main FERG finding in each group. In the NC group, the retina had typical morphologies featured by well-defined structures, clearly visible border between the inner and outer segments, and neatly arranged inner and outer nuclear layer cells. After 24 hours of illumination, the inner and outer parts of the retina in the 4,000 lux group were still neatly arranged, along with a clear border; however, the inner and outer nuclear layers were randomly arranged, and some irregular nuclei and cells were lost. The damage of the internal and external retinal segments and the internal and external nuclear layers became more evident in the 6,000 lux group, 7,000 lux group, and 10,000 lux group. The UVB group had a more obviously disordered arrangement of inner and outer nuclear layers and loss of cells. Conclusions: Continuous exposure to white LED light can cause structural and functional damage to rat retinas, and such damage is related to the intensity of illumination. Therefore, the risk of retinal damage should be considered during LED illumination, and proper LED illumination intensity may help to maintain eye health.

A photochemistry-based method for optimising greenhouse supplemental light intensity

Supplemental lighting in greenhouses can increase crop growth, improving rates of greenhouse production. The advent of light-emitting diodes (LEDs) for photosynthetic lighting presents new opportunities for optimising greenhouse supplemental lighting control. Because LED light intensity can be controlled rapidly and precisely in real time, these lights can be controlled such that supplemental light is provided when it will be most efficiently used to drive photosynthesis. This approach to supplemental lighting control has the potential to reduce the electricity cost associated with greenhouse lighting while retaining the beneficial effects on crop growth, thereby decreasing the financial cost and improving the sustainability of greenhouse crop production. In this paper, an optimisation problem is formulated to minimise the total amount of electricity used by supplemental LED lights, subject to achieving a specified daily amount of photochemistry. An algorithm to solve the problem explicitly based on sufficient conditions for a global minimiser is developed. This method represents a computationally simple and broadly applicable means for minimising the amount of electricity required for supplemental lighting in greenhouses.

Properties of indirect composites polymerized with laboratory light-emitting diode units.

This study evaluated the light intensity of light-emitting diode (LED) units and the effects of five laboratory polymerization units on hardness and flexural strength. Two indirect composite materials (Cesead N and Solidex Hardura) were polymerized with five units (α-Light II, Hyper LII, LED Cure Master, Twinkle LED, and α-Light V). The light intensity of the devices was measured with a spectroradiometer. After light exposure, Knoop hardness number, flexural strength, and elastic modulus were determined. Evaluation of light intensity, using a wavelength range of 400 to 500 nm, revealed that the α-Light V and Hyper LII units had the highest light intensity. For the top surface of the two composites, the Knoop hardness number was significantly higher for the α-Light V and Hyper LII. For the two composite materials, flexural strength did not differ among the five polymerizing units. The present results indicate that the Cesead N and Solidex Hardura composites can be adequately polymerized with laboratory LED units.

Electrochemical-to-Optical Signal Transduction for Ion-Selective Electrodes with Light-Emitting Diodes.

Optical ion sensors normally have a relative narrow sensitive detection window. Here, based on multicolor light-emitting diodes (LEDs), we report on an electrochemical-to-optical signal transduction scheme under chronoamperometry control to convert the potentiometric response of ion-selective electrodes (ISEs) to optical output with tunable sensitivity and much wider response range. The sensing principle was demonstrated on K+, Ca2+, and Pb2+. LED light intensity was found to depend linearly on the concentration of monovalent ions. Optical signals could be captured with photomultiplier tubes or digital cameras, and a visual alarming system to monitor abnormal ion concentration was also developed from super-Nernstian electrodes.