Light-emitting Diode Source Research Articles

A broadband LED source in visible to short-wave-infrared wavelengths for spectral tumor diagnostics

Various tumor types exhibit the spectral fingerprints in the absorption and reflection spectra in visible and especially in near- to short-wave-infrared wavelength ranges. For the purpose of spectral tumor diagnostics by means of diffuse reflectance spectroscopy, we developed a broadband light emitting diode (LED) source consisting of a blue LED for optical excitation, Lu3Al5O12:Ce3+,Cr3+ luminescent garnet for visible to near infrared emissions, and Bismuth doped GeO2 luminescent glass for near-infrared to short-wave infrared emissions. It emits broad-band light emissions continuously in 470–1600 nm with a spectral gap at 900–1000 nm. In comparison to the currently available broadband light sources like halogen lamps, high-pressure discharge lamps and super continuum lasers, the light sources of this paper has significant advantages for spectral tissue diagnostics in high-spectral stability, improved light coupling to optical fibers, potential in low light source cost and enabling battery-drive.

Quantitative Analysis of Color Combination from LED and Laser Light Sources Using Modified CIE 1931 Color Space Coordinates

In this study, a quantitative analysis based on the color space coordinates CIE 1931 to determine the color combination from three LEDs (light emitting diode) sources and three laser sources separately, has been investigated. The light sources used in this research were three LEDs that emit blue light, green and red colors, and three laser sources that also emit blue light, green and red colors. Result of color combination from LEDs and laser light sources were detected using a spectrophotometer. The result of the light spectra were then analyzed using a set of color matching function that has been modified specially for the spectrophotometer used. This research produced quantitative analysis for 26 color combinations of LED light sources and 7 color combinations of laser light sources. The results of colors combination were ranging from blue, cyan, yellow, orange, red to purple. Further development is still required to obtain reliable quantitative analysis results.

Wireless networks of energy efficient dynamically controlled LED sources

The paper presents the results of development and practical implementation of wireless networks of controlled spectrally tunable light emitting diode (LED) light sources using RF transceivers operating in the unlicensed frequency bands of 868 and 2400MHz. Such sources allow synthesizing either a white light with various color temperatures or a colored light with different tints; they are of significant interest in connection with general lighting and with some special applications. The problems of practical realization of light sources and their optimization with respect to luminous efficiency, dynamic range and the distance of wireless control have been investigated.

Efficient splitting of broadband LED light into narrowbands using superlensing effect and defects on its top 2D photonic crystal

In this work, design of a photonic crystal (PhC) based structure is proposed for efficient splitting of light from broadband Light Emitting Diode (LED) into multiple narrowband sources. InP based transverse junction LED is considered. A vertical stack of two-dimensional (2D) square lattice PhC made up of GaAs/air is placed on top of this LED. 2D periodicity of the PhC is in the vertical plane of the top surface of the LED. On removal of a few GaAs rods the broadband light is focussed by effect of superlensing on the resulting T-type channel. The simulated result is studied by creation of curved air hole on the superlensing PhC. Only TM polarized light of specific wavelength ranges from the LED source is considered for narrowbands splitting as the TE polarized light does not have suitable bandgap there.

Blue light hazard optimization for white light-emitting diode sources with high luminous efficacy of radiation and high color rendering index

Blue light hazard of white light-emitting diodes (LED) is a hidden risk for human’s photobiological safety. Recent spectral optimization methods focus on maximizing luminous efficacy and improving color performances of LEDs, but few of them take blue hazard into account. Therefore, for healthy lighting, it’s urgent to propose a spectral optimization method for white LED source to exhibit low blue light hazard, high luminous efficacy of radiation (LER) and high color performances. In this study, a genetic algorithm with penalty functions was proposed for realizing white spectra with low blue hazard, maximal LER and high color rendering index (CRI) values. By simulations, white spectra from LEDs with low blue hazard, high LER (≥297lm/W) and high CRI (≥90) were achieved at different correlated color temperatures (CCTs) from 2013K to 7845K. Thus, the spectral optimization method can be used for guiding the fabrication of LED sources in line with photobiological safety. It is also found that the maximum permissible exposure duration of the optimized spectra increases by 14.9% than that of bichromatic phosphor-converted LEDs with equal CCT.

Analysis and Modeling of Thermal Effect and Optical Characteristic of LED Systems With Parallel Plate-Fin Heatsink

Based on the photoelectrothermal (PET) theory, prediction methods for the thermal effect and optical properties of the light-emitting diode (LED) systems mounted on a given parallel plate-fin heatsink are proposed in this paper. With the PET theory and the heatsink characteristics (heat transfer coefficient, equivalent radius for heat source, fins efficiency), it is possible to accurately quantify junction temperature, heat dissipation coefficient, optical power, and luminous flux of the LED systems. The prediction model consists of a series of optical and thermal evaluation, with which it is simple for LED system designers to comply. The proposed model has been validated using LED sources, which shows good agreement between the calculated and experimental results.

Beneficial Effects of Transcranial Light Emitting Diode (LED) Therapy on Attentional Performance: An Experimental Design

Background: Transcranial light therapy (TCLT) is a new noninvasive interventional method, which applies red to near infrared spectrum laser or light emitting diode (LED) source on the head, transcranially. This spectrum can penetrate the skull and could improve the brain pathological conditions and cognitive functions. Despite relative advantages of the LED upon laser sources, TCLT research has been limited on the beneficial effects of LED source on human cognitive performances. Objectives: This study aimed at investigating the effectiveness of the TCLT with LED source on brain attentional performance as an important cognitive ability. Methods: This experimental intervention study was conducted in Tabriz, Iran, from September to October 2016. The study samples were selected by the convenience sampling method. Thirty-four healthy individuals (age: 18 to 24; 17 males and 17 females) were randomly assigned to sham (n = 17) or real intervention (n = 17) groups. We applied 850 nm LED with irradiation energy density 60 J/cm2 upon the frontal cortex, the brain region involved in attentional activities. Before and after TCLT, participants completed a cognitive task (Level-1 of parametric Go/No-task), which measures attentional performance. Results: Our results revealed improvement of efficiency score as the main parameter of attentional performance in the real intervention group versus sham-TCLT group. The interaction of group × time was significant (P = 0.004). Mean change of the efficiency score was higher in the real intervention group (mean = 4.6 ± 3) than the sham group (mean = 0.8 ± 3) after TCLT (P = 0.001). Conclusions: Applying the TCLT by LED source over the PFC, promotes attentional performance as an important cognitive function.

Optimization of laboratory illumination in optical dating

Abstract As part of the development of new laboratory lighting, we present a methodological approach applicable to the characterization of any light source intended for illumination in optical dating laboratories. We derive optical absorption cross-sections for quartz and feldspar from published data and compare these with the human eye response. The optimum peak wavelength giving the best clarity for non-dark adapted vision for the least trapped charge loss lies within the wavelength range 590–630 nm; we argue that it is unnecessary to consider dark-adapted vision. The predicted relative decay rates of quartz optically stimulated luminescence (OSL) and feldspar infrared stimulated luminescence (IRSL) signals by an incandescent light bulb and a compact fluorescent lamp (CFL) through an ILFORD 902 filter are first derived. These predicted decay rates are then compared with those of three relevant light-emitting diodes (LEDs); this comparison demonstrates the significant advantage of the LED sources over the filtered light sources, because essentially all of the reduction of both OSL and IRSL signals by the LEDs occurs at wavelengths to which the human eye is most sensitive. We conclude that exposure of quartz and feldspar extracts from various samples to the light from an LED with emission peak at 594 nm results in a ≤1% OSL or IRSL signal loss for a 48-h exposure at a power density of ∼0.2 μW.cm −2 .

Coverage optimization of VLC in smart homes based on improved cuckoo search algorithm

Light-emitting diodes (LEDs) are often placed on the ceiling in smart homes for visible light communications. However, the layout of LEDs will lead to the uneven distribution of the received optical power and signal-to-noise ratio (SNR) on the same receiving plane, which cannot guarantee fairness of communication. To solve this problem, we used an LED source array and introduced a power adjustment factor to determine a set of optimal power regulators to improve the power distribution on the same receiving plane. We proposed an improved cuckoo search (ICS) algorithm based on chaos theory and dimension cells to solve the normal CS algorithm convergence problem. The chaos mechanism will optimize the random distribution of the initial solution for chaotic distribution, and it can achieve an improved quality of the initial solutions. Moreover, we divided the multidimensional solutions into several dimension cells to avoid interference between dimensions. Simulation results show that the accuracy and the convergence rate of the ICS algorithm is better than that of CS, particle swarm optimization, and evolutionary algorithm. Furthermore, the fairness of the received optical power and SNR on the same receiving plane can be clearly improved.

The intensity of blue light-emitting diodes influences the antioxidant properties and sugar content of oyster mushrooms (Lentinus sajor-caju)

In this study, we examined the influences of four light intensities on mushroom biomass and effects of a blue (B) light-emitting diode (LED) source with 10–40μmolm−2s−1 of photosynthetic photon flux density (PPFD) on the antioxidant capacity and soluble sugar content of the edible oyster mushroom L. sajor-caju Fr. which is popularly cultivated in Taiwan. Fruiting body initiation and development of mushrooms cultivated on blocks made of sawdust, rice-bran, and wheat-bran media were carried out with an 8-h photoperiod at 26°C and 85% relative humidity under LEDs lights inside growth chambers. When the basidiome has began development, mushroom blocks containing primordia were exposed to different light conditions for 7days. Results showed that B-LED PPFD of mushrooms significantly promoted the accumulation of dry biomass. This study explored the relationship between the light intensity of B-LED and antioxidant properties. Different light intensities variably affected the antioxidant system of the mushroom, and higher light intensities resulted in an increased DPPH radical-scavenging effect, Fe-chelating ability, and reducing power. In addition, 40 PPFD of the B-light source caused greater accumulation of soluble sugars than other B-light intensities. Precise management of B light may hold promise in promoting the nutritional value of edible mushrooms cultivated in controlled environments with future utilization of LEDs on an industrial scale.

Evaluation of the Potential Optical Radiation Hazards with Led Lamps Intended for Home Use

The authors evaluated the potential for ocular damage from optical radiation emitted by Light Emitting Diode (LED) based lamps used for general illumination. Ten LED lamps were randomly selected off the shelf from a local home improvement store. The LEDs were behind diffusers in half of these lamps, while in the other half, the LEDs were clearly visible. In addition, a battery powered LED lantern having a LED source behind a diffuser was measured. The optical radiation emissions from two common incandescent lamps were also measured to compare the relative hazards of LED and incandescent lamps. All lamp samples were evaluated in accordance with procedures specified in the American National Standards Institute/Illuminating Engineering Society of North America (ANSI/IESNA) Standard RP-27.3. For comparison purposes, the lantern and 100 W incandescent lamps were also evaluated according to ANSI RP-27.1. These measurements indicate that no lamp evaluated poses any photobiological hazard, and therefore, all lamps fall in the RP-27.3 category of Exempt Group. However, when evaluated in accordance with RP-27.1, the 100 W incandescent lamp would be classified in Risk Group 1 (low risk), while the LED lantern would be classified in Risk Group 2 (moderate risk).

Influence of Curing Light Type and Staining Medium on the Discoloring Stability of Dental Restorative Composite

Discoloration kinetics of 4 commercial nano-filled resin composites polymerized with LED and QTH source types in 4 different staining media held at 37°C are investigated. Quartz Tungsten Halogen (QTH) and Light Emitting Diode (LED) were used. Dental composites color change was monitored with a digital spectrophotometer at one, two and four weeks for quantitative comparison. The kinetics and intensities of the color change in accelerated aging tests in staining media were monitored and discussed. Discoloring followed diffusive driven kinetics. The four composites polymerized with QTH light showed higher differences in color change intensities compared to LED cured ones. All the QTH cured samples have shown significant higher variations of color changes intensities compared to LED samples (p<0.05). LED cured composite showed comparatively more stable initial shade persistence than QTH cured ones, which may be explained in terms of higher level of polymerization and surface hardness reached by the LED light cure resinous composite matrix.

Effects of different LED light wavelengths on the resistance of tomato against Botrytis cinerea and the corresponding physiological mechanisms

New types of light-emitting diode (LED) sources were applied to irradiate Botrytis cinerea mycelium and tomato leaves that were inoculated with B. cinerea to assess the effect of different LED light wavelengths on the infection of tomato with B. cinerea, to determine the optimum light wavelengths to control B. cinerea, and to explore the mechanism of LED influence on the development of gray mold. The results showed that purple light and blue light irradiation significantly inhibited the growth of B. cinerea mycelium, and the inhibition rates were 22.3 and 15.16%, respectively, and purple light exhibited a better inhibitory effect than blue light. The lesion development of B. cinerea on tomato leaves was significantly inhibited upon irradiation with red and purple light with inhibition rates of 32.08 and 36.74%, respectively. Irradiation with red light inhibited the oxidative burst of superoxide anion (O2−) that was caused by infection with B. cinerea, and red light regulated the H2O2 content in the tomato leaf, which increased and rapidly returned to a lower level. In addition, red light irradiation improved the activity of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) in tomato leaves. However, purple light irradiation did not make tomato leaves exhibit this kind of physiological response. Therefore, red light and purple light can suppress gray mold in tomatoes, but the disease suppression mechanisms of these two types of LED light are different. In general, red light suppresses gray mold primarily by regulating the tomato defense mechanism for disease, whereas the suppression of tomato gray mold by purple light can be partially explained by the photo-inhibition of B. cinerea.

Energy feedback freeform lenses for uniform illumination of extended light source LEDs.

Using freeform lenses to construct uniform illumination systems is important in light-emitting diode (LED) devices. In this paper, the energy feedback design is used for freeform lens (EFFL) constructions by solving a set of partial differential equations that describe the mapping relationships between the source and the illumination pattern. The simulation results show that the method can overcome the illumination deviation caused by the extended light source (ELS) problem. Furthermore, a uniformity of 95.6% is obtained for chip-on-board (COB) compact LED devices. As such, prototype LEDs manufactured with the proposed freeform lenses demonstrate significant improvements in luminous efficiency and emission uniformity.

Aspheric surface lens for LED collimating illumination with low Fresnel loss

An aspheric surface lens is presented to realize collimating illumination with low Fresnel loss based on Fresnel equations and Snell’s law. The smooth 2D contour of refractive optical surface is constructed from a set of cubic Bezier segments, whose control points are computed by deCasteljau algorithm. Simulation results show that the optical efficiency of 90.82% is achieved under a divergence angle of ±2.87° for an extended light-emitting diode (LED) source with chip size of 1 mm × 1 mm and the Fresnel loss is only 8.76%, whose optical efficiency has improved 14.3% than traditional collimating lens. By employing this proposed surface construction method, the largest divergence angle of collimating lens for point source is only 0.26° with 15 feature points on each refractive surface, while more than 2° for the traditional method. Therefore, the beams are well controlled with fewer feature data points. Tolerance analyses are also conducted in detail.

Application of supplementary white and pulsed light-emitting diodes to lettuce grown in a plant factory with artificial lighting

Light-emitting diodes (LEDs) are currently undergoing rapid development as plant growth light sources in a plant factory with artificial lighting (PFAL). However, little is known about the effects of supplementary light and pulsed LEDs on plant growth, bioactive compound productions, and energy efficiency in lettuce. In this study, we aimed to determine the effects of supplementary white LEDs (study I) and pulsed LEDs (study II) on red leaf lettuce (Lactuca sativa L. ‘Sunmang’). In study I, six LED sources were used to determine the effects of supplementary white LEDs (RGB 7:1:1, 7:1:2, RWB 7:1:2, 7:2:1, 8:1:1, 8:2:0 [based on chip number] on lettuce). Fluorescent lamps were used as the control. In study II, pulsed RWB 7:2:1 LED treatments (30, 10, 1 kHz with a 50 or 75% duty ratio) were applied to lettuce. In study I, the application of red and blue fractions improved plant growth characteristics and the accumulation of antioxidant phenolic compounds, respectively. In addition, the application of green light increased plant growth, including the fresh and dry weights of shoots and roots, as well as leaf area. However, the substitution of green LEDs with white LEDs induced approximately 3.4-times higher light and energy use efficiency. In study II, the growth characteristics and photosynthesis of lettuce were affected by various combinations of duty ratio and frequency. In particular, biomass under a 1 kHz 75% duty ratio of pulsed LEDs was not significantly different from that of the control (continuous LEDs). Moreover, no significant difference in leaf photosynthetic rate was observed between any pulsed LED treatment utilizing a 75% duty ratio versus continuous LEDs. However, some pulsed LED treatments may potentially improve light and energy use efficiency compared to continuous LEDs. These results suggest that the fraction of red, blue, and green wavelengths of LEDs is an important factor for plant growth and the biosynthesis of bioactive compounds in lettuce and that supplementary white LEDs (based on a combination of red and blue LEDs) might be more suitable as a commercial lighting source than green LEDs. In addition, the use of suitable pulses of LEDs might save energy while inducing plant growth similar to that under continuous LEDs. Our findings provide important basic information for designing optimal light sources for use in a PFAL.

Selective photocatalytic oxidation of benzyl alcohol to benzaldehyde by using metal-loaded g-C3N4 photocatalysts

Replacement of traditional thermal synthesis of fine chemicals by selective photocatalysis can lead to more environmental friendly processes, carried out at milder conditions, using ambient temperature, atmospheric pressure, with more ecological and economic solvents such as water. Because benzaldehyde (BAL), as fine chemical building block, has an enormous range of applications in pharmaceutical, fragrance and agricultural industries, we analyzed its route of synthesis by the photocatalytic oxidation of benzyl alcohol (BA).In this work, we used graphitized-carbon nitride (g-C3N4) as photocatalyst for the selective synthesis of benzaldehyde from benzyl alcohol. The solid matrix of the photocatalyst was modified by loading different metals such as Au, Ru, Pd, Pt, Ir, Ag and Rh. Conversion, yield and selectivity were compared against benchmark commercial photocatalyst P25 TiO2 (by Evonik). The influence of the physical-chemical nature of the medium, by means of the pH, on the efficiency of the photocatalytic process was also evaluated. The 1wt.% Ru/g-C3N4 photocatalyst had the best compromise between conversion (73%) and selectivity (72%) for a 4h of irradiation time using 390nm activation by a light emitting diode source and it proved to be stable up to 3 consecutive runs.

Scintillations of LED sources in oceanic turbulence.

The scintillation index of light emitting diode (LED) sources is evaluated when such sources are employed in oceanic wireless optical communication (UWOC) links. In the formulation, LED source radiation is taken to be perfectly incoherent with a Gaussian field distribution. We have utilized the scintillation index solution of an incoherent source in atmospheric turbulence, together with our recently obtained expression that expresses the structure constant of atmospheric turbulence in terms of the oceanic turbulence and UWOC link parameters. Oceanic turbulence parameters of interest are the ratio of temperature to salinity contributions to the refractive index spectrum, rate of dissipation of kinetic energy per unit mass of fluid, rate of dissipation of mean-squared temperature, and viscosity. UWOC link parameters are the LED source size, link length, and the wavelength. Scintillation index results are presented for various variations of the oceanic turbulence and UWOC link parameters.

High precision three-dimensional iterative indoor localization algorithm using code division multiple access modulation based on visible light communication

To solve the problem of positioning accuracy affected by mutual interference among multiple reference points in the traditional visible light communication positioning system, an iterative algorithm of received signal strength (RSS) based on code division multiple access (CDMA) coding is proposed. Every light-emitting diode (LED) source broadcasts a unique CDMA modulation identification (ID) code, which is associated with geographic position. The mobile terminal receives a mixed light signal from each LED reference point. By using the orthogonality of the spreading codes, the corresponding ID position information and the intensity attenuation factor of each LED reference point source can be available. According to the ID information and signal attenuation intensity, the location area of each LED and the distance between the receiver end and each LED can be determined. The three-dimensional (3-D) position of the receiver can be obtained by using the iterative algorithm of RSS triangulation. The experimental results show that the proposed algorithm can achieve a positioning accuracy of 5.25 cm in a two-dimensional (2-D) positioning system. And in the 3-D positioning system, the maximum positioning error is 10.27 cm, the minimum positioning error is 0.45 cm, the average positioning error is 3.97 cm, and the proportion of the positioning error exceeding 5 cm is 25 % . With a very good positioning accuracy, this system is simple and does not require synchronization processing. What is more, it can be applied to both the 2-D and 3-D localization systems, which has a broad application prospect.

Deep Ultraviolet Light Emitting Diode (LED)-Based Sensing of Sulfur Dioxide.

With the recent development of deep ultraviolet (DUV) light emitting diodes (LEDs) comes the possibility of targeting absorption bands of several gases, including sulfur dioxide (SO2). SO2 has strong absorption bands in the 300 nm spectral region. The low cost and small size of DUV LEDs, coupled with their spectral coverage, makes them viable sources for new gas sensors. Here, we demonstrate the capability to use absorption spectroscopy with a balanced detection scheme using a 300 nm DUV LED source for SO2 detection at concentrations ranging from less than 1 ppm to 50 ppm.