Single Light-emitting Diode Research Articles

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.

Intelligent and Practical Deep Learning Aided Positioning Design for Visible Light Communication Receivers

Visible light positioning (VLP) systems can achieve high positioning precision. However, they are not compatible with visible light communication (VLC) systems. They require special positioning modules and could not reuse functional communication modules, while requiring more than two light emitting diodes (LEDs) to be deployed at user ends. In order to address the issues of weak compatibility and high complexity of VLP, we present a novel position estimation deep neural network (PE-DNN) and propose to add a PE-DNN aided module at the VLC receivers. The proposed module firstly learns features of the VLC channel from received pilot signals implicitly, then it can estimate receivers’ 2-dimension positions intelligently with a single LED. Accordingly, VLC systems can simultaneously provide positioning and information transmission services with only one LED and one photodiode (PD), thus the compatibility and the practicality are greatly improved. Simulation results show that the proposed system achieves a centimeter-level positioning accuracy, and can provide intelligent and practical positioning services for the users.

Harmonic emission of LED lighting

This paper analyses harmonic emission of different light-emitting diode (LED) lighting systems. Basic mathematical analysis of harmonic emission was presented. Paper deals with single LED lights (bulbs) and street lighting systems formed by luminaries. Harmonic emission results were obtained by measurement. More, single LED bulbs were modeled within EMTP-ATP software. Comparison of measured results and results obtained by simulation was performed. Further, one LED lighting system was compared with sodium lighting system in the harmonic emission area. Comparison was performed by replacing one sodium lighting system (in one street) with appropriate LED lighting system. Standards which deals with harmonic emission were presented and compared. More, obtained results of harmonic emission were compared with valid Standards. The goal of paper is to compare harmonic emission of various bulbs and on other side to analyze LED lighting systems with luminaries. It is important because today there are various LED lights in market made by various companies. It is due high share penetration of LED lighting in each area and their implementation in: house, buildings, business areas, factories, street lighting systems etc. On other side, LED lights are nonlinear loads which potentially can have negative effect on distribution grid. One more goal is to compare measured results and the results obtained by modeling. Correctly modeled LED lighting can be used in various research. It can be used to improve the manufacturing process of LED lights.

Ultraviolet light-emitting diode arrays using Ga-doped ZnO as current spreading layer

In this article, the authors investigate the fabrication and characterization of the 4 × 4 GaN-based ultraviolet (UV) light-emitting diode (LED) array with a pixel size of 200 × 200 μm2 and a pitch of 200 μm. For comparison, the single broad-area LED with a size of 400 × 400 μm2 is also fabricated from the same epitaxial wafer as a reference. The Ga-doped ZnO (GZO) film is used as a current spreading layer onto the ultraviolet LEDs to enhance the light output power. The GZO film with a thickness of 100 nm was deposited by atomic layer deposition (ALD) and has an electron concentration of ∼8 × 1020 cm−3, a low resistivity of ∼4 × 10−4 Ω cm, and a high transmittance of ∼84% in the near UV wavelength range. The ALD-GZO film was also used as the internal wires to connect the pixels of an LED array. The LEDs have a peak wavelength of 370 nm with a slight redshift at higher injection currents. The 4 × 4 LED array has a better performance in the maximum light output power density of 7.25 W/cm2 at 240 mA and a highly linear light output power to injection current, while the broad-area LED only exhibits the maximum light output power density of 1.34 W/cm2 at 70 mA. The single pixel of a 4 × 4 UV LED array reveals a maximum light output power density of 7.25 W/cm2 at 240 mA and a wider divergence angle of 137°, which are better than the broad-area LED of 1.34 W/cm2 at 70 mA and 128°, respectively. Finally, the authors show the demonstration of photos of an 8 × 8 LED array.

Indoor visible light high precision three-dimensional positioning algorithm based on single LED lamp

With the rapid development of information technology, there is a growing demand for people in indoor location services.This paper proposes a novel high-precision indoor three-dimensional positioning algorithm for single light emitting diode (LED). By using three tilted photodetectors (PD)and one horizontal PD as receivers.Calculating the ratio of received optical power of the three tilted PDs to the horizontal PD respectively. According to the relationship of position between the PDs and the tilt angle, azimuth angle, placement angle of the tilted PD and other parameters, establish a mathematical relationship between the received optical power ratio and the receiver's three-dimensional coordinates, calculate the three-dimensional coordinates of the receiver at any position. The simulation results show that in the positioning area of 1 × 1 × 1.5 m3, when the inclination angle α is 25°, the azimuth angle difference θ is 90°, the placement angle ω1=0°, ω2=90°, ω3=180°, the distance r between the horizontal PD center and the tilted PD center is 1 cm, the positioning accuracy is better, the point with the positioning error within 3 cm accounts for 84 % of the total test points, and the average positioning error is 2.52 cm. Compared with the traditional indoor positioning technology, the cost of the positioning technology used in this paper is greatly reduced, the positioning accuracy is significantly improved,and can get three-dimensional coordinates.

Cardiac pacing using transmural multi-LED probes in channelrhodopsin-expressing mouse hearts

Optogenetics enables cell-type specific monitoring and actuation via light-activated proteins. In cardiac research, expressing light-activated depolarising ion channels in cardiomyocytes allows optical pacing and defibrillation. Previous studies largely relied on epicardial illumination. Light penetration through the myocardium is however problematic when moving to larger animals and humans. To overcome this limitation, we assessed the utility of an implantable multi light-emitting diode (LED) optical probe (IMLOP) for intramural pacing of mouse hearts expressing cardiac-specific channelrhodopsin-2 (ChR2).Here we demonstrated that IMLOP insertion needs approximately 20 mN of force, limiting possible damage from excessive loads applied during implantation. Histological sections confirmed the confined nature of tissue damage during acute use. The temperature change of the surrounding tissue was below 1 K during LED operation, rendering the probe safe for use in situ. This was confirmed in control experiments where no effect on cardiac action potential conduction was observed even when using stimulation parameters twenty-fold greater than required for pacing.In situ experiments on ChR2-expressing mouse hearts demonstrated that optical stimulation is possible with light intensities as low as 700 μW/mm2; although stable pacing requires higher intensities. When pacing with a single LED, rheobase and chronaxie values were 13.3 mW/mm2 ± 0.9 mW/mm2 and 3 ms ± 0.6 ms, respectively. When doubling the stimulated volume the rheobase decreased significantly (6.5 mW/mm2 ± 0.9 mW/mm2).We have demonstrated IMLOP-based intramural optical pacing of the heart. Probes cause locally constrained tissue damage in the acute setting and require low light intensities for pacing. Further development is necessary to assess effects of chronic implantation.

Indoor visible light positioning combining photometry and imaging

An optical indoor positioning system using an optical receiver and camera is proposed. Compared with previous works in this field, our system improved the coverage without sacrificing accuracy. Thus, the proposed indoor positioning system is more suitable under environments with dense obstacles, such as warehouses, hospitals, and factories. Since the camera is deployed at the receiver side, the angle of arrival (AoA) can be estimated by recognizing the light source in an image. The optical receiver is able to measure received signal strength (RSS). Combining the information in AoA and RSS, the relative position of the receiver to the light source can be estimated. In this system, the position of the light source can be sent to the receiver applying visible light communication. Thus, both communication and positioning can be enabled using a single light-emitting diode on the transmitter side.

Low complexity OFDM VLC system enabled by spatial summing modulation.

Commercial-off-the-shelf (COTS) devices enabled visible light communication (VLC) for Internet of things (IoT) applications has attracted extensive attentions from both academic and industrial communities, thanks to the pervasive deployments of light emitting diode (LED) lighting infrastructure. However, due to the limitation of frequency response and non-linearity of the commercial illuminating LED light consisting of multiple LED chips, the achievable data rate is far less than that provided by the experimental VLC system with a single LED with specialized devices, e.g., lens. To this end, we propose a power-of-2 arrangement scheme for LED chips to generate spatial summing modulation with low control complexity, and demonstrate its availability in an orthogonal frequency division multiplexing (OFDM) VLC system purely built upon COTS devices. It significantly differs from a conventional OFDM VLC system relying on digital-to-analog converter (DAC) and analog signal chain, which is complex and confined by LED's non-linearity, thanks to we design a novel digital-to-light converter (DLC) which can output 256 light intensities linearly and be directly controlled by the discrete digital signals generated by the OFDM modulator. An experimental demonstration with employing the QAM-OFDM modulation scheme successfully confirms the effectiveness of the proposed spatial summing VLC system, which can achieve low BERs of below the forward error correct (FEC) threshold of 3.8×10-3 for both QAM8 and QAM16 running transmission frequency of 300 kHz under a communication distance of 0.8 m. It demonstrates the promising potential for delivering a data rate at hundred kbps level with this novel spatial summing based OFDM VLC system, which is sufficient for many IoT applications.

New high intensity fibreoptic phototherapy devices in healthy newborns: a single pad wrapped around the neonate body in comparison with a double pad device

BackgroundFibreoptic Phototherapy (FPT) allows to lower total serum bilirubin (TSB) levels in healthy neonates maintained in rooming-in with their mothers. The 2004 Cochrane review showed that, differently from preterm neonates, FPT was not as effective as traditional phototherapy in term neonates (TN), unless the simultaneous utilization of two FPT devices. Aim of this study was to compare the efficacy of two FPT devices, both equipped with a single light-emitting diode (LED): the first one has a single large pad wrapped around the infant body (Bilisoft, GE Health Care) (device A), the second one is a double-pad phototherapy device (BiliCocoon, CremascolieIris) (device B).MethodsWe studied 172 healthy neonates with non-hemolytic hyperbilirubinaemia: 57 TN and 57 late preterm neonates (LPN) treated with device A (Group 1); 47 TN and 11 LPN treated with device B (Group 2). We evaluated the differences between groups by the Student’s t-test for continuous variables and by chi square test for categorical data. A two tailed p < 0.05 was considered significant.ResultsThere were no differences in term of duration of FPT, TSB hourly reduction, percentage of TSB reduction after FPT, TSB maximum rebound, percentage of TSB increase after FPT discontinuation and number of after-discharge checks. Two neonates treated with device B showed no decrease in TSB values during FPT. Seven infants treated with device B experienced hyperpyrexia.ConclusionsThe two LED FPT devices were both effective in lowering TSB either in TN or LPN. Device A was effective in all treated neonates without negative side effects during treatment; device B was effective in all but 2 infants and 12% of the neonates in the same group experienced hyperpyrexia. According to our results, the single big pad wrapped around the infant body has the same efficacy as a double FPT device in TN and LPN.

Design and Implementation of High Power LED Lighting System for Health Care Applications

Background:A conventional front-end rectifier causes line current distortion and reduces the power factor, which result in lowering power quality for Light Emitting Diode (LED) drive system. Hence, this paper projects the design, simulation and comparison of novel PI tuned by the fuzzy logic controller with the conventional PI controller for modified SEPIC rectifier to produce the required load voltage along with supply-side unity power factor and less distorted supply current with limited harmonic content for LED lighting in healthcare applications. A prototype of 100W, 48V LED driver was developed for testing the performance of the controller.Methods:This paper presents the modified SEPIC LED driver with PI integrated fuzzy and classical PI for controlling voltage. For controlling source current, classical PI is chosen. Both are equipped with the modified SEPIC rectifier. Both conventional PI control and novel fuzzy tuned performances were compared.Results:The proposed control topology operated modified SEPIC rectifier was analyzed and the corresponding power factor and THD were measured. The operational evaluation of the proposed LED driver using fuzzy tuned-PI/PI controller combinations for different output power is provided in Table 2. Sustained regulated DC voltage of 48V was achieved even when the load resistance varied within a specific range. Power factor of 0.9995, which is close to unity, was also achieved. The relative analysis was made with conventional PI and trendy PI integrated FLC controller which is provided in Table 3. The usage of PI integrated fuzzy logic controller minimized the peak overshoot to be around 1.3% and rise time of 0.5s which are lower when compared to the conventional PI controller. With reference to Fig. (8a), the source current THD of the conventional PI controller was observed to be around 7.39%. Having PI integrated FLC, THD was further reduced and for rated load, it was found to be 1.39%. The power factor of the conventional PI controller is around 0.9974. PI integrated fuzzy logic controller improved the power factor to 0.9995 with fuzzy tuned PI controller in action as shown in Fig. (8b). A prototype of 100W, 48V LED driver was developed for testing the performance of the controller. A power quality analyser was employed for measuring power factor and THD, shown in Fig. (10a). 3.633% of harmonic distortions at the source current and 0.9980% of input power factor was achieved for rated load power. 4.510% of supply current THD with 0.9931% input power factor was achieved for low load power.Conclusion:This manuscript suggests a modified single switch SEPIC LED driver for 48V output operated healthcare equipment. Simulation study of this driver shows the better performance. In order to analyze the performance, a comparative study was conducted by using the classical PI and the novel PI integrated fuzzy controller. Satisfactory results regarding enhanced quality of power, regulated load voltage, quick rise time and settling time were achieved. The source current THD has been reduced to around 1.39% which is less than 5% as per the IEEE-516 prescribed standard and the power factor has been improved to 0.9995 by implementing the fuzzy tuned PI controller. The above results favor the suggested modified SEPIC LED driver for practical healthcare applications.

A single LED lamp positioning system based on CMOS camera and visible light communication

In this paper, a positioning system framework based on a single light emitting diode (LED) lamp is introduced. The LED lamp is used to transmit the positioning information, and the commercial mobile phone is used as the receiver. A fringe image carrying information is acquired by the rolling shutter effect of the complementary metal oxide semiconductor (CMOS) image sensor. Based on this, a piecewise fitting method is proposed to instead of the overall fitting method, which improves the decoding success rate. We also propose a method of LED light source recognition, which detects the edge of the light source based on brightness weakening, the Sobel operator and the least-squares fitting. In addition, the imaging principle of the camera in horizontal and tilted scenarios is analyzed. Accurate indoor positioning is achieved by the imaging principle of the camera lens and the attitude information of the mobile phone. The experimental results show that the system established in this paper can achieve centimeter-level positioning accuracy whether the mobile phone is placed horizontally or obliquely.

Single LED-based 46-m underwater wireless optical communication enabled by a multi-pixel photon counter with digital output

Presently, most of the long-reach underwater wireless optical communication (UWOC) systems employ laser diodes rather than light-emitting diodes (LEDs) as the transmitters. Due to lasers’ smaller divergence angles, those UWOC systems could realize longer communication links. Although LED-based long-reach UWOC has distinguished advantages, it suffers from very low received optical power. Fortunately, highly sensitive multi-pixel photon counter (MPPC) and energy efficient pulse position modulation (PPM) pave a way towards LED-based long-reach UWOC. In this paper, we investigated the underlying working principle of an MPPC and proposed a UWOC system based on single LED as well as a lens-free MPPC with digital output. The relationship between the MPPC p.e. threshold and its received optical power was theoretically studied and further proved by experimental results. Single 2.3-MHz, 3-W blue LED was used as the transmitter to generate 8-PPM to 64-PPM signals with a 5-MHz slot frequency. After a 46-m underwater transmission, the measured BERs were all below the forward error correction (FEC) limit, which were achieved with less than 100 incident photons during each pulse slot.

Illumination pattern design with deep learning for single-shot Fourier ptychographic microscopy.

Fourier ptychographic microscopy allows for the collection of images with a high space-bandwidth product at the cost of temporal resolution. In Fourier ptychographic microscopy, the light source of a conventional widefield microscope is replaced with a light-emitting diode (LED) matrix, and multiple images are collected with different LED illumination patterns. From these images, a higher-resolution image can be computationally reconstructed without sacrificing field-of-view. We use deep learning to achieve single-shot imaging without sacrificing the space-bandwidth product, reducing the acquisition time in Fourier ptychographic microscopy by a factor of 69. In our deep learning approach, a training dataset of high-resolution images is used to jointly optimize a single LED illumination pattern with the parameters of a reconstruction algorithm. Our work paves the way for high-throughput imaging in biological studies.

Enhanced Ultraviolet Emission from Hydrothermally Grown ZnO Nano-Grass on Si Substrate

Highly crystalline one-dimensional zinc oxide (ZnO) nano-grass was grown on silicon (Si) substrate by a modified hydrothermal method. A predominantly c-oriented ZnO nano-grass with an average diameter of 40–60 nm and length of 1.5–2.0 μm was obtained. From the photoluminescence (PL) measurement, we observed a defect-free, intense ultraviolet emission of as-grown ZnO nano-grass, confirming the absence of singly ionized oxygen vacancies. The absence of green deep-level emission in the PL spectrum further implies a high crystallinity of as-grown ZnO nano-grass. The high-quality ZnO nano-grass has potential applications in single nanowire-based light-emitting diodes, solar cells, themoresistive sensing, photocatalysis, ultraviolet photodetectors, optical switches, waveguides and nano-lasers.

3D Visible Light Indoor Positioning by Bokeh Based Optical Intensity Measurement in Smartphone Camera

This paper proposes a three dimensional (3D) high-resolution indoor positioning system that uses a single light-emitting diode (LED) and a complementary metal-oxide semiconductor image sensor (CIS). The proposed visible light positioning system is based on the bokeh effect for improving the positioning accuracy. The 3D position is determined by received signal strength (RSS) and angle of arrival (AOA). Optical saturation in pixels causes severe performance degradation in the RSS-based positioning based on the CIS. The bokeh-based image reception technique resolves this problem by spreading the optical power to adjacent pixels. Additionally, via the bokeh effect, the size of the LED image on the CIS is maintained regardless of the distances. The accuracy of the LED extraction for the AOA can be improved by fixed LED size. These characteristics of the proposed positioning scheme are analyzed via simulations, and the feasibility of the method is verified based on the experimental results. The experimental results indicate an estimated positioning average error rate within 4%.

Square Wave Quadrature Amplitude Modulation for Visible Light Communication Using Image Sensor

Most visible light communication (VLC) technologies use a light emitting diode (LED) as a data transmitter and a photodiode as a receiver. In this paper, we alternatively focus on the use of an image sensor or camera as a receiver due to its wide availability. However, the successful use of an image sensor mainly depends on the efficiency of the encoder-decoder and the modulation scheme. Thus, this paper proposes a novel modulation scheme based on a square wave signal called a square wave quadrature amplitude modulation (SW-QAM) method. This method can accommodate different camera settings and overcome the problem of LED flicker that is generally sensed by human eyes when the LED frequency is low. At the transmitter side, multiple LEDs can be used to increase the transmission bit rate, while, at the receiver side, a Wiener filter is used as a complementary technique to SW-QAM for solving the light interference phenomenon due to the closeness of one LED to another. Our experimental results show that the proposed SW-QAM scheme can decode symbols very well either the for close or far communication distances, dark or bright lighting conditions, and single or multiple LED points.

Single LED-Based Indoor Positioning System Using Multiple Photodetectors

This paper presents a visible light positioning system using a single light-emitting diode (LED) and a novel receiver. In the proposed system, the receiver is composed of a horizontal photodetector (PD) and two tilted PDs, and a known calibration point is deployed to improve the accuracy of the positioning. Based upon the multi-PDs’ relative positions and the received signal strength, the location of the receiver can be estimated regardless of the LED's and PDs’ characteristics. The influences of tilted PDs on the positioning errors are discussed, i.e., the polar angle α and the difference θ between two azimuth angles. The experimental results show that high accuracy can be achieved when α = 20° and θ ranges from 30° to 90°. The average and maximum errors are 2.15 and 4.01 cm, respectively, in the case of α = 20° and θ = 45°. The proposed system avoids the intercell interference caused by different transmitters and can be applied in scenarios with limited LEDs.

Single light-emitting diode-based high-accuracy indoor positioning system using symmetrical optical receiver

A visible light positioning (VLP) system based on a single light-emitting diode (LED) using a symmetrical receiver is presented. In the proposed receiver, a horizontal photodetector (PD) is located at the center and surrounded by four tilted PDs, which are arranged symmetrically to increase the accuracy in the actual VLP environments. Based on the received signal strength, the high-accuracy positioning can be easily achieved with only the LED’s location regardless of LED’s and PDs’ characteristics. In addition, the relationship between the positioning error and the PDs’ polar angles (α) is analyzed, which indicates that the polar angles changing from 20 deg to 30 deg are optimum. The experimental results show that when the polar angles are 20 deg, the positioning error changes from 0.79 to 3.97 cm and the average error is 2.32 cm. The proposed VLP system removes the intercell interference caused by multiple LEDs and can be easily applied in the LED-limited scenarios of low costs, low complexity, and high accuracy.

Single-LED Multichannel Optical Transmission With SCMA for Long Range Health Information Monitoring

This paper proposes a prototype single light-emitting diode (LED) multiple-channel transmission system with visible light communication (VLC) for electromagnetic wave-free indoor healthcare monitoring. Sparse code multiple access (SCMA) is employed for the transfer of multiple medical data with higher bandwidth efficiency in real time. Multiuser data spread to time domain chips with non-orthogonal codebook are simultaneously transmitted using a single LED, where each chip signal is transmitted as a difference voltage level, and LED illumination is detected by a single photodiode (PD). The received signal, which includes multiuser data, is separated by the message passing algorithm with high reliability, and is simultaneously rearranged for transmission to a user interface (PC or mobile). The collected multiple data are then monitored in real time and analyzed for the appropriate medical care service. With SCMA, VLC can achieve higher bandwidth efficiency (50%–200%). Furthermore, the proposed system is designed with a simple structure (single LED to single PD) for practical deployment, and multiple medical signals can be monitored via a designed user interface in real time.

Blue-Red LED wavelength shifting strategy for enhancing beta-carotene production from halotolerant microalga, Dunaliella salina.

In the present study, to improve the photosynthetic betacarotene productivity of Dunaliella salina, a blue-red LED wavelength-shifting system (B-R system) was investigated. Dunaliella salina under the B-R system showed enhanced density and beta-carotene productivity compared to D. salina cultivated under single light-emitting diode light wavelengths (blue, white, and red light-emitting diode). Additionally, we developed blue light-adapted D. salina (ALE-D. salina) using an adaptive laboratory evolution (ALE) approach. In combination with the B-R system applied to ALE-D. salina (ALE B-R system), the beta-carotene concentration (33.94 ± 0.52 μM) was enhanced by 19.7% compared to that observed for the non-ALE-treated wild-type of D. salina (intact D. salina) under the B-R system (28.34 ± 0.24 μM).