New Publications are available for Light emitting diodes
http://dl-live.theiet.org
New Publications are available now online for this publication.
Please follow the links to view the publication.The numerical simulation and reliability analysis of through-hole solder joints
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0693
In this paper, numerical simulation was performed on the through-hole solder joints of a LED driver, and reliability analysis was carried out. Taking the simulation speed and time into account, firstly the thermal field of the LED driver was simulated, which was then verified by infrared thermograph. Then the thermal-stress simulation was conducted on the solder joints which were of the highest temperature. The results demonstrated that the failure of through-hole solder joints mainly occurred in the interface between solder and substrate, which is the crack initiation zone. Analyzing the stress and strain of solder joints under temperature cycling, this paper used the modified Coffin-Manson formula to predict the life expectancy, and provided an assessment methodology of reliability analysis for through-hole solder joints.Constriction current behavior of oxide film effect observed by using LED wafer
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0670
In order to clarify the theory of contact resistance, there are many reports in these years. Mathematically the constriction current is derived from Laplace equation at one contact which shape is circle, ellipse, triangle and square. And numerical approach for constriction current analysis was also preformed by Minowa and Sawada. Although there are many reports on the contact resistance measurement, not many reports on the detailed behavior of current density distribution in the contact area experimentally. Therefore, we attempted to observe the behavior of the current density distribution in the contact by using semiconductor wafers. As a result, it was confirmed that electric current is uniformly distributed over the contact area covered by an oxide film, while it is concentrated at the periphery of the contact if there is no oxide film at contact. And the contact resistance of apparent contact area is almost same as real contact area which is also agree with the theory of multi-spot contact. Moreover, the contact resistance is influenced by wafer thickness.A novel method for illumination and communication using white LED lights
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0149
LED lighting is regarded as the most potential lighting source due to its advantages, such as low power and long lifespan which is largely dependent on the temperature of the LED. So it is possible to predict the life of the LED lamp if the temperature can be read. The conventional method of reading information about a LED lamp is based on communication buses such as RS485 and CAN, but it is inconvenient to add communication lines. This paper proposes a novel compact lighting system which integrates the communication function into the conventional LED driving. Switching frequency modulation method is applied in the system so as to modulate data in the visible light. And the design of the receiver is also proposed, which identifies different frequencies and demodulate data. The introduced system achieves control over communication and dimmer independently at the same time. An experimental system is developed to demonstrate the effectiveness of the proposed approach. (5 pages)Network-integrated positioning system for directivity measurements of led panel on fisheries engineering
http://dl-live.theiet.org/content/conferences/10.1049/ic.2011.0066
We have developed three kinds of a positioning system using an electronic track flatcar loaded on a large water tank for directivity measurements of LED-panel. Three applications are an underwater horizontal directivity measurement, an in-air horizontal directivity one, and an underwater vertical directivity one. Each measurement application is constituted of three systems that are a positioning system, an LED optical resource system, and an optical sensor system. Their control and monitoring programs have been developed using network communication protocols such as web service. An LED optical resource system includes an embedded firmware programmed using extended SPI communication protocol. And then, these multiple systems have been automatically performed by a newly-developed synchronization protocol.Research on indoor visible light communication system employing white LED lightings
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0807
An indoor visible light communication system based on LED is proposed in this paper. In our simulation, the LED arrays are used not only for lighting sources, but also for the signal sources. A model room had been set up. The illumination of this room is uniformed by reasonable layout of LED light sources, which can meet standard requirements. Matlab is utilized for the illumination simulation. Point-to-point data transmission system is simulated by VPI software. It is found that when optical signal noise ratio was around 24dB, this proposed system has a perfect performance with bit rate up to 500Mb/s at bit error ratio of 10<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">-9</sup>.Indoor optical wireless integrated with white LED lighting: perspective & challenge
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.1320
Trends in integrating communication functionality to complement existing services by next-generation energy-saving white LED lighting are reviewed. Challenges at component and system level are discussed to enable visible light communication a practical service provision infrastructure. (2 pages)Design of LED street lamps with nonsymmetrical optical distribution
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0808
A LED street lamps design with nonsymmetrical light distribution along the road was proposed in this paper. With rectangular light distribution pattern, it reduces the intervals of the largest intensity to decrease the direct glare for drivers. Comparing with the symmetry design along the road, its threshold increment reduced 50% in the same condition.Simulation of a VLC system with 1 Mb/s NRZ-OOK data with dimming signal
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.1068
We report 1 Mb/s data transmission over PWM dimming control signal for a visible light communication (VLC) system based on a simulation. The simulation program is developed using MATLAB and Simulink. In this simulation, the data stream of non-return-to-zero on-off keying (NRZ- OOK) is transmitted together with a dimming signal for brightness control, which has the form of pulse width modulation (PWM). The PWM frame rate is set to 1 kHz to avoid flickering in human eyes. The data rate is set to 20 kb/s and 1 Mb/s. We report eye diagrams of NRZ data streams for 20kb/s and 1Mb/s. (3 pages)Simulation of white light based on mixed RGB LEDs
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0814
The white light based on the mixed RGB LEDs with relative position of isosceles right-angle triangle was simulated and investigated in the paper. The colorimetric characteristics of white light were analyzed. The results show that the chromaticity coordinates x increases, y decreases, the chromaticity coordinates shift to red region and color temperature decline with side length of the isosceles triangle increases. When distance between receiving surface and RGB LEDs increase, both of x, y of chromaticity coordinates increase and the color temperatures are changed in small ranges.A safety centred approach to lighting in the process industries
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0263
Significant performance and reliability improvements made in light emitting diode (LED) technology have enabled LED-based fittings to be used in place of traditional lighting solutions such as high intensity discharge (HID) and fluorescent sources. This paper will help facility operators choose and install the safest hazardous area lighting throughout the facility by combining knowledge of human physiology with the latest advances in lighting technologies, area illumination techniques and lighting practices. Long-term case studies of LED fittings installed on end user sites reveal lighting practices that lead to direct improvements in facilities lighting and reduced total cost of ownership. (6 pages)Indoor illumination based on distributive LED lights
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0818
The distributive LED illumination design is proposed in the paper has many virtues such as more lamps, more switches controlled, and easily adjust its output light flux to satisfy the demand of indoor illumination. The result of calculation indicates that distributive illumination is more economic and environmental, and friendly.Effects of flicker on vision in LED light source dimming control process
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0806
With the capability of high precision dimming control accessibility, the white LED is widely used in research of new dimming control method. Research effects on human feeling in dimming control process, especially effects on human vision, is the precondition of the optimal LED dimming control method research. In this paper, an experiment for finding the optimal dimming control method to increase human vision during the LED dimming control process is proposed and experimentally demonstrated. The experiment result shows that people will have the best vision when the LED light source is driving by the double S dimming control method. It is significant meaning of this research in the illumination dimming control field.Influence analysis of road reflective characteristic on roadway luminary design
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0820
The influence of road reflective characteristic to the uniformity of illuminance and uniformity of luminance are discussed for roadway lighting on cement concrete road and asphalt road. The luminous intensity function designed with illuminance uniformity purpose can fulfill the lighting requirements for cement concrete road. But in asphalt road case, it leads to enormous fluctuate of luminance. Luminous intensity function based on luminance uniformity design will be feasible for cement concrete road. But it will cause poor illuminance uniformity on asphalt road due to the specular reflection.Design and development of car wheel LED display device for displaying graphics pattern
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0450
Electronic Embedded system based solution for automotive plays a dominant role in the automotive industries. Research work for displaying graphical images or text on wheel rims while the vehicle is running at presented. The very big challenge faced on implementation is without breakage of image and text displaying graphically with high resolution while the wheel rotating with different speed and different timings. This designed system had Memory and it has having the capability to upload Image and text depends upon what we integrated. This designed Device driver able to display virtually any image, including text, graphics, logos, and even digital photos when the wheel is on rotating. An Accurate time and speed of rotation of wheel for timeline is very important for proper display. To face this challenge to calculate their timeline analysis and correlation of speed of rotation to wheel must be done and Human perception timing analysis also should be carried out. All this analysis timing is carryout in this research work to face this challenge. This system design ensure with to maintain on how fast the vehicle is rotating there should be proper display of the Rims of the wheel . Thus design analysis of device driver development is associate with system and also Mechanical design with LED assembly.A novel evaluating method of the reliability of LED luminaries
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0810
In this paper, based on the study of accelerated life testing) methods, a novel evaluating method of the reliability of LED luminaries was proposed on the basis of fuzzy algorithmic approach. In this method, the different factors which affected the LED luminaries were evaluated by fuzzy comprehensive evaluation model, combining Analytic Hierarchy Process theory and based on experts' scorings, the distributing weight vector of every factor can be determined by qualitative and quantitative analysis, and then the lifetime of LED luminaries will be calculated through fuzzy algorithmic approach. The main advantage of this method is that different factors which affected the reliability of LED luminaries were considered.Field testing method of color temperature of outdoor LED lamps
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0813
In the paper, to find the only filed color temperature testing method, three kinds of color temperature testing instrument, color luminance meter, color illuminance meter, and mobile spectrometer were introduced. By comparing their construction, color illuminance seems to be most available to measure the color temperature of outdoor LED lamps. Considering disturbing factors such as vehicle light, environment light, and clothing color during the measurement, corresponding resolutions were suggested.Design of new hybrid optical system of LED cap lamp
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0817
A new hybrid optical system of LED cap lamp was designed for demand of luminous intensity distribution , which is made up of freeform refractor and freeform reflector. Simulation results show that the optical system has a better condensing performance than others, and the center illuminance of light spot is up to the requirement of national standards. The illumination uniformity of the optical system was greater than 0.8, and the radius of light spot of this optical system is 125 mm. The simulation results confirm that the cap lamp meets the requirements of mine.Sustainable development of ice landscape in Harbin
http://dl-live.theiet.org/content/conferences/10.1049/cp.2010.0469
The paper analyses the practice to realize the sustainable development of ice landscape in Harbin. The specific measures include ice landscape layout, the use of energy saving light source, ice recovery. The study methods are investigation and illumination tests around the ice lanterns on-site. All of Large-scale ice landscapes are built near the Songhua River which across the city so that we can get the free and pure ice from the river quickly. LED technique was applied to ice landscape lighting to reduce the power consumption in 2008. LED light isn't fragile and contains no toxic substances. More and more people are interested in ice landscape, and they become the internal impetus to the ice landscape development. The study also finds out some problems. The collection and reuse of ice lack feasible measures, and about 120,000 cubic meters ice aren't recycled every year. The higher price of LED source has affected its popularity, and the excessive lighting of ice landscape can lead to light pollution. Some factors decide the ice landscape sustainable development such as ice recovery, energy saving, environmental protection and related cultivation of professionals.Polymer electronics - towards the future
http://dl-live.theiet.org/content/conferences/10.1049/ic.2009.0061
This presentation discusses some key characteristics of polymers and several polymer-based electronic devices such as polymer light-emitting diodes, photovoltaic diodes, organic solar cells, field-effect transistor, and electrophoretic display. (31 pages)Plastic electronics for point-of-care diagnostics
http://dl-live.theiet.org/content/conferences/10.1049/ic.2009.0064
This presentation offers a solution for a low-cost, point-of-care tests that provide lab quality results on the spot. The merging of lab-on-a-chip technology and organic semiconductors can provide better, faster, cheaper diagnosis and treatment, hence reducing burden on clinician time. (19 pages)Using polymer electronics to treat skin cancer
http://dl-live.theiet.org/content/conferences/10.1049/ic.2009.0063
The presentation of slide shows the polymetronics (polymer electronics) its uses, advantage and founder of this medical devices like red diamond OLED, in treating skin cancer. (30 pages)Design of a LED street lighting system
http://dl-live.theiet.org/content/conferences/10.1049/cp_20080559
LED technology has rapidly developed in recent years to the point that LEDs can be seriously considered for replacing conventional halogen and incandescent lamps in general illumination, e.g. street lighting. Before wide spread adoption of this technology can be embraced, there are a number of outstanding issues that need to be addressed. The opportunity is now available for the implementation of innovative concepts for heat transfer, thermal management, optimised LED power drivers and communication systems. This paper consists primarily of three parts. Firstly, current UK street lighting regulations and requirements are outlined, shortfalls are identified and highlighted. In the second part, thermal management of the LEDs and their drivers are detailed. It is imperative that the LEDs are kept within their maximum operating temperature to ensure maximum stated lifetime and performance. Finally the third part proposes suitable topologies for providing unity power factor and regulating current through the LED arrays.Three-dimensional parallel FDTD simulation of light-emitting diodes
http://dl-live.theiet.org/content/conferences/10.1049/cp_20080231
Three-dimensional FDTD simulation of light-emitting diodes is undertaken with the use of a high-performance parallel computing cluster. It is envisaged that much larger structures was simulated resulting in an improved design process for emission enhancing structures.A circuit with good linearity based on standard optocouplers
http://dl-live.theiet.org/content/conferences/10.1049/cp_20070320
This article presents a circuit with good linearity based on standard optocouplers. The circuit takes advantage of inverse feedback to improve the linearity. It chooses two ordinary optocouplers of same characteristic. One phototransistor is typically used in a feedback mechanism to control the LED (light-emitting diode) drive current which has the effect of compensating for the LED's non-linear time and temperature characteristics. The other output phototransistor is used to provide the galvanic isolation between the input and output circuit. Simulate the circuit in Multisim, the results show that the circuit has good linearity and it can be used not only in DC circuits, but also in AC circuits of low frequency.LED lighting development for automotive environment
http://dl-live.theiet.org/content/conferences/10.1049/cp_20062223
The paper examines various methods to excite LEDs using switched-mode power converters. Examples based on flyback converter are used to illustrate methods of power connection to LEDs. One of them is integrated to coupled-inductor that is new for LEDs excitation. Using the converter methods, the dimming control can be easily regulated. The reliability and illumination formulation has been developed for the LED lighting in automotive environment. (6 pages)LEDs as both optical sources and detectors in bi-directional plastic optical fibre links
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060461
In this paper the characterization of the bandwidth of a bidirectional link, using a light emitting diode as both a transmitter and a detector, is reported. The initial characterizations of the LED as both source and photodiode are described. The bandwidth characterizations of the LED are also discussed.Gigabit optical access using WDM PON based on spectrum slicing and reflective SOA
http://dl-live.theiet.org/content/conferences/10.1049/cp_20050559
We report on the experimental results of a low cost 40 users WDM PON providing 1.25 Gbit/s per user. We focus on the upstream path using spectrum slicing of a SLED at the OLT and remote modulation at the colorless ONU with a reflective SOA. Bidirectionnal transmission over 20 km is demonstrated. (2 pages)UV-induced excess loss of Er- and Si-nanocrystal co-doped silica waveguide for optical amplifier
http://dl-live.theiet.org/content/conferences/10.1049/cp_20050792
Loss of Er- and Si-nanocrystal co-doped waveguide increased reversibly and drastically by the top-pumping using 365-nm Hg lamp, suggesting the dense pumping even if by LED might be fatal to obtain a practical signal gain. (2 pages)Spontaneous emission control - device applications
http://dl-live.theiet.org/content/conferences/10.1049/cp_19971509
Spontaneous emission engineering and the incorporation of microresonators are becoming a rather standard engineering tool to achieve high efficiency optical devices. We review the state of the art in this field and point to emerging applications in LED microcavities, and possible future quantum well laser microcavities.Simultaneous delivery of four independent broadcast television services over a wavelength-division multiplexed passive optical network
http://dl-live.theiet.org/content/conferences/10.1049/cp_19971584
We demonstrate simultaneous delivery of four independent digital broadcast television services over a WDM passive optical network (PON) by spectrally slicing Er-doped fibre amplifier (EDFA) amplified LEDs. The composite bandwidth of 2 GHz carries more than 320 channels of digital television, and is delivered independently of private point-to-point services which are possible over the WDM PON architecture. We compare the WGR as a broadcast distribution element to a passive splitter.A 24-channel WDM transmitter for access networks using a loop-back spectrally-sliced light-emitting diode
http://dl-live.theiet.org/content/conferences/10.1049/cp_19971566
A 24-channel WDM transmitter for local access has been demonstrated by applying a novel loop-back spectral slicing, optical delay, and multiplexing method to a LED. Set-and-forget transmitter operation at 50 Mb/s with self-aligned channel wavelengths was realized.Systematic study into resonant cavity light-emitting diodes
http://dl-live.theiet.org/content/conferences/10.1049/ic_19961418
Conventional LEDs exhibit a broad spectral width but do not suffer with the electrical driving complexity, temperature sensitivity and optical feedback problems found with the use of lasers. Passively filtering the light from a conventional LED can narrow the spectral width but will always reduce the spectral power density of the output light and would require additional packaging and optics. However a new class of structures, namely Resonant Cavity Light Emitting Diodes (RCLEDs), have been developed in the last few years which appear to overcome several of these issues as well as offering better high-speed modulation performance and efficiency. We have been investigating RCLED's in both the GaAs and InP material systems. The quantum well emitters in both of these systems are chosen such that emission may be through the substrate, i.e. strained InGaAs QW (on GaAs operating around 980 nm) and InAsP QW (on InP operating around 1350 nm). The results demonstrate narrower spectral widths, higher peak spectral power densities and lower temperature sensitivity than nonresonant reference devices grown with nominally the same luminescent region. In this report we concentrate mainly on the GaAs structures. (5 pages)The design of high performance porous silicon light emitting diodes using a photonic band-gap approach
http://dl-live.theiet.org/content/conferences/10.1049/ic_19961409
The discovery in 1990 that porous silicon demonstrates efficient photoluminescence in the visible spectrum caused great excitement, largely because it suggested that silicon light emitting devices (LEDs) might be possible. We present a comparison of several different designs of porous silicon microcavity including a single high porosity layer and various multi-layer stack designs chosen to exhibit strong photonic band-gap effects. (4 pages)High efficiency (>20%) microcavity LEDs
http://dl-live.theiet.org/content/conferences/10.1049/ic_19961419
The work described here was aimed towards high efficiency light emitting diodes (LEDs), thereby compromising on directionality and narrow spectrum. At present our efforts have yielded devices which have an external quantum efficiency (QE) of over 22%. This is believed to be a record QE for planar LEDs. This result relies on both careful design and material growth. For the design we developed a simulation tool which proves useful in selecting interesting structures and interpreting experimental results. The theoretical analysis includes the guided modes, reabsorption of light by the active material and subsequent photon recycling. The material is grown with MOVPE, which yields high quality material as well as allowing excellent control over layer thickness and composition. In the first part we highlight the main characteristics of the theoretical model and deal with some key issues in the design of high efficiency microcavity LEDs (MCLEDs). In part two the main experimental results are discussed. (6 pages)Conducting polymers in microelectronic devices
http://dl-live.theiet.org/content/conferences/10.1049/ic_19961288
We report progress in the processing and application of poly(phenylene vinylene), PPV, as the emissive layers in electroluminescent diodes, LEDs. Photoluminescence efficiencies above 60% for solid films of PPV are now achieved, and single-layer EL diodes achieve luminous efficiencies above 2 Lumens/W and peak brightnesses up to 90,000 cd/m2. We demonstrate that PPV of this type can show stimulated emission in sub-picosecond pump-probe experiments, and can be used as the active lasing medium when incorporated in suitable microcavity structures. (4 pages)IEC 825-1 eye safety classification of some consumer electronic products
http://dl-live.theiet.org/content/conferences/10.1049/ic_19960198
The amended IEC 825-1 (and consequently CENELEC EN 60825-1) laser safety classification document, incorporates changes from the previous issue which although improve the maximum allowed emitted LED intensity, it still poses problems to the classification of free space optical link products. The changes from the previous issue are mainly concerned with LEDs, allow approximately 50 times higher output optical power from the previous specification. We show that in spite of the changes, most of the existing free space optical links cannot be classified as class 1. Calculations are given for class 1 classification, based on accessible exposure limits (AEL), of maximum permissible source intensity in mW/Sr, for typical products available in the market. (6 pages)The opto-electronic high-frequency transconductor and circuit applications
http://dl-live.theiet.org/content/conferences/10.1049/ic_19960170
A new hybrid design approach for high gain high frequency opto-electronic transconductors is proposed. The idea exploits the high output resistance of a p-i-n photodiode to realise a high resistance current source. Measured results on a discrete circuit implementation of a bandpass filter using laser diodes, p-i-n receivers and discrete Si JFETs demonstrates that foQ products of more than an order of magnitude higher than device process f<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">T</sub> can be obtained. Simulated results of a similar filter employing CMOS technology for the front-end FET shows that using realistic device models filter Qs of the order of 800 can be achieved at 100 MHz. Finally a GaAs based cascode op-amp is realised using LEDs and PIN diodes to realise the opto-electronic current sources and simulations show that voltage gains of the order 80 dB with 5 GHz unity gain bandwidth products can be achieved. (11 pages)Materials issues for AlGaInP visible light emitters
http://dl-live.theiet.org/content/conferences/10.1049/ic_19961227
We have described the key materials issues associated with the MOCVD growth of AlGaInP based visible light emitters and have briefly highlighted their influence on the final device performance. It is important to understand, control and optimise each of these parameters in arriving at a final epitaxial device layer structure. (5 pages)Electrical characteristics of metal contacts on porous silicon
http://dl-live.theiet.org/content/conferences/10.1049/ic_19950981
I(V) and C(V) characteristics of aluminium-porous silicon (PS) contacts were measured in the temperature range of 77-300 K for a sample prepared from 8-12 Ω·cm p-type silicon. The barrier height derived from the I(V) characteristics was found to depend linearly on temperature. The ideality factor was estimated to be 11.5 for the temperature range of 77-300 K. A decrease of contact differential capacitance, measured at 1 kHz, with decreasing temperature is observed. (4 pages)Polymer electroluminescence: principles and prospects
http://dl-live.theiet.org/content/conferences/10.1049/ic_19950859
Organic electroluminescence has been the subject of considerable interest in the last few years following reports from the Eastman Kodak and Kyushu University groups, and subsequently many others, on sublimed films of low molecular weight dyes. We have shown that another class of organic, namely the conjugated polymers, can be used as the emissive layer in electroluminescent diodes and that these films have good stability. Combined with their ease of deposition over large areas, this makes them an attractive new category of electroluminescent material. Following our first report in 1990 on poly(p-phenylene vinylene) light emitting diodes, considerable progress has been made in enhancing device characteristics and in chemically tuning the colour of emission. In this paper I will review the status of progress in conjugated polymer electroluminescence and describe some results. I will also provide a personal view of the prospects that this new area offers for lighting and display applications and highlight some of the current difficulties. (1 page)Growth of GaN and related materials for light emitting devices
http://dl-live.theiet.org/content/conferences/10.1049/ic_19950972
We have shown that Group III nitrides have a huge potential for application to visible light-emitting devices, display being central to such applications. There is an important requirement for a material match between substrate and epitaxial film and we are exploring the possibility of growing either an alloy or a short period superlattice on silicon substrates which will be of major assistance in integrating light-emitting devices with silicon driving circuitry. (6 pages)A visible large area light emitting diode fabricated from porous silicon using a conducting polyaniline contact
http://dl-live.theiet.org/content/conferences/10.1049/ic_19950980
We have fabricated a light emitting diode using a p-type conducting polyaniline layer deposited on an n-type porous silicon layer. The I-V curves show rectifying behaviour and can be fitted to a Schottky barrier model which gives a barrier height of 0.8 eV. The porous silicon has an orange photoluminescence band due to recombination in the silicon quantum structures both before and after coating with polyaniline. The junction emits visible electroluminescence when a forward bias is applied. The emission band is very broad extending from 500-1000 nm with a peak at 790 nm. The implications of the data are discussed with respect to charge transport across the polymer/semiconductor interface. (6 pages)Leading lights? [LEDs have been lauded as the eco-friendly answer to all our lighting needs]
http://dl-live.theiet.org/content/journals/10.1049/et.2012.0816
LEDs have been lauded as the eco-friendly answer to all our lighting needs. LEDs are much more energy efficient, using up to 90 per cent less energy than incandescent bulbs. LED produces more light for the power that goes in and is more effective at producing light in one direction, than a filament bulb in a reflective light fitting. White light LED bulb produces around 150 lumens per watt; this figure is predicted to increase to 250 lumens per watt in the next decade. In comparison, the CFL produces 60 to 80 lumens per watt while the halogen incandescent produces around 16 lumens per watt.New Cd<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">1−<i>x</i></sub>Mn<sub xmlns="http://pub2web.metastore.ingenta.com/ns/"><i>x</i></sub>Te quantum dots for application in light-emitting diodes
http://dl-live.theiet.org/content/journals/10.1049/mnl.2012.0540
Cd<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">1−<i>x</i></sub>Mn<sub xmlns="http://pub2web.metastore.ingenta.com/ns/"><i>x</i></sub>Te quantum dots (QDs) were synthesised through a one-step approach in an aqueous medium, and a red-shift in the emission peak wavelength, from 542 nm to a long wavelength of 566 nm, was observed by doping Mn<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">2+</sup> ions into the CdTe QDs. A red light-emitting diode (LED) device was fabricated by combining red light-emitting Cd<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">1−<i>x</i></sub>Mn<sub xmlns="http://pub2web.metastore.ingenta.com/ns/"><i>x</i></sub>Te QDs with a near-UV InGaN LED chip. CIE colour coordinates of the LED at (0.56, 0.25) demonstrated a near red light-emitting LED. The results showed that the Cd<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">1−<i>x</i></sub>Mn<sub xmlns="http://pub2web.metastore.ingenta.com/ns/"><i>x</i></sub>Te QDs are good candidates for LED applications.Generation of white LED light by frequency downconversion using perylene-based dye
http://dl-live.theiet.org/content/journals/10.1049/el.2012.3084
A high efficiency white light emitting diode (LED) was fabricated by generation of frequency downconversion from a GaN/InGaN blue LED. In place of conventional inorganic phosphors, a perylene-based dye was used for colour conversion. The resulting hybrid structure is analysed by focusing on the visual performance of the realised LEDs employing the most relevant photometric parameters of a light source. Preparation of the organic polymer is described as well. The thermal stability of the dye was investigated and a simple structure which avoids colour degradation is proposed.High-power single-chip InGaN blue light-emitting diode with 3.3 W output power
http://dl-live.theiet.org/content/journals/10.1049/el.2012.2556
The characteristics of a high-power single-chip blue light-emitting diode (LED) operating with >10 W input power are reported. The LED chip was fabricated in the form of a vertical-injection structure with chip dimensions of 1.8×1.8 mm. Electrode patterns at the n-GaN surface were designed to optimise the output power and operation voltage. Electrical and optical characteristics of the LED were measured up to 3 A injection current under pulsed operation condition. Output power and forward voltage at 3 A were obtained to be 3.3 W and 3.67 V, respectively, which demonstrates the wall-plug efficiency of >30% with 10 W input power. Even higher output power and efficiency are expected from the single-chip LED by reducing the efficiency droop of InGaN-based LEDs.Multi-target stimulator SSVEP using multi-frequency embedded with multi-phase encoding sequence
http://dl-live.theiet.org/content/journals/10.1049/el.2012.1325
Presented is a novel coding method for steady-state visual evoked potential (SSVEP). To relax the limitations of SSVEP, the number of flash stimulators requires the same number of flashing frequencies for coding. However, the number of frequencies that may be required for stimulation is limited. This study proposes multi-frequencies embedded with the multi-phase flickering sequences stimulation method. In the experiments, the study considered SSVEPs induced by nine groups of light emitting diodes generated by only two frequencies. The proposed method of flickering sequences has been tested on five subjects to verify its feasibility. The average accuracy obtained was 87.3 ± 16.6% in the simulation test.Appropriate modulation scheme for visible light communication systems considering illumination
http://dl-live.theiet.org/content/journals/10.1049/el.2012.2195
Visible light communication (VLC) systems use light emitting diode (LED) technology for illumination and data transmission at the same time. The main concerns of VLC systems are illumination and BER performance. In optical systems, the modulation scheme affects the illumination and BER. Therefore, it is necessary to analyse the performance of the modulation schemes applied in the VLC system. To analyse the bandwidth requirement, power efficiency, brightness and flickering problem, four different modulation schemes, were compared: OOK, pulse position modulation (PPM), overlapping PPM (OPPM), and inverted PPM (I-PPM). It is shown that OPPM achieves better performance with flexible illumination. Moreover, trellis-coded modulation (TCM) is applied to improve the BER performance. Simulation results show that OPPM is a powerful candidate modulation scheme for VLC systems.Offset-voltage compensation for accurate current-source circuit
http://dl-live.theiet.org/content/journals/10.1049/el.2012.0739
The offset-voltage compensation technique is proposed for an accurate current-source circuit. This current source is made of a transistor, a resistor, and operational amplifier feedback in order to achieve a high output resistance as well as high accuracy of a generated current signal. Discrepancy from the ideal value mainly results from the offset voltage of the operational amplifier. The transconductance amplifier is utilised with a feedback loop that is controlled by the switched-capacitor integrator. The proposed technique is incorporated in the light-emitting diode driver circuit applications and successfully verified with hardware measurement.Dimmable driver for light-emitting diode with total harmonic distortion improved
http://dl-live.theiet.org/content/journals/10.1049/iet-pel.2011.0035
A novel dimmable light-emitting diode (LED) driver is presented. Via a simple concept, the total harmonic distortion and the power factor of the proposed LED driver are significantly improved as compared to the traditional LED drivers. Above all, there are no capacitor and no inductor in the main power stage of the proposed LED driver, thereby causing the life of the LED driver to be enhanced and the integral circuit design to be easy to achieve. Moreover, a new LED dimming strategy is presented. The basic operating principles of the LED driver are described in detail, along with some simulated and experimental results to demonstrate the effectiveness and feasibility of the proposed LED driver.