Light-emitting Diode System Research Articles

Estimation of Luminous Flux and Luminous Efficacy of Low-Power SMD LED as a Function of Injection Current and Ambient Temperature

Light-emitting diode (LED) luminous flux and efficacy as a function of temperature and current is important to qualify and optimize the design of an LED system. In this paper, the extension of light output equation was used to estimate luminous flux and efficacy of low-power surface-mounted device LED. The photometric and thermal test reports of LED parameters at a certain range of injection current and ambient temperature were obtained by the combination of T3ster and TeraLED systems. The luminous flux and efficacy as a function of injection current and ambient temperature were predicted. The agreement between the experimental and theoretical results validates the extended equation used in this paper. The optimized operating conditions of LED under test are determined.

Analysis of Factors Influencing on Heat Transfer Characteristics of Automobile LED Headlamp

Light Emitting Diodes (LEDs) are being considered for use in the automobile headlamps for front side illumination in the place of halogen and xenon headlamp systems. Although LEDs provide larger service life and better power efficiency, they generate considerable amount of heat. It is desirable to develop an advanced cooling system to effectively dissipate heat generated for a stable, continuous and reliable LED operation. The objective of this investigation is to experimentally study the factors influencing the cooling performance of the air cooled heat sink model used in an automobile LED headlamp system. The cooling performance of the heat sink model under consideration was assessed by measuring temperature and thermal resistance at significant locations. The input power, fan output and ambient temperature were varied and corresponding effects were observed. The effect of power variation on illuminance was observed. In addition, a comparative study was carried out to determine the effects of forced and natural convection, which indicated the necessity of forced convection for effective cooling of an automobile LED system.

The research on LED supplementary lighting system for plants

As an artificial light source, light-emitting diodes (LEDs) can be used to make the vegetables grow more quickly in closed-type plant production systems, especially in the environment of the light intensity is insufficient. In order to study the improvement of the cherry tomato growth rate using the LED light source, we have a design with a certain ratio of red and blue (relative spectral distribution) LED lighting system and carry out the manufacture of the LED supplementary lighting system. We carried on a track on the growth situation for a group of cherry tomatoes under the LED system and the other group of cherry tomatoes without the LED supplementary lighting system. We observed and compared with the growth of the two group of tomatoes in different growing period. In our experiment, we use supplementary lighting system with the red and blue LEDs which peak wavelenth are respectively 650nm and 460nm, and the relative spectral distribution ratio is 4:1. The experimental results showed that the LED supplementary lighting system significantly improved the growth speed of tomatoes. Because of the difference preference for the wavelength between the stem and leaf growth stage and the blooming and bearing fruit growth stage, this paper presents the red and blue light proportion choice switch which can be applied to the LED supplementary lighting system.

Investigation of the LEDs heat sinks

Junction temperature is an important parameter in thermal management of LEDs (Light emitting diodes) system. The junction temperature of three different types of LED is calculated numerically. Three dimension numerical simulation using ANSYS-Icepak 15 software package is presented for all cases. Appropriate heat sink is designed for each type of LED and investigates the effect of the fins height on the junction temperature. The increasing in electrical current utilized to driving the LEDs has concentrate high notice on the thermal management in the evolution of LED system. A felicitous design should have minimum thermal resistance between the heat sink base and the junction that depends on conduction heat transfer. The results showed the increase in a heat sink height 10% dissipate more heat transfer from the LEDs system at approximately 15%.

Thermal-Structural Optimization of Light with LED Packaging

At present, the light-emitting-diode (LED) has been a tremendous surge in its application as a new type of generation lighting source. The thermal performance and structural reliability of LED system have been investigated by different conditions in electronic package [1]. With the minimization of the LED packaging, the reliability problem, especially, the thermal reliability becomes more and more seriously. Hence the heat dissipation for LED system becomes much crucial. Lots of heat management methods have been investigated for LED system designing and manufacturing. The most popular cooling method used in the LED system is the passive cooling, however, its cooling efficiency is very low. It is very significant to develop the heat dissipation method [2, 3]. A systematic numerical and experimental method is developed to optimize a caution lamp with multichips LEDs in this paper. Here we intend to describe the thermal performance of LED caution lamp with multiple LED chips through the structural optimization by the finite element method. And to understand the thermal characteristics of the caution lamp with difference structural parameters. After the optimization, one type of caution lamp was made and the highest temperatures of LED chips have been test. This optimization method is useful for design and manufacturing of caution lamps with multiple LED chips. After numerical simulation, we prepared the caution lamp sample with six LED chips according to the results. The Thermalcouples are used to test the temperature of the lamp. Compared with the simulation and the experiment data, the high temperature of LEDs were reduced by choosing fitting parameters. It indicates that the results and methods used in this paper can provide the guidance in the understanding of thermal management for LED lamps design. Figure 1 show temperature distribution of light structures before and after thermal-structural optimization. Figure 2 show the test principle connection and test system. Figure 1

New Applications of an Automated System for High-Power LEDs

An automatic system based on thermoelectric cooler (TEC), a microfan, and microcontroller is first applied to thermal management of high-power light-emitting diodes (LEDs). Its hardware is composed of microcontroller as a control core, K-type thermocouples as acquisition devices, and TEC and a microfan with heatsink as cooling vehicles. The experiment confirms that the LEDs substrate temperature can be controlled effectively, and indicates that the LED chips are operating reliably. Specifically, in high-temperature environments of 43 °C, the system can automatically drop to the low set temperature (30 °C) due to thermoelectric effect driven by TEC. Heat transfer analysis shows that maximum LED power cooled by the system is 106.7 W, and the total power consumption of the automatic cooling system is only 8.85 W. The automatic cooling system has a high cooling efficiency.

Precise Dimming and Color Control of LED Systems Based on Color Mixing

This paper proposes a closed-loop nonlinear scheme for precisely controlling the luminosity and correlated color temperature (CCT) of a bicolor adjustable light-emitting diode (LED) lamp. The main objective is to achieve a precise and fully independent dimming and CCT control of the light mixture emitted from a two-string LED lamp comprising warm-white and cool-white color LEDs, regardless of the operating conditions and throughout the long operating lifetime of the LED lamp. The proposed control method is formulated using the nonlinear empirical LED model of the bicolor white LED system. Experimental results show that with the proposed closed-loop nonlinear approach, both CCT and dimming control of the bicolor lamp is significantly more accurate and robust to ambient temperature variations, ambient light interference, and LED aging than the conventional linear approach used in existing products. The maximum error in luminous flux employing the proposed closed-loop nonlinear approach is 3%, compared with 20% using the closed-loop linear approach. The maximum deviation in CCT is only 1.78%, compared with 27.5% with its linear counterpart.

Unidirectional visible light communication and illumination with LEDs

Visible light communication (VLC) with light emitting diodes (LEDs) has attracted interest for interactive and networked lighting control, and consumer infotainment applications. In this paper, we propose an LED system for jointly achieving unidirectional VLC while providing flicker-free illumination. At the transmitter, a redundant run-length limited encoding scheme and multi-level dimming is considered for data transmission, with a wide dimming range. The receiver uses ON-OFF keying and uses the OFF periods for VLC reception. It is allowed to be asynchronous to the transmitter, with a phase offset within a preset range. A key feature of the proposed system is that no dedicated devices are used for transmission/reception, with the LEDs used for these functions. We design a functional prototype of this system and evaluate the communication bit error rate and illumination flicker performance experimentally.

Nonlinear dimming and correlated color temperature control of bicolor white LED systems

This paper proposes a nonlinear approach of controlling the luminous intensity and correlated color temperature (CCT) of white light-emitting diode (LED) systems with dual color temperatures. This LED system is made up of a warm color LED source (2700 K) and a cool color LED source (5000 K). The luminous intensity of each of these LED sources is individually controlled by pulsewidth modulation. The overall intensity of the LED system is due to the combined emitted flux of both LED sources. Its overall CCT is the mixed average CCT of both LED sources. This proposed method is based on the nonlinear empirical luminous and CCT models of the LEDs, which take into consideration the thermal effect of LEDs on its luminance and CCT properties. With reasonable approximation, the theoretical models are simplified into practical solutions, which are translatable into real-life applications. It is experimentally validated that the proposed approach is considerably more accurate than the existing linear approaches that do not consider color variations of LED sources. The idea is applicable to LED systems with multiple color temperatures and is not limited to white LEDs.

Application of light-emitting diodes (LEDs) in cultivation of phototrophic microalgae: current state and perspectives.

The quality and regulation of the incident light is crucial in microalgae cultivation processes. Depending on wavelength, spectrum, and intensity, growth characteristics and biochemical composition of these organisms vary. With mainly fluorescent lamps (FL) used previously for illumination, such variabilities could not be studied adequately due to their broad emission spectrum. In contrast, light-emitting diodes (LEDs) emit a very narrow wavelength band and enable flexible photobioreactor designs due to their small size. This review provides a condensed overview on the application of LEDs in microalgal cultivation processes. It summarizes the current availability and applicability of LED technologies as an illumination source for research-focused photobioreactor systems. A particular focus is the use of narrow-wavelength LEDs to address fundamental as well as applied aspects of light color on algae biomass and value-added compound formation. In this respect, the application of internal and external illumination systems is reviewed together with trends in the industrial use of LED systems to intensify algae process efficiency.

LED-Based Color Sensing and Control

New ways of light interaction are being enabled with the advent of light-emitting diodes (LEDs). In this paper, we describe an LED system with LED lamps and an LED array, where the LED array is used to sense color of a source lamp and then transport it to a destination lamp to adapt its color. We present a design prototype of the LED lamps and the LED array in order to realize the dual function of color sensing and illumination. A driving protocol is proposed such that color sensing may be performed, without causing an additional flicker during illumination. Depending on the wavelength selectivity of the LED devices, two methods for color estimation are proposed. Experimental results are presented to evaluate the performance of the proposed estimation method.

Natural Convection Immersion Cooling With Enhanced Optical Performance of Light-Emitting Diode Systems

Electronics driven at high currents may experience local hot spots, which may cause thermal degradation or even catastrophic failures. This common problem occurs at light-emitting diode (LED) chips and it is not easily observed by end-users. Driving over 700 mA over a 1 mm2 chip is expected to generate local temperature gradients. In addition, bonding failures at manufacturing or during operation (cracks, delamination, etc.) may also lead to local hot spots. Therefore, possible hot spots over an LED chip have turned attention to direct cooling with dielectric liquids comprises the current study. Computational and experimental studies have been performed to understand the impact of conduction and alternatively convection with various dielectric fluids to abate local hot spots in a multichip LED light engine. To capture the local temperature distributions over the LED light engine with a dome in the domain especially over the LED chip; first, computational models have been built with a commercial computational fluid dynamics (CFD) software. Later, attention has been turned into experimental validation by using a multichip high brightness LED (HB LED) light engine. An optothermal evaluation has been made at single and multiphase heat transfer modes with dielectric fluids (LS5252, HFE7000, and silicone oil, etc.) to compare with a series of CFD models and experimental studies. While multiphase liquid-cooled LED system has a better cooling performance but lower optical extraction, single-phase liquid-cooled LED system has shown a reasonable thermal performance with a 15% enhancement at light extraction.

DC-Level Dimmable LED Driver With Primary Side On-Time Control for DC Distribution

This paper proposes a light-emitting diode (LED) lighting system using a dc-level dimming technique. This new dimming method realizes LED lamp control by having the LED drivers in the same zone recognize the level of their input voltage as a dimming signal with a dc-level dimmer and minimum communication interfaces. The proposed dc LED system also achieves improved system efficiency by matching the variable input voltage to the LED load conditions. Practical design guidelines for the LED driver circuit are presented for system implementation. The prototype circuit for a 24-W LED lamp is designed following the guidelines for verification. The proposed dc-level dimming system and the conventional dimming LED lighting system, which dispatches communication modules to individual drivers to obtain dimming signal, are implemented for a two-story parking lot and their performance is compared and evaluated. The experimental results of the prototype system show 6.8% energy saving compared with conventional lighting, which results from the improved driver efficiency and reduced standby power consumption.

Estimation Carrier Concentration of Light-Emitting Diode via Electrical–Thermal Characteristics

With the use of the capacitance, estimation techniques for the carrier concentration of the light-emitting diodes (LEDs) are introduced in this paper. The proposed model relates the carrier concentration to the forward current, the thermal resistance of the heatsink, the LED device, the device package, and the other physical parameters of the device (such as the bandgap energy, series resistance, and ideality factor), coefficients for the current, and temperature effect on the apparent capacitance altogether. It could provide a framework for analyzing LED devices. The estimation methods consist of simple procedures for electrical measurements, which are easy for LED device manufacturers and system designers to follow. The proposed model has been tested with LED devices, with reasonably good agreement between theoretical and practical results.

Power Flow Analysis and Critical Design Issues of Retrofit Light-Emitting Diode (LED) Light Bulb

For retrofit applications, some high-brightness light-emitting diode (LED) products have the same form factor restrictions as existing incandescent light bulbs. Such form factor constraints may restrict the design and optimal performance of the LED technology. In this paper, some critical design issues for commercial LED bulbs designed for replacing E27 incandescent lamps are quantitatively analyzed. The analysis involves power audits on such densely packed LED systems so that the amounts of power consumption in: 1) the LED wafer; 2) the phosphor coating; and 3) the lamp translucent cover are quantified. The outcomes of such audits enable R&D engineers to identify the critical areas that need further improvements in a compact LED bulb design. The strong dependence of the luminous output of the compact LED bulb on ambient temperature is also highlighted.

An in vivo study of the best light emitting diode (LED) systems for cut chrysanthemums

Abstract The cut chrysanthemum (Chrysanthemum ×morifolium Ramat.) is one of the most recognized cut flowers in the world. Light quality significantly affects the development and growth of plants. To conduct an in-depth investigation of the effects of light quality on the growth and development of cut chrysanthemums, seedlings of the cut chrysanthemum cultivar ‘Riqietaohong’ were cultured under four different light emitting diode (LED) systems: red (R), blue (B), red : blue = 2:1 (RB) and blue : red = 2:1 (BR). A fluorescent lamp was used for control group lighting. The Duncan multiple comparisons analysis showed that the B light promoted stem and leaf development of seedlings but inhibited photosynthesis. The R light stimulated their rooting but inhibited the accumulation of biomass. RB improved transpiration. Moreover, a comprehensive evaluation system that combined the analytic hierarchy process (AHP) method with the technique for order preference by similarity to an ideal solution (TOPSIS) method indicated that the photosynthesis index, transpiration index and biomass index were the most important indicators for the growth and development of cut chrysanthemums, and RB was the best LED system for cut chrysanthemums. The present study provides references for the lower energy consumption and industrial annual production of cut chrysanthemums.

Analysis and Modeling of High-Power Phosphor-Coated White Light-Emitting Diodes With a Large Surface Area

Modern high-power white light-emitting diodes (LEDs) composed of multiple blue LED chips and yellow phosphor coatings have been successfully commercialized because of their high-luminous efficacy. The multiple-chip LED packages usually come with flat structures that have large surface areas for considerable heat loss. Starting from the analysis and modeling of the blue LED chip, this paper introduces the thermal path through the phosphor layer to form the white phosphor-coated (PC) white LED device model for photometric, electric, and thermal performance analysis. The power distribution of the blue LED chip and that of the PC white LED device are compared. Based on this new analysis, the increase in the heat dissipation coefficient, equivalent thermal resistance, and power loss caused by the phosphor coating can be quantified. New equations suitable for device manufacturers to qualify their devices and design engineers to optimize LED system designs are derived. The analytical results are in good agreement with the practical mesurements.

Growth and stress response in Arabidopsis thaliana, Nicotiana benthamiana, Glycine max, Solanum tuberosum and Brassica napus cultivated under polychromatic LEDs.

BackgroundThe use of light emitting diodes (LEDs) brings several key advantages over existing illumination technologies for indoor plant cultivation. Among these are that LEDs have predicted lifetimes from 50–100.000 hours without significant drops in efficiency and energy consumption is much lower compared to traditional fluorescent tubes. Recent advances allow LEDs to be used with customized wavelengths for plant growth. However, most of these LED growth systems use mixtures of chips emitting in several narrow wavelengths and frequently they are not compatible with existing infrastructures. This study tested the growth of five different plant species under phosphor coated LED-chips fitted into a tube with a standard G13 base that provide continuous visible light illumination with enhanced blue and red light.ResultsThe LED system was characterized and compared with standard fluorescence tubes in the same cultivation room. Significant differences in heat generation between LEDs and fluorescent tubes were clearly demonstrated. Also, LED lights allowed for better control and stability of preset conditions. Physiological properties such as growth characteristics, biomass, and chlorophyll content were measured and the responses to pathogen assessed for five plant species (both the model plants Arabidopsis thaliana, Nicotiana bentamiana and crop species potato, oilseed rape and soybean) under the different illumination sources.ConclusionsWe showed that polychromatic LEDs provide light of sufficient quality and intensity for plant growth using less than 40% of the electricity required by the standard fluorescent lighting under test. The tested type of LED installation provides a simple upgrade pathway for existing infrastructure for indoor plant growth. Interestingly, individual plant species responded differently to the LED lights so it would be reasonable to test their utility to any particular application.Electronic supplementary materialThe online version of this article (doi:10.1186/s13007-015-0076-4) contains supplementary material, which is available to authorized users.

EFFECTS OF LED-ILLUMINATION AND LIGHT INTENSITY ON THE ACCLIMATIZATION OF IN VITRO PLANTLETS TO EX VITRO CONDITIONS

The aim of this study was to evaluate the suitability of ready-made light emitting diodes (LED) in the acclimatization process of in vitro regenerated plants from somatic embryos to ex vitro. At which the fluorescent tubes (FL) represented the reference. The plantlets were cultured for six weeks under two ready-made LED systems with different wavelength combinations: BloomPower white lamps (LED (BP)) at 300, 90, or 50 µmol m-2 s-1 and tubes of Valoya at 90 µmol m-2 s-1 together with fluorescent tubes (FL) at 90 µmol m-2 s-1 as reference. To verify the physiological state of the adapted plants six of each treatment were potted and cultured for further 60 days under former light conditions. Over all light conditions only 28.7% of the investigated plants with embryogenic origin could be well adapted. Most of them acclimatized under LED (BP) 300 and FL 90. Thereby LED (BP) 300 showed the highest biomass accompanied by shortest shoot and internode length, strong plants but with red colored leaves. Even after adaptation potted plants showed the same pattern. Indirect measurement of flavonols via Dualex indicated high stress level. The results indicated that the acclimatization of plants regenerated from somatic embryos is very susceptible against environmental alteration but 90 µmol m-2 s-1 seemed to be sufficient for proper plant development. The lower growth parameters resulted in the different wavelength compositions of the LED tubes as compared to fluorescent tubes and have to be optimized.

A wirelessly controlled implantable LED system for deep brain optogenetic stimulation

In recent years optogenetics has rapidly become an essential technique in neuroscience. Its temporal and spatial specificity, combined with efficacy in manipulating neuronal activity, are especially useful in studying the behavior of awake behaving animals. Conventional optogenetics, however, requires the use of lasers and optic fibers, which can place considerable restrictions on behavior. Here we combined a wirelessly controlled interface and small implantable light-emitting diode (LED) that allows flexible and precise placement of light source to illuminate any brain area. We tested this wireless LED system in vivo, in transgenic mice expressing channelrhodopsin-2 in striatonigral neurons expressing D1-like dopamine receptors. In all mice tested, we were able to elicit movements reliably. The frequency of twitches induced by high power stimulation is proportional to the frequency of stimulation. At lower power, contraversive turning was observed. Moreover, the implanted LED remains effective over 50 days after surgery, demonstrating the long-term stability of the light source. Our results show that the wireless LED system can be used to manipulate neural activity chronically in behaving mice without impeding natural movements.