Light-emitting Diode Light Source Research Articles

Semiconductor yellow light-emitting diodes

The development of semiconductor light-emitting diode (LED) in the visible emission range is very unbalance, as the power efficiency of yellow LED is far below other colors. Based on the GaN/Si technology, the authors and his team made a systematic research from the aspect of material growth, chip fabrication, device physics and equipment design, resolved the problems of epi-film cracking, high dislocation density, large strain in quantum well (QW), phase separation in QW, low QW growth temperature, low hole concentration, light absorption by substrate and light blocking by electrode, successfully made a breakthrough in fabricating efficient yellow LED. The yellow LED chip achieves a power efficiency of 26.7% at 20 A/cm<sup>2</sup> with 565 nm wavelength and efficacy of 164 lm/W, and the power efficiency goes up to 42.8% at 1 A/cm<sup>2</sup> with 577 nm wavelength and efficacy of 248 lm/W. New LED light source with multi-colors and without phosphor was developed based on the efficient yellow LEDs, opened up a new direction of pure LED healthy lighting.

发光二极管光源的生物学效应及临床研究新进展

发光二极管光源的生物学效应及临床研究新进展

Optically switchable bistable guest–host displays in chiral-azobenzene- and dichroic-dye-doped cholesteric liquid crystals

Optically switchable bistable guest–host displays in chiral-azobenzene- and dichroic-dye-doped cholesteric liquid crystals (CA-DD-CLCs) are demonstrated. The CA-DD-CLCs in a LC cell treated by homeotropic alignment are initially in stable unwound textures. Given that all LC molecules in unwound textures are oriented perpendicularly to the substrates, the light absorbed by the doped DDs reaches the minimum value, which is considered the transparent state of the proposed CA-DD-CLCs. The CA-DD-CLCs are switched to fingerprint (FP) textures by illumination with ultraviolet (UV) light and can be switched back to unwound textures by illumination with green light. The optical switching between unwound and FP textures is based on the photo-tunable chirality of the doped CA via photoisomerization effect. The light absorbed by the doped DDs in FP textures reaches the maximum value, which is considered the dark state of the CA-DD-CLCs. Moreover, the performances of light absorption from the doped DDs when the CA-DD-CLCs are in unwound and FP textures is independent of the polarization of the incident light. Pattern information can be optically addressed (erased) in CA-DD-CLC cells by illumination with UV (green) light through a suitable photomask. The CA-DD-CLCs can be stabilized in FP textures for several tens of minutes in the dark environment. As such, the power is consumed only for the illumination of specific lights during the switching of CA-DD-CLCs between unwound and FP textures. Moreover, a transparent active matrix organic light-emitting diode (LED) display that is superimposed on top of a CA-DD-CLC cell embedded with a transparent light-guide film with suitable LED light sources for optical switching between unwound and FP textures, is proposed for augmented reality applications.

Performance evaluation of lighting fixtures and installations for renewable energy applications

AbstractEnergy efficiency has been viewed as the most accessible and cost‐effective form of alternative energy. While lighting occupies only a small percentage in the total electric loads in homes, technological advances in light‐emitting diodes (LEDs) are becoming more convincing in their power consumption and lumens output. This article evaluates the percentage that lighting occupied in the total load spectrum in the two main buildings at Osun State University and verifies the light level in the library reading rooms—places where adequate lighting is imperative—with recommended standards and a comparison between the output of compact fluorescent lamps (CFLs) and the LEDs. The walk‐through energy audit approach was used to evaluate the percentage of energy that lighting consumes in these buildings. This approach involved identifying and grouping all of the electrical loads with their respective power ratings in Watts. Similarly, an illumination level verification campaign was conducted with the use of a digital light meter (a sensor‐based device) connected to a personal computer to log illumination levels in real time along the library's aisles and in the reading cubicles. The same light meter was used for comparing the output of installed CFL and proposed LEDs in an office space. Results indicate that lighting fixtures consume 12.2% of the load spectrum. The lighting installations also do not conform to global illumination standards for the assessed facilities, while the output of the LEDs that were tested was still low compared to the output of the CFLs. It is therefore recommended that better LED light sources be considered for efficient energy, reduction in environmental pollution associated with power generation, reduction in the power needed to maintain a cooling effect, and cost economy.

Evaluation of xenon, light-emitting diode (LED) and halogen light toxicity on cultured retinal pigment epithelial cells

Objective: To compare the possible toxic effects of three light sources used in vitreoretinal endoillumination systems; halogen, xenon, and light-emitting diode (LED) on retinal pigment epithelium (RPE) cell cultures, after two different exposure times.Material and methods: ARPE-19 human RPE cell cultures were exposed to halogen, xenon, and LED light sources at a distance of 1.5 cm for 30 and 60 min with equal lumen output levels. Cells in the control group were not exposed. RPE cell cultures were compared in terms of cell viability, DNA damage, apoptosis rate, and IL-1ß, IL-6, and TNF- α levels.Results: The halogen light group showed significantly more DNA damage, higher TNF-α, IL-1β, and IL-6 levels, and lower viable cell count at 30 min compared to the control group. The rates of early and late apoptosis were also significantly higher at 60 min. There were no statistically significant differences in any of the parameters between the xenon and LED light sources and the control group at 30 or 60 min.Conclusion: New generation lights, xenon, and LED, seem to be safe in terms of RPE cells. Halogen light may cause toxic effects on RPE cells when used for a long time with maximal power output.

Lifetime prediction of a multi-chip high-power LED light source based on artificial neural networks

A high power light-emitting diodes (LED) light source, which is assembled by many LED chips and heat sink, has a not uniform temperature distribution at working condition. Analysis and prediction of a high-power LED system lifetime are complicated and time-consuming. In this study, two artificial neural networks (ANN) are employed to simplify the LED lighting system’s lifetime prediction and increase the precision of such analysis. The temperature distribution of the high power light source is calculated by Finite element method (FEM) with LED chip photo-electro-thermal (PET) ANN. With the precise LED temperature distribution, the lifetime for multi-chip high-power LED light source can be predicted by lifetime ANN. The PET ANN is used to simplify the multi-physics coupling in LED PET analyzing. The lifetime ANN can predict the lifetime of a LED chip across a wide range of temperatures and not merely corresponding to several testing and interpolation points. This work aims to rapidly analyze multi-chip high-power lighting systems characteristics. The repeated tests and calculations of PET and lifetime are avoided with this method. This approach presents a new and effective way to assess the reliability of high-power LED light source.

Preparation of N-doped carbon dots based on starch and their application in white LED

N-doped carbon dots (CDs) were synthesized simply and economically by a one-step hydrothermal method using starch as a carbon source and ethylenediamine (EDA) as a nitrogen dopant. The prepared CDs possess the properties of excitation-wavelength dependence and emit blue fluorescence under the excitation wavelength of 365 nm. CDs/starch composite was prepared to achieve the solid-state emission of CDs and their application in light emitting diode (LED) as fluorescent materials. White LED, with CIE coordinates of (0.33, 0.37) and correlated color temperature of 5462 K, was obtained by combining CDs/starch and ultraviolet LED light source, indicating that starch-based CDs have the promising potential in the field of optoelectronic devices.

High-Throughput Analysis of Behavior Under the Control of Optogenetics in Caenorhabditis elegans.

In this unit, we describe an inexpensive and versatile method for optogenetic stimulation of a large population of genetically engineered Caenorhabditis elegans worms while quantitatively analyzing behavior. A custom light-emitting diode light source is used to deliver blue-light stimuli, causing direct depolarization of neurons expressing the light-gated cation channel Channelrhodopsin-2, which in turn evokes behavioral responses. The behavioral responses are recorded by a high-throughput machine vision-based tracking system, the Multi-Worm Tracker, for detailed analysis. This approach allows researchers to bypass technical obstacles to simultaneously deliver uniform stimuli to a large number of freely behaving animals and investigate the neural underpinnings of behavior. © 2018 by John Wiley & Sons, Inc.

A design method of freeform lens for LED based on intensity distribution

We proposed a method for the design of a freeform lens for light emitting diode (LED) light source based on intensity distribution curve. The energy mapping rules are considered in this design. The freeform lens achieves the optical requirements of the element and the geometrical requirements of the surface continuity. The method simplifies the design process of the freedom surface to avoid the repetitive optimization design and increase the design efficiency. In this paper, the modeling and optical simulation of freeform lenses for LED light source with 45°and 30°intensity distribution curves are performed. The simulation results prove the accuracy of the proposed method.

A Practical Method to Design Reflector-Based Light-Emitting Diode Luminaire for General Lighting

A reflector-based light-emitting diode (LED) luminaire structure that can achieve a large cut-off angle for general lighting is presented in this work. The proposed lighting unit mainly consists of a spherical reflector and a primary packaging lens that contains an aspheric surface and a spherical surface. The light rays emitted from the LED light source are well controlled by the spherical reflector and the aspheric surface of the lens for the purpose of obtaining a uniform illumination on the target surface. Both the ideal Lambertian LED and non-Lambertian LED light sources were employed to validate the proposed structure and the performance of the designed lighting units was analyzed by optical simulation. The results show that the light utilization efficiencies and the estimated uniformities are 92.96% and 91.11% for ideal Lambertian LED-based lighting unit and 93.31% and 91.64% for non-Lambertian LED-based lighting unit, respectively. Further analysis shows that the tolerances of horizontal, vertical, and rotational deviation of the both lighting units were about 2.0 mm, 1.0 mm, and 1.0°, respectively.

In-Use Photostability Practice and Regulatory Evaluation for Pharmaceutical Products in an Age of Light-Emitting Diode Light Sources

This article describes how the increased use of energy-efficient solid-state light sources (e.g., light-emitting diode [LED]-based illumination) in hospitals, pharmacies, and at home can help alleviate concerns of photodegradation for pharmaceuticals. LED light sources, unlike fluorescent ones, do not have spurious spectral contributions <400 nm. Because photostability is primarily evaluated in the International Council of Harmonization Q1B tests with older fluorescent bulb standards (International Organization for Standardization 10977), the amount of photodegradation observed can over-predict what happens in reality, as products are increasingly being stored and used in environments fitted with LED bulbs. Because photodegradation is premised on light absorption by a compound of interest (or a photosensitizer), one can use the overlap between the spectral distribution of a light source and the absorption spectra of a given compound to estimate if photodegradation is a possibility. Based on the absorption spectra of a sample of 150 pharmaceutical compounds in development, only 15% would meet the required overlap to be a candidate to undergo direct photodegradation in the presence of LED lights, against a baseline of 55% of compounds that would, when considering regular fluorescent lights. Biological drug products such as peptides and monoclonal antibodies are also expected to benefit from the use of more efficient solid-state lighting.

Controllable Uniform Green Light Emitters Enabled by Circular HEMT-LED Devices

This paper reports a monolithic integration of GaN high-electron-mobility transistor (HEMT) and green light-emitting diode (LED), where the circular HEMT is surrounded by a ring-shaped LED and two devices are seamlessly interconnected by the LED's n-GaN layer and the HEMT's two-dimensional electron gas (2DEG) channel. By adopting such a novel circular layout design, the green HEMT-LED shows a controllable and uniform green light emission at 507 nm by simply tuning its gate voltage. This enables a uniform, controllable green LED light source, serving as an essential element in the red–green–blue (RGB) LED solution for a wide range of applications, such as tunable-spectrum white LED illumination, multichannel visible light communication with wavelength division multiplexing, RGB-based full-color LED displays, and optogenetics.

Migratory bats are attracted by red light but not by warm-white light: Implications for the protection of nocturnal migrants.

The replacement of conventional lighting with energy‐saving light emitting diodes (LED) is a worldwide trend, yet its consequences for animals and ecosystems are poorly understood. Strictly nocturnal animals such as bats are particularly sensitive to artificial light at night (ALAN). Past studies have shown that bats, in general, respond to ALAN according to the emitted light color and that migratory bats, in particular, exhibit phototaxis in response to green light. As red and white light is frequently used in outdoor lighting, we asked how migratory bats respond to these wavelength spectra. At a major migration corridor, we recorded the presence of migrating bats based on ultrasonic recorders during 10‐min light‐on/light‐off intervals to red or warm‐white LED, interspersed with dark controls. When the red LED was switched on, we observed an increase in flight activity for Pipistrellus pygmaeus and a trend for a higher activity for Pipistrellus nathusii. As the higher flight activity of bats was not associated with increased feeding, we rule out the possibility that bats foraged at the red LED light. Instead, bats may have flown toward the red LED light source. When exposed to warm‐white LED, general flight activity at the light source did not increase, yet we observed an increased foraging activity directly at the light source compared to the dark control. Our findings highlight a response of migratory bats toward LED light that was dependent on light color. The most parsimonious explanation for the response to red LED is phototaxis and for the response to warm‐white LED foraging. Our findings call for caution in the application of red aviation lighting, particularly at wind turbines, as this light color might attract bats, leading eventually to an increased collision risk of migratory bats at wind turbines.

A water-microorganism detecting device with freeform lens

A device for detecting the microorganisms in water with a freeform lens is developed. The main components of the device include a water channel, a light-emitting diode (LED) light source, and a freeform lens. The freeform lens which plays a key role in the device is designed with a predefined light intensity distribution using a double freeform surface design method. Different from the traditional methods, during the construction of the lens, the mapping is established by an incident-emergent angle relation. As an example, a model of the device is designed. Monte Carlo ray tracing simulations are implemented to verify optical performance of the device. Installation error analyses on the LED source are also conducted. The results demonstrate that the device can generate a uniform illumination pattern at the arbitrary depth of the water and is feasible for the microorganism detection in water. Additionally, the results also show that the lens can achieve the uniform illumination without the influence of the illumination distance. An optical efficiency greater than 82% is obtained for the designed model.

Categorical color constancy under RGB‐LED light sources

AbstractThe light‐emitting diode (LED)‐based light sources have been widely applied across numerous industries and in everyday practical uses. Recently, the LED‐based light source consisting of red, green and blue LEDs with narrow spectral bands (RGB‐LED) has been a more preferred illumination source than the common white phosphor LED and other traditional broadband light sources because the RGB‐LED can create many types of illumination color. The color rendering index of the RGB‐LED, however, is considerably lower compared to the traditional broadband light sources and the multi‐band LED light source (MB‐LED), which is composed of several LEDs and can accurately simulate daylight illuminants. Considering 3 relatively narrow spectral bands of the RGB‐LED light source, the color constancy, which is referred to as the ability of the human visual system to attenuate influences of illumination color change and hold the perception of a surface color constant, may be worse under the RGB‐LED light source than under the traditional broadband light sources or under the MB‐LED. In this study, we investigated categorical color constancy using a color naming method with real Munsell color chips under illumination changes from neutral to red, green, blue, and yellow illuminations. The neutral and 4 chromatic illuminants were produced by the RGB‐LED light source. A modified use of the color constancy index, which describes a centroid shift of each color category, was introduced to evaluate the color constancy performance. The results revealed that categorical color constancy under the 4 chromatic illuminants held relatively well, except for the red, brown, orange, and yellow color categories under the blue illumination and the orange color category under the yellow illumination. Furthermore, the categorical color constancy under red and green illuminations was better than the categorical color constancy under blue and yellow illuminations. The results indicate that a color constancy mechanism in the visual system functions in color categories when the illuminant emits an insufficient spectrum to render the colors of reflecting surfaces accurately. However, it is not recommended to use the RGB‐LED light source to produce blue and yellow illuminations because of the poor color constancy.

Switched-Capacitor-Based Current Compensator for Mitigating the Effect of Long Cable Between PWM Driver and LED Light Source

It is sometimes unavoidable to have light-emitting-diode (LED) light sources and their pulsewidth modulation (PWM) drivers connected by long cables in large-scale illuminations. However, long-cable inductance delays the rate of rise of the driving current pulses and thus leads to the reduction of luminous flux output. It also causes the off-state voltage across the light sources negative, which would deteriorate the life expectancy of the LEDs. A switched-capacitor-based current compensator for correcting the wave shape of the driving current pulses is presented. The methodology is based on transferring the energy stored in the cable to a capacitor at the end of the current pulse and then momentarily boosting the voltage with the capacitor applying to the cable at the beginning of the next current pulse. Thus, the rise time of the current pulses can be shortened. The topological states and operations of the compensator will be described. A simplified design procedure will be given. A prototype for a 12-V, 3-A PWM driver has been built and evaluated. Performance comparisons between the proposed current compensator and prior art and between the systems with and without the compensators will be conducted.

Slow oscillations of cerebral hemodynamics changes during low-level light therapy in the elderly with and without mild cognitive impairment: An fNIRS study

Low-level light therapy (LLLT) is used to stimulate cell function or reduce pain by applying light emitting diodes (LED) to the skin. LLLT is known to contribute to the neuronal recovery during the reconstruction of brain tissue for the treatment of degenerative disorders. This research aims to confirm the slow oscillations of cerebral hemodynamics changes when LLLT is applied to the elderly and patients with mild cognitive impairment (MCI). Eight patients with MCI and 7 healthy elderly participated in this study. They were randomly divided into four groups; carotid artery stimulation, vertebral artery stimulation, simultaneous carotid and vertebral artery stimulation, or sham stimulation. The subjects received LLLT using Color DNA ® (Color Seven Co.) with a LED light source for 30 minutes a day during 20 days. The hemodynamic responses were recorded by an fNIRS system (NIRScout ® ) with 74 channels at the first and the 20th intervention days, before, during, and after the LLLT. The spectral power density over the very low-frequency oscillations (VLFO) of cerebral hemodynamics was calculated using Welch technique. In both healthy and MCI patients, VLFO increased in the whole cerebral area during LLLT compared to the resting state, and these changes are more contrasting in the condition with simultaneous carotid and vertebral artery stimulation condition. These characteristics were observed in both the first and 20th intervention days however, VLFO in the 20th intervention day were more increased than the first day. Increase of very low frequency oscillations demonstrated increasing spontaneous activity of cerebrovascular tone and neuronal activation. These findings may suggest a possibility of modulating effect of LLLT on neuronal activity and blood vessel reconstruction.

Application of expectation maximization and Kalman smoothing for prognosis of lumen maintenance life for light emitting diodes

Light emitting diodes (LED) have found widespread use for lighting and displays in recent times due to their high efficiency, favorable form factor, impact resistance, robustness, reliability and prolonged lifetime. The extended times to failure of LEDs make the problem of lumen maintenance life prediction for LED light sources using traditional reliability-based failure data collection and analysis methods quite challenging. Therefore, one has to resort to using prognostic approaches such as Kalman or particle filters applied to real time degradation data to make inferences on the remaining useful life (RUL) of such devices. The standard prognostic approach for predicting lumen maintenance life relies on an underlying degradation model with predetermined parameters from previous stress tests. However, these model parameters may vary quite a bit from device to device and for different manufacturing batch lots, thereby leading to large prediction errors. To address this issue, it would be better to learn the model parameters from the current measurement data directly. This study aims to achieve this by estimating the parameter values using the Expectation Maximization (EM) algorithm. Kalman smoothing is then applied to the identified parameter values for predicting the lumen maintenance life of the LED. The accuracy of the EM – Kalman smoothing approach was tested and compared with the standard nonlinear least square (NLS) approach prescribed by the TM-21 standard as well as the standard particle filter approach (without EM). Our results show that the EM method can give better, if not, similar RUL prediction accuracy with respect to the NLS and standard particle filter (PF) algorithms. Moreover, the accuracy of RUL prediction using our proposed algorithm is insensitive to the choice of the initial model parameter values, which paves way for this algorithm to be used in practice for automated predictive analytics of degrading electromechanical systems.

Photo-fermentation of purple sweet potato (Ipomoea batatas L.) using probiotic bacteria and LED lights to yield functionalized bioactive compounds.

The purpose of this study was to examine if fermentation of purple sweet potato (Ipomoea batatas L.) powder (PSP) by Lactobacillus brevis under green, red, blue, white light-emitting diode (LED) illumination or sunlight might yield functionalized products with good antibacterial, antioxidant activity, and/or cytotoxic activity. The Purple sweet potato (PSP) powder fermented with probiotic bacteria L. brevis under white LED light (1.9 ± 1.80/1.6 ± 0.52), blue LED light (1.4 ± 1.32/1.8 ± 0.83), or sunlight (1.2 ± 1.26/1.5 ± 1.83) for Propionibacterium acne and Staphylococcus epidermidis displayed good to moderate antibacterial activity based on minimum inhibitory concentration (MIC) red, blue, white LED lights and sunlight (80µg/mL) for P. acne and S. epidermidis, minimum bactericidal concentration red, blue LED lights and sunlight shows (46/48, 61/70, 50/48µg/mL) for P. acne and S. epidermidis. Antioxidant activity for dark, white, blue and green LED lights for ABTS and white, blue and green Led for DPPH assay resulted in lower activity. Fourier transform infrared spectroscopy was performed to determine the functional groups in the non-fermented (control) and fermented products of PSP powders obtained using different light sources. Sunlight, white, and blue LED light-fermented extracts contained alcohol, acid, and phenol groups, as well as aliphatic amines. The results of this study clearly indicate that fermentation of purple sweet potato with probiotic bacteria under various LED light sources can yield compounds that can be used in cosmetic and value-added food products.

Theoretical analysis and design for highly collimated planar light source based on organic light-emitting diodes using Fresnel lens

We theoretically design a versatile compact optical system comprising large-scale organic light-emitting diode (OLED) light sources and a freeform Fresnel lens to generate a highly collimated incoherent planar light source (HCIPLS) with uniform irradiance distribution. The structural parameters related to the output collimated light beam are discussed in detail. The simulated optimal full width at half maximum (FWHM) of the angular intensity distribution of the proposed structure is as high as 6.9° at both vertical and horizontal viewing angles. Moreover, the calculated normalized luminance enhancement factor reaches 25.4 in the range of normal viewing angles.