LED Color Research Articles

An Emerging and Valuable Trendson Rare Earth Silicate Based Different Colours Light Emitting Phosphors - A Review

In this present review paper, which deals on these emerging research areas indicated that deep studied the concept of rare earth doped silicate material with different colour Light emitting phosphors. We find that reliability analysis on photo luminescence properties of different colour LED’s Emission and excitation spectra with different wavelength. An application in various branches that can be better futuristic Scopes improvement. With this vision we are used new nano materials also built a suitable learning environmental and low-cost LED’s for all the aspects regarding use of new advanced technology in conformity with demand of present society

Research on Plant Lighting Driver Control Strategy Based on LED Spectral Characteristics

To realize the continuous adjustment of the light quality ratio of LED plant lighting power supply, a plant lighting driver control strategy based on the spectral characteristics is studied in this paper. First of all, the spectral mathematical model of monochromatic LED chip is established. Secondly, the mathematical model of the number of photons generated by LED the driving current is further studied and then, a new driver control strategy about the pant lighting is proposed based on the model of the number of LED photons. At last, a step-down circuit built by RT8471 chip is used as the LED driver power supply to verify the correctness of the new driver control strategy in this paper. Different color LED chips of Cree and Philips Lumileds companies are used as the circuit loads. It shows that the errors values between the results from the experiments and the theoretical model calculations of the number of LED photons are all less than 5%. So, the new plant lighting driver control strategy proposed in this paper is feasibility and has certain theoretical guiding significance and engineering value.

Low impact of two LED colors on nocturnal insect abundance and bat activity in a peri-urban environment

Artificial light at night (ALAN) is an important driver of change in ecological environments of the 21th century. We investigated the impact on nocturnal insect abundance and bat activity of two LED light colors (warm-white 2700 K, cold-white 6500 K) in a peri-urban environment. Bat activity (predominantly Pipistrellus pipistrellus) was largely driven by prey availability (insects), while insect abundance was responsive to nightly weather conditions (precipitation, temperature). Thus, both insects and bats were not differentially responsive to cold-white or warm-white LEDs. These findings are largely in contrast with literature, particularly for insects. However, as most published experiments on ALAN were conducted in areas that were lit solely for the purpose of the experiment, we would like to bring forward that (1) adaptation to environmental constraints may play a role in peri-urban environments that have been exposed to ALAN for many decades; or (2) impacts of cold-white LEDs on nocturnal insects may be lower than expected, because nocturnal insects adapted to low-light conditions may be put off by cold white light sources (6500 K).

Interaction effect of LED color temperatures and light-protective additive packaging on photo-oxidation in milk displayed in retail dairy case

Effect of varied LED color temperatures on photo-oxidation in 2% fat milk and protection efficiency of packaging with and without light-protective additives (LPA) under different color temperatures was firstly evaluated. Riboflavin (Rb) is one of the critical photo-sensitizers in 2% milk when exposed to LED light. Higher color temperature with higher relative intensity of Rb absorbance region resulted in lower Rb and vitamin A retention, lower dissolved oxygen content, and higher TBARS value in milk packaged with non-LPA packaging. Yellow pigmented packaging that completely blocked the Rb absorbance region of all three LED color temperatures successfully reduced the rate of degradation of milk nutrients and flavor. TiO2-added packaging partially block the destructive light wavelength; higher level of TiO2 provided a longer protection on milk freshness. Combination of appropriate LED color temperature and LPA-packaging provided a cost-effective solution for minimizing photo-oxidation in retail dairy case.

Exellent Color Quality and Luminous Flux of Wleds Using Triple-Layer Remote Phosphor Configuration

This study proposed a triple-layer remote phosphor (TRP) structure to improve the color and luminous flux of white LEDs (WLEDs). TRP structure consists of 3 different phosphor layers: yellow YAG:Ce3+ layer below, red CaMgSi2O6:Eu2+,Mn2+ phosphor on top and green layer Ba2Li2Si2O7:Sn2+,Mn2+ phosphor in the middle. Using red CaMgSi2O6:Eu2+,Mn2+ to control the red light component leads to increased color rendering index (CRI). Utilize the green CaMgSi2O6:Eu2+,Mn2+ phosphor to control the green light component results in the increase in luminous efficacy (LE) of WLEDs. Furthermore, when the concentration of these two phosphors increased, yellow layer concentration YAG:Ce3+ decreased to maintain average correlated color temperatures (ACCTs) in the range from 6000 K-8500K. Besides CRI and LE, color quality scale (CQS) is also analyzed through concentration control of green phosphor and red phosphor. The research results show that the higher the concentration of CaMgSi2O6:Eu2+,Mn2+, the better for CRI. In contrast, CRI decreased significantly when increasing the concentration of Ba2Li2Si2O7:Sn2+,Mn2+. Meanwhile, CQS achieve notable enhancement in the concentration range of 10% -14% CaMgSi2O6:Eu2+,Mn2+, regardless of Ba2Li2Si2O7:Sn2+,Mn2+ concentration. LE, in particular, can also increase by more than 40% along with the improvement of CRI and CQS with the reduction of the backscattered light and addition of green light. Research results are a valuable reference for producers who wish to improve the color quality and enhance the luminous flux of WLEDs. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium provided the original work is properly cited.

Modifying twisted nematic LCD screens to create dichromatic visual stimuli with LEDs

Abstract The use of computers to create and display animations/videos in the study of visually guided behaviours has been instrumental in understanding sensory mechanisms underlying complex traits. Using computer displays, scientists are able to create a wide array of colours using three differently coloured lights (Red, Green, Blue [RGB]). While it is possible to generate scenes with RGB displays that mimic animals' colour perceptual experience, this can be problematic because it requires knowledge of the spectral absorbance of the animals' photoreceptor classes, which are often unknown and are difficult to obtain. Even then, stimuli are limited to the central part of the visible spectrum (e.g. ultraviolet (UV) stimuli are not possible). We present a cost‐effective way of modifying a twisted nematic LCD screen that utilizes coloured LEDs, that allows measuring animals' sensitivity to, and discrimination between, wavelengths of light. It has the benefit of not requiring a‐priori knowledge of animals' photoreceptor classes. An LCD screen can be modified by removing the screen's back polarizer (behind the liquid crystal layer) and backlighting the screen with LEDs of two different colours. One of the LED colours transmits through a polarizer with a transmission axis parallel to the screen's front polarizer, and other LED colour transmits through a polarizer orthogonal to the first. To test colour discrimination, one can create a dichromatic stimulus in which both LED colours are ‘ON’ and the current through one LED colour is decreased, while the other is constant, which generated a maximum intensity contrast of 1.84 log units in our setup. To test colour sensitivity, one can create a monochromatic stimulus in which only one LED colour is ‘ON’, which generates a contrast similar to the dichromatic stimulus. This technique overcomes many of the limitations of RGB‐based LCD screens in a cost‐effective way, and allows more accurate testing of the role of colour in visually guided behaviours. Besides the questions in vision research, this setup can answer, it can also be used as an outreach tool in classrooms where children can learn about light, colour, polarization and technology.

Analysis on the Optical Response of Ldr and Phototransistor in Photoplethysmography

In photoplethysmography, light source and light detector are employed such that the received signal corresponds to a particular information needed. This research used five different LEDs as light sources. Phototransistor and LDR, on the other hand, were used as light detectors to assess the photosensitivity of human skin. Backscatter simulation was used to compare the photoplethysmographic detection of LDR and phototransistor. The aims of this study include: determine the optical response of a human skin, particularly the skin on the dorsal and palmar parts of the hand; conduct simultaneous simulation using modular and backscattered setup; provide measured value based on the conducted simulations. In every LED color and for both light detectors, ten test conditions were performed, namely: (1) room light on; (2) room light off; (3) room light on - black paper; (4) room light off - black paper; (5) room light on - white paper; (6) room light off – white paper; (7) room light on – dorsal skin; (8) room light off – dorsal skin; (9) room light on – palmar skin; and (10) room light off – palmar skin. Two different simulations were conducted involving all test conditions. The second simulation used light meter which showed similarity in behaviour of obtained values vis-à-vis barcode meter and ADC voltage. The modular involved a lux sensor which checked the findings on the reflectivity of skin Types III and IV of the Fitzpatrick scale and melanocytic naevi skin. The series of simulations conducted proved that the yellow LED provided highest sensor response and phototransistor greater sensitivity than LDR in detecting the received signals. Room light off condition was necessary to reduce the effects of ambient light.

The impacts of Ba2Li2Si2O7:Sn2+,Mn2+ and CaMgSi2O6:Eu2+,Mn2+ particles on the optical properties of remote phosphor LED

Abstract As implied in the title, the triple-layer remote phosphor (TRP), constructed with the yellow YAG:Ce3+ layer at the bottom, the red CaMgSi2O6:Eu2+,Mn2+ phosphor layer on the top, and the green Ba2Li2Si2O7:Sn2+,Mn2+ phosphor layer between these two layers, is suggested in this paper to improve the color and luminescence of white LEDs (WLEDs). In order to control the red light for the purpose of increasing the color rendering index (CRI), it is suggested that the red CaMgSi2O6:Eu2+,Mn2+ phosphor should be applied in the TRP structure. Simultaneously, the structure uses the green Ba2Li2Si2O7:Sn2+,Mn2+ phosphor layer to control the green light, which increases the luminous efficacy (LE) of WLEDs. In addition, when the concentration of these two phosphors increases, the yellow YAG:Ce3+ concentration must be reduced to keep the average correlated color temperatures (ACCTs) stable at 6000 K to 8500 K. Besides, appropriate adjusting of CRI, LE, and color quality scale (CQS) is also analyzed by modifying the concentration of the green phosphor and red phosphor. The results show that the CRI can get better values if CaMgSi2O6:Eu2+,Mn2+ concentration is higher. In contrast, the CRI decreases dramatically when the concentration of Ba2Li2Si2O7:Sn2+,Mn2+ increases. Meanwhile, CQS can be significantly increased in the range of 10 % to 14 % CaMgSi2O6:Eu2+,Mn2+, regardless of the concentration of Ba2Li2Si2O7:Sn2+,Mn2+. In particular, along with the improvement of CRI and CQS, LE can also be increased by more than 40 % by reducing the scattered light and adding the green light. Obtained results are a valuable reference for manufacturers for improving WLEDs color and luminescence quality to produce a broader range of WLEDs with better quality fulfilling social needs.

Facile growth and re-crystallization of polymer-based inorganic-organic 2D hybrid composites and their applications

The in-situ growth and recrystallization of inorganic-organic (IO) hybrids within the natural free volume of polymer matrices for the realization of significantly stable IO hybrid-polymer composites and its applications have been presented. A general strategy is explored to attain uniform and facile growth of IO hybrid nanocrystals (2–3 nm) within the interstitial spaces of polymer matrix. Annealing further supports the agglomeration and self-assembly of nanocrystals into highly c-oriented hexagonal microplatelets of ∼10–20 μm2 and 50–100 nm thickness within the polymer matrix. The resultant composites endow highly luminescent retaining the typical thermally and mechanically stable polymeric nature. Series of optical, structural, morphological and thermal studies are performed to understand the growth conditions and uniform distribution of IO nanocrystallites within the polymer. To exemplify, LED colour conversion using encapsulation/surface coating and polymeric blocks fabrication for optical waveguide/channel inscription are demonstrated to foresee many new flexible and robust applications. Thus, the present approach offers a new paradigm to achieve light-emitting IO hybrids in the form of polymeric composites for advanced optoelectronic device applications.

Freestanding Needle Flower Structure CuCo2S4 on Carbon Cloth for Flexible High Energy Supercapacitors With the Gel Electrolyte.

A facile hydrothermal approach was adopted to the direct synthesis of bimetallic sulfide (CuCo2S4) on carbon cloth (CC) without binders for the supercapacitor's electrodes. A possible formation mechanism was proposed. The prepared bimetallic electrode exhibited a high specific capacitance (Csp) of 1,312 F·g−1 at 1 A·g−1, and an excellent capacitance retention of 94% at 5 A·g−1 over 5,000 cycles. In addition, the asymmetric supercapacitor (CuCo2S4/CC//AC/CC) exhibited energy density (42.9 wh·kg−1 at 0.8 kW·kg−1) and outstanding cycle performance (80% initial capacity retention after 5,000 cycles at 10 A·g−1). It should be noted that the electrochemical performance of a supercapacitor device is quite stable at different bending angles. Two charged devices in series can light 28 red-colored LEDs (2.0 V) for 5 min. All of this serves to indicate the potentially high application value of CuCo2S4.

Energy Efficient IoT Home Monitoring and Automation System (EE-HMA)

The paper focuses on using ICT tools for smart home applications. It presents the design and implementation of a system to monitor and analyze the energy consumption, utilize lights when needed, program the temperature by identifying inhabitants' absence and setting the temperature appropriately high or low. The system also uses colored LEDs to alert inhabitants of different parameters, to turn their loads on and off based on the cost of electricity use as well as to enable them to control some of their home appliances usage through a mobile application to reduce electricity usage and minimize energy waste.

Characterization, packaging, and optical model of single-primary color phosphor thin films and LEDs

Blue, green, and red phosphor thin films (PTFs) used for NUV LED were prepared by hot pressing method. The excitation spectrums of PTFs have broadband absorption characteristics owing to the 4f7 → 4f65d transition of Eu2+; the emission peaks are 445 nm, 520 nm, and 627 nm, respectively. The phosphor conversion efficiency (PCE) gradually increases and finally remains unchanged with phosphor mass fractions because of absorption saturation effect. Different color LEDs are packaged by NUV chips and PTFs; spectral decomposition and data fitting methods are used to achieve the fitting of the relationship between the phosphor mass fraction and the emission light intensity of the NUV chip and phosphor. The double Gaussian model is used to express the spectral power distribution (SPD) of a single-primary color LED and compare it with the measured results. White LEDs (WLEDs) were prepared by two methods, the first is the combination of multi-LEDs, the second is NUV chip pumps three-color-mixed phosphor directly. Experimental results showed that the WLEDs prepared by first method with the light color parameters of CCT = 5342 K, LER = 274 lm/W, show small parameter difference of ΔCCT = 24 K, ΔLER = 15 lm/W, NCC = 98.94% compared with the calculated results. The WLEDs prepared by second method with the light color parameters of CCT = 5292 K, LER = 263 lm/W shows a 4.0% decrease in LER.

Comparison of Color Appearance under a High Color Rendering Index Fluorescent and LED Light

Comparison of Color Appearance under a High Color Rendering Index Fluorescent and LED Light

Impact of LED Color Temperatures on Perception Luminance in the Interior Zone of a Tunnel considering Fog Transmittance

LEDs are widely applied in highways and tunnels for their long life, low light attenuation, and being environment friendly in recent years. The influence of correlated color temperature (CCT) of LED on lighting safety has attracted people’s attention as the demand increased. In this paper, a calculation model of perception luminance of human eye considering mesopic vision and fog concentration was proposed. The influence of different CCTs on perception luminance of human eye under different levels of fog concentration and luminance was calculated and analyzed. The CCT of LED employed in the interior zone of a tunnel was selected based on the highest perception luminance in mesopic vision. Seven kinds of LEDs with different CCTs (3000–6500K) were applied in the experimental system with adjustable fog concentrations. The results showed that the main factors affecting visual perception are luminance and fog concentration. Higher luminance or lower fog concentration provides drivers with higher perception luminance. In contrast, although CCT has a less effect on perception luminance, LEDs with higher CCT (about 6500K) can provide higher perception luminance considering fog in mesopic vision. This paper provides technical support for tunnel lighting and guaranteeing traffic safety.

Introductory lecture: origins and applications of efficient visible photoluminescence from silicon-based nanostructures.

A variety of silicon-based nanostructures with dimensions in the 1-5 nm range now emit tunable photoluminescence (PL) spanning the visible range. Achievement of high photoluminescence quantum efficiency (PLQY) relies critically on their surface chemistry passivation and an impressive "tool box" of options have been developed. Two distinct PL bands are dominant. The "S-Band" (red-green emission with Slow microsecond decay) has PLQY that has steadily improved from ∼3% in 1990 to 65 ± 5% by 2017. The "F-Band" (blue-yellow with Fast nanosecond decay) has reported PLQY values that have improved from ∼0.1% in 1994 to as high as ∼90% by 2016. The vast literature on both bands is surveyed and for the S-band, size-structure-PL correlations and selective photo-excitation studies are highlighted. Resonant photoexcitation and single quantum dot studies have revealed the key role of quantum confinement and the excitonic phonon-assisted nature of the radiative transitions. For the F-band, in contrast, specific phenomenological studies are highlighted that demonstrate similar emission without the presence of silicon nanostructures. Low PLQY F-band emission from pure silicon-silica core shell systems is probably associated with oxide-related defects, but ultrahigh PLQY from many lower temperature synthesis routes is likely to be from carbon-based nanostructures or chromophores, not silicon nanostructures. Potential applications for both PL bands include sensing, medical imaging, theranostics, photovoltaics, LED colour converters and nano-thermometry. Emerging "green" synthesis routes are mentioned. If scalability and cost are significantly improved then a number of other proposed uses of ultra-efficient PL from "nano-Si" could become viable in cosmetics, catalysis, security and forensics.

Design and implementation of LED–LED indoor visible light communication system

This paper investigates the experimental performance of LEDs as both photoemitter and photoreceiver. In this work LED–LED link is established using BJT and MOSFET based drive circuits at transmitting side and resistor driver operated in photoconductive mode is used at the receiver side. The LED response as transmitter and receiver is investigated at different operating frequencies with the distance of up to 20 cm and the data rate of 1 Mbps. The SNR values of 8 dB and 11 dB are obtained using BJT and MOSFET drivers respectively at a distance of 20 cm. Furthermore, six different color LEDs are tested on both sides of transceiver to determine the best performing pair. It is observed that the red color LEDs have good responses as a photodiode due to its long wavelength in the visible spectrum. However their performance is significantly effected by ambient noise. Moreover, the responsivity of the Red color LED operated as photoreceiver with respect to different biasing voltages is also experimentally measured and discussed.

Performance evaluation of two trickling filters removing LAS and caffeine from wastewater: Light reactor (algal-bacterial consortium) vs dark reactor (bacterial consortium)

Micropollutant removal efficiencies of two trickling filters – operated under light and dark conditions were studied and compared. Linear alkylbenzene sulphonate (LAS) and caffeine were selected as model micropollutants. Both lab-scale trickling-filter type reactors were packed with polyurethane foam sponge cubes (2 cm × 2 cm × 2 cm) with 40% occupancy. The trickling filter with the white color LED light was named as Light Reactor (LR), which was operated under light: dark cycle of 12:12 h with a quantum flux of 15 μmoles/m2/s. No light was provided in the other trickling filter, named Dark Reactor (DR). Synthetic wastewater containing glucose (250 mg/L), LAS (12 mg/L), and caffeine (0.05 mg/L) was fed to the reactors at a hydraulic retention time (HRT) of 12- and 8-h at 25 °C for 2 months. The C, N, and P removal at 12-h HRT were 85%, 15%, and 49%, respectively, in LR, the corresponding values in DR were 88%, 18%, and 43%. Similarly, at 8-h HRT 90%, 24%, and 37% was observed in LR and 84%, 19%, and 37% in DR. However, the LAS and caffeine removal decreased from 99 to 96% and 96 to 86% respectively in LR, and from 96 to 79% in DR with decreasing the HRT from 12 to 8-h. The number of LAS degraders in LR (5.5×104 CFU/sponge cube) was higher compared to DR (2.2×104 CFU/sponge cube) at 8-h HRT. The above results indicate that algal-bacterial symbiotic relationship in LR was beneficial for carbon and micropollutants removal from domestic wastewater.

Realization of white LED using plasmonic-based photonic structure through reflection, absorption and transmission analysis

A novel notion is proposed in the present research to generate white color LED using plasmonic-based one-dimensional photonic crystal structure. The entire work manipulates with three distinct colors of the red, blue and green light-emitting diode to realize the aforementioned application. The physics behind the research deals with the effective refractive indices of the proposed photonic crystal, pertaining to the red, blue and green where the mathematics of the same is integrated with Maxwell’s differential equation and subsequently throughthe Helmholtz second order differential equation. However, the principle of operation deals with the reflection, absorption and transmission characteristics. The reflection and transmission can be studied through-plane wave expansion method whereas absorption is discussed through numerical investigation. Further, the generation of three distinct signal and white signal can be made using different photonic structure. Moreover, the combination of said one-dimensional photonic structure generates a signal of 350 nm–530 nm wavelength, which is the signal of white LED. Finally it is inferred that the efficiency of the proposed structures is high as compared to both cold and warm LED.

The relightables

We present "The Relightables", a volumetric capture system for photorealistic and high quality relightable full-body performance capture. While significant progress has been made on volumetric capture systems, focusing on 3D geometric reconstruction with high resolution textures, much less work has been done to recover photometric properties needed for relighting. Results from such systems lack high-frequency details and the subject's shading is prebaked into the texture. In contrast, a large body of work has addressed relightable acquisition for image-based approaches, which photograph the subject under a set of basis lighting conditions and recombine the images to show the subject as they would appear in a target lighting environment. However, to date, these approaches have not been adapted for use in the context of a high-resolution volumetric capture system. Our method combines this ability to realistically relight humans for arbitrary environments, with the benefits of free-viewpoint volumetric capture and new levels of geometric accuracy for dynamic performances. Our subjects are recorded inside a custom geodesic sphere outfitted with 331 custom color LED lights, an array of high-resolution cameras, and a set of custom high-resolution depth sensors. Our system innovates in multiple areas: First, we designed a novel active depth sensor to capture 12.4 MP depth maps, which we describe in detail. Second, we show how to design a hybrid geometric and machine learning reconstruction pipeline to process the high resolution input and output a volumetric video. Third, we generate temporally consistent reflectance maps for dynamic performers by leveraging the information contained in two alternating color gradient illumination images acquired at 60Hz. Multiple experiments, comparisons, and applications show that The Relightables significantly improves upon the level of realism in placing volumetrically captured human performances into arbitrary CG scenes.

NLoS underwater VLC system performance: static and dynamic channel modeling.

In this paper, the impact of water channels under different communication link parameters is studied for underwater visible light communication (UVLC). The objective is to highlight the best results for non-line of sight (NLoS) communication links. In addition, NLoS links are studied under different parameters: LED colors, viewing angle, receiving angle, and data rates. The results are obtained and plotted using MATLAB simulation. The performance of the received power is first measured at different wavelengths and data rates. Then, the best results are further investigated at different viewing angles and receiving angles. The obtained results show that using cyan color provides more depth for the NLoS case, as well as a low bit error rate compared to the other colors. Most of the literature is concerned with unpractical configurations in underwater scenarios, such as an empty sea or assuming no human-object or blockage environment. We use the practical setup in Zemax Optics Studio to allow a precise description of ray tracing and high order of reflections inside a sea water environment. The channel impulse response (CIR) is obtained for static channel modeling, including a blockage environment to evaluate the best transmitters in sea water. Also, we are able to compare the average delay and the average delay spread of the source colors. The reflection characteristics of the sea water are considered as wavelength dependent. The CIR obtained by Zemax Solver and MATLAB indicates that cyan is the best source in sea water for different LED chips. Moreover, other previous studies assume perfect alignment scenarios between divers, which is not practical and not suitable for real channel gain results. Accordingly, we present a comprehensive dynamic channel modeling and characterization study for UVLC. Our study is based on Zemax programming language (ZPL) combined with Zemax Optics Studio. Using ZPL enables us to apply a mobility algorithm for divers and measure the channel gain variations due to random motion. We introduce a dynamic motion in a single-input single-output scenario and a single-input multiple-output scenario in the presence of blockage divers. Statistical analyses are studied for the appropriate distributions that can fit the data with various transmitter and receiver specifications. All dynamic scenarios are performed using cyan color in sea water, as it is proven to have satisfactory performance. The statistical results are beneficial for further analysis. As case studies, we consider various underwater scenarios, and the resulting parameters of statistical distributions can be used for future analysis in UVLC dynamic environments.