Development of Dynamic Light Controller for Variable CCT White LED Light Source

In this article, Design and development of a LED based outdoor luminaire is proposed and its performance parameters have been analyzed. Variable Correlated Color Temperature (CCT) of the light source can be controlled wirelessly. This light source consists of two arrays of Warm White (WW) and one array of Cool White (CW) LEDs. Light control logic has been developed to control the light output and Correlated Color Temperature (CCT). The range of CCT variation of the test light source lies within the CCT values of the WW and the CW LEDs. Pulse Width Modulation (PWM) technique has been applied to implement the light control logic and embedded in a microcontroller to control the light outputs of two WWLED arrays and a CWLED array of the light source. The developed system has been connected with the light source and controllable by a Smart Phone as a Hand Held Device (HHD) through WiFi connection. Experimental results establish the satisfactory performance of the developed system. It has wide variation in the CCT range, improved illuminance and can provide a controllable soothing nighttime landscape lighting environment as and when necessary.

Simultaneous illumination and communication using solid-state lighting devices like white light-emitting diode (LED) light sources is gaining popularity. The white light LED comprises a single-colored yellow phosphor excited by the blue LED chip. Therefore, color-quality determining parameters like color-rendering index (CRI), correlated color temperature (CCT), and CIE 1931 chromaticity coordinates of generic white LED sources are poor. This article presents the development of multi-color phosphors excited by a blue LED to improve light quality and bandwidth. A multi-layer stacking of phosphor layers excited by a blue LED led to the quenching of photoluminescence (PL) and showed limited bandwidth. To solve this problem, a lens-free, electrically powered, broadband white light source is designed by mounting multi-color phosphor LEDs in a co-planar ring-topology. The CRI, CCT, and CIE 1931 chromaticity coordinates of the designed lamp (DL) were found to be 90, 5114 K, and (0.33, 0.33), respectively, which is a good quality lamp for indoor lighting. CRI of DL was found to be 16% better than that of white LED (WL). Assessment of visible light communications (VLC) feasibility using the DL includes time interval error (TIE) of data pattern or jitter analysis, eye diagram, signal-to-noise ratio (SNR), fast Fourier transform (FFT), and power spectral density (PSD). DL transmits binary data stream faster than WL due to a reduction in rise time and total jitter by 31% and 39%, respectively. The autocorrelation function displayed a narrow temporal pulse for DL. The DL is beneficial for providing high-quality illumination indoors while minimizing PL quenching. Additionally, it is suitable for indoor VLC applications.

Lighting does Matter: Preliminary Assessment on Office Workers

Single‐source white light‐emitting diodes (WLEDs) with smart regulation of correlated color temperature (CCT) are indispensable for the next generation of WLEDs aimed at healthy and high‐quality illumination, where a suitable CCT value is closely related to our emotions and circadian rhythm. Herein, this work constructs a single‐component emission layer WLED with high performance for controllable daily lighting through Bi3+/Te4+ dual‐doped Cs2SnCl6 engineering. The efficient energy transfers between triple self‐trapped exciton states from Bi3+/Te4+ doping allow two tunable broadband emissions that can cover the full‐color region, thereby yielding a standout color‐rendering index of 94 for the fabricated WLED. The robust stability against heat, ultraviolet light, and environmental oxygen/water induces a long half‐lifetime of WLED up to 1104 h. Moreover, the dual‐doped strategy endows the emitter with excitation‐dependent luminescent characteristics, enabling the single emissive layer device to realize switching control of cold‐, positive‐, and warm‐white light by converting the excitation chip. Meanwhile, continuous regulation of CCT for different application scenarios can be achieved by adjusting the current of different chips. This work constitutes a solid step toward building single‐source WLEDs for smart and healthy lighting based on dual‐doped lead‐free metal halides.

With the expanding application of light-emitting diodes (LEDs), the color quality of white LEDs has attracted much attention in several color-sensitive application fields, such as museum lighting, healthcare lighting and displays. Reliability concerns for white LEDs are changing from the luminous efficiency to color quality. However, most of the current available research on the reliability of LEDs is still focused on luminous flux depreciation rather than color shift failure. The spectral power distribution (SPD), defined as the radiant power distribution emitted by a light source at a range of visible wavelength, contains the most fundamental luminescence mechanisms of a light source. SPD is used as the quantitative inference of an LED’s optical characteristics, including color coordinates that are widely used to represent the color shift process. Thus, to model the color shift failure of white LEDs during aging, this paper first extracts the features of an SPD, representing the characteristics of blue LED chips and phosphors, by multi-peak curve-fitting and modeling them with statistical functions. Then, because the shift processes of extracted features in aged LEDs are always nonlinear, a nonlinear state-space model is then developed to predict the color shift failure time within a self-adaptive particle filter framework. The results show that: (1) the failure mechanisms of LEDs can be identified by analyzing the extracted features of SPD with statistical curve-fitting and (2) the developed method can dynamically and accurately predict the color coordinates, correlated color temperatures (CCTs), and color rendering indexes (CRIs) of phosphor-converted (pc)-white LEDs, and also can estimate the residual color life.

Evening residential illumination possesses the capacity to impair sleep quality via the suppression of endogenous melatonin production, a process largely driven by short-wavelength (blue) light. In this investigation, we characterized the light emissions from 52 distinct examples across three common lamp technologies: light-emitting diodes (LED), incandescent, and compact fluorescent (CFL) lamps. To estimate the differential circadian impact of these sources, we determined the Melatonin Suppression Value (MSV), melanopic illuminance, and photopic illuminance for each. Our findings reveal that “cool” white LED (median 12.3% MSV) and “cool” white CFL (12.1% MSV) lamps induce considerably greater melatonin suppression than “warm” white LED (3.6%), “warm” white CFL (2.6%), or traditional incandescent (1.5%) lamps. As potential countermeasures, we examined the efficacy of tunable Correlated Color Temperature (CCT) lamps and “blue-light–filtering” (BLF) lenses. The four tunable LED lamps demonstrated a profound ability to mitigate circadian disruption, reducing estimated melatonin suppression from 10% at a 5700 K (cool white) setting to 0.1% at 2100 K (warm white). An analysis of eight BLF lenses identified variable performance; while six had moderate impacts compared to uncorrected vision, their benefit was limited relative to standard clear lenses. Only two BLF lenses, distinguished by a “brown” tint, proved highly effective, reducing estimated suppression to below 0.3%. These results suggest that cool white CFL and LED lamps may exert a greater disruptive influence on sleep physiology than other lamp types. Conversely, tunable lamps adjusted to warm settings and “brown”-tinted BLF lenses represent beneficial strategies for ameliorating this effect. (Detailed measurement methodologies are available in a previously published study, with supplementary calculations provided separately).Supplementary InformationThe online version contains supplementary material available at 10.1038/s41598-025-29882-7.

White light-emitting diodes based on quaternary Ag–In-Ga-S quantum dots and their influences on melatonin suppression index

Emerging neuroscience research shows that environmental-related activity such as wayfinding, perception, cognition, and their behavioral consequences—anxiety, stress, happiness, and arousal—are both reflected in our brains' neural structures and electro-chemical processes (Amor, Oboyle, Pati, Pham, & Jou, 2014; Amor, Pati & OBoyle, 2013; Pati, Amor, & OBoyle, 2012; Eberhard, 2007; Mallgrave, 2011; Swanson, 2011; Zeisel, 2006). Behavioral evidences indicate that fluorescent lighting, among the indoor environmental variables, plays a critical role in facilitating or hindering daily activities for a neuro-typical population (Rashid & Zimiring, 2008). For a neuro-diverse population (ADHD), this becomes more complex. While there is a growing body of debatable environment behavior literature relative to the impact of fluorescent lighting on cognitive, behavioral, and psychosocial outcomes, little is known about the correlation between neural activity and fluorescent lighting. The purpose of this research is to 1) explore and compare behavioral and neural responses of twenty ADHD subjects, when exposed to 3 types of fluorescent lighting color temperature: a) Warm White WW with a 2800 CCT, b) Cool White CW with a 4100 CCT, and c) Daylight DX with 6000 CCT when presented in three different settings—commercial, educational, and healthcare (see figures 1, 2, and 3), and 2) explore the impact of different color temperatures on the activation of the prefrontal and parietal areas, brain regions associated with cognition that experience minimal neural activity for people with ADHD (see figure 4). A purposive sampling strategy was used to generate twenty ADHD subjects. This permitted the selection of subjects including gender, age, ethnicity, brain lateralization, as well as the exclusion of color blindness. The participants underwent 1) an anatomical scan T1 (5 minutes) and 2) an Eco-Planar Imaging (EPI) functional scan (17 minutes), while a random sequence of 72 digitally generated high resolution illustrations from the aforementioned settings were projected by a computer controlled visual presentation system (E-Prime). Concomitantly, the participants were asked to respond to each image by fiber optics Button Response Unit (BRU)rating each image on a seven-point Likert satisfaction scale of 1=very dissatisfied and 7=very satisfied. Behavioral data was analyzed using t-test factor analysis and one-way analysis of variance, while the neural data maps were analyzed using Statistical Parametric Mapping (SPM8). The comparison of neural and behavioral data indicated that the least satisfying color is the White Warm Color Temperature 2800K. The Cool White 4100K and Full Spectrum 6000K correlated color temperatures generated better levels of satisfaction. Important to note that under the Cool White and Full Spectrum, the activation of the Cerebellum, the Superior Temporal Gyrus, the Middle Frontal Gyrus, and the Angular Gyrus respectively responsible for critical structure of social interaction, analytical tasks, and memory retrieval are very suggestive for the activation of the neural cognitive processes. This study is provides fresh neural benchmark data for designers, architects, planners, decision makers, academicians, and industry professionals to assess, design, and produce built environments using neural evidence-based data.

Energy saving and visual comfort are two main considerations in designing of automatic illumination control systems. However, energy-saving-oriented illumination control always causes optical spectra drifting in light-conversion-material-based white light-emitting diodes (WLEDs), which are conventionally used as artificial luminaires in indoor areas. In this study, we propose a method for InP quantum dot (QD)-based WLEDs to minimize optical energy consumption by considering the influence caused by the outdoor environment and neighboring WLED units. Factors of (a) dimensions of room window and WLED matrix, (b) distance between WLED units, lighting height, species of InP QDs, and (c) user distribution are taken into consideration in calculation. Parameters of correlated color temperature (CCT) and color rendering index (Ra) of the WLED matrix are optimized according to the lighting environment to improve user visual comfort level. By dynamically controlling the light ingredients and optical power of WLEDs, we optimize the received illuminance distribution of table tops, improve the lighting homogeneity of all users, and guarantee the lowest energy consumption of the WLED matrix. The proposed approach can be flexibly applied in large-scale WLED intelligent controlling systems for industrial workshops and office buildings.

Microwave synthesis of composite of AgInS2 quantum dots and zeolitic imidazolate framework-8 for application in white light emitting diodes

We show recent results of GaN based LEDs, the high efficiency blue LED, the high efficacy white LED, the high color rendering LED, the warm white LED, and the high output power 365-nm UV LED. The output power and the external efficiency of the high efficiency blue LED at 20 mA were 19.3 mW and 35.8%, respectively. Moreover, the lifetime of the molded this lamp was improved. For the high efficacy white LED using this high efficiency blue LED, the correlated color temperature (CCT) and the luminous efficacy (ηL) at 20 mA were 5470 K and 61.4 lm/W, respectively. This luminous efficacy is close to that of a fluorescent lamp. When the high color rendering LED using new red phosphor and shorter-YAG was operated at 20 mA, the CCT, ηL and the general color rendering index (Ra) were 4670 K, 28.3 lm/W and 87.7, respectively. In particular, the red color reproduction was improved. For the warm white, the CCT, ηL and Ra at 20 mA were 2830 K, 18.9 lm/W and 87.5, respectively. It can be used as a replacement for incandescent bulbs. When the high output power 365-nm UV LED was operated at a forward bias direct current (DC) of 500 mA, Po and ηex were 210 mW and 12.4%, respectively.

Zinc phosphate glasses activated with Dy3+/Eu3+/Sm3+ and Tb3+/Eu3+/Sm3+ for reddish-orange and yellowish white phosphor applications

The effect of the phosphor curvature in the range 0.1766–0.2589 mm−1 on the luminous efficacy of Y2.95Al5O12:0.05Ce3+ (YAG)‐based white‐light‐emitting diodes (WLEDs) was investigated at the similar correlated color temperature (CCT) of ~6300 K by tuning the concentration of YAG phosphors in the phosphor layer ranging from 7.5 to 15 wt%. It was found that both the luminous efficacy and luminous power increased monotonically with the increasing curvature. The luminous efficacy (=82.4 lm/W) and luminous power (=297.85 mW) of the YAG‐based WLED at the preferable phosphor curvature of 0.2589 mm−1 were 19.44% and 17.36%, respectively, higher than those at the curvature of 0.1766 mm−1 under 350 mA. This finding reveals that the surface curvature of phosphor layers is a critical factor which cannot be ignored for the investigation of the light output of phosphor‐converted WLEDs. Moreover, the color rendering index (CRI) enhancement of YAG‐based WLED with substitution of Y2.94Al5O12:0.05Ce3+, 0.01Pr3+ (YPrAG), Y2.45Gd0.5Al5O12:0.05Ce3+ (YGdAG), and Y2.95Al4.8Si0.2O11.8N0.2:0.05Ce3+ (YAlSiON) for YAG were assessed under the same phosphor curvature of 0.2589 mm−1 and the similar CCT ~6350 K. Taking the luminous efficacy, preparation cost of phosphors, and CRI into consideration, we suggest that the YGdAG is a preferable candidate for replacing the YAG for use in WLEDs among the four kinds of phosphors. Compared with the YAG (7.5 wt%)‐based WLED, the YGdAG (7 wt%)‐based WLED exhibited an improved CRI, less preparation cost of phosphors, and the acceptable reduction in luminous efficacy under 350 mA.

CdSe quantum dots (QDs) with the emission wavelength of 577 nm, full width at half maximum (FWHM) of 28 nm, quantum yield (QY) of 40% and average particle size of 3.7 +/- 0.5 nm are prepared. 1, 3 and 5 wt% of CdSe QDs is blended with commercial YAG:Ce phosphor (called as composite phosphor) and the device performance of YAG-based and composite phosphor-based white light-emitting diode (WLED) is investigated. The color rendering index (CRI) and luminous efficiency could be improved simultaneous for composite phosphor-based WLED. As the applied current increases, the correlated color temperature (CCT), Commission International d'Eclairage (CIE) chromaticity coordinates and CRI of both WLEDs are almost the same when compared with standard condition (20 mA), while the luminous efficiency of both WLEDs decreases with increasing applied current. It is interesting to find that there is a positive effect of QDs on the luminous efficiency and CRI value. This result also reveals that adding a small amount of yellow emitting QDs can not only reduce the scattering of light effectively but increase utilization efficiency of reflection and refraction light, thereby enhancing the efficiency of composite phosphor-based WLED. Moreover, the emission wavelength of 577 nm QDs is longer than that of YAG, it redound to extends emission range resulting in increase the CRI of devices.

The impact of LED spectrum and correlated color temperature on driving safety in long tunnel lighting