Power Distribution Of Light Research Articles

A Novel 4 × 1 MISO-VLC System with FBMC-OQAM Downlink Signals

A novel visible-light communication (VLC) system with 4 × 1 multi-input–single-output (MISO) channels is designed. In the system, the filter bank multicarrier (FBMC) and offset quadrature amplitude modulation (OQAM) techniques are used to generate downlink signals. The principles and implementation methods are proposed and analyzed, and the light intensity and received light power distribution of four LED emitters are discussed. The results demonstrate that it not only satisfies the requirements of indoor information access but also provides daily lighting. The used FBMC-OQAM signals exhibit better reception performance than orthogonal frequency division multiplexing (OFDM) signals. The system used has a lower bit error rate (BER) and larger access bandwidth compared to a 1 × 1 single-input–single-output (SISO) system. It has the potential for application advantages in future indoor VLC system applications.

Study of the lighting characteristics of Uniel retrofit LED lamps

The paper considers the photometric characteristics of LED retrofit lamps produced by the Russian-Chinese company Uniel: Uniel LED-G45-6W/4000K, Uniel LED-A60-8W/6500K, and Uniel LED-A60-9W/4000K, designed to replace traditional incandescent bulbs. During the research, comprehensive measurements of photometric parameters (luminous flux, power consumption, color temperature, color rendering index, ripple factor, power factor) have been carried out and the luminous efficacy has been calculated. The results of the measurements have been presented in relation to the supply voltage. Based on the data obtained, an analysis is carried out of the compliance of the initial measured characteristics of the lamps with the values declared by the manufacturer. The analysis of the emission spectra leads to the conclusion that the Uniel LED-A60-8W/6500K lamps are equipped with white light-emitting diodes, the spectrum of which consists of a blue emission band from the semiconductor crystal with a maximum at ~450 nm and a phosphor band with a maximum at ~560 nm, which converts some of the blue emission from the crystal into long-wavelength spectrum. The emission spectra of the Uniel LED-G45-6W/4000K and Uniel LED-A60-9W/4000K lamps, in addition to the blue emission band from the semiconductor crystal with a maximum at ~450 nm, contain emissions from two phosphors, the bands of which have maxima at ~560 nm (green) and ~630 nm (red), which results in a lower color temperature of the LEDs. The paper also provides a detailed analysis of the light power distribution curves, thermal operating conditions, and structural features of the lamps. The research results lead to the conclusion that it is advisable to recommend Uniel LED-G45-6W/4000K and Uniel LED-A60-9W/4000K lamps for use as light sources to replace traditional incandescent lamps because their photometric characteristics comply with the declared parameters and permissible deviations specified in the regulatory standards.

The Influence of Light Wavelength on Human HPA Axis Rhythms: A Systematic Review.

Environmental light entrains many physiological and behavioural processes to the 24 h solar cycle. Such light-driven circadian rhythms are centrally controlled by the suprachiasmatic nucleus (SCN), which receives information from the short-wavelength-sensitive intrinsically photosensitive retinal ganglion cells. The SCN synchronizes local clocks throughout the body affecting sleep/wake routines and the secretion of neuroendocrine-linked hormones such as melatonin from the pineal gland and cortisol via the hypothalamic pituitary adrenal (HPA) axis. Although the effects of light parameters on melatonin have been recently reviewed, whether the experimental variation of the spectral power distribution and intensity of light can induce changes in cortisol rhythms remains unclear. Thus, this systematic review evaluated the effects of daytime exposure to lights of different spectral wavelength characteristics and luminance intensity on the cortisol levels in healthy individuals. A search of the PubMed, Web of Science, EMBASE, CINAHL, Medline, PsycINFO and Cochrane Library databases on 19 June 2023 identified 3418 articles, of which 12 studies (profiling 337 participants) met the inclusion and risk of bias criteria. An analysis of the literature indicated that exposure to bright lights of any colour during the late night or early morning can induce significant increases in cortisol secretion relative to time-matched dim light comparison conditions. Furthermore, exposure to bright lights with stronger short-wavelength (blue/green) components in the early morning typically induced greater increases in cortisol relative to lights with stronger long-wavelength (red) components. Thus, the circadian regulation of cortisol is sensitive to the wavelength composition of environmental lighting, in line with the more commonly studied melatonin. As such, wavelength characteristics should be optimized and reported in light intervention studies (particularly for the investigation of cortisol-associated disorders and HPA axis function), and exposure to short-wavelength light during sensitive periods should be carefully considered in constructed environments (e.g., bedroom and classroom lighting and device screens).

Utilising spectral lighting simulation technique for evaluating transmitted daylight through glazing: Exploring the non-visual effects and colour appearance

Modern humans spend more time indoors than their ancestors. In indoor environments, windows are the primary building elements that provide access to daylight and views. The advancement of the building industry has introduced new glazing and coating technologies for windows. Electrochromic glazing, in particular, has gained popularity in recent decades. These glazings’ tint varies with light exposure and electrical voltage, affecting the spectral power distribution of transmitted daylight. The growing knowledge of the impacts of light on sleep and health encourages an evaluation of the non-visual effects of daylight transmitted through glazing. Therefore, the aim of this paper is to investigate the non-visual effects of transmitted daylight through one clear and one smart glazing and evaluate the colour appearance variations. However, conventional visualisation tools are inadequate for this purpose, necessitating the use of alternative techniques that consider the spectral power distribution of light. To accomplish this, the Radiance-based Lark spectral lighting simulation tool was utilised. The non-visual effects were analysed by examining the responses of the five photoreceptors (Short-, Medium-, Long-wavelength cones, Rods, and ipRGCs) to light using the CIE spectral sensitivity functions. Additionally, the changes in colour appearance were assessed using six attributes: lightness, hue, chroma, vividness, depth, and clarity. The results demonstrate the effect of the studied glazing on non-visual light stimulation and colour appearance while presenting the challenges, applicability, and limitations of spectral simulation techniques. The proposed method yields promising results and can be a valuable tool for evaluating the effects of glazing on humans.

Long term experimental verification of a single chip quantum random number generator fabricated on the InP platform

This work presents the results from the experimental evaluation of a quantum random number generator circuit over a period of 300 minutes based on a single chip fabricated on the InP platform. The circuit layout contains a gain switched laser diode (LD), followed by a balanced Mach Zehnder Interferometer for proper light power distribution to the two arms of an unbalanced MZI incorporating a 65.4 mm long spiral waveguide that translates the random phase fluctuations to power variations. The LD was gain-switched at 1.3 GHz and the chip delivered a min-entropy of 0.5875 per bit after removal of the classical noise, resulting a total aggregate bit rate of 6.11 Gbps. The recoded data set successfully passed the 15-battery test NIST statistical test suite for all data sets.

Assessment of melanopsin-based quantities: Comparison of selected design tools and validation against on-field measurements

Melanopsin-based quantities (circadian stimulus and melanopic illuminance) depend on the spectral irradiance at the eye level, in turn resulting from the light sources' spectral power distribution and the interactions between light and materials. Software used in design practice (as DIALux) do not consider light and materials' spectral characteristics. Consequently, circadian stimulus and melanopic illuminance are calculated based on the illuminance at the eye and the sources' spectrum. Although software including spectral interactions (as ALFA - Adaptive Lighting for Alertness) exist, it is not clear how much the accuracy of various modelling approaches affects melanopsin-based quantities assessment. This research aims at investigating the applicability of the popular lighting design software for evaluating non-visual effects. For this purpose, two different approaches, based on the use of ALFA (method A) and DIALux (method B) are described, validated against on-field measurements and compared. Spectral irradiance is measured at the work plane and at the eye in a test room where the walls' finishes and the luminaires’ spectrum are changed, obtaining 21 scenarios. When simulating the space with the two methods, acceptable results are obtained for horizontal illuminance (percentage errors within the range ±10%), whereas for the vertical plane, errors depend on the software and the lighting scenario. Overall, method A performs better than B, but it gives percentage errors trespassing ±10% in 38.10% and 52.38% of the scenes in estimating circadian stimulus and melanopic illuminance respectively. This research informs ALFA and DIALux users on the reliability of both simulation tools in melanopsin-based quantities evaluation.

Using ground-based measurements to recover the spectra of radiation escaping from distant light-pollution sources

ABSTRACT A professional dark sky assessment normally requires the numerical modelling of light propagation from ground-based sources into the atmosphere. The spectral power distribution (SPD) of light escaping from an artificial source is one of the key parameters needed in predicting models to simulate the optical signatures of the night sky as a function of distance. SPD at zero distance is due to a non-trivial superposition of light beams, but does not necessarily coincide with the weighted SPD of individual lights. This is because most photons can be removed by obstacles or can interact with many surfaces before being directed into the atmosphere. We have developed an experimental and theoretical method for obtaining the initial SPD from ground-based spectroscopy of the night sky. The method is applicable to distant sources of light and is demonstrated in field measurements conducted on the light dome of Chicago with a new sky glow spectrometer. We show that the method requires analysing the relative impact of local light sources scattered around the measuring site on the radiance of the light dome. Our theoretical method along with ground-based spectroscopy represents a new approach to characterizing light-pollution sources which are otherwise difficult to study due to lack of information on either light-source inventory or a heterogeneous 3D structure of light-emitting and blocking environments.

Evaluation of Visual and Nonvisual Levels of Daylight from Spectral Power Distributions Considering Orientation and Seasonality

The evaluation of both visual and nonvisual effects from the spectral power distribution (SPD) of outdoor light is critical in lighting design. The dome-light SPD characteristically changes continuously depending on the seasonality, orientation, altitude of the sun or hour of the day. Traditional photopic parameters, such as the illuminance, luminance or correlated colour temperature (CCT), have been widely studied, but presently, there is no melanopic measurement or evaluation method. This article discusses the processes involved in establishing a simple method to determine the SPD of daylight and solar radiation over the skydome in a location to accurately account for the effects of both photopic and circadian levels around a location. Once per month for one year, natural daylight was spectrally measured in the city of Zaragoza (Spain); radiometric and photometric characteristics were analysed by season; and circadian effects were calculated in terms of standard parameters described by the Commission International de l’Eclairage (CIE), factors recommended by normative and scientific backgrounds. Finally, we suggest that the best parameter is the melanopic versus photopic irradiance ratio, which achieves reliable results at simplifying and correlating calculations.

Research on Indoor Visible Light Positioning Algorithm Based on K-means Clustering

In order to improve the indoor positioning accuracy and reduce the impact of a reflected light on the positioning performance, based on the analysis of the existing RSS positioning algorithm, an improved positioning algorithm based on K-means clustering is proposed. According to the indoor visible light communication system model and optical power distribution, 10*10 receiving points are uniformly selected on the receiving surface of 5m*5m. Through the collection of the received optical power of each receiving point, the K-means clustering algorithm is used to classify 100 receiving points: the first cluster of points is less affected by a reflected light, and the second cluster of points is greatly affected by a reflected light. The second cluster of receiving points is weighted after classifying, and the simulation results show that the algorithm significantly reduces the room edge positioning error, and the positioning performance of the entire room is improved by 28%.

Optical Design for Laser Diode Scanner Headlamp with Efficiently Distributed Optical Power for Adaptive Driving Beam System of Automobiles

The illumination optical system using a laser diode has advantages such as small size and high efficiency compared to an optical system using a conventional light source. In particular, its advantages can be maximized in high-resolution spatial light modulation. Based on these advantages, research to apply laser diode scanning to high-resolution adaptive driving beam (ADB) is currently being actively conducted. To construct a high-resolution illumination optical system for an ADB system using a single laser diode as a light source, the configuration of an optical scanning system is essential. In the general high-speed scanning method, the optical power at the center is relatively smaller compared with that at the edge because of the faster scanning speed when the center is illuminated. This causes large losses in automotive lighting optical system where the optical power in the center should be higher. Herein, we propose an optical system that can change the light power distribution of the center and the edge by applying a prism. In addition, by producing a prototype of an optical scanning system, the effect of efficiently distributing optical power by the designed optical scanning system was experimentally verified.

Analysis on light power and three-dimentional temperature distribution characteristics of gain guided and index alternate-guided fiber lasers

Gain guided and index alternate-guided (GGIA-G) fiber was suggested by our group recently. In this work, the improved rate equations of the GGIA-G fiber laser were established and solved. The pump and signal light power distribution along the fiber longitudinal axis were simulated under the conditions of forward, backward and bidirectional pump. Furthermore, a theoretical three-dimensional temperature distribution model of the GGIA-G fiber laser was established, and the temperature distribution characteristics along both the fiber longitudinal axis and radius were simulated and compared when the fiber was pumped with different methods. The research results show that different pump method has obvious influence on both signal light power distribution and the fiber temperature. When the fiber is forward pumped, the signal light power in the fiber is the highest, and when the fiber is bidirectionally pumped, the temperature of the fiber is the lowest. The research conclusions are helpful in the application of the GGIA-G fiber.

$\pi$ -Phase-Shifted Fiber Bragg Grating for Strain Measurement With High Spatial Resolution

Because the static strain measured by a uniform fiber Bragg grating is a mean value along the grating length, it is difficult to precisely measure a local strain when encountering nonuniformity. It is found that phase-shifted fiber Bragg gratings have short effective grating length and reflectivity approaching one at the central peak; these properties are beneficial for improving the spatial resolution. These advantages have been validated by calculating the light power distribution along the grating and by spectrum simulation using the transfer-matrix method integrated with finite element simulation. An interrogation system integrated with a newly designed algorithm has been used to automatically track the wavelength shift in the central peak. A set of comparison experiments that mimicked symmetrically parabolic strain and linearly increasing strain were conducted to demonstrate the advantage of the phase-shifted fiber Bragg grating over the conventional fiber Bragg grating in static measurements.

$1\times2$ Optofluidic Switch for Optical Beam Routing and Variable Power Distribution

We report a $1\times 2$ optofluidic switch which consists of a fluidic chamber and an electrowetting chamber. The fluidic chamber can realize light routing and power distribution. The electrowetting chamber can switch the light on and off. On the whole, the device can achieve a distribution of the incident light power to two outputs in any proportion (from 0% to 100%), and the light in each output can be switched on and off completely. Besides, due to light routing, the light loss of the proposed optofluidic switch is relatively low. The measured light loss of the device is less than ~0.35 dB. The proposed optofluidic switch has potential applications in optical switching networks, beam splitters, variable optical attenuators, and optical routers.

Light correlated color temperature and task switching performance in preschool-age children: Preliminary insights.

Data from a growing number of experimental studies show that exposure to higher correlated color temperature (CCT) ambient light, containing more blue light, can positively impact alertness and cognitive performance in older children and adults. To date, few if any studies have examined whether light exposure influences cognitive task performance in preschool-age children, who are in the midst of rapid developmental changes in attention and executive function skills. In this study, healthy children aged 4.5–5.5 years (n = 20; 11 females) completed measures of sustained attention and task switching twice while being exposed to LED light set to either 3500K (a lower CCT) or 5000K (a higher CCT). A control group (n = 18; 10 females) completed the tasks twice under only the 3500K lighting condition. Although the lighting condition did not impact performance on the sustained attention task, exposure to the higher CCT light lead to greater improvement in preschool-age children’s task switching performance (F(1,36) = 4.41, p = 0.04). Children in the control group showed a 6.5% increase in task switching accuracy between time points, whereas those in the experimental group improved by 15.2%. Our primary finding–that exposure to light at a higher correlated color temperature leads to greater improvement in task switching performance–indicates that the relationship between the spectral power distribution of light and executive function abilities is present early in cognitive development. These data have implications for designing learning environments and suggest that light may be an important contextual factor in the lives of young children in both the home and the classroom.

Parametric optimization and performances analysis of four secondary optical elements for concentrator photovoltaic systems

t he study concerns a general, parametric and performances analysis of four secondary optical elements (SOE) to use for Concentrator Photovoltaic Systems (CPV) using the same primary optic element: the Fresnel lens (FL). It concerns the Compound Parabolic Concentrator (CPC), the Crossed Compound Parabolic Concentrator (CCPC), the Cone and Pyramid. The study starts from optical modeling and considers several classical materials, with various refractive indexes in order to get a clear idea about their influences on the efficiencies, the sizes and the geometrical needs of the SOEs. The performances of the whole concentrator systems are compared in term of achieved effective concentrations, acceptance angles, output light power distribution and tolerances in the placement of the secondary element regarding the FL. Based on the etendue law, the geometrical considerations reveal that the length and the input aperture size of the whole SOEs increase with the increase of the refractive index of the considered material. Results show that the pyramid-based concentrator gives the more uniform irradiance distribution and the high optical efficiency whatever the used material, and the largest tolerance angle never reported. At the end, to easiest the comparison of the four elements, a merit graph is developed and proposed

Appraising the intention of other people: Ecological validity and procedures for investigating effects of lighting for pedestrians

One of the aims of outdoor lighting in public spaces, such as pathways and subsidiary roads, is to help pedestrians to evaluate the intentions of other people. This paper discusses how a pedestrians' appraisal of another persons' intentions in artificially lit outdoor environments can be studied. We review the visual cues that might be used, and the experimental design with which effects of changes in lighting could be investigated to best resemble the pedestrian experience in artificially lit urban environments. Proposals are made to establish appropriate operationalisation of the identified visual cues, choice of methods and measurements representing critical situations. It is concluded that the intentions of other people should be evaluated using facial emotion recognition; eye-tracking data suggest a tendency to make these observations at an interpersonal distance of 15 m and for a duration of 500 ms. Photographs are considered suitable for evaluating the effect of changes in light level and spectral power distribution. To support investigation of changes in spatial distribution, further investigation is needed with three-dimensional targets. Further data are also required to examine the influence of glare.

Amorphous silicon-lithium niobate thin film strip-loaded waveguides

The heterogeneous integration of an amorphous silicon (a-Si) film with a lithium niobate (LN) thin film combines both the mature micro-processing technology of Si and the excellent optical properties of LN. An a-Si thin film was deposited on an LN thin film, and strip-loaded waveguides were designed, fabricated, and characterized. A full-vectorial finite difference method was used to explore the single-mode conditions and appropriate dimensions for the strip-loaded waveguides. The waveguide mode size could be as small as 0.36 μm2. By adjusting the thickness and width of the a-Si loading strip, the distribution of light power could be mainly confined in the LN layer. The maximal light power that could be confined in LN was 91%, which was obtained at an a-Si thickness of 65 nm. A set of waveguides with widths of 2‒7 μm were prepared by inductively coupled plasma (ICP) etching of the a-Si thin film. Following annealing at 300°C in air for 1 hour, light transmission was observed in the waveguide. The 2-μm-wide waveguide showed propagation losses of 20 dB/cm for the quasi-TM (q-TM) mode and 42 dB/cm for the quasi-TE (q-TE) mode at 1550 nm. The root-mean-square (RMS) surface roughness of the a-Si thin film before and after annealing was 1.04 and 0.35 nm, respectively. High-resolution transmission electron microscopy (HRTEM) was performed to investigate the interface morphologies. A well-defined interface was clearly observed, and the structure of the a-Si thin film was proved to be amorphous.

Light dominates colour preference when correlated colour temperature differs

Colour preference for lighting is generally influenced by three kinds of contextual factors, the light, the object and the observer. In this study, a series of psychophysical experiments were conducted to investigate and compare the effect of certain factors on colour preference, including spectral power distribution of light, lighting application, observers’ personal colour preference, regional cultural difference and gender difference. LED lights with different correlated colour temperatures were used to illuminate a wide selection of objects. Participant response was quantified by a 7-point rating method or a 5-level ranking method. It was found that the preferred illumination for different objects exhibited a similar trend and that the influence of light was significantly stronger than that of other factors. Therefore, we conclude that the light itself (rather than, e.g. the objects that are viewed) is the most crucial factor for predicting which light, among several candidates with different correlated colour temperatures, an observer will prefer. In addition, some of the gamut-based colour quality metrics correlated well with the participants’ response, which corroborates the view that colour preference is strongly influenced by colour saturation. The familiarity of the object affects the ratings for each experiment while the colour of the objects also influences colour preference.

3D thermal analysis of end-pumped Nd3+-doped index-crossover gain guided–index antiguided fiber laser

Improved rate equations are established for the new model of index-crossover gain guided-index antiguided (IGG-IAG) fiber, then the pump and signal light power distribution along the IGG-IAG fiber are investigated. Based on the thermal conduction equations, the 3D temperature distributions of a one-end-pumped and dual-end-pumped Nd3+-doped IGG-IAG fiber laser are further analyzed. The simulation results show that many factors have an important influence on fiber temperature. The temperature of the fiber with the dual-end-pump method is obviously lower than that with the one-end-pump method, and the temperature distribution is more uniform. The larger the R value, the lower the fiber temperature, and the smaller the −Δn, the lower the fiber temperature. Thus proper fiber parameters and pump scheme may help to reduce the fiber temperature.

The spectral power distribution of light and twilight photometry

The influence of spectral light distribution of light sources for visibility in twilight conditions photometry is considered. Study of this subject is analyzed. The calculations of S/P ratio of samples of the lights of the leading Ukrainian companies and recommendations as for improvement of the efficiency of lighting conditions for driving conditions in twilight time are submitted.