Source Spectral Distribution Research Articles

Specifying Non-White Light Sources in Outdoor Applications to Reduce Light Pollution

ABSTRACT Anthropogenic (“human-generated”) light at night (ALAN) from outdoor lighting produces light pollution and as a result causes a range of deleterious responses in humans, plants, and animals. An emerging strategy to combat light pollution, especially sky glow, is to use “amber” LEDs in lieu of phosphor-converted white LEDs with high correlated color temperatures. Importantly, however, there is no standardized terminology or chromaticity designation that is applicable to “amber” LED lighting products for outdoor illumination. In this work, we propose a specification structure for light sources with nonstandard chromaticities to increase the precision of language used in the architectural lighting industry and demonstrate that light sources with well-defined chromaticity ranges outside of the ANSI C78.377–2017 quadrangles may be useful for reducing the portion of relative sky glow related to light source spectral power distribution. We encourage lighting standards development organizations to consider standardizing such a system.

A Method for the Reduction of Out-of-Band Measurement Errors in Multi-band Instruments using Synthetic Source Distributions

A method to reduce multi-band sensor measurement biases due to finite out-of-band response is described. The method takes advantage of the fact that out-of-band measurement errors cancel if the calibration source and the measured source have the same spectral distributions—independent of their spectral distributions or the magnitude of a sensor band’s out-of-band response. Using a known spectral responsivity, a synthetic, arbitrary source spectral distribution can replace a realized spectral distribution in the measurement equation and the signal can be calculated rather than measured. Given the freedom to select any arbitrary distribution for the synthetic source, the efficacy of the approach depends on the fidelity of the replication of the measured spectrum by the synthetic source spectrum. To illustrate the method, an example application is given of top-of-the-atmosphere measurements of water-leaving radiance by multi-band filter radiometers on celestial Earth-viewing sensors.

Optimized light source spectral power distribution for RGB camera based spectral reflectance recovery

The accuracy of recovered spectra from camera responses mainly depends on the spectral estimation algorithm used, the camera and filters selected, and the light source used to illuminate the object. We present and compare different light source spectrum optimization methods together with different spectral estimation algorithms applied to reflectance recovery. These optimization methods include the Monte Carlo (MC) method, particle swarm optimization (PSO) and multi-population genetic algorithm (MPGA). Optimized SPDs are compared with D65, D50 A and three LED light sources in simulation and reality. Results obtained show us that MPGA has superior performance, and optimized light source spectra along with better spectral estimation algorithm can provide a more accurate spectral reflectance estimation of an object surface. Meanwhile, it is found that camera spectral sensitivities weighted by optimized SPDs tend to be mutually orthogonal.

Influence of transmissometers’ light source spectral distribution in measuring visibility

Presently, the difference in the spectral distribution of light sources is not been sufficiently taken into account when measuring and calibrating the transmissometers. As such, the visibility measurement result cannot be to be traced to the World Meteorological Organization (WMO) definition of meteorological optical range (MOR). In this study, a method is proposed to trace the spectral distribution of transmissometers’ light sources to the 2700 K incandescent light’s spectral distribution in MOR definition. Then a traceability basis of the light source’s spectral distribution is proposed, and a model is established to determine the influence of the light source’s absolute color temperature on the MOR measurement accuracy. At the transmissometers’ typical baseline lengths of 10, 20, 30, 50, and 75 m, the absolute color temperature range and their corresponding spectral simulation error range equivalent to 2700 K incandescent lamp are obtained. Finally, the Monte Carlo method is used to simulate and analyze the MOR error corresponding to the absolute color temperature of different spectral simulation errors at five typical baseline lengths. The results show that in 10 m–600 m of MOR, the maximum simulated MOR absolute error is 42 m, which is less than 50 m, in 600 m–1500 m of MOR, the maximum simulated MOR relative error is 2.9%, which is much lower than 10% and in 1500 m–10 km of MOR, the maximum simulated MOR relative error is 18.6%, which is less than 20%, the MOR measurement accuracy is improved to the International Civil Aviation Organisation (ICAO)’s recommended requirements, thus confirming the accuracy of our theoretical research. We expect that this work will help establish the standard procedure for the SI-traceable calibration of transmissometers.

Methods for Assessment and Monitoring of Light Pollution around Ecologically Sensitive Sites.

Simple SummaryImaging and photometric techniques are used to characterize the brightness of nighttime conditions in protected areas in support of conservation efforts.Since the introduction of electric lighting over a century ago, and particularly in the decades following the Second World War, indications of artificial light on the nighttime Earth as seen from Earth orbit have increased at a rate exceeding that of world population growth during the same period. Modification of the natural photic environment at night is a clear and imminent consequence of the proliferation of anthropogenic light at night into outdoor spaces, and with this unprecedented change comes a host of known and suspected ecological consequences. In the past two decades, the conservation community has gradually come to view light pollution as a threat requiring the development of best management practices. Establishing those practices demands a means of quantifying the problem, identifying polluting sources, and monitoring the evolution of their impacts through time. The proliferation of solid-state lighting and the changes to source spectral power distribution it has brought relative to legacy lighting technologies add the complication of color to the overall situation. In this paper, I describe the challenge of quantifying light pollution threats to ecologically-sensitive sites in the context of efforts to conserve natural nighttime darkness, assess the current state of the art in detection and imaging technology as applied to this realm, review some recent innovations, and consider future prospects for imaging approaches to provide substantial support for darkness conservation initiatives around the world.

The impact of light source spectral power distribution on sky glow

The effect of light source spectral power distribution on the visual brightness of anthropogenic sky glow is described. Under visual adaptation levels relevant to observing the night sky, namely with dark-adapted (scotopic) vision, blue-rich (“white”) sources produce a dramatically greater sky brightness than yellow-rich sources. High correlated color temperature LEDs and metal halide sources produce a visual brightness up to 8× brighter than low-pressure sodium and 3× brighter than high-pressure sodium when matched lumen-for-lumen and observed nearby. Though the sky brightness arising from blue-rich sources decreases more strongly with distance, the visual sky glow resulting from such sources remains significantly brighter than from yellow sources out to the limits of this study at 300km.

On measuring task performance

This paper describes the approaches that can be used to measure task performance and illustrates them by reviewing what is known about the impacts of illuminance and light source spectral power distribution on task performance. The approaches can vary from real tasks studied in the field through simulated tasks or standard tasks to basic visual functions measured in the laboratory. Each approach has different strengths and weaknesses. Understanding what these are is essential for anyone proposing to measure task performance or wishing to appreciate what such performance measurements imply. The review of the effects of spectral power distribution on task performance reveals that there is still much to learn. The effects of spectral power distribution on basic visual functions are well established, but, for tasks where the role of colour is to enhance visibility and conspicuity, there is little more than a qualitative understanding. As for the effects of spectral power distribution on task performance when operating through perception, this is largely unexplored territory.

Astrometric signal profile fitting for Gaia

A tool for representation of the one-dimensional astrometric signal of Gaia is described and investigated in terms of fit discrepancy and astrometric performance with respect to number of parameters required. The proposed basis function is based on the aberration free response of the ideal telescope and its derivatives, weighted by the source spectral distribution. The influence of relative position of the detector pixel array with respect to the optical image is analysed, as well as the variation induced by the source spectral emission. The number of parameters required for micro-arcsec level consistency of the reconstructed function with the detected signal is found to be 11. Some considerations are devoted to the issue of calibration of the instrument response representation, taking into account the relevant aspects of source spectrum and focal plane sampling. Additional investigations and other applications are also suggested.

Deep Chandra observations of TeV binaries - I. LS I +61°303

We report on a 95ks Chandra observation of the TeV emitting High Mass X-ray Binary LSI +61 303, using the ACIS-S camera in Continuos Clocking mode to search for a possible X-ray pulsar in this system. The observation was performed while the compact object was passing from phase 0.94 to 0.98 in its orbit around the Be companion star (hence close to the apastron passage). We did not find any periodic or quasi-periodic signal (at this orbital phase) in a frequency range of 0.005-175 Hz. We derived an average pulsed fraction 3 sigma upper limit for the presence of a periodic signal of ~10% (although this limit is strongly dependent on the frequency and the energy band), the deepest limit ever reached for this object. Furthermore, the source appears highly variable in flux and spectrum even in this very small orbital phase range, in particular we detect two flares, lasting thousands of seconds, with a very hard X-ray spectrum with respect to the average source spectral distribution. The X-ray pulsed fraction limits we derived are lower than the pulsed fraction of any isolated rotational-powered pulsar, in particular having a TeV counterpart. In this scenario most of the X-ray emission of LSI +61 303 should necessarily come from the interwind or inner-pulsar wind zone shock rather than from the magnetosphere of the putative pulsar. Furthermore, we did not find evidence for the previously suggested extended X-ray emission (abridged).

Characterization of tissue cells by full information from spectral interferogram

A new method for characterizing living tissue cells is demonstrated using both phase and amplitude information derived from the spectrally resolved interferogram in a single measurement. The effect of the light source spectral distribution can be cancelled out with the help of the zero order spectrum of the Fourier transform of the interferogram. The ratio of amplitudes between the two interference beams is acquired without this effect. The group delay, the first and second order dispersions, and the absorption, etc., for the full wavelength range can be measured. The results of the culture medium and the HeLa living cells are given. In addition, the measured values of d2n/d λ2 and absorption of the distilled water are also provided for comparison.

Comparison of Calibration Methods for Tristimulus Colorimeters.

Uncertainties in source color measurements with a tristimulus colorimeter are estimated for calibration factors determined, based on a known source spectral distribution or on accurate measurements of the spectral responsivities of the colorimeter channels. Application is to the National Institute of Standards and Technology (NIST) colorimeter and an International Commission on Illumination (CIE) Illuminant A calibration. Detector-based calibration factors generally have lower uncertainties than source-based calibration factors. Uncertainties are also estimated for calculations of spectral mismatch factors. Where both spectral responsivities of the colorimeter channels and the spectral power distributions of the calibration and test sources are known, uncertainties are lowest if the colorimeter calibration factors are recalculated for the test source; this process also avoids correlations between the CIE Source A calibration factors and the spectral mismatch factors.

Light source spectrum, brightness perception and visual performance in pedestrian environments: a review

This review considers the impact of light source spectral power distribution (SPD) on brightness perception and visual performance in mesopic conditions, with emphasis on the comparison of metal halide (MH) and high pressure sodium (HPS) lamps. Models of mesopic vision predict that SPD is a significant variable in that at a HPS photopic luminance of 0.100 cd/m2, MH need only produce about 0.070-0.075 cd/m2 to be seen as equally bright. However, attempts to validate the predictions of these models in the field have met with mixed success. As for visual performance, experimentation has shown that there are effects of SPD in mesopic conditions, but the magnitude of these effects depends on the nature of the task. Three alternative approaches are suggested for comparing light sources with different SPDs in mesopic conditions.

Polymerization quality testing of composite resins cured by led light source

The quality of interface between composite resin materials and hard dental tissues is highly dependent on the polymerization light source. Newly developed blue light- emitting diode units for light polymerization of dental restorative materials are the most innovative light source technology in dentistry nowadays. The aim of this work was to estimate the depth of cure of five different light-activating composite resins exposed to different irradiation times (5s, 10s, 20s and 40s) when the experimental LED light source was used. The tested materials were: Tetric Ceram (Vivadent), Point 4 (Kerr), Admira (VOCO), Filtek Z250 (3M) and Diamond Lite (DRM Lab., Inc). The depth of cure testing was determined using a penetrometer. Results after 40s curing time were as following: the deepest depth of cure was achieved after application of Filtek Z 250, Diamond Lite Point 4 and Tetric Ceram. For the restorative material Admira was found the lowest depth of cure for the light exposure of 40s. An experimental LED light source achieved a sufficient depth of cure (over 2 mm) for all tested materials after curing time of 10s. The polymerization light source spectral distribution should be considered in addition to irradiance as a depth of cure indicator.

Polymerization quality testing of composite resins cured by led light source

The quality of interface between composite resin materials and hard dental tissues is highly dependent on the polymerization light source. Newly developed blue light- emitting diode units for light polymerization of dental restorative materials are the most innovative light source technology in dentistry nowadays. The aim of this work was to estimate the depth of cure of five different light-activating composite resins exposed to different irradiation times (5s, 10s, 20s and 40s) when the experimental LED light source was used. The tested materials were: Tetric Ceram (Vivadent), Point 4 (Kerr), Admira (VOCO), Filtek Z250 (3M) and Diamond Lite (DRM Lab., Inc). The depth of cure testing was determined using a penetrometer. Results after 40s curing time were as following: the deepest depth of cure was achieved after application of Filtek Z 250, Diamond Lite Point 4 and Tetric Ceram. For the restorative material Admira was found the lowest depth of cure for the light exposure of 40s. An experimental LED light source achieved a sufficient depth of cure (over 2 mm) for all tested materials after curing time of 10s. The polymerization light source spectral distribution should be considered in addition to irradiance as a depth of cure indicator.

Broadband sound generation by confined turbulent jets.

Sound generation by confined stationary jets is of interest to the study of voice and speech production, among other applications. The generation of sound by low Mach number, confined, stationary circular jets was investigated. Experiments were performed using a quiet flow supply, muffler-terminated rigid uniform tubes, and acrylic orifice plates. A spectral decomposition method based on a linear source-filter model was used to decompose radiated nondimensional sound pressure spectra measured for various gas mixtures and mean flow velocities into the product of (1) a source spectral distribution function; (2) a function accounting for near field effects and radiation efficiency; and (3) an acoustic frequency response function. The acoustic frequency response function agreed, as expected, with the transfer function between the radiated acoustic pressure at one fixed location and the strength of an equivalent velocity source located at the orifice. The radiation efficiency function indicated a radiation efficiency of the order (kD)2 over the planar wave frequency range and (kD)4 at higher frequencies, where k is the wavenumber and D is the tube cross sectional dimension. This is consistent with theoretical predictions for the planar wave radiation efficiency of quadrupole sources in uniform rigid anechoic tubes. The effects of the Reynolds number, Re, on the source spectral distribution function were found to be insignificant over the range 2000<Re<20000. The source spectral distribution function approximately obeyed a St(-3) power law for Strouhal number values St<0.9, and a St-5 power law for St>2.5. The influence of a reflective open tube termination on the source function spectral distribution was found to be insignificant, confirming the absence of a feedback mechanism.

Effect of UV light source intensity and spectral distribution on the photopolymerisation reactions of a multifunctional acrylated monomer

The goal of this study was to examine the possibilities of preparing thin surface spatial crosslinked polymer films by UV curing using 1,6-hexandioldiacrylate as a multifunctional monomer and 1-hydroxycyclohexyl acetophenone as a radical photoinitiator. Different UV light sources were used with different light spectral distributions and light intensities. It is found that the light source characterised at least by a particular overlap of its emission spectrum with the photoinitator’s absorption spectrum is the best system used for effective cure. Low polymerisation rate achieved in the case of smaller overlap of spectrums is easy to regulate by extending the energy of the emitted light.

Source deconvolution and system identification of flow-excited acoustic systems

A method for the characterization of flow-excited acoustic systems in the frequency domain was investigated. The approach, based on dimensional analysis and the hypothesis that the system may be described using a linear source-filter model, allows the source spectral distribution and the magnitude of the frequency response function to be obtained directly from sound-pressure spectra measured over a range of flow velocities. The objective as to determine whether the method could be used to predict the noise emissions of a small axial-flow cooling fan in a given installation from source and response functions evaluated using different calibration facilities. The spectral decomposition algorithms were first validated using a theoretical model. The influence of discretization errors and random errors in the input spectra was evaluated. The noise emissions of two different fans were then measured for two different computer enclosures and a calibrated plenum, following standardized procedures. The results demonstrated that the use of the spectral decomposition method as a pre- dictive tool was accurate in this case, provided the fan inflow was reasonably uniform. In addition, the method was found to be very robust to random errors in the input data. Discretization errors, however, had a significant impact on accuracy.

Experimental investigation of flow-excited cavity pressure fluctuations

Cavity pressure fluctuations induced by flow grazing over a long, narrow, open cavity were investigated. The apparatus stimulated a typical road vehicle door gap/door cavity/primary bulb seal assembly, tested using a wind tunnel. The cavity pressure distribution was measured over a range of flow velocities. Pressure spectra were decomposed into a source spectral distribution function and an acoustic frequency response function, using a system identification method based on dimensional analysis and a linear source-filter model. The results indicated a weak coupling between the cavity response and the flow excitation. The excitation mechanism was dominated by flow-edge interactions, i.e., the ‘‘edge tone.’’ The characterization method was validated by varying the acoustic properties of the cavity and the excitation strength. The source function was independent of sensor location. The system response was shown to be associated with transverse standing waves. Tapering the orifice trailing edge simultaneously reduced the excitation strength, the excitation frequency, and the cavity response. The presence of flow aspiration through the seal raised the broadband noise floor of the system response function. This anomaly underlined one limitation of the spectral decomposition method.

A method for characterizing aerodynamic sound sources in turbomachines

A method based on Weidemann’s acoustic similarity laws [1] was used to investigate the aerodynamic sound generated by a partially ducted centrifugal pump rotor. The primary objective of the method was to determine the spectral characteristics of the sound source by isolating the effects of acoustic phenomena such as duct resonances or sound reflections. Pump-radiated sound pressure spectra were measured for different impeller rotational speeds, keeping the operating condition constant. The spectra, assumed to be expressed as the product of a source spectral distribution function and an acoustic frequency response function, were then decomposed into a product form following a computer-implemented algorithm. The method was successful in accurately determining the spectral distribution of the broadband aerodynamic noise generating mechanisms involved and that of the acoustic frequency response of the system. The absolute levels of the source function and the acoustic function were established by assuming that, over a limited low frequency range, the average gain of the frequency response function is unity so that comparisons between different pump operating conditions could be made. The source spectral distribution was found to be independent of the microphone location and the acoustic loading. When applicable, this method therefore allows the characterization of aerodynamic sound sources by measuring ordinary sound pressure spectra, at any one point around the source, without having to isolate the source from the system. The source characterization method was instrumental in the study of sound generation by rotating stall presented in a previous publication [2].

Generation of superthermal electrons interacting with waves in lower-hybrid range of frequency revisited

The problem of quasilinear diffusion of plasma electrons, resonantly interacting with waves in lower-hybrid range of frequency launched from the exterior, is examined within a self-consistent one-dimensional homogeneous model. An analytical solution is obtained, which allows the derivation of a simple formula for the plasma current in terms of the parameters characterizing the spectral distribution of the RF power source. The major outcome is a dramatic sensitivity of the plasma current to the presence of a small, high-N/sub /// component in the RF power source spectral distribution, in agreement with previous numerical calculations.