White lighting

White is a color sensation absent hue. Manufacturers describe practical light sources used for illumination as tinted warm‐white or cool‐white, but these informal designations do not seem to be based upon measured human color perceptions of white illumination. This article describes the results of a series of psychophysical experiments that more precisely measured subjective perceptions of white illumination from light sources of different correlated color temperatures (CCTs). Generally, perceptions of untinted white illumination for sources with high CCTs (above 4000 K) are associated with chromaticities that fall above the blackbody locus. In contrast, perceptions of untinted white illumination for sources with low CCTs (below 4000 K) are associated with chromaticities that lie well below the blackbody locus. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2013     

单光照条件变化的镨/钕元素组分含量软测量

针对镨/钕稀土萃取工业生产现场光照条件变化导致具有颜色特征的镨/钕组分含量难以准确检测的问题，提出了一种基于单光照条件变化的组分含量软测量方法。首先，采用参数优化的Grey Edge算法，将不同光照条件下的稀土溶液图像校正到标准光照下；然后，以镨/钕溶液图像HSI颜色空间中的H、S、I分量一阶矩为模型的输入变量，利用加权最小二乘支持向量机（WLSSVM）建立组分含量软测量模型；最后采用工业数据对所提方法进行仿真实验，结果表明所提方法在不同光照条件下均能满足稀土萃取过程组分含量检测的准确度和快速性要求。     

Computer simulation study of images in contact and near-contact printing

Versatile computer programs capable of simulating near-contact images from arbitrary objects and illumination were reported. Their capability was demonstrated in examples of combinations of different types of object and illumination. From the specific examples, we were able to derive certain general rules: (1) Polychromatic illumination is always better than monochromatic illumination. (Besides observing the examples given above, polychromatic illumination also helps when standing waves in photoresist are considered.) (2) Negative masks are easier to print than positive ones. Note that a negative mask in the sense of optical diffraction means smaller dimension for transparent parts of the mask. (3) Some well designed irregularities in the mask pattern improves the image. (4) The effective depth tolerance is between the limits set by the focussing effect and the image spreading effect. (5) Holographic mask should relax flatness and exposure tolerance.     

Visual clarity and feeling of contrast

The visual clarity of a lighting environment is significantly affected by changing the general color rendering index (Ra) of its illumination. This effect has been studied by a number of researchers, but the cause of this effect has not been thoroughly studied. In order to clarify this, the mutual relations between visual clarity, lightness perception, and feeling of contrast are analyzed by using object colors under illuminations with various Ra values. the results obtained are as follows. (1) the visual clarity of a lighting environment is different from the lightness perception of the object colors in the environment. (2) the change in visual clarity of a lighting environment is highly correlated to a feeling of contrast between object colors under the illumination. (3) the effect of visual clarity is estimated effectively by assessing the feeling of contrast using a specially selected four-color combination. (4) the illuminance for equal visual clarity for any illumination is predicted by the equality of feeling of contrast under the same illumination specified by the gamut area made by the component colors of the four-color combination in a brightness and colorfulness space. (5) the effect of visual clarity under various illuminations cannot be predicted by using their Ra values.     

Perceived illumination measured

We consider a method of measurement of apparent illumination using the perceptual phenomenon of fluorescence to which we give a psychophysical explanation based on the hypothesis of direct relation of perception of self-luminosity to the apparent illumination of the scene observed by the viewer. We report results of three experimental studies: (1) measurements of apparent illumination when a flat mondrian in the darkness is observed; (2) measurements of apparent illumination in a “rich” 3D scene; (3) testing linearity of the subjective illumination space. Based on the obtained data, we confirm the basic hypothesis of a relation between the self-luminosity phenomenon and the perceived illumination, and show that the suggested method of measurement of apparent illumination gives reliable and accurate (errors were in the range 4–10%) values of its chromatic components. Apparent illumination in the case of a mondrian observed in the darkness is found unstable, which can be expected given that the context of such a scene is insufficient for obtaining a unique solution for all the components of the photometric problem. In the second experiment, we show that the measurement results remain constant when the context of a “rich” 3D scene is changed and that they follow the changes in illumination conditions. In the third experiment, we study the composition of different illuminations and show that the simple relation f = f₁ + f₂ holds for the measurement of the illumination (f) when two other illuminations (f₁, f₂) are applied simultaneously. © 1998 John Wiley & Sons, Inc. Col Res Appl, 23, 159–168, 1998     

White lighting: A provisional model for predicting perceived tint in “white” illumination

Recently, a line of minimum tint in chromaticity space for sources of illumination of different correlated color temperatures (CCTs) from 2700 K to 6500 K has been reported. This line of minimum tint did not correspond to the line of blackbody radiation implicitly associated with sources of white illumination used in architectural applications. It was noted that chromaticities along the line of minimum tint were not metamers but, rather, should represent, for a given CCT, chromaticities where the neural signals from the two spectral opponent channels were minimized. Earlier work provided a theoretical framework for representing the four unique hues where the neural signals from one spectral opponent channel are minimized. This framework was used here to quantitatively represent the line of minimum tint and then to empirically test whether this representation could predict the amount of tint perceived in six different sources of “white” Illumination.” Based on these results, a provisional model is proposed for describing the tint and the amount of tint perceived in “white” Illumination used in architectural applications. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 466–479, 2014     

Visual and instrumental assessment of interference pigments

Discrepancies often exist between visual assessment and instrumental assessment. These are due to different geometries with which samples are viewed or measured: In visual observation at the window or in the light booth, the sample panels are usually moved up and down. This changes the angle of illumination and observation. The current measuring devices have a fixed illumination.     

Spectrophotometric error in colour coordinates introduced by fluorescence of white calibration tile

Fluorescence has been detected in some white standard tiles intended for the calibration of spectrophotometers for colour measurements. The problem is that usually no warning is given to the user about it, giving raise to errors if they are calibrated using conventional spectrophotometric techniques. This work analyzes the differences on the colour coordinates of one of these standards measured with a polychromatic illumination spectrophotometer and with a monochromatic illumination one. This work also analyzes the colour coordinates error obtained when other coloured standards are calibrated against one of these white fluorescent standards, when reflectance measurement is done with a polychromatic illumination spectrophotometer as well as with a monochromatic illumination instrument. These are the two most typical situations found in practice where the use of fluorescent standards may produce errors. © 2004 Wiley Periodicals, Inc. Col Res Appl, 29, 111–114, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10233     

Chromaticity changes of inorganic pigments in Chinese traditional paintings due to the illumination of frequently‐used light sources in museum

Optical radiation can cause permanent damage to the color of Chinese traditional paintings, which have extremely high responsivity in the museum illumination. In order to obtain quantitative influence laws of artificial illumination on inorganic pigments in Chinese traditional paintings and provide basis for choosing light sources, a long periodic illumination experiment was carried out to examine how prolonged exposure of three light sources (tungsten halogen, metal halide and white light emitting diodes), frequently‐used in museums, affect the chromaticity of five inorganic pigments [azurite (blue), cinnabar (red), orpiment (yellow), ancient graphite (black), clam shell powder (white)], commonly used in Chinese traditional paintings. Through the experiment, we found that the illumination causes a color change to inorganic pigments, and the degree of which is related to the photochemical stability of pigments and the high energy shortwave radiation in the light source spectrum. We also obtain the color change laws of the five pigments and the quantitative relationships of color damage for different painting types. These results can provide data basis for related research on Chinese traditional painting illumination and choice basis for light sources in museum lighting designs.     

Remote adaptation effect on perceived subjective color: A model approach

An elaborated subjective color model is presented that includes the predictions of emulated Benham disk results and additional predictions that refer to local and remote achromatic illuminations on perceived subjective color shifts. A computer emulated Benham disk pattern was used as a stimulus to test the effects of remote illumination on its color sensation. An analytical model and its predictions are proposed in order to account for the results of the perceived hue shift, when changing either the remote illumination area or the stimulus illumination. This model is based on previous retinal color‐coded cells responses which yield the subjective color, and on local and remote adaptation mechanisms. The similarity between the role and mechanism of remote illumination (achromatic or chromatic) in subjective and perceived color is also discussed. © 2003 Wiley Periodicals, Inc. Col Res Appl, 28, 197–208, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10145     

Reflection measurement and visual evaluation of the luminosity of skin coated with powder foundation

This article aims to identify the essential components of the luminosity of skin coated with powder foundation, based on two processes: reflection measurement and visual evaluation of the skin surface. The luminosity refers to the state of being “luminous,” “brilliant,” or “radiant” of the foundation‐coated skin. First, a flat piece of artificial skin is used, and an experimental device is developed to visually evaluate the appearance of the foundation‐coated artificial skin at different conditions of viewing angle, illumination angle, and illumination intensity. The luminosity score is analyzed from the point of view of optical reflection. Next, the same assessment of luminosity is executed for real human skin. The luminosity is evaluated for cheek and forehead coated with powder foundation at different observation conditions using another experimental device. Finally, all luminosity scores are analyzed in color spaces to identify the color region relating to luminosity perception. © 2012 Wiley Periodicals, Inc. Col Res Appl, 39, 45–55, 2014     

Color-rendering capacity of light

Two types of questions, both related to color-rendering properties of light, can be identified. Type A: Given a spectral reflectance chip under illumination of a certain spectral power distribution, What color can appear? Does the appearing color, in comparison with a reference one, look right or distorted? Type B: Given a great many chips of different spectral reflectance functions under illumination of a certain spectral power distribution, How many different colors, no matter what colors, can appear? Are there a great many different colors or just a few different colors appearing? Questions of type A reflect an important aspect of color-rendering properties and can be tackled with an established measure, the CIE color-rendering index. Questions of type B, related to quite another aspect of color-rendering properties, have particular relevance when illumination's function of making things visible is of most concern. This article discusses a new measure, the color-rendering capacity (CRC), developed for dealing with questions of type B, and explains the measure's derivation, calculation, and implications.     

Photoluminescence Decay and Hydrogen Desorption of n-Type Porous Silicon

The decay under illumination of the photoluminescence (PL) intensity ofn-type porous silicon (PS) samples prepared by electrochemical etching has been investigated. We have found that the PL evolution with illumination time presents two different stages: an initial very fast decay which lasts 300 s, followedby a second one, much slower, which extends for times longer than 10⁴ s. Thisevolution suggests that two different mechanisms could be responsible for the PLintensity decay. Samples subjected to different illumination times were studied byThermal Desorption Spectroscopy (TDS). The desorption rate of H₂ and SiH_x species was monitored during linear heating of the samples. A qualitative correlationbetween the decay of the PL intensity under illumination and the amount of H₂ and SiH_x species evolved from the illuminated samples has been observed. Experimentaldata suggest that H₂ could be desorbed from the sample during the illuminationtime through a photoinduced H₂ desorption process, inducing the decrease of the PLintensity.     

Multi‐wavelength excitation method for measuring FWA‐treated paper

Colorimetric properties of fluorescent materials depend on the SPD of the illumination. That is why most standards for evaluating them specify the illuminations, which are often hard‐to‐realize daylight illuminants. The presented method using commercially available LEDs enables accurate enough colorimetric measurements of FWA‐treated papers or prints on them illuminated by the specified illuminant. The total spectral radiance factor of a fluorescent specimen, from which most colorimetric values are derived, consists of the luminescent spectral radiance factor and the spectral reflectance factor. This method separately estimates those of FWA‐treated paper to add up to the total spectral radiance factor. The luminescent spectral radiance factor is obtained by estimating the SPD of luminescence excited by the specified illuminant as the weighted sum of the multiple SPDs of luminescence excited by the respective narrow band LED emissions at different wavelengths. The LEDs and their weights are determined optimally for generally used papers. The spectral reflectance factor is derived from the estimated SPD of the radiation with fluorescence excluded from the paper illuminated by visible illumination. The method was applied with five different illumination systems each using two or three narrow band LEDs in the excitation range. They were evaluated by measuring the total spectral radiance factors by D50 of seven FWA‐treated papers and CMYK prints on four papers. The derived colorimetric values were compared to the respective references by the ideal D50.     

Color corrected single scale retinex based haze removal and color correction for underwater images

Underwater images are affected by scattering of dust particles leading to hazy images. The difference in absorption of light at different wavelength leads to colorcast. Restoring underwater images from haze and colorcast degradation is a challenging task. This article proposes color corrected single scale retinex algorithm for the restoration of hazy and colorcast underwater images. Further, the illumination of the underwater image is enhanced through illumination enhancer. In order to correct colorcast, the underwater images intensity shifters are proposed. Blur, natural image quality evaluator, blind/referenceless image spatial quality evaluator, entropy, peak signal to noise ratio are the metrics used to evaluate the performance of the proposed restoration technique and compared the output with the existing techniques. Compared to the existing techniques the proposed algorithm prominently removes haze and colorcast present in underwater images. The study excludes retinex-with-reset models from consideration.     

光照条件对可见光固化乙烯基酯树脂固化物性能的影响

本文通过对不同光照条件下得到的可见光固化及过氧化物固化的乙烯基酯(VLC)树脂的弯曲、拉伸性能和玻璃化转变温度及残留苯乙烯含量的比较研究,发现只要保证可见光照射的照度和光照量,VLC树脂可见光固化物性能和过氧化物固化物性能相当,高照度光源照射下双酚型VLC-760浇铸体的断裂伸长率及玻璃化转变温度会有明显提高。     

Illuminant estimation for object recognition

Comparing colour histograms of images has been shown to be a powerful technique for discriminating among large sets of images. However, these histograms depend not only on the properties of imaged objects but also on the illumination under which the objects are captured. If this illumination dependence is not accounted for prior to constructing the colour histograms, colour‐based image indexing will fail when illumination changes. This failure can be addressed by correcting the RGBs in an image to corresponding RGBs representing the same scene but under a standard reference illuminant prior to constructing the histograms. To perform this correction of RGBs, it is necessary to have a measurement or, more commonly, an estimate of the illumination in the original scene. Many authors have proposed illuminant estimation (or colour constancy) algorithms to obtain such an estimate. Unfortunately, the results of colour histogram matching experiments under varying illumination conditions have shown that existing estimation algorithms do not provide a sufficiently good estimate of the scene illuminant to enable this approach to work. In this article we report on the results of our repetition of those experiments, but this time using a new illuminant estimation algorithm—the so‐called color by correlation approach, which has been shown to afford significantly better performance than previous algorithms. The results of this new experiment show that when this new algorithm is used to preprocess images, a significant improvement in colour histogram matching performance is achieved. Indeed, performance is close to the theoretically optimal level of performance, that is, close to that which can be obtained using actual measurements of the scene illumination. © 2002 Wiley Periodicals, Inc. Col Res Appl, 27, 260–270, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10064     

Absolute reflectance factor calibration for goniospectrophotometry

Currently, spectrophotometric standard reference materials are calibrated only using the CIE recommended illumination and viewing geometries. A need exists for standards that have been calibrated at many other combinations of illumination and viewing angles. The common practice has been to assume that a primary transfer standard such as BaSO₄ is Lambertian even though its non-Lambertian behavior is well documented. This study was undertaken to develop a practical standard for this type of metrology. Two diffuse materials, BaSO₄ and PTFE, were characterized goniospectrophotometrically. Bidirectional absolute spectral reflectance factors were determined for 60 combinations of illumination and view angles in a single plane. Neither material was found to be Lambertian and both failed to completely depolarize reflected radiation. The results were modeled using principal components analysis. The resulting model allows the determination of bidirectional spectral reflectances factors with a minimum effort. PTFE powder can be prepared repeatably with no significant effect on the measured reflectance properties, thus indicating that it would be a suitable primary transfer standard for goniospectrophotometry.     

Performance assessment of multijunction solar cells incorporating GaInNAsSb

We have measured the characteristics of molecular beam epitaxy grown GaInNAsSb solar cells with different bandgaps using AM1.5G real sun illumination. Based on the solar cell diode characteristics and known parameters for state-of-the-art GaInP/GaAs and GaInP/GaAs/Ge cells, we have calculated the realistic potential efficiency increase for GaInP/GaAs/GaInNAsSb and GaInP/GaAs/GaInNAsSb/Ge multijunction solar cells for different current matching conditions. The analyses reveal that realistic GaInNAsSb solar cell parameters, render possible an extraction efficiency of over 36% at 1-sun AM1.5D illumination.

PACS

88.40.hj; 88.40.jm; 88.40.jp; 81.15.Hi     

Fabrication and analysis of side‐emitting poly(methyl methacrylate) fibres with non‐circular cross‐sections

We present a novel type of side‐light‐emitting fibre with trilobal cross‐section. The fibre is especially designed for indirect illumination applications and the special shape of the filament cross‐section permits the formation of a distinct asymmetric radiation pattern. These fibres can focus the radially emitted light on particular locations, e.g. in order to cure resins or polymers at well‐defined positions, or may be used as indirect illumination sources in car interiors. The polymer material is commercial optical‐grade poly(methyl methacrylate) (PMMA) that is compounded with different concentrations of a TiO₂‐nanofiller‐modified PMMA. © 2018 Society of Chemical Industry