Interior and exterior daylight illuminants for the colorimetry of fluorescent materials

The difficulties in simulating CIE Standard Illuminant D₆₅ are considered and an interior daylight illuminant is described, Illuminant ID₆₅, representing exterior daylight attenuated by average window glass. The benefits of Illuminant ID₆₅ are that it represents the daylight source which most commonly occurs in the viewing of critically coloured merchandise, and that it can be practically simulated using a filtered tungsten-halogen source. Its applicability to measurements, particularly to the assessment of fluorescent samples, is considered. The results of measurements on the two common classes of fluorescent samples are discussed and indicate that an Illuminant ID₆₅ simulator can be used validly for the measurement of fluorescent materials, even including materials intended specifically for exterior use.     

Color scales in simulated daylight

The pigmentation plan used for production of the color cards made available by the Optical Society of America (OSA) for its Committee on Uniform Color Scales (UCS) was designed in such a manner that the color scales should, within the production tolerances, appear uniform in all phases of daylight. The production specifications were based on D₆₅ of the Commission International de L'Eclairage (CIE) and the CIE supplementary observer (1964) for 10° visual-field subtense. To test for the intended invariance of uniformity of the scales in daylight, for normal observers, the effects on color differences between all nearest neighbors of the OSA colors have been studied for CIE Illuminant C with the 1931 observer, and for a “daylight” fluorescent luminaire (color temperature 6500 K) with both the 1931 and 1964 CIE observers. Although the colorimetric specifications (Y, x, y) of each color card are different for those three illuminant + observer combinations, the color differences computed with the formula of the OSA-UCS committee are, within the production tolerances, unchanged. The purpose of this article is to show how well the aim and expectation is fulfilled—that the uniformity of color differences between nearest neighbors in the scales of the OSA-UCS colors be essentially unchanged for normal observers and for ordinary variations of the quality of natural and artificial daylight. This invariance is found, even for daylight-quality fluorescent-lamp light.     

Color effect of light sources on peridot based on CIE1976 L*a*b* color system and round RGB diagram system

Previous research indicated that the peridot's color is dominated by the selective absorption of visible light caused by ferrous ion, the hue angle of which is in an inverse ratio of the concentration of Fe²⁺. This article focuses on the color effect of peridot under different standard light sources based on the CIE1976 L*a*b* color space system and round RGB diagram system and tries to find the best one for its grading and display. Based on the results of a series of experiments, including electron microprobe analysis, spectrophotometer, UV‐Vis spectrum, standard illumination box, and Munsell neutral color chips, it was suggested that the spectral power distribution and color temperature of a standard light source significantly influence the color of peridot in terms of lightness and chroma, particularly in the hue of peridot. As for color grading and displaying of peridot, standard light source A fails to fit in, and the color of peridot under a fluorescent light source has a higher chroma but a lower hue angle than that under daylight light source. The best choice for grading and displaying peridot is the standard light source D₆₅. It is better to distinguish the hue of peridot when it is calculated by the round RGB diagram system.     

Illuminants for Colour Matching

CIE Illuminant C, although primarily established for colorimetry, was adopted as the basis for colour-matching lamps in both the U.K. (1941) and the U.S.A. (1937). In the U.S.A. it was soon replaced because its colour temperature was too low (6740°K), the replacement eventually being a source having the Abbot-Gibson 7400°K curve. In the U.K. the recent British Standard for colour-matching lamps (BS 950:1967) is based on D 6500, a curve destined to replace Illuminant C as the CIE colorimetric standard for daylight. The requirements of BS 950:1967 have been met by a single source, a fluorescent tube, the cheapness and ease of installation of which permit it to be extremely widely used for colour appraisal as well as for colour matching.     

Smoothing spectral power distribution of daylights

CIE Division 1 entrusted TC 1–74 to investigate the possibility to develop a smooth curve version of the D illuminants. This article investigates the possibility to create such smoothed curves with minimal colorimetric error. Six different smoothing algorithms were investigated; the best method, using a locally weighted regression and smoothing algorithm, enabled a smooth function, where the worst colour difference for a 100 000 sample set was less than ΔE_ab^* = 0.5, comparing calculations using the CIE standard daylight spectrum and the smoothed function. Thus, the smoothed function can be recommended for redefining the daylight spectra for colorimetry without loosing continuity to results using the current calculation tables and for designing daylight simulator spectra. © 2012 Wiley Periodicals, Inc. Col Res Appl, 38, 316–321, 2013     

Daytime colorimetry of retroreflective materials

The daytime color of retroreflective materials is a mixture of sensations caused by diffusely reflected light plus a small amount of retroreflected light, the exact mixture depending on the illumination geometry and the goniophotometric characteristics of the material. The most nearly comparable results of color measurement can be obtained with instruments having 45°/0° geometry instead of sphere geometry. Spectrophotometers or colorimeters can be used. The calibration of these instruments is discussed. Most specifications for the daytime color of retroreflective materials call for the use of CIE standard illuminant D₆₅. However, one can use colorimeters designed to give color coordinates for illuminant C provided that color standards calibrated for D₆₅ are used.     

Detailed analysis of the UV‐adjustment techniques used in paper and graphic industries

Many commercial materials (papers and boards) contain optical brightening agents also known as fluorescent whitening agents. Adequate adjustment of the UV content of a measurement device (e.g., spectrophotometers) is essential for accurate color measurement. As specified in the ISO standards, the UV content is adjusted against an assigned value of an international reference transfer standard, for example, CIE whiteness (D₆₅/10°) for the CIE illuminant D₆₅ or ISO brightness for the C illuminant. Because of the simplicity, these approaches have gained great popularity in papermaking industry. Yet, there has been little evidence indicating how accurate the total spectral radiance factor corresponding to the single assigned value is reproduced. Hence, we present a method that quantitatively evaluates the accuracy of the UV‐adjustment technique, through comparing the total spectral radiance factors obtained from UV adjustment with the assigned ones. This method has been applied to three second‐level international reference transfer standard illuminated by three standard illuminants, D₆₅, C, and D₅₀. We found that the major differences between the assigned spectra and those obtained from the UV adjustments occur in the blue band where fluorescence is strong. At a few wavelengths, the differences may be up to 4–5%. Nevertheless, their color differences corresponding to the assigned spectra and those obtained from the UV adjustments are still smaller than unity (1 ΔE*) for all of the illumination conditions. Two instruments using the representative UV adjusting techniques, for example, the conventional UV‐adjusting with an adjustable (GG395) UV filter and the numerical UV‐filtering, have been studied. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 19–26, 2017     

Measurement and assessment of substrates containing fluorescent whitening agents

White, as a color sensation, can be determined by colorimetric methods of measurement. With other than colorimetric methods, no satisfactory correlation between measured value and visual assessment can be expected. The contribution of hue, saturation and luminosity to the degree of whiteness as found by six formulas widely used in industry was analyzed and the results were plotted in the form of a graph. An easy-to-use nomogram for whiteness determination was developed, based on the CIE 1931 2°-color system. Another nomogram is presented which provides an easy means to determine the hue of a sample treated with fluorescent whiteining agents (FWAs). The new whiteness determination is based on the measurement of true tristimulus values for fluorescent samples using the new International Commission on Illumination standard illuminant D 65. The magnitude of the just perceptible difference in whiteness was determined in a panel test using 11 samples and 22 observers. The results were evaluated statistically. Pending standardization of an illuminant, not only for colorimetric measurements, but also for visual assessment of white samples containing FWAs, it would scarcely seem possible to arrive at a more accurate determination of degrees of whiteness. All visual rankings of fluorescent white substrates are widely scattered around a mean value for the different phases of natural daylight. The relative energy emitted by artificial daylight lamps in the near UV region is insufficient in many cases. Xenon lamps are quite satisfactory for instrumental evaluation. In an internationally approved system, with a known hue preference, it would be possible to compare an objective measured value with each subjective result obtained by visual evaluation.     

Calculation of the Spectral Radiance Factors of Luminescent Samples

It is often desirable to calculate the spectral radiance factor (SRF, the sum of the reflected and fluorescent radiances) which a photoluminescent—commonly called a fluorescent—sample would exhibit if it were irradiated by a standard illuminant, such as CIE D₆₅, which is not available as a source for direct measurement. Several methods described in the literature for calculating the desired SRF from measurements made using available sources are tested experimentally using measurements made on commonly available one-monochromator integrating-sphere spectrophotometers. The choice of the calculation method is shown to be less important than the closeness of the match of the spectral distribution of irradiance on the sample to that from the standard illuminant. This is influenced by both the selection of the experimental source and the effects of the integrating sphere. With all variables properly controlled, comparison of calculated and directly measured SRFs leads to color differences less than one CIELAB unit.     

New method for measuring an optical property of a sample treated by FWA

In this article, a new method for measuring a total spectral radiance factor of a FWA‐treated sample illuminated by a specific standard illuminant is introduced. The method replaces an unstable real fluorescent standard by a bi‐spectral luminescent radiance factor data, which works as a virtual fluorescent standard (VFS) by knowing spectral intensity distributions of illuminations applied to the sample. The method utilizes two illuminations I₁ and I₂ whose relative spectral intensity distributions are different from each other and synthesizes a virtual illumination presenting the identical fluorescent spectral radiance factor to that presented by the standard illuminant with the VFS of the specific bi‐spectral luminescent radiance factor by linearly combining I₁ and I₂ with the suitable weighting factors. The applicability of the method is examined in principle by comparing ISO brightness and CIE whiteness index of fluorescent standard paper as a test sample obtained by this new method to the assigned values. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 195–200, 2007     

The effect of glass transition on gas permeabilities

Gas permeabilities of a copolymer of acrylonitrile and methyl acrylate were examined at the temperature range of 25° to 80°C. The change of activation energy of gas permeability constant at the glass transition temperature (65°C) was observed with N₂, Ar, O₂, and CO₂, but no change was observed with He. The observation of the change of slope of the Arrhenius plot of gas permeability is discussed as a function of the diffusion constant (D) of a permeant gas at the glass transition temperature (T_g). The change occurs only if the value of D at T_g is smaller than a certain value (i.e., 5 × 10^?8), according to the analysis of data appearing in the literature.     

Intercomparison on measurement of (total) spectral radiance factor of luminescent specimens

This article is based on a CIE Technical Report that describes an intercomparison of measurements of the (total) spectral radiance factor (SRF) of luminescent materials. Seven luminescent specimens were provided as painted panels: two were white containing fluorescent whitening agents and five were chromatic [green, yellow, orange (two), and red]. The SRFs were measured with direct specimen illumination by a source simulating CIE D₆₅. The SRFs that would have been obtained under D₆₅ illumination were calculated by a method selected from among those previously studied by the committee. Data sets from four laboratories (one supplying two sets) gave useful results. The mean CIELAB color difference from the mean of the five data sets was 2.6 units averaged over all data sets and specimens, with a range among specimens from 1.9 to 3.4 units and among data sets from 1.5 to 4.2 units. The mean color difference from the results of an arbitrary reference laboratory was 3.6 units averaged over all data sets and specimens, with a range among specimens from 3.0 to 4.2 units and a range among data sets from 2.1 to 5.3 units. Maximum values of the SRFs varied considerably among the data sets, from 11.4% to 33.6% among the samples. It was the CIE Technical Committee's feeling that these results are representative of the present state of the art for this measurement, despite the relatively poor performance seen.     

Gas permeation of polymer blends. I. PVC/ethylene–vinyl acetate copolymer (EVA)

The transport behavior of O₂ and N₂ were studied for series of physical blends of PVC with EVA having different vinyl acetate (VAc) contents in the EVA (45 and 65 wt-%) and using different milling temperatures (160° and 185°C). The polymer blends were further characterized by dynamic mechanical measurements, density measurements, and x-ray diffraction. At higher VAc content in EVA and with higher milling temperature, the rate of permeation (P) and the rate of diffusion (D) decrease, and the activation energy of D (from Arrhenius plots) increases. Furthermore, the experimental density values of PVC/EVA-45 blends agree well with calculated values, assuming volume additivity of the two components, while those of PVC/EVA-65 blends are higher than the calculated densities. These results are interpreted as due to denser packing of polymer molecules and increased PVC-EVA interaction at higher VAc content and with higher milling temperature, indicating better compatibility between the blend components. The x-ray diffraction data give no evidence of crystallinity. Sharp increases in P and D values at about 7.5% EVA (by weight) are found for PVC/EVA-45 blends (in agreement with our previous work) but not for PVC/EVA-65 blends. This is interpreted as due to a phase inversion at increasing EVA content in the former blends but not in the latter blends. The dynamic mechanical measurements show that the PVC/EVA-65 blends milled at 160°C behave largely as semicompatible systems with maximum interaction between the two polymers at compositions of about 50/50 by weight.     

Visible dichroism of polypropylene–disperse dye system at high temperatures

The dichroism of polypropylene film dyed with C. I. Disperse Yellow 7 was investigated at various temperatures up to 160°C. The dichroic value D drops as the temperature is raised. So long as the amorphous structure does not change irreversibly, D changes reversibly with temperature. The experimental results agree qualitatively with those obtained on poly(ethylene terephthalate) in our previous paper, although the effect of temperature on the extent of the reversible change in D is larger in PP than in PET. The plot of D versus temperature exhibits breaks at 40°–50°C (T₀), 70°–80°C (T₁), and 115°–120°C (T₃). These temperatures agree with the transition points of polypropylene in the literature. From the change in the intrinsic dichroism D₀ with temperature, it is concluded that the decrease in D at high temperatures is due to the drop of D₀ caused by the disorientation of dye molecules in the amorphous region, while the amorphous polymer chain is not disoriented. Such a conclusion is supported by the fact that Δn of a heat-set specimen is kept constant during heating, in contrast to D.     

Experimental failure analysis of two‐serial‐bolted composite plates

In this study, a failure analysis of two‐serial‐bolted glass‐fiber‐reinforced epoxy composite plates was performed. To determine the influences of the joint geometry and stacking sequences on the bearing strength and failure mode, parametric studies were carried out experimentally. Three different geometrical parameters—the ratio of the edge distance to the hole diameter (E/D), the ratio of the plate width to the hole diameter (W/D), and the ratio of the distance between two holes to the hole diameter (K/D)—were considered. For this reason, the E/D, W/D, and K/D ratios were designed to range from 1 to 5, from 2 to 5, and from 3 to 5, respectively. Furthermore, the tests were performed with various preload moments (2, 3, 4, and 5 Nm) and without any preload moments (0 Nm). Because of the observed effect of the material parameters on the failure behavior, composite laminated plates were stacked in two different stacking sequences: [0°/0°/30°/30°]_s and [0°/0°/45°/45°]_s. The experimental results indicated that the failure response of the two‐serial‐bolted joints were strictly affected by the material parameters, geometrical parameters, and values of the applied preload moments. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Quantification of illuminant metamerism for four coloration systems via metameric mismatch gamuts

Illuminant metamerism was evaluated by generating achromatic metamers for an acrylic-enamel coating, an acrylobutadiene styrene polymer, a polyester textile, and a nylon textile using computer colorant formulation techniques. The tristimulus matching algorithm used to generate the metamers was based on Kubelka-Munk turbid media theory. By definition, each set of metamers that were formulated to match under CIE illuminant D₆₅ for the 1964 CIE standard observer would mismatch under a test illuminant, forming a gamut of colorimetric coordinates. These metameric mismatch gamuts were evaluated quantitatively using multivariate statistics. Illuminants A, F2, and F11, representing incandescent, cool-white fluorescent, and narrow-band fluorescent, respectively, were used as test illuminants. Illuminant similarities, coloration system similarities, tristimulus variability, and reference illuminant selection criteria were evaluated.     

Temperature stability of vitamin D2 and color changes during drying of UVB-treated mushrooms

The study investigates the effect of drying temperature on vitamin D₂ content and color changes of UVB-treated shiitake (Lentinula edodes), oyster (Pleurotus ostreatus), and white and brown button mushrooms (Agaricus bisporus). Fresh samples were UVB treated up to 1.5?J/cm² for 20?min at 25°C and either dried in a high precision dryer (temperatures: 40, 60, 80°C, specific humidity: 10?g/kg, air velocity: 0.6?m/s) or frozen at ?25°C, and then freeze-dried (pressure: 0.28?mbar). Vitamin D₂ content was not negatively affected by the increased temperatures of the drying air. The highest content of vitamin D₂ was detected in freeze-dried (171.84?µg/g) and hot-air dried shiitake at 60°C (169?µg/g), followed by oyster (121.96?µg/g), whereas the lowest amount was observed in brown button mushrooms at 40°C (34.65?µg/g). Although vitamin D₂ indicated a remarkable stability even at 80°C, the dried samples were characterized by intensive tissue darkening.     

Bearing strength of pin‐connected polymer composites subjected to dynamic loading

In this study, static load bearing strength of pin‐connected carbon fiber‐reinforced polyphenylenesulphide (PPS) composites that have [(0°/90°)]_3s stacking sequence was investigated. Firstly, the samples were loaded dynamically, and then the same samples were loaded statically. The results obtained from this sequential experiment were compared with the results obtained from samples that were loaded only statically. In addition, the fatigue life and failure mechanisms were investigated with respect to the selection of the geometrical parameters. Dynamic and static loading experiments were performed according to the ASTM STP 749 and ASTM D953 standards, respectively. To obtain optimum load bearing values, the ratio of distance between the edge and hole center to hole diameter (E/D) and ratio of sample width to hole diameter (W/D) has been systematically changed. According to the experimental results, maximum load bearing values have been obtained when E/D ratio was equal to 2. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Colour-Rendering Assessment of Ultraviolet Emission in Light Sources

A number of different ways for the assessment of the ultraviolet emission of light sources are surveyed. A method of assessment using a set of three hypothetical near-white fluorescent samples is described in which the sum of the excitation curves for the fluorescent samples has been made to resemble the spectral emission curve of Standard Illuminant D₆₅ when plotted on a quantum scale of ordinates. The chromaticity shift of each fluorescent sample produced when the reference illuminant D₆₅ is replaced by the test illuminant is used to produce a special fluorescent-rendering index in a manner analogous to that used for colour-rendering indices. The index is scaled in such a way that values greater than 100 indicate an excess of ultraviolet for the test lamp compared with the reference illuminant. Special fluorescent-rendering indices are given for a number of real lamps, and they accord reasonably well with the known performance of the lamps.