Planckian Locus Research Articles

Quantitative Determination of Flame Color and Its Determining Factor in Hydrocarbon/Air Laminar Diffusion Flames.

The color of laminar diffusion flames burning propane, methane and ethylene was determined by chromaticity coordinates (x, y) defined by the CIE 1931 standard colorimetric system. The differences in flame color attributed to burning condition and fuel types were examined with a colorimeter. Spectroscopic measurement and numerical analysis using a simplified radiation model were also carried out to discuss the determining factors of the flame color. The relation between x and y measured on the central axis of the flames was expressed in the experimental equations. The (x, y) in the luminous region plotted on a chromaticity diagram changed along Planckian locus with the burning conditions. The contribution of the thermal radiation of soot particles and the chemiluminescence to the flame color was successfully evaluated by introducing the concept of additive mixture of color stimuli. The (x, y) profiles from the numerical analysis agreed well with the experimental results.

The Colors of the Stars

The brightness and colors of the stars have fascinated observers of the night sky for millennia. It is difficult however, to portray the depth and amount of visual information of the heavens on actual displays. This paper applies principles of reproduction, color science, and perception, to generate attractive and information-rich starfield images.Although the casual appearance of stars is bluish-white, starlight actually ranges along the entire black-body locus. Scotopic (night) vision cannot see the full color that would result, but we can use color as a natural way to depict the various types of stars and their surface temperature. This is done in three steps. First, a relation between the astronomical color index of a star (the difference in power between two historically established spectral bands) and the star's effective surface temperature is obtained. From this black body temperature, colorimetric coordinates are calculated. Finally, the colorimetric values are converted to device coordinates for the display.

高演色形高圧ナトリウムランプの定色温度化制御条件

In order to find the electrical conditions for operating high-pressure sodium lamps with a constant correlated color temperature to get high color rendering from lamps of the same type having different correlated color temperatures, we conducted a set of experiments. We operated 150W lamps under various electrical conditions to determine the relationship between the correlated color temperature and the electric properties. Based on the results, we derived the following formula:Tcp=a·W1a+b· V1a+c, where Tcp is the correlated color temperature, W1a is the lamp power, Via is the lamp voltage, and a, b, and c are constants. This formula gives the electrical conditions of W1a and V1a for a specific value of Tcp. The same formula is also applicable to lamps of other wattages by changing the values of the constants a, b, and c. If the correlated color temperature of the lamp is limited to±150K by controlling these electrical conditions, the deviation of the lamp from the black body locus is preferable for vision. In the same manner, we derivedTcp=d· V1a+e· I1a+f, where Tcp is the correlated color temperature, V1a is the lamp voltage, I1a is the lamp current, and d, e, and f are constants. The sensing circuits for a specific value of Tcp can be the simple sensing circuits of V1a and I1a.

Twilight and daytime colors of the clear sky

Digital image analysis of the cloudless sky's daytime and twilight chromaticities challenges some existing ideas about sky colors. First, although the observed colors of the clear daytime sky do lie near the blackbody locus, their meridional chromaticity curves may resemble it very little. Second, analyses of twilight colors show that their meridional chromaticity curves vary greatly, with some surprising consequences for their calorimetric gamuts.

Determination of correlated color temperature based on a color‐appearance model

AbstractThe present method of determining the correlated color temperature of an illuminant is based on the obsolete CIE 1960 u,v chromaticity diagram. A new method is proposed that is based on Hunt's color‐appearance model for unrelated colors. Analytic functions were derived for the blackbody locus in appearance space to simplify the computation. CCT was calculated for some light sources and the results were compared to those obtained by the present method.

Combination of illuminants and its effect on colour rendering

It is shown how to represent the relation between a spectral power distribution (SPD) and its general colour rendering index by means of three spectral parameters By, Gy and Ry. Using this parametric approach, the combination of two illuminants and its effect on colour rendering are analysed. The main conclusion is that the usual illuminants (whose chromaticity lies near the black-body locus) behave as if they could be classified into two classes. If two SPDS are mixed in a proportion α, the law a(α) is concave without maximum if they belong to the same class and with maximum if not. Some variations to this law may occur when the illuminants differ greatly in chromaticity.

Effect of filters upon object color naming.

Color constancy refers to the phenomenon that the perceived colors of objects are largely unaltered by changes in the illuminant or by viewing through colored filters. Deviations from perfect constancy, induced by filters similar to ophthalmic tints, were investigated in this study. Munsell color chips were forced-choice categorized into R, Y, G, or B. This accurately located the boundaries between these colors on the chip color circle. Testing was performed through 23 different adaptive conditions and chromaticity shifts created by filters. The technique simulates real world situations in which the chromaticity of the objects and the adaptation of the observer both change. Generally, color constancy held quite well. The boundaries between the four colors shifted for some filters, indicating some deviation from perfect constancy. Red filters resulted in more color chips appearing red, blue and green filters resulted in more chips appearing blue, and filters along the Planckian locus resulted in more chips appearing green.

Spectral distribution of global and diffuse solar radiation in Ny-Alesund, Spitsbergen

Spectral distributions of solar radiation were measured over the wavelength range 300 to 800 nm in Ny-Alesund (7855'N, 1 I56'E). The apparatus consisted of a grating monochromator with an automatic scanning system, an integrating sphere supposed to give a good picture of the radiation received on a horizontal surface from the whole celestial hemisphere, a photomultiplier tube with S-20 response, and a strip chart recorder. Great importance was attached to the calibration procedure, which was carried out by means of a 1000 W quartz-iodine lamp with known spectral irradiance (calibration traceable to NBS, delivered by Eppley Laboratory). The main part of the discussion is based on relative spectral distributions. Spectra in absolute units were obtained by comparison with simultaneous pyranometer recordings of total solar energy, which by means of filter measurements could be reduced to the same wavelength range as for the spectral scans. In addition, the pyranometer recordings served as a means of judging whether the radiation conditions were sufficiently stable to give reliable spectral curves. Spectral measurements were made of radiation from: (I) clear sky and sun, (2) clear sky alone, a sky totally covered by (3) clouds or (4) fog, ( 5 ) zenith clear and (6) zenith overcast sky. The spectral curves of (I), (3), (4) and (6) do not differ very much, but deviate markedly from those of (2) and (5). An overcast sky has relatively higher spectral irradiances towards the short-wave end of the spectrum than the corresponding spectrum for a clear sky. Three groups of solar altitudes are considered, with mean altitudes of about 30 (noon), 18 (evening), and 10 (night). Comparison of the spectra of these groups clearly reveals the effect of increasing absorption by atmospheric gases with decreasing solar altitude. At the same time, due to growing importance of selective scattering processes, the proportion of long-wave to short-wave irradiances increases. The Ny-Alesund noon spectrum for clear-sky global radiation seems to agree quite well with spectra from lower latitudes referring to a correlated colour temperature close to 6500 I(. This also applies to the CIE standard daylight source De5. Considering the spectra in absolute units, it turns out that while the spectral irradiances of global radiation on an overcast day are about 40% of those for a clear day in the ultraviolet part, the corresponding relation decreases to about 30% in the near infrared. Sky radiation on a clear day is responsible for more than half of the ultraviolet content of global radiation, but does not contain more than about 5% of the near infrared radiation. Comparable spectra from Nottingham and Pretoria seem to be considerably more influenced by aerosol scattering. Nevertheless Pretoria has as high irradiances in the ultraviolet as Ny-Alesund, in all probability due to a smaller ozone absorption at the former station. A Few characteristic deductions of the spectral distributions are discussed. For situations with a clear sky daylight illuminances calculated on the basis of absolute spectral irradiances and the spectral sensitivity of the human eye agree well with directly observed illuminances for the same solar altitudes. The chromaticity co-ordinates representing different phases of daylight in Ny-Alesund are slightly on the green side of the black body locus. Somewhat unexpected is the fact that daylight at midnight has a slightly higher correlated colour temperature (is more bluish) than that observed during the middle of the day. Estimates demonstrate the significant part played in this connection by the ozone absorption in the Chappuis bands.

An algorithm to calculate correlated colour temperature

AbstractA new algorithm to calculate correlated colour temperature is given. This algorithm is based on a rational Chebyshev approximation of the Planckian locus in the CIE 1960 UCS diagram and a bisection procedure. Thus time‐consuming search procedures in tables or charts are no longer necessary.

A metal halide lamp with ultra-high-color rendering property

In the field of the high intensity discharge lamp, a metal halide lamp with ultra-high-color rendering property that has the general color rendering index (Ra) of over 99 has been developed. Up to now by the fillings of SnBr2 and Snl2,separately or combinationally, at most Ra=94,though maximum in the highintensity discharge lamp, was attainable and its special color rendering index for red color (R9) was under 80. By the fillings of SnBr2+Cal2, the molecular spectrum of CaBr that radiates at the wavelengths of 625 nm and 627 nm compensates for the shortage in the red zone spectrum of SnBr2-Snl2 fillings and it makes possible for the chromaticity of the new lamp to lie almost on the Planckian locus. It is attainable in the new lamp that Ra value is over 99, all special color rendering indexes are over 98, color temperature is 4000 K ∼ 5000 K, and luminous efficacy is about 60 lm/W (at 400-watt input power).

Color rendering Optimization of High-Pressure Mercury Vapor Lamps

High-pressure mercury vapor (HPMV) lamps were studied in their color appearance and color rendition to obtain appropriate properties to be introduced to the general indoor lighting.The general color rendering index in this type of lamps was examined and it was realized that the blue-green emitting phosphors were effective to raise the index when combined with the current red emitting phosphors.A series of new Ba-Mg-aluminate phosphors was developed and this proved to be suitable for application to HPMV lamps. These phosphors have two emission bands having peaks at 450 and 520nm, and maintain high efficacy at elevated temperature.The color appearance and the appearance of human complexion were optimized mainly through subjective estimations of various test lamps.Basing on the estimation results, the final lamps were designed to the color temperature of 4200 K and DUV of+4.0 (the deviation from blackbody locus). These lamps seemed suitable to the general indoor lighting, they go well with standard fluorescent lamps or natural daylight. The distinctive feature of this new type of lamps is in its temperate appearance.In order to appreciate the feature prorerly, a new view point is also suggested, viz. the numerical evaluation of color rendering properties of this kind of lamps.

Corrections for chromatic adaptation in the determination of colour rendering indices. Part 2

The increase of general index Ra for some illuminants having chromaticities on the purple side of the Planckian locus compared with those on the green side is only partly due to the von Kries correction in the revised CIE method, and the location of the Judd PDT primaries used has little effect. Uniformity of the u, v diagram in the area involved is questionable, and its geometry is a likely cause of some of the results. Gamut areas of the eight test colours suggest a correlation between colour discrimination and colour rendering but only for certain illuminants. Variable sensitivity of Ra to the spectral distribution of the illuminant is demonstrated; for wavelengths near 580 nm there is evidence of a marked effect on the index.

Corrections for chromatic adaptation in the determination of colour rendering indices

The revised CIE Test Colour method for determining the colour rendering properties of light sources introduces a von Kries type of correction to allow for chromatic adaptation of the eye. Calculations have been made to discover the effect of this correction in comparison with other possible corrections, including that used in the original CIE method. A wide variety of spectral power distributions has been used to represent the test light sources, including many types of real lamps and some theoretical distributions. In general the von Kries correction produces an increase in the general index Ra if the chromaticity of the illuminant is on the purple side of the Planckian locus. Possible reasons for this bias are discussed. Details are given of a method of calculation with the use of 3 x 3 matrices as applied in colour television work.

Color and Efficiency of Fluorescent and Fluorescent–Mercury Lamps

Calculations are presented for the range of color and luminous efficiency to be expected when typical phosphors are employed with either low-pressure or high-pressure mercury-vapor discharges. In the case of binary phosphor blends corresponding to colors lying on the planckian locus, maximum efficiency is always obtained when the wavelengths of peak emission for the two components lie near 445 and 580–590 nm.

Perception of white in a 10 degree field.

The ranges of stimuli that are perceived as white were investigated in a dark surround. Stimulus light was supplied by three gas-filled tungsten lamps modified with three glass filters and an opal glass. Chromaticity and luminance were changed by adjusting distances between the opal glass and each of the lamps. We employed the method of minimal changes and the constant-stimulus method. In the former case, the luminances of two of the stimulus components were kept fixed, while the observer was allowed to change the luminance of the other component. Ranges of chromaticities reported as white with a probability of 0.5 or more by three observers were located along straight lines near the blackbody locus, at color temperatures higher than 5500 K. With the constant-stimulus method, 45 observers judged 18 stimuli located at different positions in the neighborhood of CIE standard source C in the chromaticity diagram, all of which had luminances equal to 20 asb. The result was that an oval range of points reported as white with a 0.5 probability was obtained around CIE standard source C.

Typical Spectral Distributions and Color for Tropical Daylight

The recording spectroradiometer for collecting data on the spectral distribution of daylight at Delhi is briefly described. The chromaticities calculated on the 1931 CIE system from 187 spectral curves, recorded over about a year, are presented and their distribution about the Planckian locus is discussed. The typical spectral distributions for the correlated color temperatures 4800, 5500, 6500, 7500, and 10 000°K, derived from the characteristic vectors are presented and discussed.

楕円近似による白色感域

The experimental apparatus used of three gas-filled tungsten lamps, three glass filters and a flashed opal glass. The flashed opal glass was illuminated by three colored lights actuated by the three lamps in conjunction with the three filters. The transmitted light through this glass was the stimulus light. The distance between the surface of the flashed opal glass and each of the lamps could be varied continuously by means of a driving motor.The chromaticity and the luminance of the stimulus light were calibrated by a spectrophotometer, a phototube, etc. The positions of the two of the three lamps were fixed so that the locus of the stimulus light was straight on the chromaticity diagram and the luminance in the white sensory region was about 20 abs. The observers changed the position of remaining lamp by the method of minimal changes to determine the white points.The results are summarized as follows.1) The white points were determined which could be judged white with a probability of 0.5 by three observers experienced in color experiments, and the white sensory region was obtained from these white points by elliptical approximation. It was found that the white region varied in position in the different observers, but for every observer, it was located below the black body locus. This is different from a common opinion that the central point of white on the chromaticity diagram is the chromaticity coordinate of the C. I. E. standard source C. In the experiment, the light of the C. I. E. standard source C was recognized frequently as white only by one of the observers.2) The white sensory region which was judged at least as white by any one of the three observers was a rather broad zone along the downside of the black body locus (color temperature 4, 500°K to 25, 000°K).3) The white sensory region which was judged at least once as white by an observer inexperienced in color experiments was very wide and presented an approximate ellipse having the normal line on the black body locus (color temperature 4, 500°K to 30, 000°K).4) When the surrounding field was illuminated by a red light or a green light or a blue light or a tungsten lamp, the white sensory region moved towards the chromaticity of the adaptation field in all the three experienced observers.5) When the white judgement was made arbitrarily only in each experiment, the variation was 0.007 to 0.02 on the x-y chromaticity diagram. When the same judgement was made ten times in each experiment for a given time, the variation for the time was 0.004 to 0.008.

Spectral Distribution of Typical Daylight as a Function of Correlated Color Temperature

Spectral distributions of 622 samples of daylight (skylight, and sunlight plus skylight) have been subjected to characteristic vector analysis, as composite data and in three subgroups (99 distributions measured by Budde; 249, by Condit; and 274, by Henderson and Hodgkiss). The chromaticity coordinates (x,y) computed from these distributions have been compared with direct visual determinations of chromaticity coordinates of daylight by Nayatani and Wyszecki, and by Chamberlin, Lawrence, and Belbin. It was found that the chromaticities indicated by the spectral distributions and by direct visual colorimetry cluster about the curve: y = 2.870x−3.000x2−0.275. This curve of typical daylight chromaticities falls slightly on the green side of the Planckian locus. From the mean and the first two characteristic vectors of the composite data, spectral distribution curves have been reconstituted by choice of scalar multiples of the vectors such that the chromaticity points fall on the curve of typical daylight chromaticities at places corresponding to correlated color temperatures of 4800°, 5500°, 6500°, 7500°, and 10 000°K. The representative character of these reconstituted spectral-distribution curves has been established by comparison with the measured curves from each subgroup yielding the closest approximation to the same chromaticities. The agreement so found suggests that this family of curves is more representative of the various phases of daylight between correlated color temperatures 4800° and 10 000°K than any previously derived distributions.

Lines of Constant Correlated Color Temperature Based on MacAdam’s (u,υ) Uniform Chromaticity Transformation of the CIE Diagram

The chromaticities of hot bodies (such as the filaments of incandescent lamps) and the various phases of daylight are often expressed on the color–temperature scale. Such chromaticities do not usually coincide precisely with those of the blackbody at any temperature, but are specified by giving the temperature of the blackbody yielding the nearest chromaticity match. Thus each chromaticity point near the Planckian locus is correlated with a chromaticity point on it, and the color temperature corresponding to the Planckian chromaticity is called the correlated color temperature. If the decision as to the nearest Planckian chromaticity is based on a uniform-chromaticity-scale (UCS) diagram, the chromaticity points correlated with each Planckian chromaticity fall on a straight line (isotemperature line) on the chromaticity diagram normal to the Planckian locus at that Planckian chromaticity. The UCS diagram proposed by MacAdam in 1937 and recommended in 1959 by the International Commission on Illumination (CIE) has been used here to define the isotemperature lines. Graphs showing the Planckian locus and the isotemperature lines both in the CIE (x,y)-diagram and in the MacAdam CIE (u,υ)-diagram are shown at every 10 microreciprocal degrees for all color temperatures higher than 1515°K.

Photometry and Colorimetry of Natural Objects

Apparent luminances and colors of natural objects were measured by three types of telephotometers, which were designed originally as telephotometers to measure distant light sources and extinction of light in the atomsphere, but used as brightness meters in this study. Two of them are based on the photoelectric and photographic spectroradiometric methods and the third on the visual color matching with a comparison light consisting of an incandescent lamp and three Lovibond glasses.The range of the luminance observed in the daytime for the sky near the horizon is 6, 600-7, 400 cd/m2 on a clear day and 1, 200-5, 500 cd/m2 on an overcast day. The luminance of the snow surface in the vicinity of the instrument on a clear day. ranging 10, 000-14, 300 cd/m2, is largest among the natural objects. The luminance of other objects near the observer is generally much smaller than that of the sky. But with the increasing distance it approaches the luminance of the sky.The colors of natural objects are chiefly yellow green or yellow when the distances are small. With the increasing distance their chromaticity points on the chromaticity diagram move into blue green region along the blackbody locus. The domain, in which the chromaticity points of natural objects aredistributed, is fairly wide in the direction extending from blue to yellow green approximately parallel blackbody to the locus but much narrower in the direction vertical to it. Foliage at a distance less than 1 kilometer has yellow-greenish colors of dominant wavelength 542-582 mμ. Field crops and vegetables have a dominant wavelength of 561-570 mμ. Their colors are most saturated among the observed objects, having a maximum excitation purity of 52%. Earth colors are yellow of 561-585 mμ. With the increasing distance the colors of natural objects changes to blue. The chromaticity points for buildings, sea, snow, sky and distant objects are distributed over a small area around the achromatic point and its blue side.Spectral distribution curves for natural objects are characterized by their flat appearance, especially when the distances are large, in accord to the low saturation of their apparnet colors.These data were applied for discussing the visual range of colored lights, for instance signal lights, and objects through the atmosphere in the daytime.