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Colorimetry
Published in John G. Webster, Halit Eren, Measurement, Instrumentation, and Sensors Handbook, 2017
Illuminants and sources are sometimes confused. Sources are actual physical entities that produce visible radiation, whereas an illuminant may only be a numerical table of values of a spectral power distribution. Initially, the CIE recommended three light sources for colorimetry in 1931. Source A, which is still in use, is an incandescent, tungsten filament light. An illuminant is the spectral power distribution of a light source. Thus, Illuminant A is the spectral power distribution of Source A. An illuminant may be defined, even when a source for that illuminant does not exist. Examples of illuminants without sources are the D series of illuminants recommended by the CIE. The D illuminants represent various phases of daylight. Illuminant D65 represents average daylight and is the most common illuminant used in colorimetry. No sources were recommended for the D series of illuminants.
Light Sources
Published in Toru Yoshizawa, Handbook of Optical Metrology, 2015
This method of grading of colorimetric shifts obtained in test samples is called CIE test-color method, and is applicable for light sources that have chromaticity close to the reference illuminant. The CRI is a measure of how well balanced the different color components of white light are. A standard reference illuminant has a general CRI Ra = 100. The two primary standard illuminants are the CIE Standard Illuminant A (representative of tungsten-filament lighting with color temperature of 2856 K) and the CIE Standard Illuminant D65 (representative of average daylight with color temperature of 6500 K). Color rendering is a very important property of cold illuminants such as LEDs and discharge lamps, whose emission spectrum contains certain wavelengths. More information about the test-color samples, standard colorimetric illuminants and observers, and CRIs can be found in related references [3,5,24,45] and CIE reports [47–50], as well as in the literature on LEDs [9–11].
Basic concepts in photometry, radiometry, and colorimetry
Published in John P. Dakin, Robert G. W. Brown, Handbook of Optoelectronics, 2017
Figure 8.13 shows the trace of the (x, y) chromaticity coordinate of blackbody radiation (see Section 8.4.4) at its temperature from 1600 to 20,000 K. This trace is called the Planckian locus. The colors on the Planckian locus can be specified by the blackbody temperature in kelvin and is called color temperature (see also Section 8.3.9). The colors around the Planckian locus from about 2500 to 20,000 K can be regarded as white, 2500 K being reddish white and 20,000 K being bluish white. The point labeled “Illuminant A” is the typical color of an incandescent lamp, and “Illuminant D65” the typical color of day light, as standardized by the CIE [41]. The colors of most traditional lamps for general lighting fall in the region between these two points (2800–6500 K). Strictly speaking, color temperature cannot be used for colors away from the Planckian locus, in which case correlated color temperature (CCT) is used. CCT is the temperature of the blackbody whose perceived color most closely resembles that of the light source in question [2]. Due to the nonuniformity of the x, y diagram, the iso-CCT lines are not perpendicular to the Planckian locus on the x, y diagram (see Figure 8.13). To calculate CCT, therefore, one of the improved uniform chromaticity diagrams is used. Due to the long tradition, CIE specifies that the 1960 (u, v) diagram (now obsolete for other purposes) be used, where the iso-CCT lines are perpendicular to the Planckian locus by definition. From (u′, v′) coordinates, (u, v) can be obtained by u = u′, v = 2v′/3. On the (u, v) diagram, find the point on the Planckian locus that is at the shortest distance from the given chromaticity point. CCT is the temperature of the Planck’s radiation at that point. A practical way of computing CCT is available [44].
Estimation of daylight availability in Kolkata and approximation of indoor daylight levels for different daylighting methods
Published in International Journal of Sustainable Energy, 2022
Sourin Bhattacharya, Sudipta Majumder, Subarna Roy, Imran Hossain Sardar
Daylight is considered to be the best source of illumination for colour rendering, it can provide 110 lumens of luminous flux per Watt of solar radiation (a luminous efficacy of 110 lm/W) and its spectra closely match the human spectral visual response (Kandilli and Ulgen 2008). However, the luminous efficacy of daylight varies with sky clearness, solar altitude and atmospheric conditions. It is 70–105 lm/W for direct sunlight, approximately 130 lm/W for the clear sky and around 110 lm/W for the overcast sky under diffuse skylight (Littlefair 1985). Furthermore, daylight is a natural, temporally variant (Ferenčíková and Darula 2017), dynamic source of illumination (Deroisy and Deneyer 2017) and its spectral power distribution (SPD) for the 330 –700 nm wavelength range was measured by Henderson and Hodgkiss (1963). The CIE Standard Illuminant D65 is a hypothesised illuminant to simulate the naturally occurring standard illumination conditions under daylight and attempts have been made to design and simulate the D65 (Powell 1996; Lam and Xin 2002). Moreover, the human circadian clock is entrained to sunlight or more specifically the 24-h solar cycle (Duffy and Wright Jr 2005; Roenneberg et al. 2013; Woelders et al. 2017) and exposure to daylight assumes much importance in the everyday life of human beings since human health and wellness are intricately linked to it and various studies have indicated that daylight is preferred to artificial illumination in different settings or fields of human activity (Markus 1967; Cuttle 1983; Heerwagen and Heerwagen 1986; Galasiu and Veitch 2006).
Judgment of White Appearance for Surface Colors under Individual and Simultaneous Observations
Published in LEUKOS, 2018
Whiteness specification for surface colors is also important in the surface color industry, because whiteness is commonly associated with the quality and cleanness of a surface. The CIE whiteness formula, the most widely used formula, was also developed based on psychophysical experiments [CIE 2004a]. It characterizes the whiteness of a surface color under CIE Illuminant D65, with a perfect reflector being assigned to have a value of 100. For surfaces containing fluorescent whitening agents (FWAs), the FWAs absorb the ultraviolet and violet radiations contained in D65 and re-emit blue light, which simultaneously increases the luminance factor and introduces blue tint to enhance the whiteness appearance. Thus, FWA-enhanced whites typically have CIE whiteness values beyond 100. Past studies, however, found that the CIE whiteness formula failed to characterize the whiteness under the illumination other than D65 [Wei and others 2017], especially under typical blue-pumped white light emitting diodes (LEDs) [Houser and others 2014; Wei and others 2014], and samples were still perceived as white though they were outside the CIE whiteness limit [Ma and others 2016; Uchida 1998].
Comparing the potential of different strategies for colour tuning in thin film photovoltaic technologies
Published in Science and Technology of Advanced Materials, 2018
Enrique Pascual-San José, Antonio Sánchez-Díaz, Marco Stella, Eugenia Martínez-Ferrero, Maria Isabel Alonso, Mariano Campoy-Quiles
Illuminant. It corresponds to the theoretical lighting source of visible light defined by its spectral power distribution. The illuminant is typically a fixed variable for a given application. Among illuminant sources, standard daylight illuminant D65 is often chosen as model light for indoor conditions, while AM1.5G solar spectrum is the common choice as sunlight reference for colour determination. Although illuminants have different spectra, the colour appreciation tends to be very similar to a typical healthy human eye response. The corresponding International Commission on Illumination (CIE) coordinates for these illuminants are (x,y) AM1.5G = (0.3322,0.3443) and (x,y) D65 = (0.3129,0.3295).