Correlated color temperatures

Typical values of correlated color temperature (CCT) and color rendering index (CRl) for some common electric light sources. 

The International Commission on Illumination (CIE) International Commission on Illumination (CIE) has defined a set of standard illuminants to be used for colorimetry (International Commission on Illumination 1996). Figure 3.21 shows the CIE illuminants A, C, Z>5o, Z>55, Z>65, and D15. Illuminant A represents the power spectrum of light from a black-body radiator at approximately 2856 K. If this type of light is required for experiments, a gas-filled tungsten filament lamp that operates at a temperature of 2856 K is to be used. Illuminant Z>65 represents a phase of daylight with a correlated color temperature of approximately 6500 K. The CIE recommends to use this illuminant wherever possible. 

Similarly, illuminants D o, D55, and >75 with correlated color temperatures of approximately 5000 K, 5500 K, and 7500 K respectively were also defined. These illuminants should be used whenever cannot be used. 

Judd DB, MacAdam DL and Wyszecki G 1964 Spectral distribution of typical daylight as a function of correlated color temperature. Journal of the Optical Society of America 54(8), 1031-1040. 

For instrumental evaluation spectrophotometers are preferred. The colorimetric values obtained depend on the instrument and its instantaneous state (chiefly the sample illumination conditions) and must be controlled by suitable methods [174], The influence of the instrument can be eliminated by conversion to the standard illumination D 65, representing daylight with a correlated color temperature of 6504 K [175]. The degree of whiteness and the tint values can then be calculated from these colorimetric data with appropriate formulas. A selection of currently used whiteness formulas can be found in [176,177], For recent attempts at standardizing the assessment methods for white objects, see [9,178-185],... 

The actual color appearance of light that comes from a "black body" source is called its color temperature or chromaticity. Correlated color temperature (CCT) is the terminology used when referring to the color of an artificial source. Because the color temperature of an artificial source will most likely not fall on the normal black body curve, it is the accepted practice to refer to their temperature as the temperature of the closest CIE daylight (D) temperature value. Hence, a CCT of 6500 K means that its color temperature is closest to that of CIE D6500 daylight standard. 

Table 3 Some Sources That Have Been Used for Pharmaceutical Photostability Testing and Their Respective Color Rendering Indexes and Correlated Color Temperatures...

Abbreviations, f, fluorescent CRI, color rendering index CCT, correlated color temperature. 

Fluorescent lamps are rated in catalogs by two indices, their correlated color temperature (CCT) and color-rendering index (CRI). The CCT is the temperature of a black body whose chromaticity most nearly matches that of the subject light source. Because a fluorescent lamp only approximates a "black body," it is called correlated to distinguish it from actual. The CRI on the other hand is a subjective method developed by the CIE in which eight test colors are viewed under the test and a reference lamp(s) and its ability to reproduce the test colors numerically rated. Both numbers are not absolute but useful in selecting lamps for color rendering applications. 

The color of a light source is typacally characterized in terms of its color temperature. If the x,y coordinates of an illumination source do not exactly sit on the blackbody locus, the color of a light source is characterized in terms of its CCT. The CCT is the temperature of a blackbody radiator that has a colour that most closely matches the emission from a non-blackbody radiator. For high quality white light illumination the CCT should between 2500K and 6500 K. There is an accepted method (Wyszelki et al 1982) to determine lines of constant correlated color temperature in x, y space. CIE, CCT and CRI for common white light sources are given in Table 1 for comparison purpose (Misra et al 2006). 

See correlated color temperature, color rendering index, and spectral power distribution curve. 

Correlated color temperature Term used to describe the color of white light sources. Specifically, it is the temperature of the Planckian (black body) radiator, which produces the chromaticity most similar to that produced by the light source in question. The temperature is expressed in degrees on the absolute or Kelvin scale, or in mireds (micro-reciprocal degrees), 10 /T. See color temperature. 

Desoo ot Des (idj. Refers to the dayhght special power distribution curve with a correlated color temperature of 6500°K. 

Daylight da- llt (13c) n. Natural illumination that is the result of various mixtures of direct sunlight covering a wide range of correlated color temperatures. 

Illuminant A (CIE) n. Incandescent illumination, yellow orange in color, with a correlated color temperature of 2856K. It is defined in the wavelength range of 380-770run. 

Illuminant D (CIE) n. Daylight illuminants, defined from 300 to 830 nm, the UV portion 300-380 nm being necessary to describe correctly colors which contain fluorescent dyes or pigments. They are designated as D with a subscript to describe the correlated color temperature Dss having a correlated color temperature of 6504 K, close to that of Illuminant C, is the most commonly used. They are based on actual measurements of the spectral distribution of daylight. 

Kelvin temperature scale An absolute temperature scale, in which the unit is the Kelvin (K), defined as 1/273.16 of the temperature difference between absolute zero (OK) and the triple point of water. K = °C -h 273. This scale is used to describe the correlated color temperature of light sources and illuminants in color designations and color rendition. Symbol K. See correlated color temperature and Kelvin. Kelvin is used extensively in gas laws and calculation for expansion of gases. Theoretically, all molecular motions cease at OK or absolute zero temperature. Paint pigment, drying oils, polymers, resins, naval stores, cellulosics esters, and ink vehicles, vol 3. American Society for Testing and Material, Conshohocken, PA, 2001. 

Temperature, correlated color See correlated color temperature. 

Fig. 9.16 Correlated color temperature (CCT) with color coordinates. Table 9.1 shows the range of CCT changes with temperature changes from 0 to 100 °C [61]...

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