Fig. 5. Total spectral reflectance factors of the IR2 reference standards, for standard illuminations, D 50 , D 65 , and C. The solid lines are the values computed with the factors listed in Table I (CT2), and the assigned values are denoted by differ- ent symbols, that is, “*,” “o,” and “ 1 .”
Fig. 6. Total spectral reflectance factors of the IR2 reference standards, for standard illuminants, D 50 , D 65 , and C. The solid lines are the values computed with the factors listed in Table I (CM3630d), and the assigned values are denoted by different symbols, that is, “*,” “o,” and “ 1 .”
UVX (420 nm) have only marginal differences at all wavelengths. The weighting factors representing the filter combina- tions corresponding to the three standard illuminations, C, D 65 , and D 50, are given in Table I. As previously explained, the factor a denotes for the portion of the UV- reduced illumination by the GG395 UV filter. Hence, the UV contents of these illumination conditions come, above all, from the UV-full, represented by the magnitude of 1 2 a . As expected, the D 65 illuminations of the both appa- ratuses possess the highest UV contents, followed by the D 50 and the C illuminations. With the CT2, the respective contributions from UV-full are 63%, 41%, and 19%. As the UV-full from the CM3630d has lower UV content, it actually needs more than 100% of the UV-full to match the UV content of the D 65 illumination. Consequently, the factor a takes a negative value. The D 50 has also signifi- cant UV content as it comprises more than 66% of the UV-full in CM3630d. Relatively speaking, the C illumina- tion has the lowest UV content as the UV-reduced (repre- sented by the factor a ) is the biggest, 64% in the case of CM3630d. All of these are in line with expectations.
Xenon lamp (UV-full), the CT2 gives a significantly higher reading than that by the CM3630d in the fluorescence-intensive spectral range from 400 to 500 nm. There are a couple of possible origins that cause the dif- ference. First, the Xe lamp in the CT2 may operate in a higher electric voltage and has significantly higher UV emissions than that in the CM3630d. Even though a higher voltage does not affect the SPD of Xe flash radia- tion, it does increase the UV radiation flux. Unlike ordi- nary light reflection that is independent of its incident light flux, the fluorescent component [Eq. (3)] increases with stronger UV radiation. Second, it may also be attrib- uted to a visible-suppressing filter often inserted in the illumination flux of G € artner–Griesser method (applied in CT2) to guarantee the match with the illuminant D 65 in the condition of 0 < a < 1 even after aging of Xe lamp. Obviously, both cases can cause differences in the total spectral radiance factors as shown in Fig. 5 and in the colorimetric values shown later in this section. The plots also suggest that these spectrophotometers are equipped with similar UV-reducing and UV-cutoff filters, as their spectral radiance factors of UV-reduced (400 nm) and
24
COLOR research and application
Made with FlippingBook Annual report maker