ANSI T 1216 SP-2007 Indices for whiteness yellowness brightness and luminous reflectance factor.pdf

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1、T 1216 sp-12 FORMERLY TIP 0804-05 STANDARD PRACTICE 1998 REVISED 2003 REVISED 2007 REVISED 2012 2012 TAPPI The information and data contained in this document were prepared by a technical committee of the Association. The committee and the Association assume no liability or responsibility in connect

2、ion with the use of such information or data, including but not limited to any liability under patent, copyright, or trade secret laws. The user is responsible for determining that this document is the most recent edition published. Approved by the Standard Specific Interest Group for this Test Meth

3、od TAPPI CAUTION: This Test Method may include safety precautions which are believed to be appropriate at the time of publication of the method. The intent of these is to alert the user of the method to safety issues related to such use. The user is responsible for determining that the safety precau

4、tions are complete and are appropriate to their use of the method, and for ensuring that suitable safety practices have not changed since publication of the method. This method may require the use, disposal, or both, of chemicals which may present serious health hazards to humans. Procedures for the

5、 handling of such substances are set forth on Material Safety Data Sheets which must be developed by all manufacturers and importers of potentially hazardous chemicals and maintained by all distributors of potentially hazardous chemicals. Prior to the use of this method, the user must determine whet

6、her any of the chemicals to be used or disposed of are potentially hazardous and, if so, must follow strictly the procedures specified by both the manufacturer, as well as local, state, and federal authorities for safe use and disposal of these chemicals. Indices for whiteness, yellowness, brightnes

7、s, and luminous reflectance factor 1. Scope This Standard Practice deals only with simplified color indices applicable specifically to white colors. There are approximately 5000 distinguishable white colors. As with any other color, three numbers are necessary for the complete identification of any

8、white. All the color and color difference scales regularly used for color specification are applicable to white colors. 2. Significance 2.1 White is the color of purity or freshness and of cleanness. The consumer judges the whitest shirt to be the freshest and cleanest and automatically selects it f

9、rom several on display. In some products, whiteness is not only psychologically associated with purity, but is actually an indicator of freedom from contaminants, and as such can be a measure of the quality of the product. Good white base colors are necessary where products are to be dyed, printed,

10、or otherwise colored. The cleanness, brightness, and full range of color in color printing depend to a large extent upon the whiteness of the base paper. 2.2 In physical terms, a white surface is one which reflects strongly (usually more than 70%) throughout the visible spectrum. The higher and more

11、 uniform this spectral reflectance, the whiter the surface usually appears. From the point of view of geometry, a white surface is one that reflects diffusely in all directions. Mirrors, because they reflect only opposite the direction of illumination, are not called white, although a good mirror re

12、flects strongly throughout the visible spectrum and would thus be judged white by its spectral reflectance curve. 3. Safety precautions There are no specific safety precautions associated with this standard practice. T 1216 sp-12 Indices for whiteness, yellowness, brightness, / 2 and luminous reflec

13、tance factor 4. Procedure 4.1 In tests for preferences of white colors used in commerce, it is almost always shown that in the opponent-colors L,a,b-type systems, the b dimension measuring blueness-to-yellowness is the most critical of the three. In preference studies, minus b receives from three to

14、 four times the weight of any of the other scales. L is the next most important of the three dimensions, and a the least important in normal practice. It is probably true that any white would be undesirable as a white, if it attracted the attention of the layman by appearing bluish, pinkish, or gree

15、nish. In everyday practice, such whites are seldom encountered. 4.2 With many problems involving color technology of white materials, only one index of color is needed. The type of number required varies with the character of the problem. Thus, blue reflectance is used to measure progress in bleachi

16、ng, but luminous reflectance is used to measure efficiency of white reflector surfaces. Table 1 lists four different single-scale measurements which have proved useful for problems involving the colors of white materials. These four single-number attributes of white surfaces are: 1. Whiteness index

17、(WI) 2. Yellowness index (YI) 3. Paper brightness (blue reflectance) 4. Lightness (L) or luminous reflectance factor (Y or G) 4.3 Uses of each of these four indices in five industries are identified in Table 1. Equations for the four types of indices, the associated instruments and published test me

18、thods and their applications are listed in Table 2. Note that seven alternate equations for different whiteness indices and five alternate equations for different yellowness indices are provided. 4.3.1 Whiteness indices (WI) are widely measured to yield numbers correlating closely with consumers pre

19、ferences for white colors. An example of a simple whiteness index is that given by the equation WI = 4B - 3G. A colorimetrically similar equation yielding different numbers is WI-CDM= L - 3b. In both of the equations, yellowness is given three to four times the weight of grayness in the determinatio

20、n of visual departure from ideal white. These equations are presented for illustrative and historical reasons but are not recommended for current usage. 4.3.1.1 Note that two groups of scales are listed in Table 2 under whiteness indices. The first group comprises scales which favor neutral white. F

21、or these equations the whitest color possible is the color of the ideal white total reflecting standard. This ideal white is neither bluish nor yellowish and any departure from the chromaticity of this white standard results in values of whiteness index lower by one hundred than each of the three sc

22、ales in this first group. The second group of scales comprises those which favor blue whites over neutral whites. With these scales as with the first group, the perfect white reflector is assigned the value 100, but with scales of the second group, it is quite possible to get bluish whites with whit

23、eness indices well above 100. This is because bluishness counts more in the whiteness index equation than does high reflectance alone. Current experiments in visual grading of new white products tend to confirm the blue-white preferences expressed by the second group of whiteness indices. 4.3.1.2 In

24、 the Stensby whiteness index equation listed in Table 2, not only bluishness but pinkishness is favored. Here pink tints are rewarded and green tints are penalized. 4.3.1.3 The last equation provided for WI in Table 2 was adopted by the CIE in 1976 and by ASTM in 1996. It is designed to penalize bot

25、h greenness and pinkness. 4.3.2 Yellowness index (YI) measurements are used primarily to study degradation of white color from raw materials, processing, or subsequent service exposure. The yellowing of paper due to light exposure should be measured by change in YI. The yellowness index equations al

26、l involve difference between Z (or B) and the other tristimulus values. 4.3.3 Paper brightness (blue reflectance factor) is, as was noted above, widely used to follow progress of bleaching and to evaluate a product for adequacy of bleaching or the addition of optical brighteners. The paper industry

27、has for sixty years been using blue reflectance as its primary determinant of optical quality of paper pulp after bleaching. Since pulp is more likely to absorb blue light than the rest of the spectrum, brightness is a proper index of the optical quality of pulp. Brightness is an incomplete color in

28、dex. For color of paper, one of the established tridimensional color scales should be used. 4.3.4 Luminous reflectance factor (Y) correlates with L and is used to evaluate the efficiency of surfaces as reflectors of light. As such, it is used for the specification of reflectors in floodlights. Lumin

29、ous reflectance is also widely used to measure freedom of textile fabrics from dirt. This function is frequently used in the paper industry in the determination of opacity and scattering (see TAPPI T 425 “Opacity of Paper (15 /d Geometry, Illuminant A/2, 89% 3 / Indices for whiteness, yellowness, br

30、ightness, T 1216 sp-12 and luminous reflectance factor Reflectance Backing and Paper Backing”) because the spectral distribution (Y) is the same as that of visual efficiency (V). 4.3.5 Fluorescent brighteners are colorless dyes which absorb ultraviolet radiation and emit blue fluorescence. They are

31、widely used in detergents, textiles, and paper, and to a lesser extent in plastic and other materials. These brighteners affect the optical characteristics of paper in four ways: a. They improve visual whiteness and paper brightness by supplementing natural blue reflectance with ultraviolet - genera

32、ted fluorescence. b. The ultraviolet-absorbing dyes decrease the tendency of residual lignin in the paper to yellow from ultraviolet exposure. c. They provide bacterial and fungicidal protection to paper. d. Where fluorescent brighteners are used, measured blue reflectance factors and whiteness indi

33、ces are affected by the ultraviolet content of the illumination used for the measurement. 5. Keywords Whiteness, Yellowness coefficient, Brightness, Reflectance, Luminous reflectance, Visual efficiency 6. Additional information 6.1 Effective date of issue: April 24, 2012. 6.2 This Standard Practice

34、was previously TIP 0804-05. 6.3 In the 2007 edition, the % from Z % in Table 2 was eliminated, and a footnote was added to Table 2 referring to the constants in Table 2a. In Table 2a, tint index t was changed to tint index TI. In the 2012 edtion, an equation in Table 2 was corrected, the Scope and S

35、ignificance sections were reversed, and other editorial changes were made. Table 1. Colorimetric indices for white surfaces and their uses in five industries Industry Luminous Brightness Yellowness Whiteness Reflectance (B) (YI) (WI) (Y) Paper Opacity Pulp and paper Supercalender Paper whiteness bri

36、ghtness after scorching, yellowing beaching or addition of optical brightener Paint Reflectance efficiency, Yellowness, and Paint whiteness opacity yellowing in use Textiles Raw fiber grading, Textiles after bleaching Yellowness, Textile whiteness soiling studies yellowing in processing Soap, Effici

37、ency of Effectiveness of Contribution of Product whiteness detergents, cleaners and cleaning bleaches bleaches and after cleaning cleaners processes. and optical brighteners optical brighteners Redeposition of in cleaners to elimination soil on clean fabrics of yellowness Plastics Yellowness, and Pl

38、astic whiteness yellowing in service T 1216 sp-12 Indices for whiteness, yellowness, brightness, / 4 and luminous reflectance factor Table 2. Important color attributes of white surfaces, the measurement scales, instruments and major applications of each to products of commerce* Color attributes and

39、 scales Instruments and published Applications of color used for their measurement test methods attribute measurements WHITENESS INDEX (WI) Four very different measurement scales are used: 1. WI(Taub)= 4Z 3Y = Y 4(Y Z) Tristimulus reflectometer with To evaluate blue and pink = 4B 3G blue and green f

40、ilters dyes, fluorescent whitening agents and other whitening ingredients for effectiveness. 2. WI(CDM-L) = L 3b Color difference meter with L, a, b scales. 3. WI(Stensby)= L 3b + 3a Color difference meter with L, a, b scales. 4. WI(CIE)= Y + 800(xnx ) + 1700(yny ) Automatic colorimeter or The highe

41、r the value of WI, Tint(CIE)= 1000 (xn- x) - 650 (yn- y) spectrophotometer. the greater is the indicated for illuminant C, 2 observer. whiteness. Equal differences Tint(CIE)= 900 (xn - x) for 10 in WI do not always observer. represent equal perceptual differences in whiteness. where WI is the whiten

42、ess value Restricted to samples that Y is the CIE tristimulus value Y are called “white” x, y are the CIE chromaticity coordinates commercially and that do not of the specimen differ much in color or xn,ynare the CIE chromaticity fluorescence. coordinates of the perfect diffuser. For illuminant C/2

43、Must be measured xn= 0.3101, yn= 0.3163 on the same instrument at For illuminant D65/10 nearly the same time. xn= 0.3127, yn= 0.3291 Recommended limits for white materials are: These formulae provide relative, not absolute, 5Y 280 W 40 evaluations of whiteness -2T4 and tint. * Constants for use in t

44、he equations above can be found in Table 2a.5 / Indices for whiteness, yellowness, brightness, T 1216 sp-12 and luminous reflectance factor Table 2a. Coefficients for the Equations for CIE Whiteness Index and Tint CIE Standard Illuminant and Observer Value C, 31 D50, 31 D65, 31 C, 64 D50, 64 D65, 64

45、 xn0.3101 0.3457 0.3127 0.3104 0.3477 0.3138 yn0.3161 0.3585 0.3290 0.3191 0.3595 0.3310 WI, x 800 800 800 800 800 800 WI, y 1700 1700 1700 1700 1700 1700 T, x 1000 1000 1000 900 900 900 T, y 650 650 650 650 650 650 Equation for Whiteness Index WI: WI = Y + (WI, x) (xn x) + (WI, y) (yn y) where: Y,

46、x, y = the luminance factor and the chromaticity coordinates of the specimen, xnand yn= the chromaticity coordinates for the CIE standard illuminant and source use, and WI, x and WI, y = numerical coefficients. Values for all these except those measured for the specimen are given in Table 2A Equatio

47、n for Tint Index TI: TI = T, x (xn x) T, y (yn y) YELLOWNESS INDEX (YI) Four numerically different measurement scales: 1. YIHUNTER= 100(1-B/G) Simplest colorimeter scale; To evaluate a yellowness not currently used. counteracting ingredient for effectiveness. 2. Used with two-or-three filter reflect

48、ometer (ASTM E313). 3. BLUE REFLECTANCE FACTOR Reflectometer with specified blue Freedom of white-product SUCH AS PAPER INDUSTRY filter; (TAPPI T 452, ASTM D985, ingredient, such as paper- “BRIGHTNESS” ISO 2470). pulp or cotton fiber, from yellowish, blue-absorbing ingredients. To establish whether

49、white product conforms to specification. To assess progress in bleaching and efficiency of bleaching process. 4. Recommended by ASTM Std. General purpose yellowness Practice E313. formula. Factors Cxand Czare available for standard illuminant/observer conditions. Your comments and suggestions on this procedure are earnestly requested and should be sent to the TAPPI Standards Department. g GB) -(G 100= Y)Z- (Y 100= YI%E313) (ASTMYZ)C- X C( 100= YIzx