HunterLab SpectraTrend HT, User Manual

Page: 99 / 109

SpectraTrend HT User’s Guide 3.2
99
dL*dC*dH*
This scale yields the color difference between the sample and the standard via the CIE L*C*h scale.
dL* = L*
sample
- L*
standard
dC* = C*
sample
- C*
standard
dH* = h°
sample
- h°
standard
where
If h°
sample
> h°
standard
, then dH* is regarded as positive.
If h°
standard
> h°
sample,
then dH* is regarded as negative.
Absolute Indices (available when Display Type is Absolute)
457-nm Brightness
457-nm brightness (displayed as 457B) can be used to indicate the relative brightness of paper. 457-nm
brightness is calculated over the range of 400 nm to 510 nm in accordance with TAPPI document T452.
Tint ASTM E313
ASTM E313 Tint (displayed as Tint) is calculated as follows:
( ) ( )
y y 650 - x x 1000 = E313 Tint
n n
− −
when the 2° observer is in use
and
Tint E313 = 900 x
n
-
x
( )
- 650 y
n
-
y
( )
when the 10° observer is in use
Where x
n
and y
n
are the chromaticity coordinates for the CIE illuminant and standard observer used.
These values are provided in the table given in ASTM E313. This index is only displayed when the data
view is configured for either the C or the D65 illuminant, as these are the only relevant illuminants.
A few caveats regarding measurement of tint:
•
The application of this equation is restricted to samples that are called “white”
commercially, that are similar in color and fluorescence, and that are measured on the same
instrument at the same time. Under these conditions, their use should give relative, but not
absolute, evaluations of tint that are adequate for commercial use.
•
The more positive the value of tint, the greater is the indicated greenish tint of the sample.
The more negative the value of tint, the greater is its reddish tint. Lines of equal tint are
approximately
parallel to the line of dominant wavelength 466 nm. For the perfect reflecting
diffuser, tint = 0.
•
Equal differences in tint do not always represent equal perceptual differences in tint.
•
This equation should only be used for samples having tint values between -3 and +3.
Whiteness Index