Gardner LCS IV User Manual

Graph for the red scale R.

If the CIE L*a*b* value of the sample does not correspond to any 
reference solution in a selected scale, the > (next) symbol 
appears, followed by the next reference solution with the smallest 
color difference 

E*. In this case, select Auto for a color 

matching in all scales to see which color scale and color 
reference solution is the closest to the sample color. 

If the color space of the sample is outside the graph of a color 
comparison scale, the error message Value outside! appears 
above the graph.

The method used to determine color according to the US 
Pharmacopoeia  corresponds to the specifications in Chapter 631 
"Color and Achromicity"

 and in Chapter 1061 "Color - 

. A total of 20 color reference 

solutions (identified by the sequential letters A to T) are defined in 
the US Pharmacopeia. The color of the measured sample is 
automatically correlated to the color reference solutions. This 
means that the color reference solution that is closest to the 
sample (i.e. the reference solution with the smallest color 
difference 

E* to the color of the sample) is displayed. The values 

L*, a* and b* are the quantitative differences between the L*, 
a* and b* values of the sample and those of the displayed USP 
solutions.

The measurements can be taken using cuvettes with path lengths 
of 10 mm, 11 mm or 50 mm. The use of longer path lengths 
increases the accuracy of the measurement.