The Klett Color Scale, based on the old Klett-Summerson transmission filter colorimeter, is usually used for measuring transmission color of liquids, and for measuring bacterial cultures. It was developed around the 1940's and popular into the 1960's before other options became available. It is still used in limited markets today, primarily for measurement of bacterial cultures.
This unit can select any of a dozen colored, filters peaking at different points across the spectrum. The most common filter used peaks at 420 nm and is measuring yellowness in clear transparent liquids and 540 nm for measuring cultures. This Klett 420 specification has almost faded from industrial use but is still found in a few applications.
The klett-Sumerson colorimeter scale is graduated in units proportional to Optical Density (OD). The actual numerical values represent the OD divided by two, with the decimal point omitted. For eg., a scale of 250 corresponds to OD of 0.500
The formula relating scale reading and OD (Optical Density) is: D = R X 2/1000 where D is density and R is the reading.
it is more accurate to relate the reading in terms of percent transmittance but would require looking up an already computed chart available in the manual accompanying the old Klett meters (see attachment)
Or 1) get OD value from reading as above 2) subtract OD from 2.000 The result is the logarithm of the percent transmittance. eg. scale reading =150 OD = 150 X 0.002 = 0.300 log% transmittance = 2.000 - 0.300 = 1.700 % transmittance = 50.2%
HunterLab does not have a correlation to the legacy Klett Color Scales as there is insufficient demand from our customers. Our recommendation for an equivalent and modern metric would be to measure Yellowness Index E313 D65/10 or C/2 in TTRAN Total Transmission using the HunterLab Vista or HunterLab UltraScan products.