How Is Color Measured - LaMotte TC-3000 Manual

of water causing quick color change. Major contributors are tannins, humic acids, and
inorganic minerals. Color can be critical, since as the color increases, the amount of
light that penetrates the water decreases, and thus submerged plant life, that depend
on this light for photosynthesis, will decrease.

How is Color Measured?

Color can be measured by visual comparison methods or electronically with
colorimeters and spectrophotometers. To better define color values, the APHA adapted
color standards made from dilutions of a solution of chloroplatinate and cobalt. These
are usually used within a comparator containing 6-9 standards, for visual comparison.
However, visual methods suffer due to the subjective observations of the person
judging the colors. The chloroplatinate and cobalt colors can also be measured with a
colorimeter, like the TC-3000.
The TC-3000 is calibrated with the APHA color standards. The meter electronically
measures color in comparison to a colorless water sample. First it measures the
intensity of a light beam passing through a clear colorless sample, the blank. Then it
measures the intensity of light passing through the colored sample. The TC-3000 uses
the ratio of these two measurements to calculate the color and displays the result. The
color determination in the TC-3000 uses a 375 nm wavelength. This UV light was
found to give the greatest sensitivity in reading the APHA color standards. The results
are expressed as APHA color units (cu). The TC-3000 can use signal averaging to
measure very low levels of color. The TC-3000 is very useful for measuring colors
similar to the APHA color standards. It is not appropriate for measuring colors that are
not the same hues at the APHA color standards.
Taking Color Water Samples
Samples should ideally be collected in glass containers. Perform the analysis soon after
sampling since the color may change with time. For true color determinations, remove
turbidity by filtration or centrifugation.
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