Colorimeters and Turbidity meters both employ optical measurements. Optical measurements use light to quantify the amount of a colored or cloudy sample. Colorimeters are used to measure the concentration of a sample component. Turbidity meters can determine how cloudy the sample is and report a number value for the turbidity.
Colorimetic measurements use a small light source to pass a narrow band of light straight through a reacted test sample in a vial. The light beam exiting the sample vial is collected in a detector at 180 degrees from the initial beam. The detector reading that was measured is converted to a concentration for that specific test. Some single parameter colorimeters have only one measurement performed. Multi-parameter meters require the user to select the appropriate method number to match the test and reagent type being used.