Water quality photometers and colorimeters are ion-specific computer-interfaced probes designed to determine the concentration of a solution from its color intensity. The color of a solution may be inherent or derived by adding another reagent to it. Monochromatic light from an LED light source passes through a cuvette containing a solution sample. Some of the incoming light is absorbed by the solution. As a result, light of a lower intensity strikes a photodiode. The amount of light that penetrates a solution is known as transmittance. Transmittance can be expressed as the ratio of the intensity of the transmitted light, I_t, and the initial intensity of the light beam, I_o, as expressed by the formula:

T = I_t / I_o

Water quality photometers and colorimeters are ion-specific computer-interfaced probes designed to determine the concentration of a solution from its color intensity. The color of a solution may be inherent or derived by adding another reagent to it. Monochromatic light from an LED light source passes through a cuvette containing a solution sample. Some of the incoming light is absorbed by the solution. As a result, light of a lower intensity strikes a photodiode. The amount of light that penetrates a solution is known as transmittance. Transmittance can be expressed as the ratio of the intensity of the transmitted light, I_t, and the initial intensity of the light beam, I_o, as expressed by the formula:

T = I_t / I_o

Photometers and colorimeters produce an output voltage, which varies in a linear way with transmittance, allowing a computer to monitor transmittance data of a solution thus producing an output that can be converted to concentration.

Mounting options for water quality photometers and colorimeters are quite varied. They can be handheld, portable meters or benchtop or fixtured instruments. Handheld meters are popular for laboratory use, where a scientist may be taking readings from many different samples. Portable meters typically have wheels, handles or another device for transportation. Benchtop and fixtured instruments are permanently mounted for long-running use.

Displays for the instruments can be analog meters, a numeric or alphanumeric digital display or video, CRT or LCD. Another option is to have no local display at all and have the data gathered by another instrument. Likewise, the user controls can also be analog or digital or can be operated through a host computer. To simplify the instruments, preprogrammed devices without user controls are available.

Electrical output options for water quality photometers and colorimeters are the standard voltage and current outputs as well as an analog pulse or frequency or a change in state of switches or an alarm. Serial and parallel interfaces can help connect these instruments to a host computer.

Some features for water quality photometers and colorimeters are battery power for greater mobility, auto wavelength selection and automatic calibration. Temperature compensation is available in some models, as are self-test diagnostic routines to verify sensitivity, zero point, etc. Water resistant housings and data storage and logging capabilities enhance the versatility of these instruments.