What is the Difference Between Photometry and Spectrophotometry?

The main difference between photometry and spectrophotometry lies in the way they measure light intensity. Here are the key differences between the two:

Photometry measures the total brightness or intensity of light as seen by the human eye. It is only applicable to the visible light range and provides a single value for the intensity of light at a specific wavelength.
Spectrophotometry quantifies the intensity of light that is either transmitted or reflected per wavelength. It is applied to the whole electromagnetic spectrum and provides values for different wavelengths. Spectrophotometers often comprise a monochromator to separate the various wavelengths of light and a scanning device.

In terms of applications, photometers are well-suited for measuring parameters at certain wavelengths, such as water (1.94 microns) or oil (1.72 microns). Spectrophotometers, on the other hand, can distinguish between various components being tested for, such as different kinds of alcohols or saturated and unsaturated fats. They also offer benefits over photometers when dealing with more challenging applications, such as salt, sugar, ash, and so on.

Photometers are generally less costly, simpler to calibrate, and easier to use for inexperienced personnel than spectrophotometers. If a photometer fulfills your measurement requirements, it is a superior option for on-line, at-line, and laboratory measurements. However, spectrophotometers are more suitable for applications that require precise measurements at specific wavelengths.