What is the Difference Between a Photometer and Spectrophotometer?

Best NIR Product Differentiation is Based On Application, Price, and Ease of Use Considerations

Photometers and spectrophotometers are both well suited and established for the measurement of moisture, oil/fat and other easy to identify applications. Photometers typically use targeted measure wavelengths where the parameter absorbs such as 1.94 microns for water and 1.72 microns for oil. The Photometer then compares the response with non-absorbing wavelengths. Sugar sprays can be measured based on the water carrier and flavourings based on the oil. Photometers are typically the best choice for these types of applications.

Spectrophotometers measure the full spectrum and then use slices of that spectrum, not the whole spectrum, to generate factors via chemometrics or mathematical modelling such as PCR, PLS, Neural Networks and other treatments. When the parameters being measured have overlapping absorption bonds such as different types of alcohols or saturated and unsaturated fats, they can discriminate between the constituents. Also, for more difficult applications such as protein, salt, sugar, ash etc. spectrophotometers have advantages over photometers.

Calibrations for Photometers typically need 3 to 7 samples throughout the range of interest. Calibrations for Spectrophotometers typically need 10 to 15 samples per modelling factor and can require as many as 200 or more samples to calibrate.

Photometers are significantly less expensive, easier to calibrate and easier for unskilled workers to operate. If a Photometer meets your measurement needs, it’s a better choice for on-line, at-line and lab measurements.