Colorimeters and spectrophotometers are used in the medical, research, and scientific industries to provide rapid results of unknown samples through the use of colour. Although both the colorimeter and the spectrophotometer use colour to analyse samples, they operate differently.
Colorimeters use a coloured light beam to measure sample concentration. Spectrophotometers use a white light that is passed through a slit and filter to analyse samples.
In colorimetry, coloured light passes through an optical filter to produce a single band of wavelengths. With spectrophotometers, the white light is passed through a special filter that disperses the light into many bands of wavelengths.
Both of these techniques use the Beer-Lambert Law to determine concentration. The difference is that colorimeters measure the absorbency of light in a sample while spectrophotometers measure the amount of light that passes through it.
The colorimeter uses psychophysical analysis, comparing colour in the same manner as human eye-brain perception. The spectrophotometer uses only physical analysis, using different wavelengths of light to determine the reflection and transmission properties of colour.