Detectors which allow the selection of the operating wavelength called variable wavelength detectors and they are are particularly useful in three cases:
| offer best sensitivity for any absorptive component by selecting an appropriate wavelength; |
| individual sample components have high absorptivity at different wavelengths and thus, operation at a single wavelength would reduce the system's sensitivity; |
Depending on the sophistication of the detector, wavelength change is done manually or
programmed on a time basis into the memory of the system.