This would be an absorption photometer or something similar. You shine light of a known wavelength through your sample and measure the intensity that's transmit

This would be an absorption photometer or something similar. You shine light of a known wavelength through your sample and measure the intensity that's transmitted. If you have enough wavelengths and they're useful (ie you're looking for some feature in your sample that is either present or absent, or is a proxy for something you want to measure), you can do some basic analysis of your sample. It might be enough for QA in some industries. You can also do fluorescence spectroscopy where you illuminate with multiple wavelengths and image in multiple filters (or a single filter). You end up with a grid of measurements that can be used to fingerprint samples. Monochromators are a cheap way of measuring spectra, but since you need to measure each wavelength individually they're pretty slow. Most lab spectrometers are real-time.