The emission filters falls into three categories:
- Fixed low band pass filters
- Variable band pass filters
- Full spectrum diode array spectrophotometers
Variable optical band pass filters are mostly realized as scanning grating mono-chromators and are used to select the right peak emission wavelength. The main benefit is off course the flexibility to choose any wavelength but the drawback is a high cost, large size, need for electronics control and stability issues due to the moving parts inside the mono-chromator. Therefore, variable bandpass filters are mostly used in versatile large laboratory instruments. The fixed filters main benefit is that they are small, simple, relatively low cost and very stable. However, the price you pay is a limited flexibility in the choice of emission wavelength. You may design your fluorescent instrument with multiple filters but, when you need more than 3 – 4 filter this very quickly becomes bulky and expensive. Full spectrum diode array spectrophotometers will – as the name says – collect the full spectrum. This means you have all emission peaks and details about their shape and the back-ground level. For this reason diode array spectrophotometers are a good choice when you are going to measure multiple fluorophores and/or more complex spectra.