A cartridge (10, 60, 80, 110, 130, 140, 170, 180, 200, 222, 224, 226, 228, 230, 240, 242, 246, 280, 282, 300) and cartridge system (220) for use in an apparatus (12) for analyzing a sample (16) is provided. The cartridge has one or more light sources (18) and/or optical systems (22, 34, 84, 120, 162) and other components that are specific for a certain type of application such as fluorescence, absorbance, or luminescence. The light source, optical systems, and other components for a specific application are housed in a single cartridge. The system has a plurality of cartridges for different applications for a multimode instrument. The cartridges are removably engaged with the apparatus in a 'plug-in' format such that one cartridge may be removed from the apparatus and another cartridge may be easily installed.