Excitation-wavelength multiplexing is an efficient way to record FLIM of several fluorophores with different excitation spectra simultaneously. Lasers of different wavelength are alternatingly switched on and off synchronously with the frames, the lines, or the pixels of the scan. The TCSPC process marks each photon with an identifier of the laser or laser wavelength that was active in the moment of the detection. It then uses this information to build up separate images for the individual lasers. Excitation-wavelength multiplexing is available in the bh DCS-120 confocal and multiphoton FLIM systems, and in the bh FLIM systems for the Zeiss LSM 980. Typical applications are metabolic imaging, the investigation of effects of variable environment conditions or drugs on the cell metabolism, or photodynamic-therapy effects.