Bleaching (also photobleaching) is the progressive fading of the emission intensity of the sample under study. High intensity excitation light often leads to irreversible decomposition of the fluorescent molecules apparent as fading of the emitted fluorescent light. This in particular affects images from widefield microscopes 3D and widefield Time Series and images from spinning disc and confocal Time Series.

Huygens Professional and Huygens Essential have a tool (Equalize Flux) that corrects for bleaching in some situations. See → Bleaching Mode for more details. See also Bleaching Vs Sampling.