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The use of ultrabright light-emitting diodes as a potential substitute for conventional excitation light sources in fluorescence microscopy is demonstrated. We integrated ultrabright light-emitting diodes in the filter block of a conventional fluorescence microscope together with a collimating Fresnel lens, a holographic diffuser and emission filters. This setup enabled convenient changes between different excitation light sources and resulted in high excitation efficiencies. Quantitative comparison of image intensities of test samples revealed that light-emitting diodes yielded intensities in the range of a mercury arc lamp depending on the wavelength. The use of ultrabright light-emitting diodes also enabled luminescence lifetime imaging without the need for image intensification.