The CoolLED pE-300white is a perfect fluorescence illumination system for fixed fluorescence samples. We used it on a Nikon E400 upright microscope with four fluorescence channels. With a triple-band filter, it can also be used for simultaneous illumination of three fluorescent proteins. As a system running in a microscope facility, it provides excellent flexibility, enough brightness in all bands to most samples, and is cost-effective, stable, trouble-free, and easy to operate