Broadly speaking, it all depends on the brightness of the fluorescence you are trying to measure. However, other factors such as speed , resolution , noise and price will all be relevant.
High fluorescence means much dimmer than brightfield, but still relatively bright.
Dynamic means video rates or at least 10-20 frames per second are required. In the following series of pictures, all images in the same row were taken at approximately the same light level. Click on each image to see the full size version - better still, save the target image and open it in a viewer that reports the numeric intensity value under the cursor, so that you can see the extent to which image and background really differ. Polyview is one such shareware viewer for Windows. Are available with high resolution chips, high green sensitivity, shutterless operation and other such marvels.