LED illumination is awesome for epifluorescence. No mechanical shutters, no changing mercury lamps every 200 hours, no hot lamphouses, no worries about letting it cool down before turning the lamp back on, less wasted electricity, immediately ready to use after turning it on, etc.
We have a Lumencor SpectraX on our Nikon TE2000 scope and we love it. It contains multiple LED that are independently triggerable. For high-speed imaging, we bought one new Chroma quad-band dichroic and emission filter set, as well as 4 separate single-band emission filters for our emission filter wheel (although this latter set is not absolutely necessary).
The amazing thing is to be able to run color sequences at the frame rate of the camera (because the SpectraX accepts TTL triggering of each line independently). It is beautiful to see the rainbow of light flashing out of the scope at 20+ frames per second!
We haven’t run into any issues with brightness: the SpectraX is bright enough for all our cell imaging experiments. Typically, we run it at 20% power. That said, I’m aware that the very bright peaks in an arc lamp spectrum (e.g. UV, 435, 546) aren’t there in the LED spectra. So for FRAP or something, you may not be able to bleach as fast.
And, of course, a fancy illuminator like the Spectra X is not cheap. But for run-of-the-mill epi imaging, white-light sources like the Lumencor Sola might be a good option. Another downside is that the fans on the Spectra X are audible, but not annoying. Despite that minor issue and the cost, I highly recommend LED illumination (and the Spectra X, specifically).
I recommend you demo a few LED sources from a few companies (e.g. ScopeLED, Lumencor, Sutter, etc.) and make sure it will fit your needs.
* Make sure your camera supports TTL triggering of an external shutter.