Normal LED fans are clear fans with colored LEDs mounted in the sides. The UV LED fans are colored UV sensitive fans that have UV LEDs mounted in them. When off they look very different:
LED off
UV LED off
When running they look similar, but the UV LED fans seem to have more color.
LED on
UV LED on
The other big difference is price, about double for the UV LED fans. Plus, if you have other UV sources (like a blacklight cold cathode) they will allow the fans to react even when switched off.