I'm trying to modify my B5 tail lights to have the LED look of some of the newer cars out there. I've yet to see something aftermarket that I like. One of my bosses has a Cadillac Deville with factory LED tails. These tails create a solid panel of light with no bright spot in the center. The entire panel goes on/off, simply appearing and disappearing as one uniform block of light. There are two sections of panel on the Cadi tail so it can indicate running, brake, turn lighting. If you get an opportunity, notice how the Cadi tails look next time you're behind one of them.
I'm going for a similar effect, with solid, uniform blocks of light flicking on/off without the glow-on/glow-off of incandescent lights and no "hot spot" in the center. I've tried upgrading the bulbs to LED plug-in bulbs and that gives a nice digital on/off. But they still have a hot spot and aren't a uniform panel of light.
I saw a Deville with a smashed tail and looked at how GM gets the "panel effect". They have a layer of refractors between the bulbs and the outer shell of the tail light.