I had some PLCC2 surface mount white LEDs (also used for lighting up our gauge cluster and controls), so I strung 4 LEDs in series for each visor LED light.
Pry both ends of the visor light cover away from the mirror. Try to avoid scratching the mirror or chipping the edges. Then pop off the original light bulb. Here's what it looks like.
Here's a comparison shot of the LED mod:
