Re: Arduino + 12V 5050 LED
it's not clear exactly what you've got or what you're trying to do. i'm guessing you're after an adalight, but it sounds as though you've got an led strip that's probably only addressable three leds at a time.
do you know what controller chip your led strip is based on? what is the ratio of ic's to leds on the strip. it's probably 1:6. if so, that's not really what you need.
"If I had known it was harmless, I would have killed it myself." - Phillip K. Dick, A Scanner Darkly