I go onto the Google Image search and type in Blue LED, and you get a pic of a motorbike come up, I just use the Eliptical Marquee tool, select part of it then transform it to the size I want, I then get the brush tool on 50% opacity and make the big blob of light if you like (I made sure the brush was big enough to cover all of the LED's) and the brush that fades away around the edge
Hope that explains it
Oh and Ben, I wish mate. Car Design must be a quality job, especially when you see it made.