I didn't think the original Knight Rider effect (Larson Scanner) had any dimming.
...I've made sound-activated versions of it (where volume affects speed) and I didn't use any dimming. ...Sharing my code would probably just be confusing because I might have a different number of lights/LEDs and I'm using bits in a variable for the LED states. That makes it easier to shift left & right but I have to store the bits that shift off the ends and a function to write-out the bits, etc. To keep things interesting, I also randomly vary the number of LEDs that are on at a time, and how far pattern shifts off the ends.