OK. Back when I was in college I worked part time for a company called
Coastal Sales NW. They manufactured and distributed sign parts. Their rotors
were especially good. What you want is called a "chaser." These devices were
once very expensive, but now they can be had for less than $100. Digital
Lighting Systems makes good ones. http://digitallighting.com/index.html You
probably want the BC series for your low voltage system. A guy could go nuts
wandering through their on-line catalog. Christmas light chasers are
probably too low voltage for your application, although blue LED Christmas
lights might work well and the whole string only uses 5 volts.

If the lights are too bright they will indeed induce seizures in the
susceptible. Red lights and white lights are worse than the blue lights you
propose. This is a problem at theme parks where a lot of rides have flashing
and chasing lights. You will often see signs warning epileptics of the
danger, but under the right circumstances these lights have induced seizures
in persons not known to have had epilepsy. I suspect that having the lights
overhead will increase the level of discomfort.