I'm not familiar with that UT level, but how about using a map entity with a single green texture, an albedo of 0, and an 'ambient' value that ranges from 0 to 100?

code:

---

action my_band {
  my.albedo=0;
  my.skill32=0;

  while(1) {
    my.skill32+=time;
    my.ambient=cos(my.skill32)*50+50;
    wait(1);
  }
}

---

=thomas