Add a ferrite filter to the digital ballast AC line input and ballast cord output and suppress ugly interference to surrounding electronic devices (yours and your neighbors)! Order 1 set for each ballast.
You get a ring filter (1.4" ID) for the AC power line and a snap on filter (3/4" ID) for the lamp cord. Wrap as many turns as possible on both cables as close as possible to the ballast.
Ballast shown is a Lumatek LK400.
All ballasts in a particular location must have a filter otherwise RFI may not be suppressed to a measurable value. Suppresses RFI in range of .15-10 MHz.