I seem to recall that tiny lightbulbs where used inside Palpatines hood to make his eyes glow. The lightsbulbs themselves would be visible by accident as he was moving his head and was therefore covered by a black traveling matte.
Probably they were much less apparent in theaters compared to home-video formats.
Can't remember if I ever saw a screengrab of it in Team -1's thread though..
Keep up the good work Harmy!