The ghosts are not glowing but the eyes.
The flickering is not happening in exactly equal intervals but I guess that is almost impossible to see. In the end the feeling about the animation is what counts, so thanks for your impressions!
However I dislike the idea of adding just a pure strobelight festival (which would be sharp and random flickering).
I tried to combine the idea of the calm flickering with the rather rapid ones. Additionally I added a shade for the darkest frames - using the darkest blue tone.

This is still work in progress and I have already some thought but I would really like to hear your opinions!
Thanks for your support, HarveyDentMustDie and PsylentKnight!